Upland cotton (Gossypium hirsutum L.) can move leaves to track the sun throughout the day, so-called leaf diaheliotropic movement. This paper reports an experimental test of the hypothesis that leaf diaheliotropic movement in upland cotton can enhance carbon assimilation and not increase the risk of stress from high energy load. In this experiment, cotton leaves were divided into two groups: one was that leaves could track the sun freely; another was that leaves were retained to the horizontal position. The diaheliotropic leaves recorded higher incident irradiance than the restrained ones, especially in the morning and late afternoon. Compared with restrained leaves, diaheliotropic leaves were generally warmer throughout the day. As expected, diaheliotropic leaves had significantly higher diurnal time courses of net photosynthetic rate (PN) than restrained leaves, except during 14:00-18:00 of the local time. Higher instantaneous water-use efficiency (WUE) was observed in diaheliotropic leaves in the early morning and late afternoon than in the restrained leaves. During the given day, diaheliotropic and restrained leaves had similar diurnal time courses of recovery of maximal quantum yield of PSII photochemistry (Fv/Fm). Diaheliotropic leaves recorded lower or similar photochemical quenching coefficient (qp) than restrained leaves did throughout the day. These results suggest that cotton leaf diaheliotropic movement can improve carbon gain and water use efficiency and not intensify photoinhibition. and Y.-L. Zhang ... [et al.].
Gas exchange and chlorophyll fluorescence parameters of PSII were analyzed in the bracts and leaves of cotton plants after anthesis. Photosynthetic activity and photorespiration were measured in the leaves and bracts of cotton grown under either normal or reduced water-saving drip irrigation. The photosynthetic performance, amount of chlorophyll and Rubisco, and net photosynthesis were greater in the bracts than that in the leaves under water stress. The actual photochemical efficiency of PSII decreased in both the bracts and leaves after anthesis under reduced irrigation. However, the decrease was smaller in the bracts than in the leaves, indicating that the bracts experienced less severe photoinhibition compared to the leaves. The greater drought tolerance of bracts could be related to differences in relative water content, instantaneous water-use efficiency, and photorespiration rate. The ratio of photorespiration to net photosynthesis was much higher in the bracts than in leaves. Furthermore, water deficiency (due to the water-saving drip irrigation) had no significant effect on that ratio in the bracts. We hypothesized that photorespiration in the bracts alleviated photoinhibition and maintained photosynthetic activity., C. Zhang, D.-X. Zhan, H.-H. Luo, Y.-L. Zhang, W.-F. Zhang., and Obsahuje seznam literatury