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401.
To evaluate the effect of different naturally occurring irradiation conditions on the sensitivity of bean (Phaseolus vulgaris cv. Label) to increased UV-B levels, plants were grown under six different light treatments. In the control series (at ambient levels of UV-B), UV-B and visible light were decreased in parallel, resulting in three different total irradiation treatments with the same UV-B/PAR ratio. A second series with a 15% increase in UV-B irradiation at each PAR level was used to investigate the effect of UV-B under the varying total irradiance levels. The different total irradiance levels resulted in large differences in total dry weight, specific leaf weight, photosynthesis-light response and pigment concentrations. Nevertheless, the 15% increase in UV-B resulted in equal reductions in total dry weight (from 24.5 to 34.3%) and effective photosynthesis for all light levels. The accumulation of protective pigments in the primary bean leaves was strongly correlated to the total irradiance level (200% increase from the lowest to the highest light level), but was not influenced by increasing UV-B levels. As the UV-B/PAR ratio outside increases with decreasing total irradiance (when induced by cloud cover) this implies that low radiation levels are potentially dangerous to some plants, even though the UV-B levels may seem negligible. 相似文献
402.
403.
Investigations were carried out to clarify sporopollenin biosynthesis. Tracer experiments were focussed on the incorporation of specifically labeled 14C-phenylalanine into sporopollenin. In addition, the incorporation of further 14C-labeled substances, such as glucose, acetate, malonic acid, mevalonate and tyrosine, was investigated. The sporopollenin fraction was isolated and purified by a gentle method including extractions by different solvents, incubations with hydrolyzing enzymes and fractionated saponifications. During the purification procedure the whereabouts of the initially applied radioactivity was followed. After each step the remaining as well as the released radioactivity was determined. Saponification of samples labeled after application of phenylalanine yielded p-coumaric acid and p-coumaric acid methyl ester as labeled products. In comparison with the other substances applied, the highest incorporation rates were obtained with phenylalanine, regardless of the position of labeling. After degradation of the sporopollenin sample labeled with ring-14C-phenylalanine, p-hydroxybenzoic acid was detected as the main labeled product. These results unequivocally show that an integral incorporation of the aromatic ring system occurred. Tracer experiments were carried out at different stages of development. Their results show that, although the incorporation rates of 14C-phenylalanine into sporopollenin differ, the substantial incorporation of this substance is not bound to defined stages of development. 相似文献