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Why are newly grown leaves red?

Why are newly grown leaves red?


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After a period of heavy rain, several trees in my garden will put out an impressive burst of new leaves, with an incredible vibrant red colour, almost the colour of port wine. The new leaves will then slowly turn green.

I understand that the leaves turn green once they start producing chloroplasts and chlorophyll, but what is responsible for this initial red colour that is so very vibrant? And what biological role does it play?


It is anthocyanins that are produced to protect the developing photosystems (chlorophylls) from being damaged by sunlight.

As you have noted, it dissipates as the photosystems become adapted to the ambient light levels. Were you able to shade your trees for several weeks, you would likely also see their leaves turn red right after you removed the shade (easily done with trees in pots). Again, it is anthocyanin positioned in the leaf in a layer above the chloroplasts, but it will not be as vibrantly red because of the green chloroplasts below.


Why are newly grown leaves red? - Biology

Leaves are the main sites for photosynthesis: the process by which plants synthesize food. Most leaves are usually green, due to the presence of chlorophyll in the leaf cells. However, some leaves may have different colors, caused by other plant pigments that mask the green chlorophyll.

The thickness, shape, and size of leaves are adapted to the environment. Each variation helps a plant species maximize its chances of survival in a particular habitat. Usually, the leaves of plants growing in tropical rainforests have larger surface areas than those of plants growing in deserts or very cold conditions, which are likely to have a smaller surface area to minimize water loss.


How Does a Plant With Red Leaves Support Itself Without Green Chlorophyll?

A. Some parasitic plants lack chlorophyll entirely and steal the products of photosynthesis from their green hosts, said Susan K. Pell, director of science at the Brooklyn Botanic Garden. Other plants, like a red-leafed tree, have plenty of chlorophyll, but the molecule is masked by another pigment.

Chlorophyll absorbs red and blue light, “reflecting, and thus appearing, green,” Dr. Pell said. Chlorophyll uses this electromagnetic energy, along with carbon dioxide and water, to make glucose and oxygen.

Most plants also have other pigments: carotenoids, which usually appear yellow to orange, and anthocyanins, which are red to purple. One pigment usually dominates. So a plant with red leaves probably has higher than usual amounts of anthocyanins, Dr. Pell said. But chlorophyll is still present and at work.

“We used to think that all fall foliage color change resulted from the revealing of already-present carotenoids and anthocyanins when chlorophyll was broken down in preparation for dormancy,” she said. We now know that leaves actually produce additional anthocyanins into old age, she said.

The evolutionary advantages are not fully understood, Dr. Pell said. One theory is that extra anthocyanins provide shade under which chloroplasts (structures within cells) can break down their chlorophyll, helping the plant reabsorb its building blocks, especially valuable nitrogen. Another theory is that anthocyanins, which are powerful antioxidants, protect the plants in preparation for winter.


Why Are Plant Leaves Turning Purple?

When you notice a plant with purple leaves rather than the normal green color, it is most likely due to a phosphorus deficiency. All plants need phosphorus (P) in order to create energy, sugars and nucleic acids.

Young plants are more likely to display signs of phosphorus deficiency than older plants. If the soil is cool early in the growing season, a phosphorus deficiency may develop in some plants.

The underside of marigold and tomato plant leaves will turn purple with too little phosphorus while other plants will be stunted or turn a dull dark-green color.


Discussion

During the process of light-controlled growth, it is stated that photoreceptors modulate light-responsive nuclear genes by perceiving and interpreting incident light and transduce signals. In the light spectra, R and B wavelengths can strongly affect plant photosynthesis, physiological metabolism and morphology as the main spectral wavelengths [37,38,39]. In this study, the photomorphogenesis and photosynthetic characteristics of sweet pepper seedlings were significantly influenced by the light qualities. Biomass is an important indicator of seedling quality. In this study, the seedling DW under RB was significantly greater than those under other treatments, which suggested that this spectrum was optimal because it promoted plant development and drove photosynthesis by increasing Chl a and total Chl contents in the seedlings [33, 40]. Previous studies also found that mixed R and B light could promote fresh weight (FW) and DW in many other plant species, such as chrysanthemum, upland cotton and tomato [41,42,43]. The biomass of pepper seedling was significantly increased under RB compared with other treatments and this was probably due to the enlarged leaf area (LA) [44] and changes to the leaf anatomy.

Light is absorbed by chloroplasts when it passes through the PT and SPT, which are both important photosynthetic tissues. In our study, RB treatment greatly increased the PT, SPT, as well as upper and lower epidermis thickness, which led to thicker leaves, and this was consistent with the results of Arena et al. [45] and Liu et al. [46]. The vertically elongated PT cells minimized light scattering, which allowed deeper penetration into the chloroplasts, while the changes to the SPT cells enhanced light capture by scattering the light [47]. This improved the photosynthetic structure, which should increase the light capture and absorbance capacities, and contribute to better photosynthetic light acclimation. In addition, leaf thickness plays a key role in determining space availability for chloroplast development [48]. The RB treatment increased leaf thickness, which enhanced the chloroplast ultrastructure [49]. The results suggested that a larger LA and increased leaf, as well as PT and SPT cells thickness improved light interception by the pepper seedlings. and this could be another important reason why RB was able to improve photosynthetic efficiency. Furthermore, the thinner leaves recorded under R light can be explained as a reaction to radiation stress on plant development and metabolic processes, as suggested by Macedo et al. [50].

