| In this stuty,we used figleaf gourd（H）as the control,and selected pumpkin rootstock with higher chilling tolerance by comparing the ability on cold tolerance of9 white seed pumpkin rootstock varieties.Then the relationship between endogenous ABA and chilling tolerance of seedlings was studied with selected pumpkin rootstock and ’Jinyou 35（JY35）’,’Zhongnong 6（ZN6）’.Meanwhile,we measured the response of endogenous ABA in Cs/Cs（cucumber scion/cucumber rootstock）and Cs/Cm（cucumber scion/pumpkin rootstock）seedlings to 25℃/25℃,5℃/5℃,5℃/25℃and25℃/5℃and the effect of sodium tungstate（Na2WO4）-and fluridone（Fluridone）-pretreatments,which mean the removal of ABA,on the low temperature tolerance of Cs/Cs,Cs/Cm,Cm/Cs（pumpkin scion/cucumber rootstock）and Cm/Cm（pumpkin scion/pumpkin rootstock）seedlings under 5℃/5℃intensity.The main results are as follows:1.After chilling stress,the chilling injury index,electrolyte leakage and the content of MDA increased,while net photosynthesis and daily increments decreased notably in all the different rootstocks and the different rootstocks showed different response to low temperature intensity.Through the analysis of comprehensive evaluation of cold resistance index in different rootstocks with membership function value,we found M5 rootstock showed the highest chilling tolerance,then B105rootstock,and the low temperature tolerance of the two rootstocks was both higher than that of’H’,however it was lower in the rest of the rootstocks than that of’H’.M5 was selected as the rootstock in follow-up experiments.2.The EL,MDA and reactive oxygen species（ROS）content of ZN6,JY35cucumber and M5 pumpkin seedlings increased significantly under low temperature stress.And M5 with the lowest increase in EL,MDA and ROS showed the highest cold resistance,followed by cucumber JY35,and ZN6 showed the lowest cold resistance.Moreover,M5 seedlings still maintained higher photosynthetic activity under chilling stress,that is,Pn,PSⅡactual photochemical efficiency under light（ΦPSⅡ）,PSⅡmaximum photochemical efficiency under dark（Fv/Fm）,ribulose-1,5-Diphosphate carboxylase/oxygenase（Rubisco）and Rubisco activase（RCA）activity and mRNA expression of M5 seedlings were significantly higher than those of JY35and ZN6 seedlings;In addition,low temperature induced an increase in endogenous ABA and the activity of its key enzymes for synthesis（NCED,AAO,ZEP）in seedling leaves and roots,and the upward trend was M5>JY35>ZN6.It can be seen that endogenous ABA responds to low temperature stress,and chilling tolerance of seedlings showed a positive correlation to ABA content.3.Compared with the control,the ABA content in leaf increased by 14.39%,14.38%,and 43.37%under 5℃/5℃,5℃/25℃and 25℃/5℃intensity,respectively;ABA content in root only increased by 15.39%under 25℃/5℃,that was similar to that in stem of Cs/Cs seedlings;However,the ABA content in leaf,root and stem of Cs/Cm seedlings obviously increased from 5.49%to 102.16%under the three chilling treatments and the ABA content of Cs/Cs seedlings was lower than that of Cs/Cm seedlings under the same chilling treatment.In addition,the mRNA abundance of ZEP in Cs/Cs seedlings upregulated with 6.97-and 7.90-fold under 5℃/5℃and5℃/25℃treatments and the mRNA abundance of ZEP in Cs/Cm seedlings upregulated with 5.53-fold under only 5℃/5℃stress.The results implied the root zone chilling could not induce the mRNA abundance of ZEP in leaf and rootstock can increase endogenous ABA levels in leaves by exporting ABA to the ground.Furthermore,the output of ABA from root in Cs/Cm seedlings was higher than that of Cs/Cs seedlings.4.Both the Cs/Cs and Cs/Cm seedlings showed the decline of relative water content and photosynthesis function as well as electrolyte leakage and increase of MDA and ROS contents in leaf and root,while,the change of chilling indexes in Cs/Cm was lower than that of Cs/Cs under 5℃/5℃,5℃/25℃and 25℃/5℃stresses.Among all the chilling treatments,5℃/5℃stress caused the highest chilling damage to the seedlings and 5℃/25℃stress caused higher injury to leaf than root,however,25℃/5℃showed the opposite results.5.To further verify the relationship between ABA and the chilling tolerance of grafted seedlings,Cs/Cs,Cs/Cm,Cm/Cs and Cm/Cm seedlings were used as the experimental material and the data showed that chilling intensity caused a significant increase of EL,MDA and ROS,while,decrease of Pn,Fv/Fm,ΦPSⅡ,activities and mRNA abundance of Rubisco and RCA.The change ranges of chilling parameters in different grafted seedlings represented Cs/Cs>Cs/Cm≥Cm/Cm or Cs/Cs>Cm/Cs≥Cm/Cm.And the application of Na2WO4 and Fluridone aggravated the chilling damage.The results indicated that there was interaction between section and rootstock and grafted seedlings with cold-tolerant rootstock have higher cold resistance and ABA was involved in this process. |
