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 ultravioletB rays in sunlight harm plants? How do plants protect themselves from UVB? How do plants make their own sunscreen? How do plants ‘see’ UVB? Sunlight contains a very small amount of ultravioletB (UVB) light (see panel to right) which, because of its high energy, is potenIally damaging to living organisms, including humans. UVB 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 UVB. So how do plants, which are constantly exposed to sunlight, avoid damage by UVB? Why don’t plants get sunburn!? The answer is that plants are able to shield themselves from UVB…….. Plants protect against UVB in several ways. For example, in some species, surface waxes and hairs reflect UVB. However, there is a more important type of UVprotecIon: 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 UVB 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 UVB causes flavonoid producIon, so UVB actually helps to protect plants from UVdamage! UVB sImulates sunscreen producIon by increasing the amounts of enzymes that make the flavonoids. When the plant ‘sees’ UVB it acIvates genes that encode the informaIon to make the relevant enzymes. Plants detect light using ‘photoreceptors’. The UVB photoreceptor is a doughnutshaped 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 UVB the charges are neutralised and the doughnuts separate. The single molecules of UVR8 are then able to acIvate genes to produce flavonoids. Why is this research useful? UVB 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 UVB make leaf Issue less palatable to insects and other pests. So by understanding how plants detect and respond to UVB we may be able to produce crops with beXer nutriIonal properIes and which are more pest resistant. Our research is supported by funding from the Biotechnology and Biological Sciences Research Council and The Leverhulme Trust. 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800 Flavonoids UVB Wavelength of light (nm) Amount of light Sunlight spectrum in Glasgow Flavonoids UVB Genes Enzymes UVprotecIon + - + - UVB Flavonoid producIon UVR8 UVR8 UVR8 SecIon through a leaf Upper epidermis Lower epidermis Spongy mesophyll Vascular Issue Palisade cells