The ability to do well out of the increments in optical energy and CO2 of plants is reflected by the light- and CO2-response curves, which provides interesting opinions on the mechanisms based on light capture and CO2 fixation. In this study, Pn-PPFD under the different light qualities was significantly lower than Pn-CO2. This might be due to a CO2 concentration limitation. The AQY and CE values showed the initial slopes of the light- and CO2-response curves, respectively. They stand for the ability to obtain low levels of light energy and CO2 of plants. Our results confirmed a previous study [51], which showed that mixed R and B light promoted AQY and CE, and that these increases led to a rise in Pnmax and maximized the RuBP regeneration rate. The RB light led to significant increases in AQY, CE, Pnmax and the maximum RuBP regeneration rate. This indicates that mixed R and B light exerts an synergistic effect on increasing photosynthetic capacity [52]. The LSP values, which reflect the plant ability to use the highest light intensity level, were also significantly higher under RB. This showed that RB improved the ability of the leaves to utilize mixed light qualities. Furthermore, the LCP and CCP values were significantly decreased under RB, which showed that this treatment improved photosynthetic performance and light energy utilization efficiency. These results indicated that the energy conversion of mixed R and B light into chemical energy by the leaves was very efficient, as this fraction of visible light had, by far, the highest quantum yield for CO2 fixation compared with other light treatments [53].

Light qualities can regulate photosynthesis by affecting the formation of different types of chloroplast proteins and electron transport between light systems [54]. Chl fluorescence can partly reflect the photosynthetic ability of plants [55] and the efficiency of PSII photochemistry (ΦPSII) can be used to reveal the physiological state of plants [56]. Our results showed that there was a reduction in ΦPSII in pepper seedlings after exposure to the RB treatment. Fv/Fm represents the maximal efficiency of the excitation energy captured by the PSII reaction centers and the significantly higher value observed in RB-treated seedlings indicated that resistance to photoinhibition was up-regulated under this treatment [57]. Additionally, the higher Fv/Fm and ΦPSII levels under RB treatment showed that mixed R and B light increased the openness and electron transport efficiency of PSII, which meant that more electrons could be absorbed, captured and transported.

There is a correlation relationship between the J-step, I-step and IP phases of Chl fluorescence transients and the redox states of quinone electron acceptor (QA), plastoquinone and the end acceptors at the side of PSI electron acceptor [58, 59]. The finding that R-treated leaves increased the J- and I-step suggested that electron transport at both the donor and acceptor sides of PSII was inhibited. Therefore, CO2 assimilation was decreased by the imbalance of excitation energy distribution between PSI and PSII. Monochromatic B and mixed R and B light induced a decrease in all the OJIP steps during the experimental period compared with other treatments, which altered both the donor and acceptor sides of PSII and affected electron transport [60]. These changes maintained electron transportation on both the donor and acceptor sides. Furthermore, we found that RB increased Sm, PIABS, PItotal, ΦRo and δRo, but decreased RC/ABS, DIo/RC and TRo/RC (Fig. 7), which less damaged the photochemical and non-photochemical redox reactions, enhanced the ability of electron transport and sped up ATP synthesis and RuBP regeneration [61].

In C3 plants, the Calvin cycle is the predominant pathway for CO2 assimilation [62]. Rubisco is a representative and unique enzyme in the Calvin cycle and other Calvin cycle enzymes, including FBPase, FBA, GADPH and TK, play an important part in modulating this pathway [63, 64]. As a significant environmental signal, light provokes gene expression and regulates related enzyme activities during the growth of plants. How light adjusts the expressions and activities of enzymes in photosynthesis was examined by several researches [52, 65]. These previous studies were verified by the present study. The Rubisco activity in B- and RB-treated plants was significantly higher than those in the plants treated with other light wavelengths. This finding suggested that the application of B or RB could increase carbon assimilation and RuBP regeneration in the Calvin cycle. It was also found that under R light, photosynthetic rate has decreased as the number of Rubisco activities and the transcriptional levels of most genes in the Calvin cycle reduced. This result was consistent with an earlier observation and implied that the inhibition of CO2 carboxylation in the Calvin cycle and PSII slow down as a result of the impaired activity of Rubisco activase, which removes inhibitors bound to Rubisco, are probably responsible for the decreased CO2 assimilation rate in R-grown seedlings compared with other light treatments [36, 66]. Furthermore, according to a previous research, the stomatal factor regulating the availability of RuBP differentially, and CO2 may participate in adjusting gene expression because there is a high correlation between the expression levels of the genes examined and the changes in stomatal conductance [36].

