Photoinhibition in indica and japonica subspecies of rice (Oryza sativa) and their reciprocal F1 hybrids

Abstract

Photoinhibitory performance and its physiological basis have been studied in Oryza sativa L. subspecies indica and japonica, and their reciprocal F₁ hybrids. The results demonstrate that the japonica ssp. was usually more tolerant to photoinhibition, indicated by higher maintaining capacity of D1 protein (less degradation), higher induced superoxide dismutase (SOD) activity and longer duration of the activity. Compared with japonica, the indica ssp. was more sensitive to photoinhibition, and exhibited more degradation of D1 protein and a much larger xanthophyll pool. A statistically significant positive correlation exists between D1 protein content and F_v/F_m, PSII activity and P_n during photoinhibition (r² = 0.98, 0.93, 0.95, respectively, P < 0.01). This result further supported the hypothesis that D1 protein encoded by plastid genes might play an important physiological role in the mechanism of photoinhibition. This hypothesis is also enhanced by the fact that the capacity of D1 protein synthesis mediated the components and cycle of xanthophyll and non-photochemical quenching in treatment with streptomycin, a D1 protein synthesis inhibitor, while the xanthophyll cycle had a photoprotective role for D1 protein and F_v/F_m in treatment with DDT, a xanthophyll cycle inhibitor. The photoinhibition of reciprocal F₁ hybrids between japonica and indica is mainly intermediate, but somewhat inclined to the maternal line. This demonstrates that the basic feature of photoinhibition was controlled by the interaction of an intrinsic factor, D1 protein encoded by plastid genes, with the xanthophyll cycle, as well as SOD, controlled by nuclear genes. Since the response to photoinhibitory treatment of indica–japonica F₁ hybrids seems to depend on female parents, we propose to select and use photoinhibition-tolerant varieties as female parents for generation of photoinhibition-tolerant hybrids.