Photosynthetic and biochemical activities in flag leaves of a newly developed superhigh-yield hybrid rice (Oryza sativa) and its parents during the reproductive stage

Abstract

Responses of net photosynthetic rates to intercellular CO(2) concentration (P (n)/C (i) curves) and photochemical characteristics were investigated in flag leaves of newly developed superhigh-yield hybrid rice (Oryza sativa L.) LiangYouPeiJiu (LYPJ) and its maternal PeiAi64S (PA64S) and paternal WuMang9311 (WM9311) lines grown in the field during the reproductive stage. The results showed that photosynthetic functions, such as the electron transport activities of photosystems and photophosphorylation, assessed in vivo from P (n)/C (i) curves under field conditions declined more or earlier than those obtained in vitro. The degradation of polypeptides of thylakoid membranes was slower than those for P (Ca=360) (light-saturated net photosynthetic rate measured at 360 mumol mol(-1)) and CE (carboxylation efficiency, obtained from the initial slope of the P (n)/C (i) curve). The initial inhibition of the PSII electron transport and oxygen-evolving activity induced by senescence occurred before the degradation of the oxygen-evolving complex. In comparison, LYPJ had intermediate photosynthetic functions in the early stage of leaf development, but greater photochemical activities in the mid and late stages. WM9311 showed a similar pattern of changes but lower values, and PA64S had higher values in the early stage but showed a faster rate of senescence than LYPJ. These findings implied that the hybrid LYPJ demonstrated intermediate photosynthetic activities between its parents in the early stage of leaf development, whereas it had higher photosynthetic activities than its parents in the mid and late stages, which may be responsible for its high yield.

Photosynthesis performance, antioxidant enzymes, and ultrastructural analyses of rice seedlings under chromium stress

“…Photophosphorylation activity is the capacity of chloroplasts to produce ATP under light conditions, using light energy to transform ADP into ATP (Zhang et al, 2007), a reaction catalyzed by ATP-synthase in chloroplast thylakoid membranes. The altered photophosphorylation activity suggests that Cr 6+ treatment of rice seedlings decreases the capacity of chloroplasts to produce ATP and transform light energy into chemical energy (Fig.…”

Epigenetic Changes in Hybrids

“…The CO 2 assimilation rate measured in rice, wheat (Triticum aestivum), and Arabidopsis hybrids shows no increase in photosynthesis rate per unit leaf area in the hybrids compared with the inbred parents (Yang et al, 2007;Zhang et al, 2007;Fujimoto et al, 2012), but hybrid plants with their greater leaf area and increased number of chloroplasts have a greater total photosynthetic capacity (Fujimoto et al, 2012).…”

The xanthophyll cycle and antioxidative defense system are enhanced in the wheat hybrid subjected to high light stress

“…Recent studies have suggested that the differentially expressed genes and proteins between the wheat hybrids and their parents involved in diverse physiological process pathways, including metabolism, materials transport, photosynthesis, and signal transduction, could play important roles for hybrids (Yao et al, 2005;Wang et al, 2006;Song et al, 2009). In rice, it has been demonstrated that higher photosynthetic activities in the hybrid than in its parents in the mid and late stages may be responsible for its super-high-yield (Zhang et al, 2007(Zhang et al, , 2010. A serial analysis of gene expression study in rice indicated that the higher yield in a hybrid may be due to up-regulated genes involved in carbon-and nitrogen-assimilation, including photosynthesis in leaves (Bao et al, 2005).…”