Induction of UV-B resistance in rice (Oryza sativa L. cv. ADT 43) through adaptive mutagenesis. II: Changes in pigments, photosystem II proteins and DNA damage in UV-B selected and non-selected somaclones

摘要

Increased level of solar UV-B radiation affects the plants by altering their growth, biochemistry and physiology. Our previous study in rice showed that somaclones regenerated through tissue culture by UV-B selective pressure caused changes in pigment composition and damage to the PSII proteins. Chlorophyll (Chl) content was increased to a large extent in UV-B selected plants, especially by low dose of UV-B irradiation (10 min day-1 for 30 days). However, high dose of UV-B (30 min day-1 for 30 days) showed marginal decrease in total chlorophyll content but maintained high Chl a/b ratio. Carotenoid accumulation decreased by about 50% under both levels of UV-B irradiation. Further photoreactivation (PR) under white light increased the amount of carotenoids more in UV-B treated plants than that of the control. Maximum increase was observed in somaclones selected by 10 min UV-B irradiation. The synthesis level of UV-screening flavonoids was found to increase in both UV-B treatments even after PR. UV-B treatment inhibited anthocyanin accumulation. PR for 22 days promoted its synthesis but declined thereafter. SDS-PAGE analysis of photosystem II proteins of UV-B selected somaclones revealed the induction of 73 kDa protein upon UV-B selection. Immunoblot of photosystem II proteins of UV-B selected somaclones showed UV-B incurred damage to D1 and OEC 33 proteins. The damage was more in the latter but PR induced the synthesis of this protein. However, 10 min UV-B selection enhanced the D1 content. UV-B selected plants showed lesser damage to DNA and the repair was efficient in 30 min UV-B selected plants.