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This study used comparisons across nine populations of Trifolium repens (white clover) in conjunction with drought to examine physiological responses to ultraviolet-B radiation (UV-B). Plants were exposed for 12 weeks to supplementation with 13.3 kJ m ----2 d ----1 UV-B, accompanied by 4 weeks of drought under controlled environmental conditions. UV-B increased the levels of UV-B-absorbing compounds and of flavonol glycosides and this effect was synergistically enhanced by water stress. These changes were more pronounced for the ortho -dihydroxylated quercetin, rather than the monohydroxylated kaempferol glycosides. UV-B increased leaf water potential ( y y y y L ) by 16% under drought and proline levels by 23% under wellwatered conditions. The intraspecific comparisons showed that higher UV-B-induced levels of UV-B-absorbing compounds, of quercetin glycosides and of y y y y L were linked to lower plant productivity and to higher UV-B tolerance under well-watered conditions. These findings suggest that: (1) slow-growing T. repens ecotypes adapted to other stresses have higher capacity for physiological acclimation to UV-B; and (2) that these attributes also contribute to decreased UV-B sensitivity under drought.

Background and Aims:New Zealand is exposed to relatively high solar ultraviolet (UV) radiation; such high irradiances of UV radiation having the potential to change the biochemical composition of plants. The aim of this study was to investigate the effects of UV radiation and the role of canopy leaves on berry biochemical composition in Vitis vinifera var. Sauvignon Blanc. Sauvignon Blanc is the major grape variety grown in New Zealand. Methods and Results: Leaves were removed from around the fruiting zones of vines and screens that altered UV radiation exposures were placed over the grape bunches. Samples taken throughout development were analysed for changes in total phenolic compounds (including flavonols), amino acids and methoxypyrazines. Total phenolic compounds increased substantially in response to UV-B exposure and this was reflected in changes taking place within the skins of the berries. Flavonol levels were determined by UV-B radiation exposure and accumulated to maximum concentrations at veraison, subsequently declining to harvest. UV radiation did not have a significant effect on the majority of amino acids or methoxypyrazine concentrations. The most noticeable change in amino acid and methoxypyrazine accumulation was caused by the presence of leaves over the fruiting zone, retaining these leaves maintained significantly higher concentrations in the berries at harvest. Conclusions: UV-B radiation determines the composition of flavonols in the skins of grapes. Amino acid and methoxypyrazine concentrations are not predominantly determined by UV-B, but retention of leaves over the fruiting zone promotes their accumulation in berries. Significance: Canopy manipulations are routinely used commercially in the vineyard to help control vigour and reduce disease pressure. The findings presented here are important for viticulturists to understand how management of the vine leaf canopy can determine the biochemical composition of the grapes and can therefore, ultimately affect wine quality. Gregan et al.Effects of ultraviolet on grape berry biochemistry 227