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Shade Avoidance Syndrome (SAS)

Have you ever seen some shaded plants grow tall and spindly very fast, while ones in sunlight are shorter and thicker? Plants that grow tall and spindly trying to reach the sunlight are usually "suffering" from Shade Avoidance Syndrome, or SAS. Now scientists have identified the molecular process that controls the onset of SAS. When a plant that requires bright sunlight detects shade from another plant, it will switch into SAS mode and try to quickly grow taller, up into sunlight again.  A pretty clever strategy!

To figure out how SAS worked, researchers at the Salk Institute in California searched through a large collection of mutated plant seedlings for individual plants that didn't turn on shade responses even when in their neighbor's shadow. From these plants, the researchers were able to identify genes involved in the shade response. They found that one of the genes produces an enzyme that speeds up production of a plant growth hormone called Auxin when the plant is shaded.  The hormone causes the plants to grow faster.

The plants have receptors in their cells that are sensitive to light. When these photo-receptors detect the presence of neighboring plants, it triggers the Auxin-producing pathway, which triggers the stem to start growing rapidly. However, growing taller diverts the plant's resources away from reproductive efforts like making flowers, fruits and seeds. This is one reason that understanding SAS has such exciting potential. Crop breeders and farmers could eventually use these new discoveries to maximize the yield of grains or fruits in their fields.

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