Etiolation (pronounced /iːtɪəˈleɪʃən/) is a process in flowering plants grown in partial or complete absence of light.[1] It is characterized by long, weak stems; smaller, sparser leaves due to longer internodes; and a pale yellow color (chlorosis). It 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. The cause of the elongation is due to auxins. Auxins are not active in light; when they are active they stimulate proton pumps in the cell wall which increases the acidity of the cell wall and activates expansin (an enzyme that breaks bonds in the cell wall structure) that weaken the cell wall and allow the cell to expand.[2]

Chloroplasts that have not been exposed to light are called etioplasts (see also plastids).

De-etiolation, on the other hand, is a series of physiological and biochemical changes a plant shoot undergoes in response to sunlight. This process is also known informally as greening. The changes triggered in the plant shoot all occur in preparation for photosynthesis.[3]

Some of the changes that occur include:

  1. Inhibition of hypocotyl lengthening.
  2. Stimulation of cotyledon expansion.
  3. Opening of the apical hook.
  4. Stimulation of synthesis of anthocyanins.
  5. Stimulation of chloroplasts development from etioplasts.

This process is regulated by the exposure of various photoreceptor pigments to light. Phytochrome A and phytochrome B both respond to an increasing proportion of red light to far-red light which occurs when the shoot comes out into the open. Cryptochrome 1 responds to increasing amounts of blue light when the shoot reaches the surface.[4]


  1. ^ Burgess, Jeremy (1985). An Introduction to Plant Cell Development. CUP Archive. p. 55. ISBN 0-521-31611-1. Retrieved 2011-01-17. 
  2. ^ Purves, William K.; Sadava, David; Orians, Gordon H. (2004). Life: The Science of Biology. Volume III: Plants and Animals. Macmillan. p. 745. Retrieved 2011-01-17. 
  3. ^ "Biology 7th Edition" Campbell and Reece (2004)
  4. ^ "Plant Physiology 4th Edition" Taiz and Zeiger (2006)

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Look at other dictionaries:

  • Etiolation — E ti*o*la tion, n. 1. The operation of blanching plants, by excluding the light of the sun; the condition of a blanched plant. [1913 Webster] 2. (Med.) Paleness produced by absence of light, or by disease. Dunglison. [1913 Webster] …   The Collaborative International Dictionary of English

  • etiolation — etiolation. См. этиоляция. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • etiolation — noun 1. a pale and sickly appearance his etiolation signaled years in prison • Derivationally related forms: ↑etiolate • Hypernyms: ↑appearance, ↑visual aspect 2. the act of weakening by stunting the growth or development of something the et …   Useful english dictionary

  • etiolation — An abnormal increase in stem elongation, accompanied by poor (if any) leaf development. Physiological etiolation is caused by a lack of chlorophyll, and is typical of plants growing under low light intensity or in complete darkness. It can also… …   Glossary of Biotechnology

  • etiolation — noun see etiolate …   New Collegiate Dictionary

  • etiolation — Growth habit adopted by germinating seedlings in the dark. Involves rapid extension of shoot and/or hypocotyl and suppression of chlorophyll formation and leaf growth …   Dictionary of molecular biology

  • etiolation — See etiolate. * * * …   Universalium

  • etiolation — noun Growth process of plants grown in the absence of light, characterized by long, weak stems, fewer leaves and chlorosis …   Wiktionary

  • etiolation — 1. Paleness or pallor resulting from absence of light, as in persons confined because of illness or imprisonment, or in plants bleached by being deprived of light. 2. The process of blanching, bleaching, or making pale by withholding light. [Fr.… …   Medical dictionary

  • etiolation — n. process of whitening a plant by depriving it of sunlight …   English contemporary dictionary

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