Plants, stuck in one spot as they are, sit there passively soaking up the rays. The sun shines, the sun doesn't shine; there's not much they can do about it. Right?
Maybe not.
A study at Chapel Hill, University of North Carolina, led by Alan Jones, Kenan Distinguished Professor of Biology, showed that by detecting variations in light, plants can maximize their efficiency for capturing this life source.
It's all about photosynthesis, the process by which they secure photons from the sun and convert them to sugar. When shadows form, plants need to make a choice. If they were to increase the efficiency of photosynthesis, and let the protons pour in right away, when the sun reappears they would burn up.
Jones and colleagues at Michigan State University showed that a plant protein called RGS1 detects changes in light and measures changes in glucose to control how efficiently photosynthesis works. This protein can tell the difference between the temporary darkness that accompanies a shadow and actual nightfall.
Next, Jones and his team placed plans engineered to lack RGS1 in a special chamber that mimicked natural changes in light throughout the day. The RGS1-lacking plants were able to adjust their photosynthesis when the light source followed the same pattern as the open prairie, where the sun rises and sets with no transient changes in light.
But when the scientists introduced shadows, periods of darkness, mimicking cloud cover or flickering light, into the equation, the RGS1-lacking plants could not adjust. They overreacted to brief changes in light intensity and eventually burned up, clearly illustrating the important role that RGS1 plays.
Moreover, plants with RGS1 are smart enough not to just adjust their photosynthesis for just any old shadow or light fluctuation. Researchers found that the chamber had to go dark for four minutes before the plants perceived a shadow. Darkness for less than four minutes was ignored.
The RSG1 in plants detects the rate at which different molecular components decay in their leaves and this decay signals whether a change in light is a shadow or not. RGS1 has the abil- ity to count the number of these molecules and decide how efficiently to take in photons and undergo photosynthesis.
Almost all plants have RGS1, but grasses lack it. Like the plants in the study, grasses are generally out in the open where there is no canopy, no trees and no shadows.
- Shirley Byers