Effects of NaCl stress on changes in the ultraviolet-B radiation-induced cyclobutyl pyrimidine dimer and ultraviolet absorbing compound contents in mung bean.

In two mung bean cultivars (Phaseolus raditus L. cv. 'Qindou-20' and 'Zhonglv-1') with different sensitivities to UV-B grown in growth chamber under supplemental or no supplemental UV-B radiation (0.4 W/m(2)) with or without 0.4% NaCl, the effects of NaCl stress on UV-B-induced DNA damage and repair were studied. The results showed that, under NaCl stress, (i) CPD accumulation was lower in the tolerant cultivar 'Zhonglv-1' but was the same in the sensitive cultivar 'Qindou-20', (ii) CPD formation in both cultivars was weakened, (iii) the photorepair and dark repair capacity were higher in the tolerant cultivar and (iv) the photorepair was weakened and dark repair capacity did not change in the sensitive cultivar. There was a negative correlation between susceptibility of CPD formation and levels of UV-absorbing compounds. These results demonstrate that NaCl stress can affect not only the susceptibility to CPD formation, but also the capacities for photorepair and dark repair of DNA, which together result in the change in UV-B-induced CPD accumulation and thereby that in sensitivity of plant to UV-B. The results also suggest that the differences in susceptibilities to CPD formation are due to the differences in levels of UV-absorbing compounds.