Photomorphogenesis
In developmental biology, photomorphogenesis is light-mediated development, where plant growth patterns respond to the light spectrum.
Phytochromes, cryptochromes, and phototropins are photochromic sensory receptors that restrict the photomorphogenic effect of light to the UV-A, UV-B, blue, and red portions of the electromagnetic spectrum.
[2] Most research on photomorphogenesis is derived from plants studies involving several kingdoms: Fungi, Monera, Protista, and Plantae.
In 1686, John Ray wrote "Historia Plantarum" which mentioned the effects of etiolation (grow in the absence of light).
Later, with growth of the shoot (particularly when it emerges into the light) there is increased secondary root formation and branching.
This type of photomorphogenesis is known as photoperiodism and involves using red photoreceptors (phytochromes) to determine the daylength.
[2] Typically, plants are responsive to wavelengths of light in the blue, red and far-red regions of the spectrum through the action of several different photosensory systems.
If it absorbs red light it will change conformation to the biologically active Pfr form.
[6] PHYB is involved in regulating photoreversible seed germination in response to red light.
Based on studies with action spectra, mutants and molecular analyses, it has been determined that higher plants contain at least 4, and probably 5, different blue light photoreceptors.
The cryptochromes have evolved from microbial DNA-photolyase, an enzyme that carries out light-dependent repair of UV damaged DNA.
[10] There are two different forms of cryptochromes that have been identified in plants, CRY1 and CRY2, which regulate the inhibition of hypocotyl elongation in response to blue light.
[10] Cryptochromes control stem elongation, leaf expansion, circadian rhythms and flowering time.
In addition to blue light, cryptochromes also perceive long wavelength UV irradiation (UV-A).
[10] Since the cryptochromes were discovered in plants, several labs have identified homologous genes and photoreceptors in a number of other organisms, including humans, mice and flies.
