And in so doing, they reinforce the very dynamics that led to the state's etiolation in the first place.
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De-etiolation is the transition of seedlings from below-ground growth to above-ground growth form.
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This does not happen in seedlings grown in the dark, which undergo etiolation. An underexposure to light can cause the thylakoids to fail. This causes the chloroplasts to fail resulting in the death of the plant. Thylakoid formation requires the action of vesicle-inducing protein in plastids 1 (VIPP1).
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Dicot seedlings grown in the light develop short hypocotyls and open cotyledons exposing the epicotyl. This is also referred to as photomorphogenesis. In contrast, seedlings grown in the dark develop long hypocotyls and their cotyledons remain closed around the epicotyl in an apical hook. This is referred to as skotomorphogenesis or etiolation.
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Growth is also determined by environmental factors, such as temperature, available water, available light, carbon dioxide and available nutrients in the soil. Any change in the availability of these external conditions will be reflected in the plant's growth and the timing of its development. Biotic factors also affect plant growth. Plants can be so crowded that no single individual produces normal growth, causing etiolation and chlorosis.
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Recent evidence suggests fluctuations in GA concentration influence light-regulated seed germination, photomorphogenesis during de-etiolation, and photoperiod regulation of stem elongation and flowering. Microarray analysis showed about one fourth cold-responsive genes are related to GA-regulated genes, which suggests GA influences response to cold temperatures. Plants reduce growth rate when exposed to stress. A relationship between GA levels and amount of stress experienced has been suggested in barley.
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Upon binding the chromophore, the holoprotein, an apoprotein combined with its prosthetic group, becomes sensitive to light. If it absorbs red light it will change conformation to the biologically active Pfr form. The Pfr form can absorb far red light and switch back to the Pr form. The Pfr promotes and regulates photomorphogenesis in response to FR light, whereas Pr regulates de-etiolation in response to R light.
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Spanish bluebells Hyacinthoides hispanica, showing both leaves and flowers in both etiolated and non-etiolated states. The longest etiolated leaves are about 50 cm long Etiolation is a process in flowering plants grown in partial or complete absence of light. It is characterized by long, weak stems; smaller leaves due to longer internodes; and a pale yellow color (chlorosis). The development of seedlings in the dark is known as "skotomorphogenesis" and leads to etiolated seedlings.
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De-etiolation, is a series of physiological and biochemical changes a plant shoot undergoes when emerging from the ground or in response to light after a period of insufficient light exposure. This process is known informally as greening. These changes that are triggered in the plants shoots or already formed leaves and stems occur in preparation for photosynthesis."Biology 7th Edition" Campbell and Reece (2004) Some of the changes that occur include #Inhibition of hypocotyl lengthening.
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Etiolation increases the likelihood that a plant will reach a light source, often from under the soil, leaf litter, or shade from competing plants. The growing tips are strongly attracted to light and will elongate towards it. The pale color results from a lack of chlorophyll. Some of the changes that occur include # elongation of stems and leaves; # weakening of cell walls in stems and leaves; # longer internodes, hence fewer leaves per unit length of stem; # chlorosis, a pale yellowish-white coloration.
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The photoreceptors phytochromes A, B, C, D, and E mediate red light-based phototropic response. Understanding the function of these receptors has helped plant biologists understand the signalling cascades that regulate photoperiodism, germination, de-etiolation, and shade avoidance in plants. The UVR8 protein detects UV-B light and mediates the response to this DNA damaging wavelength. A. thaliana was used extensively in the study of the genetic basis of phototropism, chloroplast alignment, and stomatal aperture and other blue light-influenced processes.
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Theophrastus of Eresus (371 to 287 BC) may have been the first to write about photomorphogenesis. He described the different wood qualities of fir trees grown in different levels of light, likely the result of the photomorphogenic "shade-avoidance" effect. In 1686, John Ray wrote "Historia Plantarum" which mentioned the effects of etiolation (grow in the absence of light). Charles Bonnet introduced the term "etiolement" to the scientific literature in 1754 when describing his experiments, commenting that the term was already in use by gardeners.
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A strategy of "species-packing" was practiced to ensure that food webs and ecological function could be maintained if some species did not survive. The fog desert area became more chaparral in character due to condensation from the space frame. The savannah was seasonally active; its biomass was cut and stored by the crew as part of their management of carbon dioxide. Rainforest pioneer species grew rapidly, but trees there and in the savannah suffered from etiolation and weakness caused by lack of stress wood, normally created in response to winds in natural conditions.
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Plants perceive light through internal photoreceptors absorbing a specified wavelength signaling (photomorphogenesis) or transferring the energy to a plant process (photosynthesis). In plants, the photoreceptors cryptochrome and phototropin absorb radiation in the blue (B: λ=400–500 nm) spectrum and regulate internal signaling such as hypocotyl inhibition, flowering time, and phototropism. Additional receptors called phytochrome absorb radiation in the red (R: λ=660–730 nm) and far-red (FR: λ>730 nm) spectra and influence many aspects of plant development such as germination, seedling etiolation, transition to flowering, shade avoidance, and tropisms. Phytochrome has the ability to interchange its conformation based on the quantity or quality of light it perceives and does so via photoconversion from phytochrome red (Pr) to phytochrome far-red (Pfr).
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Although preliminary experiments have shown a wide range of effects due to the magnetic field, the mechanism has not yet been elucidated. Having known that the delay of flowering is downregulating in cryptochrome related genes affected by the near-null magnetic field under blue light, cryptochrome is taking as a potential magneto-sensor by a few considerations. Based on the radical pair model, cryptochrome would be the magneto-sensor in the light-dependent magnetoreception since cryptochrome has evolved a significant role of plant behavior, including blue-light reception and regulation, de-etiolation, circadian rhythm, and photolyase. In the photoactivation process, blue light hits cryptochrome and accepts a photon to Flavin while tryptophan receives a photon by another tryptophan donor simultaneously.
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He sees clearly that literary study will undergo the same re-direction of energy and etiolation of purpose that all human activity undergoes when deeply bureaucratized. It will feel especially the embarrassing contrast between its permanently adversative stand toward constituted authority and its own increasingly bureaucratic personality and language." Laurence Lerner, writing in Comparative Literature, found Kernan's book to be of a piece with other books written by "the eminent scholar on retirement, who places a crown upon a lifetime's effort by publishing a book on the state of literary studies today, less carefully documented than the learned works which earned his reputation, and often polemical in intent, and which, with luck, may end up on the best- seller lists. Alvin Kernan's book fits this pattern, and whether or not it becomes a best-seller, it will take its place among the best informed and best written of such works.
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