Heat Tolerance Of Tree Peony Seedlings Induced By Exogenous Chemical Substances

This research aims to study the effects of exogenous substances on the heat-resistance of tree peony cultivars and the mechanism of heat tolerance of tree peony cultivars induced by exogenous substances under high temperature stress.The plant materials in this study were Paeonia ostii 'Fengdan' and Paeonia suffruticosa'Xiangdan' seedlings.Different concentrations of salicylic acid(SA),CaCl2,and abscisic acid(ABA)were sprayed on the two tree peony seedlings to study their effects on heat tolerance of these two tree peony seedlings.Thus,the most effective SA,CaCl2,and ABA concentration in enhancing heat tolerance in tree peony seedlings was determined.Based on these results,we studied the mechanism of heat tolerance of two tree peony seedlings induced by SA,CaCl2,ABA under high temperature stress.In addition,a comprehensive evaluation of their effects on the heat resistance of tree peony seedlings was conducted by principal component analysis and membership function method.The main results were concluded as follow:1.Two tree peony cultivars were sprayed with different concentrations of SA,CaCl2 and ABA and stressed at 40? for 2 days.With the increasing of concentration,the heat injury index(HII)and relative electrical conductivity(Rec)of two tree peony cultivars both increased initially and decreased afterwards.The optimum concentration of three exogenous substances were 100 ?mol/L SA,40 mmol/L CaCl2,and 40 mg/L ABA respectively.There was no significant difference between'Xiangdan' and 'Fengdan'.2.The HII of tree peony seedlings continued to rise with the prolongation of high temperature stress time,and the trend of 'Fengdan' and 'Xiangdan' was uniform.The optimum concentration of SA,CaCl2,ABA were favorable for reducing HII of tree peony seedlings during stress.The effects of CaCl2,SA and ABA were in descending order and there was no difference between 'Fengdan' and 'Xiangdan'.3.The stem,leaf and root dry weight of tree peony seedlings under high temperature stress were significantly reduced compared with that under normal temperature,and the reduction of stem and leaf dry weight of 'Fengdan' was smaller than that of 'Xiangdan',but the reduction of root weight was more than 'Xiangdan'.The optimum concentration of SA significantly increased stem,leaf and root weight of 'Fengdan' and 'Xiangdan'.The optimum concentration of CaCl2 and ABA significantly increased stem,leaf and root dry weight of 'Xiangdan',but only significantly increased the root weight of 'Fengdan'.4.Chlorophyll(Chl)content of tree peony seedlings showed a continuous decreasing with the extension of stress time,and the trends of 'Fengdan' and'Xiangdan' were uniform.The optimum concentrations of SA,CaCl2 and ABA could slow the rate of decrease of Chl content of two cultivars at the later stage of stress(?4 d),and the reduction of Chl content of 'Xiangdan,was more than 'Fengdan'.5.Rec and malondialdehyde(MDA)content of 'Fengdan' and Rec of 'Xiangdan'all showed a continuous rising trend with the prolongation of stress time,but the MDA content of 'Xiangdan' raised firstly and then dropped with the prolongation of stress time.The optimum concentrations of SA,CaCl2,and ABA reduced the Rec and MDA content of two tree peony seedlings.The optimum concentrations of SA and CaClb reduced the 'Fengdan 'Rec less than 'Xiangdan',while the optimal concentration of ABA reduced the 'Fengdan' Rec more than 'Xiangdan'.The optimal concentrations of SA,CaCl2 and ABA were more helpful in the reduction of MDA content of 'Xiangdan'.6.The activity of superoxide dismutase(SOD)of 'Fengdan' decreased firstly,then rose and finally decreased with the prolongation of high temperature stress time.The SOD activity of 'Xiangdan' firstly decreased and then rose with the extension of stress time.The optimum concentrations of SA,CaCl2 and ABA all increased the SOD activity of tree peony seedlings during stress.The optimum concentration of SA was more conducive to the increase of SOD activity during the high temperature stress,and the optimal concentration of CaCl2 and ABA was more conducive to the increase of the SOD activity of 'Tengdan'.7.The contents of soluble protein(SP),free proline(Pro)and soluble sugar(SS)contents of 'Fengdan' were all continuously increased with the prolongation of high temperature stress time.The Pro and SS contents of 'Xiangdan' increased continuously with the prolongation of stress time,but the SP content of 'Xiangdan'increased firstly and then decreased with the prolongation of stress time.The optimum concentrations of SA,CaCl2,and ABA all increased SP,Pro,and SS contents of tree peony seedlings during stress.The optimum concentrations of SA,CaCl2,and ABA are more conducive to the accumulation of 'Fengdan' SP content and the accumulation of 'Xiangdan' Pro content.The optimum concentrations of SA and ABA showed a greater increase in the content of 'Xiangdan'SS than in 'Fengdan'.The optimum concentration of CaCl2 increased the content of 'Fengdan' SS more than'Xiangdan'.8.The results of principal component analysis showed that SA improved the heat resistance of tree peony seedlings mainly by alleviating the degradation of Chl under high temperature stress,decreasing Rec,reducing MDA content,and increasing SOD activity and SP content.CaCl2 mainly improved the heat resistance of tree peony seedlings by alleviating the degradation of Chl under high temperature stress,decreasing Rec,and increasing the activities of SOD and SP content.ABA mainly improved the heat resistance of peony seedlings by alleviating degradation of Chl under high temperature stress,decreasing Rec,and increasing SP content.9.The results of correlation analysis and principal component analysis showed that the indicators,which were HII,Chl content,Ree,and SP content,had a greater impact on heat tolerance of tree peony seedlings induced by exogenous substances.The results of principal component analysis and membership function showed that the heat tolerance of 'Fengdan' was better than 'Xiangdan'.The effect of three exogenous substances on the heat resistance of tree peony seedlings was not different between'Fengdan' and 'Xiangdan',indicated that SA,CaCl2,and ABA was in descending order.