We provided information about Light and Retinal Cells last week. This week, we will share a story of Light and Plants with you.
Plants transform CO2 into sugar to fuel their life; literally, light is the source of life of plants. Thus plants leave out in the way plants get the most light at any given developmental stage (Fig 1), and when the light is not sufficient, they change even the locations, angles and shapes of leaves.
When plants are shaded by the foliage of neighboring plants, how do plants recognize the shades and furthermore, how do plants tell the shades are made by neighboring plants or neighboring rocks or buildings? And how plants elongate stems to escape the shades and get more light?
Plants recognize the shades of neighboring plants by sensing the ratio between red and far red light using specific light sensors so called the phytochrome. In the shades formed by the foliage of neighboring plants, the ratio of red over far red light increases because red light is mostly absorbed by chlorophylls whereas far red light is reflected by leaves. When the ratio of red over far red light increases, phytochrome change their structure from Pr to Pfr, which leads to shade avoidance responses including stem elongation via increase of auxin concentrations in plant cells (Fig 2).
In addition, plants sense the seasonal change in light intensity, the length of daytime, temperature, etc. and decide when to germinate, when to grow and when to bloom. Daily and seasonal change in plants are cued by changes in the quality and quantity of sunlight and orchestrated by the biological clock in plants. Perilla plants were reported to produce only 6% of seeds when grown next to street lights. It is because the biological clock of plants was disturbed by the artificial light overnight.