The FBA and FBPase activities directly affect photosynthetic efficiency and carbon accumulation [67]. Furthermore, a previous study showed that a significantly decrease in TK activity led to a significant reduction in RuBP regeneration and significantly inhibited the plant photosynthetic rate [68]. In our study, the activities of these enzymes under B and RB and the relative expression of their associated genes, except for FBA and TK, were significantly elevated, which promoted RuBP regeneration and increased Pn [67, 68]. Chloroplast GAPDH is a key enzyme involved in the carbon reduction process during photosynthesis [69] and the greater GAPDH expression level under RB light in the present study may be due to the increased demand for carbon flux [70], suggesting that maintenance of active GAPDH expression in the carbon reduction process could be an important factor contributing to superior photosynthesis under RB light [71]. Changes in activities of FBA and TK as well as their expression under all treatments were not positively correlated, suggesting that transcript abundance is poorly linked to de novo protein synthesis due to profound regulation at the level of translation Oelze et al. [72]. Moreover, the different patterns of gene expression and activity are probably correlated with regulatory factors other than light quality, but this needs further investigation.


Potato Growing Problems: Troubleshooting

Plant potatoes in early spring after the danger of frost has passed. Use disease-free seed potatoes.

Potato growing success can be had with well-drained, deep, sandy loam containing plenty of humus paired with cool, moist conditions.

Plant potatoes in early spring after the danger of frost has passed. Use disease-free seed potatoes cut each potato so that two eyes are on each piece.

Even under these ideal growing conditions, potatoes are not always problem free. Potatoes are susceptible to a host of setbacks.

Here is a list of possible potato growing problems matched with cures and controls:

Potato Growing Problems and Solutions:

• Plants do not emerge after planting seed pieces. Most store-bought potatoes are treated to prevent sprouting. Plant only certified seed potatoes. Cut seed potatoes when sprouts form, two eyes on each piece, and plant immediately. Plant when the soil has warmed to 45°F or greater.

• Plants are eaten or cut off near soil level. Cutworms are gray grubs ½- to ¾-inch long that can be found curled under the soil. They chew stems, roots, and leaves. Place a 3-inch paper collar around the stem of the plant. Keep the garden free of weeds sprinkle wood ash around the base of plants. Use oakleaf mulch. Companion plant tansy between rows.

• Large holes in leaves, leaves and shoots are stripped. Colorado potato beetle is a humpbacked yellow beetle ⅓ inch long with black stripes and an orange head. Handpick off beetles. Keep the garden free of debris. Spray with a mixture of basil leaves and water. Companion plant with eggplant, flax, or green beans.

• Young sprouts fail to grow or die back. Blackleg, black scurf, or frost damage. Blackleg is a bacterial disease which leaves sprouts rotting at soil level–“blacklegs.” Black scurf is a fungal disease stems will have brown sunken spots below the soil level. Remove infected plants and destroy infected tubers. Frost damage follows a frost wait until after the last frost to plant.

• Leaves are yellowish and slightly curled with small shiny specks. Potato aphids are tiny, oval, pinkish to greenish pear-shaped insects that colonize on the undersides of leaves. They leave behind sticky excrement called honeydew which can turn into a black sooty mold. Spray away aphids with a blast of water from garden hose. Use insecticidal soap.

• Tiny shot-holes in leaves small bumps or corky spots on tubers. Flea beetles are tiny bronze or black beetles a sixteenth of an inch long. They eat small holes in the leaves of seedlings and small transplants. The larvae feed on tubers. Peel away tuber damage. Pick beetles off plant. Spread diatomaceous earth or wood ashes around seedlings. Cultivate often to disrupt life cycle spade deeply in early spring. Keep garden clean

• Leaves are chewed. Blister beetles are long, slender reddish-bronze colored beetles with red-coppery legs that feed on leaves. They secrete oil that can cause the skin to blister. Wear gloves and handpick them from leaves and destroy.

• Coarse white speckling or stippling on upper surface of leaves leaf margins turn brown leaves appear scorched and wilted. Leafhoppers are green, brown, or yellow bugs to ⅓-inch long with wedge-shaped wings. They jump sideways and suck the juices from plants. Use insecticidal soap. Cover plants with floating row covers to exclude leafhoppers.

• Leaves turn pale green, yellow, or brown dusty silver webs on undersides of leaves and between vines. Spider mites suck plant juices causing stippling. Spray away with a blast of water or use insecticidal soap or rotenone. Ladybugs and lacewings eat mites.

• Leaves are mottled and become crinkled. Mosaic virus is transmitted by aphids. Control aphids with pyrethrum or rotenone. Plant disease free seed potatoes. Plant resistant varieties: Chippewa, Katahdin, Kennebec, Monona, and Snowflake.

• Gray blotches on older leaves tunneling in leaves. Potato tuberworms are small caterpillars, the larvae of a moth that lays eggs on foliage. They tunnel through interior of leaves. Handpick and destroy. Hill up soil over tubers to keep worms from reaching tubers.

• Plants are green topped, no tubers. Temperatures are too warm. Potatoes require cool nights below at about 55°F for good tuber formation. Plant so that tubers mature in cool weather.

• Spindly cylindrical stems. Witches bloom is a virus disease transmitted by leafhoppers. Stems are elongated and plants set many small tubers. Plant is mostly leafy growth leaves roll up and have yellow margins. Destroy diseased plants. Plant disease-free seed potatoes. Control leafhoppers.

