Etiolated

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An etiolated plant is one that it is characterized, due to lack of light, by symptoms of yellowing, failure of leaf expansion, thin stems and elongation.

Obtaining these symptoms (as well discarding them in the presence of light) is the active, complex reaction of the plant, governed by light receptors and controlled by many genes and plant hormones,[1] not just a result of the bad growth conditions.

Green color is primarily caused by chlorophyll that is needed for photosynthesis. There are two pathways so synthesize the chlorophyll, and one of them is light dependent. Algae, ferns and coniferous have both pathways and synthesize chlorophyll also in the darkness. Hence they grow in green in the darkness as well. Flowering plants that only have the light-dependent pathway can only become green in the presence of light.[2]

References

  1. James B. Reid, Natasha A. Botwright, Jennifer J. Smith, Damian P. O'Neill, and L. Huub J. Kerckhoffs. (2002). Control of Gibberellin Levels and Gene Expression during De-Etiolation in Pea. Plant Physiology, 128(2): 734–741. Available online (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC148934).
  2. J Y Suzuki and C E Bauer (1992). Light-independent chlorophyll biosynthesis: involvement of the chloroplast gene chlL (frxC). Plant Cell. 1992 Aug; 4(8): 929–940. Available online (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC160185/).