cryptochromes that have been identified in plants, CRY1 and CRY2, which regulate the inhibition of hypocotyl elongation in response to blue light. 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). 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. There are blue light photoreceptors that are not a part of photomorphogenesis. For example, phototropin is the blue light photoreceptor that controls phototropism. UV light Plants show various responses to UV light. UVR8 has been shown to be a UV-B receptor. Plants undergo distinct photomorphogenic changes as a result of UV-B radiation. They have photoreceptors that initiate morphogenetic changes in the plant embryo (hypocotyl, epicotyl, radicle) Exposure to UV- light in plants mediates biochemical pathways, photosynthesis, plant growth and many other processes essential to plant development. The UV-B photoreceptor, UV Resistance Locus8 (UVR8) detects UV-B rays and elicits photomorphogenic responses. These response are important for initiating hypocotyl elongation, leaf expansion, biosynthesis of flavonoids and many other important processes that affect the root-shoot system. Exposure to UV-B rays can be damaging to DNA inside of the plant cells, however, UVR8 induces genes required to acclimate plants to UV-B radiation, these genes are responsible for many biosynthesis pathways that involve protection from UV damage, oxidative stress, and photorepair of DNA damage. There is still much to be discovered about the mechanisms involved in UV-B radiation and UVR8. Scientists are working to understand the pathways responsible for plant UV receptors response to solar radiation in natural environments. References External links Plant development