• Stems have irregular dead streaks. Manganese level in acid soils may be high. Test the soil. Apply lime if manganese level is high. Grow resistant varieties: Canso, Green Mountain, McIntyre.

• Plants stunted yellowish-black streaks inside stems. Fusarium wilt is a soil fungus that infects plant vascular tissue especially where the soil is warm. Fungal spores live in the soil. Remove and destroy infected plants. Rotate crops. Plant certified disease-free potatoes. Plant resistant varieties: Irish Cobbler, Kennebec.

• Leaves turn yellow and then brown from the bottom up plants lose vigor plants appear stunted stems, roots, and tubers have tunnels. Wireworms are the soil-dwelling larvae of click beetles they look like wiry-jointed worms. Check soil before planting flood the soil if wireworms are present. Wireworms can live in the soil for up to 6 years. Remove infested plants and surrounding soil.

• Leaves yellow between veins leaf margins brown and curl upward stem base becomes dark brown, black, and slimy tubers become slimy brown-black at stem end. Blackleg is a fungal disease. Add organic matter to planting bed make sure soil is well-drained. Plant certified disease-free potato tubers. Rotate crops. Cover seed potatoes shallowly for quick emergence.

• Leaves and stems have irregular grayish brown water-soaked spots or rings gray-white growth appears on the underside of leaves. Tubers have brown-purple surface scars tubers rot in storage. Late blight is caused by fungus that infects potatoes, tomatoes, and other potato family members. It favors high humidity and temperatures around 68°F. Keep the garden free of all plant debris and avoid overhead irrigation. Remove volunteer potatoes before planting. Plant certified seed potatoes and resistant varieties such as Kennebec, Cherokee, and Plymouth. Keep tubers covered with soil. Cut vines 1 inch below the soil surface and remove vines 10 to 14 days before harvest. Do not harvest under wet conditions.

• Young leaves fail to enlarge, new leaflets roll upward and turn reddish purple color, or topmost leaves, become yellow. Potato purple-top wilt is synonymous with aster yellow it is a viral disease spread by leafhoppers. Plant certified disease-free seed potatoes. Remove and destroy diseased plants. Keep the garden clean of plant debris. Control leaf-hoppers.

• Lower leaves cup or roll, lose their dark green color and become streaked and leathery brown speckling at the stem end of tubers. Potato leafroll virus is transmitted primarily by aphids. Control aphids. Remove diseased plants and weeds. Spray with pyrethrum or rotenone. Plant certified seed potatoes. Do not save potatoes from infected crops. Plant resistant varieties: Cherokee, Houma, Merrimack.

• Leaves curl upward: older leaves turn yellow, then brown young leaves show purple margins. Nodes and petioles are enlarged. Tubers may be visible. Plant may turn brown and dry. Potato psyllid is light gray-green to dark brown or black winged insects about the size of an aphid they are flat and disk-like before plumping up at maturity. They inject a toxin into leaves as they feed causing the plant to yellow. Use yellow sticky traps to control psyllid.

• Tiny bumps on tubers, brown spots on tuber flesh. Nematodes are microscopic worm-like animals that live in the film of water that coats soil particles some are pests, some are not. Pest root nematodes feed in roots and can stunt plant growth. They are more common in sandy soils. Rotate crops. Solarize the soil with clear plastic in mid-summer.

• Leaves yellow and margin roll plants are stunted and dwarfed tuber is malformed and cracks. Potato yellow dwarf virus is transmitted by leafhoppers. Destroy diseased plants and control leafhoppers. Plant disease free seed potatoes.

• Leaf tips and margins yellow, gradually brown and die tubers have irregular brown spots throughout flesh. Lack of moisture or inconsistent moisture during hot, dry weather. Place 2 to 3 inches of organic mulch across planting bed to conserve soil moisture. Deep water potatoes 2 to 3 hours at a time do not water again until the soil has dried to a depth of 4 to 8 inches.

• Older leaves yellow and die brown streaks on lower leaves stems split lengthwise stem end of tubers discolored around eyes. Verticillium wilt is caused by a soil fungus. It favors cool soil and air temperatures. Avoid planting where tomatoes, potatoes, peppers, eggplant, and cucumber family plants have been recently growing. This disease is most evident in hot weather when the plant is loaded with fruit and water is short. Plant resistant varieties: Houma, Cariboo, Red Beauty. Bacterial wilt also can cause these symptoms black-brown ooze seeps from cut stems.

• Tubers have brown streaks and roots are growing from inside tubers. Nutsedge is a perennial weed that grows in many potato growing regions. The weed’s rhizomes will penetrate potato tubers. Keep potato plantings free of nutsedge. Nutsedge tends to grow in areas that are not well drained.

• Leaves turn light green, wilt, then dry tubers turn watery and brown. Plants and tubers exposed to hot sun and dying winds after cloudy weather. Screen plants during extremely hot weather. Do not leave tubers in hot sun.

• Pink areas around eyes of tubers. Pinkeye occurs on tubers in wet soil. The cause of pinkeye is not known. Plant in well drained soil.

