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 (256Kb)
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45,106,000 Yen (FY1995 16,139,000 Yen)
We have studied the mechanism of UV-B retardation of growth in irradiated plants. Growth of the first leaves of fertilized cucumber seedlings was markedly retarded by UV-B radiation. A decrease in Photosynthetic activity and an increase in ascorbate peroxidase activity in these plants were observed, suggesting that active oxygen might be involved in the growth retardation. Growth promoting activity normally present in the extracts of the first leaves, decreased upon UV-B irradiation.
Ultraviolet-B induced lesions in DNA, namely cyclobutane pyrimidine dimer(CPD) and pyrimidine(6,4) pyrimidone(6-4PP), in several plants were determined. In cucumber and sorghum, induction of these photolesions was dependent on temperature and their extent was reduced by simultaneous irradiation with white light. Dark repair of both types of photolesions was undetectable in cucumber. Light dependent removal of 6-4PP was very slow with 50% removal in 4 h. In contrast, 50% of initial CPDs were removed within 15 min. Both photorepair processes were dependent on the intensity of white light and were sensitive to temperature. Inhibition of plant anthocyanin synthesis was correlated with the amount of CPD present. CPD and 6-4PP were also detected in chloroplast DNA isolated from UV-B irradiated spinach leaves. No photorepair activity of these lesions was detected in the chloroplasts.
Thirteen Arabidopsis thaliana mutants were isolated to identify the genes involved in UV-B sensitivity.
Growth retardation, Photorepair, Chloroplast, Mutant, DNA