Shade avoidance
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Shade avoidance is a set of responses that plants display when they are subjected to the shade of another plant. It often includes elongation, altered flowering time, increased apical dominance and altered partitioning of resources. This set of responses is collectively called the shade-avoidance syndrome (SAS).
Plants can tell the difference between the shade of an inanimate object (e.g. a rock) and the shade of another plant. In the shade of a plant, far red light is present in a higher irradiance than red light, as a result of the absorption of the red light by the pigments involved in photosynthesis. Phytochrome can be used to measure the ratio of far-red to red light, and thus to detect whether the plant is in the shade of another plant, so it can alter its growth strategy accordingly (photomorphogenesis). In Arabidopsis, phytochrome B is the predominant photoreceptor that regulates SAS.
Over the past few decades, major increases in grain yield have come largely through increasing planting densities. As planting densities increase so does the proportion of far red light in the canopy. Thus, it is likely that plant breeders have selected for lines with reduced SAS in their efforts to produce high yields at high density.
- Harry Smith The shade avoidance syndrome: multiple responses mediated by multiple phytochromes. Plant, Cell & Environment 1997. Vol. 20, pages 840-844.