• Marble-sized potatoes grow directly from potato eyes. Cell sap is concentrated in tubers. Store seed potatoes in a cool, dark place. Plant seed potatoes later in season.

• Stems at soil level are covered with purplish, dirty grey fungus foliage curls, turns pinkish to yellowish dark brown or black masses on tubers. Black scurf or Rhizoctonia is a fungal disease that favors warm soil. Remove infected plants and plant debris that harbor fungal spores. Rotate crops. Be sure transplants are not diseased. Rotate crops regularly. Solarize the soil in late spring or summer. Black scurf is resting spores peel away spores before using the potato.

• Irregular black and brown spots to ½ inch in diameter appear on lower leaves and stem leaves turn yellow to brown tubers may have brown, corky, dry spots. Early blight is a fungal disease spread by heavy rainfall and warm temperatures. It is seen near the end of the season when vines near maturity. Keep weeds down in the garden area they harbor fungal spores. Destroy infected plants. Avoid overhead watering.

• Leaves yellow between veins and leaves curl upward shoot tips are stunted cut stems reveal a white ooze cut tubers reveal a yellow to light brown ring of decay. Bacterial ring rot. Discard all infected tubers and plants. Plant certified seed stock plant whole small potatoes instead of seed potatoes. Practice crop rotation. Plant resistant varieties: Merrimack, Saranac, Teton.

• Rough, scabby or corky spots on surface of tubers. Scab is caused by soilborne bacterium. Disease can be cosmetic. Modify soil to a pH of 4.8 to 5.2 work sulfur into the soil to make it slightly acid and reduce disease. Plant resistant varieties: Alamo, Arenac, Cherokee. If scab occurs, change varieties next year. Use long rotations.

• Green tubers. Tubers have been exposed to the sun during growing or after digging sun causes tubers to form chlorophyll green spots. Keep growing tubers covered with soil. Do not eat green sections of potato tubers they contain toxins cut away the green sections before using. Store potatoes in complete darkness.

• Tubers are knobby-shaped. Inconsistent moisture, erratic watering, alternating wet and dry conditions. Tuber growth is uneven. Keep soil evenly, moist. Slow, deep water for 2 to 3 hours do not water again until the soil has dried to a depth of 4 to 8 inches. Mulch to conserve soil moisture. Plant potatoes closer together. Avoid planting knobby varieties.

• Cavities at the center of the potato, hollow center. Hollow heart occurs when potatoes grow too fast because as a result of too much water or too much fertilizer. Cavity can be discolored and lined with powdery decay, verticillium fungus. Cut away the brown areas before using. Fertilize plants early when tubers are about to form. Avoid planting varieties that develop hollow heart: Chippewa, Katahdin, Mohawk, Irish Cobbler, Sequoia, Russet, White Rose.

• Large shallow hole in tubers. Grayish white grub is the larvae of the Japanese beetle, a shiny metallic green, copper winged beetle to ½-inch long. Grubs feed on potato tubers. Cut away damaged areas and use the rest of the tuber. Handpick grubs and beetles. Use pheromone traps to control beetles. Spray with pyrethrum or rotenone.

• Rotten tubers. Bacterial soft rot enters tubers wounded by tools insects or disease. The vascular bundles in leaves, stems, and tubers turn black and bad smelling. Rot can not be cured. Plant potatoes in well-drained soil. Remove and destroy infected tubers. Remove all plants and plant debris at the end of the season. Promote good drainage by adding aged compost and organic materials to planting beds. Avoid over-head watering. Rotate crops.

Sulfur applied to the garden may reduce rots. Protect tubers from injury.

Potato Growing Success Tips:

Planting. Grow potatoes in full sun. Potatoes require well-drained soil rich in organic matter. Prepare planting beds with aged compost. If drainage is an issue, plant potatoes in raised beds. Plant seed potatoes grown specifically for crop growing. Keep the base of potato plants and tubers shielded from light and pest injury use soil or mulch to cover plants. Plant seed potatoes in a 4-inch-deep trench and cover the seed with 2 inches of soil as the plants grow continue to hill up loose soil around the plant eventually mounding the plants. An alternative planting method is to set seed potatoes on the soil surface and cover them with mulch–shredded leaves or straw. Continue to add mulch as plants grow through the season always keeping tubers well covered. This method can be used where the soil is heavy, clay-like, and not well-drained however, the yield will be less.

Planting time. Potatoes grow best where the soil temperature is at least 50°F. Potatoes are usually planted in spring as early as 3 weeks before the last expected frost. Planting time can vary to avoid hot, dry conditions and to minimize disease and pest problems.

• In cooler summer regions, plant one potato crop in mid-spring for late summer harvest.

• In moderate temperature summer regions, plant one crop in late spring or midsummer for fall harvest. If you plant in midsummer, choose an early harvest variety.

• In long warm and humid summer regions, plant three crops: one in late winter for late spring harvest a second fast-maturing crop in mid-spring and a third late summer crop for a fall harvest.

