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S, 1995, Inhihition of hypocotyl ekmgatioB by ukraviolel-B radiation in de-eliolating tomato seedlings, 11. Time-course, comparison with flavonoid responses and adaptive significance. -Physiol. Plant. 93: 591-601.UV-B radiation inhibits hypocotyl elongation in etiolated tomato {Lycopersicon escuientum Mill. cv. Alisa Craig) seedlings acting through a photoreceptor system with peak apparent effectiveness around 300 nm. In order to further characterize the response and gain insight into its potential ecological significance, the time-course of inhibition was measured and compared with the time-course of flavonoid accumulation in the same seedlings, W^hen a background of strong (> 620 jjmol m--^ s-') white light (WL) was supplemented v^ith low irradiance UV-B (~ 3 pmol m-s-'), suhstantial (5 0%) inhihiti(m of elongation occurred within 3 h of the light treatment. The magnitude of UV-B-induced elongation inhibition was similar in wild type (WT) and uu-mutant seedlings, in spite of the large differences between genotypes in rate and temporal pattern of elongation. In comparison to the effect of UV-B on elongation, induction of llavsmoid accumulation in WT and au seedlings undergoing de-etiolation was a much slower response. Several UV'-ahsorbing compounds appeared to he specifically induced by light, and some of them accumulated faster under the WL -f UV-B treatment than under WL alone. However, there was litlie or no detectable effect of WL on flavonoid levels until up to 3 h of treatment, and the specific L'V-B effect was measurable only after 6 h of continuous treatment. Indeed. UV-B-screening properties of crude alcoholic extracts were not different between WL and WL + UV-B treatments until after 9 or 24 h. When the light treatments were applied to seedlings thai v, ere jus( breaking through the soil surface. UV-B v\as found to consistently retard seedling emergence. These results suggest that the rapid inhibition of elongation in de-etiolating seedlings is an evolved response lo UV-B. which ma\ ser\'e to minimize seedling exposure lo sunlight until protective pigmentation responses (triggered by WL and UV-B) have taken place in the seedlings" epidermis.

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One- and two-year-old `Pinot noir' grapevines were irrigated with Hoagland's nutrient solution and shaded with 60% shade cloth to investigate the effect of shading on inflorescence necrosis (IN), tissue ammonium, and nitrate status. Shading increased IN, tissue ammonium, and nitrate concentrations of laminas, petioles, and rachis in two-year-old vines. IN was positively correlated with tissue ammonium and nitrate levels. In one-year-old vines, tissue ammonium and nitrate concentrations were increased by shading in most tissues except for nitrate in tendrils and old roots. Tissue ammonium correlated with nitrate concentration in various tissues after anthesis in one-year-old vines and in laminas, petioles, fruit, and rachis of two-year-old vines. Elevated tissue ammonium in rachis has been suggested as a possible cause of IN.