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Why don’t plants get sunburn? Research in Professor Gareth Jenkins’ laboratory, University of Glasgow Ins$tute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow G12 8QQ, UK. Why don’t ultraviolet-‐B rays in sunlight harm plants? Sunlight spectrum in Glasgow Daylight Spectrum - Glasgow Summer Afternoon - 4th August 2008 (Bobby Brown and Jane Findlay) -2 -1 s ) Fluence Rate (_mol Amount of lmight 6 5 4 3 2 1 0 760 740 800 720 780 700 680 660 640 620 600 580 500 560 480 540 520 440 420 400 460 380 UV-‐B 360 340 260 320 300 280 240 Sunlight contains a very small amount of ultraviolet-‐B (UV-‐B) light (see panel to right) which, because of its high energy, is potenIally damaging to living organisms, including humans. UV-‐B causes sunburn, skin aging, cataracts and some forms of skin cancer. Hence many people avoid staying in bright sunlight for too long and apply sunscreen loIons or creams to reduce exposure to UV-‐B. So how do plants, which are constantly exposed to sunlight, avoid damage by UV-‐B? Why don’t plants get sunburn!? The answer is that plants are able to shield themselves from UV-‐B…….. Wavelength (nm) Wavelength of light (nm) How do plants protect themselves from UV-‐B? How do plants make their own sunscreen? Plants protect against UV-‐B in several ways. For example, in some species, surface waxes and hairs reflect UV-‐B. However, there is a more important type of UV-‐protecIon: plants make their own chemical sunscreens which they deposit in their outer Issues – which is much easier than using sun loIon! The main sunscreen chemicals are called flavonoids. They absorb UV-‐B just like the sun loIons we use and limit penetraIon into the leaf. The flavonoid sunscreen is made through a series of chemical reacIons in plant Issues. Each step in the manufacture of flavonoids is controlled by the acIon of enzymes – proteins that facilitate chemical reacIons. Exposure of plants to UV-‐B causes flavonoid producIon, so UV-‐B actually helps to protect plants from UV-‐damage! UV-‐B sImulates sunscreen producIon by increasing the amounts of enzymes that make the flavonoids. When the plant ‘sees’ UV-‐B it acIvates genes that encode the informaIon to make the relevant enzymes. Flavonoids Upper epidermis Palisade cells Spongy mesophyll SecIon through a leaf Vascular Issue Lower epidermis UV-‐B Genes Enzymes Flavonoids UV-‐protecIon How do plants ‘see’ UV-‐B? Why is this research useful? Plants detect light using ‘photoreceptors’. The UV-‐B photoreceptor is a doughnut-‐shaped protein called UVR8. Normally two units (molecules) of UVR8 are held together by the aXracIon of posiIve and negaIve charges on their surface, rather like two baXeries! When UVR8 detects the presence of UV-‐B the charges are neutralised and the doughnuts separate. The single molecules of UVR8 are then able to acIvate genes to produce flavonoids. UV-‐B exposure changes the chemical composiIon of leaf Issue, including in crops that we consume. Flavonoids in foods and drinks have posiIve health benefits. Furthermore, chemical changes caused by UV-‐B make leaf Issue less palatable to insects and other pests. So by understanding how plants detect and respond to UV-‐B we may be able to produce crops with beXer nutriIonal properIes and which are more pest resistant. UV-‐B Flavonoid producIon + - + UVR8 UVR8 UVR8 Our research is supported by funding from the Biotechnology and Biological Sciences Research Council and The Leverhulme Trust.