• In regions where there is little or no frost, plant in fall when the heat subsides for a late spring harvest (plants will go dormant in winter and begin growing again in early spring).

• In mild winter and desert regions, plant in the fall for spring harvest, or plant an early-harvest variety in early spring.

Care. Potatoes are shallow rooted and require consistent, even watering from planting time until tubers are fully developed. Do not let the soil go dry during the growing season. When the foliage starts to yellow at the end of the growing season, stop watering so that the tubers do not rot. Keep tubers well covered with soil or mulch from planting to harvest light, temperature fluctuations, and exposure are responsible for many potato disease and pest problems. Crop rotation will shield potatoes from many soilborne diseases and pests.

Harvest. Harvest “new potatoes”–young, small tubers–when plants are blooming lift the full plant and its tubers. Mature potatoes can be harvested when vines die back on their own if vines do not die back, cut the vines at soil level 2 weeks before you want to lift the tubers–this will cause the tubers to harden.


Why are newly grown leaves red? - Biology

Why are ivy leaves grown in the shade, larger in area but lighter in terms of weight than leaves grown in direct sunlight? I am doing a study into the relative size of different ivy leaves from different amounts of sun and shade.

It is strange that you have chosen Ivy leaves for your study. Ivy (Hedera helix) shows enormous variability in its leaves. There are pictures of this on our website. There are differences between the leaves of ground creeping and aerial shoots, flowering and non-flowering shoots and juvenile and mature shoots. How far differences relate to sun and shade is not clear and it may prove difficult to isolate the variables.

However, the observation which you have made on Ivy has also been observed in many other species e.g. brambles, nettles.

Debbie Eldridge comments:- Populations of Brachypodium from shaded populations (non hairy edged morphs) have inherently higher SLA's (SLA = leaf area/leaf dry mass) than unshaded. This can be explained by greater leaf expansion. It is generally thought by many authors that there is fewer layers of palisade cells. What was interesting in my work was that the Leaf Area Ratio (leaf area to total plant dry mass) was not greater in the shaded populations as they channelled a lot of effort into stem growth (much taller than the unshaded) and reproduction. However, SLA (leaf area/leaf dry mass) was consistently higher. The leaves were also arranged along a taller stem which would minimise self shading.
Packham and Willis found the SLA of Oxalis increased as shading increased and Clough et al. found the same in Solanum dulcamara.

Charles Hill comments:- In the summer I did a simple experiment with Y8 measuring nettle leaves and those in the shade were almost twice the area as those in a sunnier spot. Out of interest we did some crude leaf peels with sellotape and found a higher density of stinging hairs on the shade leaves. This is hardly rigorous research but it does suggest the larger area is consistent with cell enlargement which would require a bigger vacuole (mainly water) than increased cell division leading to more cells.

Anne Bebbington has produced a comprehensive review of the subject:

Plants growing in shade often show morphological and physiological differences compared with plants of the same species growing in full sunlight.

The table shows differences which have been found between sun and shade plants.

This table is based on my observations and the table in Adds, Larkcom and Miller The organism and the environment Nelson 1997 ISBN 0174482744

  • The large leaves of the shade shoot provide a larger area for trapping light energy for photosynthesis in a place where light levels are low.
  • Plants subjected to low light intensity often grow rapidly producing long internodes (the part of the stem between each leaf). Rapid growth may help the shoot to reach light. Pupils can relate this to work they may have done comparing the growth of plants/seedlings in the light and dark.
  • The small leaves of the sun plants will provide less surface area for the loss of water through transpiration. Evaporation rates will be high where leaves are exposed directly to the sun
  • Various things may cause the colour difference in the leaves e.g. sun leaves may have a thicker cuticle and several layers of palisade cells with the chloroplasts concentrated in them. There may also be a difference in the amounts of different pigments in the leaf. Anthocyanin pigments are produced in the stems and leaves of the sun shoots. These red pigments help to protect the chlorophyll from excess ultra-violet radiation.

In carrying out a number of A level fieldwork projects we have found that:

Dog’s mercury, stinging nettle and bramble all show clear differences in at least some of the above characteristics. Leaves on the outside and inside of the canopies of trees such as beech, lime, plane, elder and hazel also showed differences. I suspect most deciduous trees with a dense enough canopy may show some differences. Working with single trees or rhizomatous plants such as the nettle and dog’s mercury allows you to separate environmentally determined differences from those which have been genetically inherited.

We concentrated in the main on those characteristics which could be readily measured in the field e.g.
Leaf area, internode length and wilting time are all fairly easy to measure.
Leaf thickness can be measured using microcalipers. Broad differences in leaf colour can be recorded using specially devised colour charts.

If facilities are available chromatography may reveal differences in pigmentation. I am also sure that there are also differences in internal anatomy. Differences in the amount of supporting tissues such as collenchyma and lignified cells could probably be seen in fairly crude hand sections with the help of some staining. This would tie in with Barry’s ideas and would be very interesting to look at. Obviously thin sections would reveal any other anatomical differences.

I wonder whether there are differences in the rate of carbon dioxide uptake in sun and shade leaves.

