MadSci Network: Botany |
Dear Lewis:
Five minutes of light per day isn’t very much. Plants need light to make their own food through the process called photosynthesis. Without sufficient light, the plant will, in the long term, starve to death.
In the short term, however, a very curious thing will happen....the plant will start to elongate very dramatically. It does so in a last ditch effort to reach any available light. All available resources within the plant will be marshalled in a vain attempt to reach the light (which you so cruelly have taken away!). The plant will grow tall, pale and spindly, and will eventually topple over and die.
There is a pigment in the plant called phytochrome that controls this process (a pigment is simply a molecule that absorbs visible light). Phytochrome is a bit like a light switch: it exists in two conformations, Pr and Pfr. Red light causes phytochrome to be in the Pfr form and this promotes normal growth. Darkness causes phytochrome to accumulate in the Pr form and this promotes the last-ditch growth described in the first paragraph. By complex mechanisms. the Pr form alters the normal growth hormone concentrations within the plant, thereby causing the last-ditch spurt of growth
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