Shade avoidance
Encyclopedia
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 (eg 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.
Shade
Shade is the blocking of sunlight by any object, and also the shadow created by that object. Shade also consists of the colors grey, black, white, etc...
of another plant. It often includes elongation
Etiolation
Etiolation is a process in flowering plants grown in partial or complete absence of light. It is characterized by long, weak stems; smaller, sparser leaves due to longer internodes; and a pale yellow color . It increases the likelihood that a plant will reach a light source, often from under the...
, altered flowering time, increased apical dominance
Apical dominance
In plant physiology, apical dominance is the phenomenon whereby the main central stem of the plant is dominant over other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets....
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 (eg a rock) and the shade of another plant. In the shade of a plant, far red light is present in a higher irradiance
Irradiance
Irradiance is the power of electromagnetic radiation per unit area incident on a surface. Radiant emittance or radiant exitance is the power per unit area radiated by a surface. The SI units for all of these quantities are watts per square meter , while the cgs units are ergs per square centimeter...
than red light, as a result of the absorption of the red light by the pigments involved in photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
. Phytochrome
Phytochrome
Phytochrome is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night and to set circadian rhythms...
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
Photomorphogenesis
In developmental biology, photomorphogenesis is light-mediated development. The photomorphogenesis of plants is often studied by using tightly-frequency-controlled light sources to grow the plants.-Germination:...
). 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.