Barry Meatyard was interested in the investigations which could be done to follow up your observations:- Could it be that the leaves nearer the 'outside' get more buffeting by wind / rain etc and produce more support tissue in response? There's a whole heap of investigations that could be done here - for example looking at the area of lignified tissue in the petioles, midribs and veins, measuring the thickness of the leaf etc. The key thing to find out is the source of the density differences - is the dry mass difference the same as the fresh mass difference I wonder?

Other resources:-
There is an exercise with Teacher and Student resources on the Field Studies Council website.

How is the long stem of the stinging nettle an useful adaptation?

It could be said that the stem of any plant is designed to support the leaves so that they can gather the maximum amount of sunlight.

In the case of nettles, the situation is more interesting.

You should read a discussion about plants grown in sun and shade above.

You will find reference there to the longer internodes of plants grown in shade as well as discovering that nettles are especially adaptable to growing in shade conditions.


Why are newly grown leaves red? - Biology

Scientific name: Acer rubrum
Common name:
Red Maple

The red maple, like its close relative the silver maple, is sometimes called the "swamp maple" or the "soft maple". These names summarize significant features of the ecology and the physical nature of these trees. The red maple is quite possibly the most common and the most widely distributed hardwood tree in eastern North America. It is especially found in the wet soils along streams and in swampy areas and has a dense, shallow root system well adapted to the poor soil aeration properties of these sites. It can also, however, grow abundantly in well-drained, upland and even rocky soils. The soft nature of its wood (although it is stronger than the wood of the silver maple) can lead to weakness in its limbs and trunk that can contribute to its relatively short expected life span of typically less than one hundred years.



Appearance
The red maple is a medium sized tree ranging from fifty to seventy feet tall at maturity with a trunk one to two feet in diameter. Its crown is irregular or rounded and is highlighted by reddish colored terminal twigs. Its leaves are two to six inches in diameter and are often nearly as wide as they are long. The leaves have three major, short pointed lobes that are dull green above and whitish-green below. The leaves turn a bright red in the fall after frost. The red maple's bark is light gray and smooth on young trees becoming increasingly furrowed and plate-like on older trees.

Flowers, Fruit and Seedlings
The red maple is one of the first trees to flower as spring approaches. Flowering may begin in the late winter or early spring. On the Nature Trail the first red maple flowers opened (in the year 2000) on March 14. The flowers are dominantly red with some yellow. In mid-March the abundance of the red maples on the ridges and in the ravines of our area is incredibly obvious. The reddish blur to the tree canopies throughout Western Pennsylvania shouts the presence of the red maple. The fruit (small samara that are also red in color) from these pollinated flowers matures by early to mid-May and falls in abundance to the forest floor. Germination of seedlings may occur immediately or may be delayed until the next spring. Seedlings grow well in the shaded conditions of the forest floor and also in the sunnier conditions of more open sites. The seedlings grow rapidly and may reach mature heights in as little as seventy years. In forested areas red maples may also stump sprout, but these sprouts are typically not as sound as new growth seedlings.

The red maple has been planted in urban areas very extensively. It is a common and important ornamental and shade tree around many homes and along many streets and roadways. The rapid growth, dense canopy and beautiful autumn color display make the red maple a very poplar urban species. Its abundant production of spring samara, the brittleness of its branches and its relatively short life expectancy, however, are major landscaping drawbacks to this species.

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Why are newly grown leaves red? - Biology

Red Pine Tree (Pinus resinosa)

The red pine is a native North American tree species sometimes erroneously called the "Norway pine". Its natural range is around the upper Great Lakes through southern Canada west to Manatoba. It can be found further south in the United States (as in eastern West Virginia) on high mountainous ridges. The red pine has been extensively planted far outside of its natural range in re-forestation projects, in parks and in landscaping around buildings. It grows best in light, sandy, well-drained soils that are relatively low in nutrients. It does not tolerate urban conditions very well or shading by other tree species.

Red pines grow very rapidly for their first 60 or 70 years of life. They can live for up to 350 years and reach heights of 120 feet and diameters of up to three feet.

Seeds and Seedlings
Seeds of the red pine are formed in its small, egg-shaped cones. Seeds begin to be produced when the tree reaches 15 to 25 years of age and are especially abundant every 3 to 7 years. Seeds best germinate when they fall on bare, mineral soil. The young pine seedlings also need lots of intense, direct sunlight in order to grow. Because of these germination and seedling requirements, red pines are not able to grow well in undisturbed pure stands in which the forest floor is shaded and covered with thick layers of decomposing pine needles. It is only after forest fires or some other event causing tree loss that young red pines have a chance to germinate and grow. The seeds of the red pine are eaten by a great variety of songbirds and small mammals (including mice, chipmunks etc).

Needles, Bark and Roots
The needles of a red pine are in groups of two and are from 4 1/2 to 6 1/2 inches long. Needles last between four to five years and then fall to the forest floor where they can accumulate in a thick acidic, mulch layer on the soil surface. The bark of the red pine is flaky and orange-red in color. As the tree ages the bark becomes increasingly thick and irregularly diamond shaped. The roots of the red pine are moderately deep and wide spreading. The lateral root masses also send down "sinkers" which anchor the tree very well in the soil. Red pines are very wind firm because of this dense root system. The dead and damaged red pines that have fallen out on the Nature Trail, in fact, have not wind-thrown by pulling up their roots masses but instead have broken near their bases leaving their stumps and root systems intact.

