Exogenous Calcium Alleviates Diurnal Chilling-Induced Feedback Inhibition Of Photosynthesis By Improving Sink Demand In Peanut (Arachis Hypogaea L.)

Based on the international and domestic oil crops capacity demand during the"14th Five-Year Plan"period,improving the chilling adaptation abilities of the peanut is essential for relieving bottlenecks,expanding the temperate cultivation area,and alleviating the restrictions of chilling injury on its growth,development and photosynthetic carbon assimilation.Due to the complex understanding of the destructive effects photosynthesis have on chloroplast structure,thylakoid membrane function,cyclic electron flow and stomatal movement,the effects of non-freezing（0-12℃）temperatures and light（low diurnal temperature stress,LDT）on peanuts remain relatively unknown in terms of the primary target of a light-chilling episode.The identification of the limiting site of photosynthesis of peanuts under diurnal chilling stress,and the key physiological mechanism of calcium regulation will lay an important theoretical foundation for improving the technical system of chilling resistance plus calcium enhancement under the early sowing of high-yielding peanuts in northern China.Therefore,this study was taken the common high-yielding peanut cultivar（Arachis hypogaea L.cv.Xiao Baisha）and was measured by gas exchange-chlorophyll fluorescence technology,scanning electron microscope（SEM）,X-ray energy spectrum（EDS）analysis,and other methods,confirmed the photosynthetic restriction sites and its physiological mechanism of calcium regulation.The exogenous calcium and its inhibitors（TFP）compensation experiments proved positively and negatively that there were close links between the physiological response difference in plant growth,leaf anatomical structure,gas exchange parameters,palisade tissue element distribution,and chlorophyll fluorescence parameters.The key results were listed as follows:1.The experiment demonstrated that the exogenous calcium significantly promoted the leaf and root growth,and was mediated by the Ca²⁺-CAM complex to stimulate the carbohydrate transport,reducing the secondary metabolites for regulating source-sink balance under chilling in light（including the root zone microthermal and warming）.2.It was found that the exogenous calcium increased the leaf thickness and stomatal opening,promoted the proportion of palisade tissue and spongy tissue,and adjusted the element allocation strategy of palisade tissue to increase the ratio of CO₂/O₂exposed to chloroplast and maintain the photosynthesis rate.Meanwhile,correlation analysis showed that O,N,P,Ca and S were the main nutrient limiting factors of the photosynthetic rate of peanuts under diurnal cold stress.3.It was clear that the effect of exogenous calcium on photosynthetic ability was mainly caused by the stomatal restriction under the root zone microthermal stress,while the root zone warming was caused by the non-stomatal restriction.Exogenous Ca²⁺can effectively alleviate PSI photoinhibition in the root zone microthermal,which is dominated by Y（ND）restriction.Relatively,the root zone warming mainly occurred in PSII,dominated by Y（NO）restriction.After recovery from diurnal chilling stress,PSII and PSI showed irreversible inactivation under two kinds of stress.4.It was confirmed that exogenous Ca²⁺can effectively remove the photosynthetic disorders caused by photophosphorylation feedback inhibition in light reaction and photo-terminal product feedback inhibition in carbon reaction under two kinds of stress.The photosynthetic activities of PSII and PSI were maintained by photo-protective mechanisms such as cyclic electron transport and non-photochemical quenching.