Photochemical Efficiency of PSⅡ and Characteristics of Photosynthetic CO2 Exchange in Indica and Japonica Subspecies of Rice and Their Reciprocal Cross F1 Hybrids Under Photoinhibitory Conditions
Abstract:To elucidate photoinhibitory characteristics and their genetic background in rice (Oryza sativa L. ), PS Ⅱ electron transport activities, D1 protein contents, chlorophyll a fluorecence parameters, net photosynthetic rates (PN), photorespiratory rates (PR) and RuBPCase/Oase activities were measured, and kinetic analysis of RuBPCase was carried out in indica and japonica subspecies of rice and their reciprocal cross Fl hybrids after photoinhibitory treatment in 21% O2 and CO2-free gases under a PFD of 1 000/anol photons‘m-2 · s-l for 3 h. The results are as follows: Japonica rice, keeping less net degradation of D1 protein and maintaining higher PS Ⅱ electron transport activities and photo chemical efficiency of PS Ⅱ (FV/Fm), was more tolerant to photo inhibition as compared with indica rice. However, the D1 protein contents, PS Ⅱ electron transport activities and Fv/Fm in their reciprocal cross F1 hybrids, though lying between the values of their parents, were closer to those in their maternal lines rather to their paternal lines. Characteristics of photosynthetic CO2 exchange were further observed. The Pa was relatively stable, yet the PN decreased obviously and, as a results, the PR/PN increased in all genotypes. There were more decrease in PN and more increase in PR/PN in photoinhibition-sensitive indica than in the photoinhibition-tolerant japonica. However, the PR/PN in the reciprocal cross Fl hybrids, though lying between the values of their parents, was closer to that in their maternal lines than to paternal lines. No obvious changes were observed in the activities of RuBPCase/Oase, Km (CO2) and Vmax (CO2) of RuBPCase in indica and japonica rice and their reciprocal cross F1 hybrids before and after photoinhibitory treatment. Furthermore, markedly positive correlation between D1 protein contents and Fv/Fm(r = -0.950 1), and negative correlation between D1 protein contents and PR/PN(r = 0.976 8) were demons trated. These results infer that the D1 protein encoded by the plastid gene from maternal line was the molecular basis of photoinhibitory characteristics and their physiological inheritance.