Mortality
The red pines on the Nature Trail have been dying at a very rapid rate over the past fifteen years. Some of this mortality is probably due to the stress of moist soils and edge shading by the encroaching hardwood species, but much of the loss of these pines is without question the result of subtle climatic and seasonal stresses generated by existence outside of the species' natural range.

A common fate of a red pine stand in many natural forest systems is to be shaded out by hardwood tree seedlings (like maple or oak or aspen) that readily germinate and grow in the moist, protected, shaded conditions of the pine forest floor. These hardwood trees slowly grow up and through the established canopy eventually kill the standing pines. This interaction and change in these forest ecosystems is an example of a process called succession (see "Exploring Succession"). On the Nature Trail, the growth of white ash and white oak up into the canopy of the red pine or the surge of yellow poplar into the sun gaps of the failing pine forest are major, local successional events.

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Why are newly grown leaves red? - Biology

There are three main types of tissue in a plant. They are the dermal tissues, which includes the outer most layers of epidermal cells, vascular tissues, the xylem and phloem, and the ground tissues, that includes everything else. Plants grow in height and width with the help of meristems. New cells are produced in the meristematic tissue, and when this happens they are undifferentiated. The apical meristemis the meristem at the ends of all the roots and stems, they extend the twig or root when it can.

There are two groups of roots a taproot, one main root with lots of little secondary roots, and the fibrous roots, thin, shallow roots that are typical in grasses. On the outside of a root there is the epidermis layer of cells and then there is the cortex or ground tissue. Then there is the endodermis, which contains the Caspian strip, and on the very inside of the roots is the vascular cylinder, which is the xylem and phloem. At the tip of the root there is a region called the root cap, which contains the apical meristem for the root. As the leaves release water and gases into the air, water and nutrients are sucked up from the soil, the process of osmosis. Roots don't actually pump water from the soil, they move water and nutrients across the membrane of the cortex and they then move into the vascular cylinder. The wall of the vascular cylinder is made up of a layer of cell walls and sandwiched in between is the Caspian strip. Nutrients are allowed to move into the vascular cylinder, but not out. This is the function of the Caspian strip. You may still be wondering how water is pushed, against gravity, to the leaves. What you are thinking of is the root pressure. When water is lost in the leaves, the roots suck up the same amount of water. The water in the Caspian tube has nowhere to go, but up.

Stems are divided up into two groups the monocot stems and the dicot stems. The monocot stem, in a cross section, has an epidermis followed by random placement of vascular tissue. The vascular tissues tend to be denser towards the epidermis. The rest of the space is filled in with ground tissue. Dicot stems, in a cross section, have an epidermis on the outside and a thinner cortex just on the inside of that. Next is the vascular tissue that is in a very neat ring. In the center of the stem is the pith. Primary growth is when the plant grows upward, and secondary growth is when it grows outward. The secondary growth that I am talking about is the secondary growth in a dicot stem. In conifers and dicots, secondary growth takes place in later meristem systems called the vascular cambium and the cork cambium. The vascular cambium creates vascular tissue and increases the thickness of the stem over time. The cork cambium forms the protective outer layer. What we call heartwood is mostly dead xylem tissue, which has impurities that can't be removed. The sapwood is the working xylem and it moves water to the leaves. The bark contains the cork, the cork cambium and the phloem. The cork cambium acts as another barrier, so that water can't escape the phloem and cambium layer. The vascular cambium produces new xylem and phloem, which increases the width of the stem.

Leaves are the main photosynthesizing parts on the plant. Because of this, they have to have the most photosynthetic surface. A simple leaf has a bud, petiole (stem of the leaf), and a blade. What we call the leaf is the blade. A compound leaf has the same parts as a simple leaf, but it has leaflets instead of a single, full blade. The bulk of the leaf is made up of mesophyll, a specialized ground tissue. Photosynthesis in most plants happens here. The palisade mesophyll is located underneath both cuticle and epidermis. These specialized cells absorb light that comes into the leaf. Beneath the palisade mesophyll is the spongy mesophyll. This tissue is a loose tissue that has many air spaces that connect to the outside world through the stoma. Basically the stoma is a hole in the bottom of the leaf that controls water evaporation and gas flow. There are two guard cells that are responsible for opening and closing the stoma. When water pressure is high in the leaf, the guard cells swell and the stoma opens. When the water pressure is low, the guard cell shrinks and the stoma closes. Remember that the guard cells are half circles.

You may still be wondering what is it called when the molecules in the water are attracted to each other or if the water molecules are attracted to other molecules of another substance? Well it's capillary action and adhesion. And if you aren't thinking of that then you need to be. This is a plant's ultimate secret. That, and osmosis. An idea that puts these two together is the pressure-flow hypothesis. Basically, the sugars enter the phloem at one spot called the source, and they then travel down to the roots to a sink cell, where it is stored.