Responses of the Photosynthetic Electron Transport Reactions Stimulate the Oxidation of the Reaction Center Chlorophyll of Photosystem I, P700, under Drought and High Temperatures in Rice

Abstract

It is of interest how photosynthetic electron transport (PET) reactions respond to excess light energy caused by the combination of drought stress and high temperatures. Since such information is scarcely available for photosystem I (PSI), this question was explored in rice (Oryza sativa L.) plants subjected to drought stress, using culture solutions that contain poly(ethylene glycol) at different concentrations under two day/night temperature regimes. At 27/22 °C (day/night), drought stress led to the oxidation of the reaction center of the chlorophyll of PSI (P700), and also led to decreases in the quantum efficiencies of photosystem II (PSII) and PSI, and a reduction of the primary quinone electron acceptor of PSI. Such drought stress responses were wholly stimulated at 35/30 °C. These parameters were strongly correlated with each other and were minimally affected by temperature. These results indicate that the drought stress responses of the respective PET reactions are closely associated with each other in the oxidization of P700 and that such responses are stimulated at high temperatures. The underlying mechanisms of these phenomena were discussed. While P700 oxidation is thought to suppress reactive oxygen species (ROS) production, PSI photoinhibition was observed under severe stress conditions, implying that P700 oxidation is not sufficient for the protection of PSI under drought stress.

Photorespiration Coupled With CO2 Assimilation Protects Photosystem I From Photoinhibition Under Moderate Poly(Ethylene Glycol)-Induced Osmotic Stress in Rice

“…It has been observed that PSI suffered from photoinhibition under severe drought stress, whereas PSII was not largely affected in some tropical tree species (Huang et al, 2013). Similar phenomena were observed when rice plants were subjected PEG-induced osmotic stress, which are widely used to mimic drought stress (Wada et al, 2019). These results show that PSI is more sensitive to drought or osmotic stress than PSII.…”

“…The culture solutions containing PEG at concentrations of 16 and 20% (w/v) were used to impose osmotic stress to the plants. We have previously observed that values of the relative water content of leaves of wild-type rice plants only marginally decreased under these PEG treatments (Wada et al, 2019). In the present study, the relative water content of leaves was not significantly affected by the PEG treatments, and did not significantly differ among genotypes (Figure 1).…”

“…The rate of CO 2 assimilation (A), chlorophyll fluorescence, and P700 absorbance were simultaneously measured using the combination system of GFS-3000 and DUAL-PAM-100 (Heinz Walz GmbH, Effeltrich, Germany). The detailed conditions are described in Wada et al (2019). Briefly, F v /F m and P m were measured after the leaves were dark-adapted, followed by the measurements of chlorophyll fluorescence and P700 absorbance under the conditions of an actinic light intensity of 1,200 mmol photon m −2 s −1 , an ambient CO 2 partial pressure of 40 Pa, a leaf temperature of 27°C, and a relative humidity of 60-70%.…”

“…The relative water content of the leaves (RWC) was determined after the stress treatment, following the methods of Zhou et al (2007), as described in Wada et al (2019), using leaf fresh weight measured just after the stress treatment, leaf weight after overnight immersion in deionized water at 4°C, and leaf dry weight.…”

Photorespiration Enhances Acidification of the Thylakoid Lumen, Reduces the Plastoquinone Pool, and Contributes to the Oxidation of P700 at a Lower Partial Pressure of CO2 in Wheat Leaves

“…Photorespiration is thought to contribute to P700 oxidation [1,20]. For the PSI reaction center chlorophyll P700 to be kept in a higher oxidized state, the regeneration rate of the ground state of P700 in the photo-oxidation/reduction cycle must be limited by the P700 + reduction rate.…”