H₂O₂and Ca²⁺/CaM Involving In SHSP26Protecting Maize Chloroplast From The Combination Of Drought And Heat Stress

Small heat shock proteins (sHSPs) play an important role in enhangcingplant tolerance under adversity stress. Meanwhile, sHSPs localized in chloroplast canprotected PSⅡ from the heat stress. It has been shown that H2O2and Ca2+/CaM canincrease production of HSPs and induced the defense system of chloroplastantioxidant of plants under heat or drought stress. However, it is still not clearwhether H2O2and Ca2+/CaM affects sHSP26and antioxidant defense system in maizechloroplast under combined heat and drought stresses. Therefore, the aim of presentstudy is to confim the efffect of the H2O2and Ca2+/CaM on sHSP26expression,antioxidant defense system and the function of PSII under combined heat and droughtstress using Zhengdan958as experimental materials. The main results were asfollows:1. H2O2production in chloroplast affects sHSP26expression of maize leaves undercombined heat and drought stressAfter pretreated maize with chloroplast-specific inducer PQ for8h, maize plantswere subjected to drought, heat or combined heat and drought stress for another8h.The western-blot showed that sHSP26expression was higher under heat, combinedhea and drought stress than that under control or drought stress, but was not differentbetween control and drought in the fifth leaf. The expression level of sHSP26wassignificantly increased after PQ pretreatment. These results demonstrated that H2O2involved in the expression of sHSP26induced by heat stress.2.H2O2and Ca2+/CaM Regulating chloroplast antioxidant enzyme induced by drought,heat, combined heat and drought stress.Compared to control, the activity superoxide dismutase (SOD), glutathioneperoxide (GR), ascorbate peroxidase (APX) was increased with different extent in thechloroplasts under drought, heat, combined drought and heat stress, but was increasedby heat and combined heat and drought stress. The activity of the antioxidant defenseenzymes was increased by H2O2inducer PQ, especially under heat, combined heatand drought stress. Pretreated with Ca2+inhibitor EGTA and CaM analogist TFP or W7, the activity of these enzymes was significantly decreased compared to control,but the degree of decline under heat, combined heat and drought stress is more. Incontrast, the activity of these enzymes was significantly increased by CaCl2or PQtreatment and increased more by CaCl2treatment。These results indicated that H2O2and Ca2+/CaM involved in chloroplast antioxidant enzyme induced by drought, heatand combined drought and heat stress.The results showed that H2O2and Ca2+/CaMinvolved in the regulation of chloroplast antioxidant enzyme under drought, heat,combined heat and drought.3. Effect of H2O2and Ca2+/CaM on PSII function under drought, heat, combined heatand drought stress.The maximum photochemical efficiency (Fv/Fm) of PSⅡ,thylakoid physicalfitness of the inherent efficiency of PSII (Fv′/Fm′), actual photochemical efficiency(ΦPSⅡ), photochemical quenching (qP), and photosynthetic electron transfer rate(ETR) were significantly reduced under drought, heat, combined drought and heatstress, especially under heat, combined heat and drought stress. Treatment with CaCl2reduced the damage of PSII function, especially under heat, combined heat and droughtstress. But treatment with PQ, EGTA, TFP or W7aggravated the damage for PSII function.The results showed that Ca2+/CaM involved in the protection of chloroplast underdrought, heat, combined heat and drought.