| The ozone depletion in the stratosphere could result in increased UV-B irradiation at the Earth's surface. There have been many reports on the deleterious effects of enhanced UV-B irradiation on several crops. However, few information is available in the effects of enhanced UV-B irradiation on the rice of globe importance as a staple food crop. The objective of the present studies is to address on the physiological response of rice and its dynamic genetics of resistance to enhanced UV-B irradiation.1 The effects of enhanced UV-B irradiation on growth and development as well as its physiological response and adaptive mechanism in rice ( Oryza saliva L.)Effects of enhanced ultraviolet-B irradiation (280-320nm) on growth and development as well as yield formation and grain quality in three rice cultivars ( Oryza stativa L.) of Shanyou63,Namcheun,and IR65600-85 with different genetic background under pot condition were investigated for two years. The results showed that enhanced UV-B irradiation treatment reduced plant height, tiller numbers and total leaf areas of 3 rice cultivars, significantly decreased plant dry weight, grain yield as well as grain quality , and made the leaf emergence delayed , resulting in postponed time of flowering, in turn prolonged total growth period. But the inhibitory rate varied in different extents in the three cultivars and the investigated development periods .Under the pot condition, the results obtained from the present experiment indicated that the grain yield and its amylose content were reduced by 24.7%-31.1%, 5.1%-20.5% respectively , but protein content and total amonia acids of grains were increased by 16.2%-20.5% ,9.5%-14.2%.The time of flowering in Shanyou 63, Namcheun and IR65600-85 were delayed by 2d-3d , 3d and 7d-8d, total growth duration were prolonged by 3d-4d, 4d-5d and 9d respectively.Significant reduction in biomass and grain yield, which resulted fromenhanced UV-B irradiation ,was related to decreased photosynthetic capacity, disordered nitrogen metabolism and altered balance of phytohormone in rice plant .The results also showed that chloroplast ultrastructure was destroyed, and total chlorophyll and carotenoid contents on leaf fresh weight basis were significantly reduced, Chla/Chlb ratio and the fluorescence induction kinetics parameters of chlorophyll a were declined in all investigated cultivars after 3-week treatment of enhanced UV-B irradiation ,meanwhile, the net photosynthesis rate was also decreased , in turn reduced the dry matter weight and grain yield of rice .This study indicated that net photosynthesis rate of Shanyou 63, Namcheun and IR65600-85 were decreased by 11.9%, 12.8% and 29.7% respectively after 3-week treatment of enhanced UV-B irradiation. The results also showed that enhanced UV-B irradiation decreased the activity of NR, however, increased the activities of the proteinase, RNase , GS, and the content of total free amino acids , led to decreased content of soluble protein and nucleic acid in rice leaves, thereby resulted in disorder of the physiochemical metabolism and retarded plant growth. It was demonstrated that the contents of IAA and GA were declined, but the reverse was true in the case of ABA in rice exposed to enhanced UV-B irradiation, in turn resulted in unbalanced phytohormone system, and delayed time of flowering , consequently depressed plant growth.Further study showed that different cultivars had different resistance to enhanced UV-B irradiation under the adverse circumstances, attributed to its different adaptive abilities and protective mechanisms in different rice genotypes. It was found that enhanced UV-B irradiation promoted the activities of PAL and GS, resulting in increased accumulation of flavonoid, coupled with increased assimilation and accumulation in leaves of rice. Therefore it could be inferred that nitrogen metabolism tended to be conducted favoring to enter flavonoid synthesis pathway in rice subjected to enhanced UV-B irradiation .The findings suggested thatthe accumu... |
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