Photosynthesis Regulation by Glucohexaose Through Redox Changes in Cucumis sativus

Abstract

To investigate the effects of glucohexaose (P6) on cucumber, leaf CO2 assimilation, chlorophyll fluorescence parameters, chlorophyll content, and carbohydrate metabolism were examined in cucumber plants. The net photosynthetic rate (Pn) of cucumber leaves was enhanced after being treated with 10 μg mL−1 P6. The increase was correlated with increases in transpiration rate (E) and stomatal conductance (Gs), whereas the intercellular CO2 concentration (Ci) was not different from the control plants. Chlorophyll content, absorption of light energy per unit area (ABS/CS), capture of light energy per unit area (TRo/CS), quantum yield of electron transport per unit area (ETo/CS), maximum photochemical efficiency of PSII (φPo), quantum yield of photosynthetic institution electron transfer (φEo), probability of other electron acceptors that captured exciton-transferred electrons to the electronic chain which exceeds QA (ψo), number of reaction centers per unit leaf area (RC/CSo), and the performance index on absorption basis (PIABS) were improved, but heat dissipation per unit area (DIo/CS) and maximum quantum yield of non-chemical quenching (φDo) were reduced. In addition, increases in sucrose, soluble sugars, and starch contents were observed in P6-treated plants. However, H2O2 scavenger (DMTU) or NADPH oxidase inhibitor (DPI) pretreatment significantly abolished the effect of P6 on photosynthesis. The results demonstrated that ROS played a critical role in P6-induced photosynthesis. The increase in chlorophyll content together with efficient light absorption, transmission, and conversion in P6-treated plants is important for increasing photosynthesis.