UVA and UVB
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CRYPTOCHROMES , phototropins , and Zeitlupe ( ZTL ) are the three primary photoreceptors that mediate the effects of UVA . UVB light is primarily mediated by the UV-R8 monomer .”
Sunlight is the portion of the sun ’ s electromagnetic radiation that includes infrared , visible , and ultraviolet ( UV ) light . It ’ s these ultraviolet light waves that can cause harmful radiation to our dermal tissue . But , how have our floral friends evolved to deal with this UV light energy ? Well , UV radiation can be harmful to plant tissue too , but modern research is proving there are also several distinctly positive responses to UV radiation .
WHAT IS UV LIGHT ? Let ’ s take a step backwards and look at the basics . Ultraviolet light is an electromagnetic radiation with a wavelength from 10-400 nanometers ( nm ). This is a shorter wavelength than visible light but longer than x-rays . This radiation can be broken down into three bands : UVA ( 320-400 nm ), UVB ( 290-320 nm ), and UVC ( 100-290 nm ). Radiations with wavelengths from 10-180 nm are sometimes referred to as vacuum , or extreme , UV . These radiations propagate only in a vacuum . Thanks to the ozone layer , only UVA and UVB rays reach the Earth ’ s surface . UVC rays can ’ t make it through , which is lucky as they could have catastrophic effects .
HOW DOES UV LIGHT AFFECT PLANTS ? As sunlight shines down upon a crop , plants expose the surface of their leaves to capture solar rays . While some of this light energy is used in photosynthesis , some regulates different developmental processes — such as advancing growth in good conditions or causing deviations for survival during periods of stress — to optimize the photosynthetic processes and detect seasonal changes . This light-mediated development of form and structure is known as photomorphogenesis .
The different developmental or physiological changes are induced by a plant ’ s photoreceptors , which detect specific wavelengths of light . Photoreceptors are also sensitive to light quantity , quality , and duration . For example , plants growing beneath the canopy use phytochromes to sense the reduced amount of light reaching the plant and regulate such processes as shade-avoidance , competitive interactions , and seed germination . However , it is extremely difficult for scientists to match specific responses to individual photoreceptors . Typically , multiple photoreceptors will interact to produce a single change . Also , some photoreceptors like phytochromes are sensitive to more than one light wavelength . ( Phytochromes , which mediate many aspects of vegetative and reproductive development , are responsible for absorbing red and far-red light but also absorb some blue light and UVA radiation .) When it comes to UV radiation , there are several other photoreceptors responsible for absorbing those wavelengths . Cryptochromes , phototropins , and Zeitlupe ( ZTL ) are the three primary photoreceptors that mediate the effects of UVA . UVB light is primarily mediated by the UV-R8 monomer . It has been proven that UV light influences photomorphogenic responses including gene regulation , flavonoid biosynthesis , leaf and epidermal cell expansion , stomatal density , and increased photosynthetic efficiency . However , don ’ t forget that UV radiation can also damage membranes , DNA , and proteins . That ’ s why many plants undergo photomorphogenic changes designed to protect them from these rays when their photoreceptors sense the presence of radiation .
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