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Takuma Tanada observed that the root tips of barley adhered to the sides of a beaker with a negatively charged surface after being treated with red light, yet released after being exposed to far-red light. [8] For mung bean it was the opposite, where far-red light exposure caused the root tips to adhere, and red light caused the roots to detach ...
When Emerson exposed green plants to differing wavelengths of light, he noticed that at wavelengths of greater than 680 nm the efficiency of photosynthesis decreased abruptly despite the fact that this is a region of the spectrum where chlorophyll still absorbs light (chlorophyll is the green pigment in plants - it absorbs mainly the red and blue wavelengths from light).
Oat phytochrome absorption spectrum (Devlin, 1969). Phytochromes are a class of photoreceptor proteins found in plants, bacteria and fungi.They respond to light in the red and far-red regions of the visible spectrum and can be classed as either Type I, which are activated by far-red light, or Type II that are activated by red light. [2]
This range of wavelengths not only includes FR, but also UV-A and UV-B. The Emerson Effect established that the rate of photosynthesis in red and green algae was higher when exposed to R and FR than the sum of the two individually. [13] This research laid the ground work for the elucidation of the dual photosystems in plants.
In land plants, leaves absorb mostly red and blue light in the first layer of photosynthetic cells because of chlorophyll absorbance. Green light, however, penetrates deeper into the leaf interior and can drive photosynthesis more efficiently than red light.
Other experiments have proven this by exposing plants to extra red-light in the middle of the night. A short-day plant will not flower if light is turned on for a few minutes in the middle of the night and a long-day plant can flower if exposed to more red-light in the middle of the night. [9]
Phototropism in plants such as Arabidopsis thaliana is directed by blue light receptors called phototropins. [13] Other photosensitive receptors in plants include phytochromes that sense red light [14] and cryptochromes that sense blue light. [15] Different organs of the plant may exhibit different phototropic reactions to different wavelengths ...
Red edge refers to the region of rapid change in reflectance of vegetation in the near infrared range of the electromagnetic spectrum. Chlorophyll contained in vegetation absorbs most of the light in the visible part of the spectrum but becomes almost transparent at wavelengths greater than 700 nm .