Study On Regulation Of Strawberry Ripening And Softening By Exogenous Polyamines And Calcium

Strawberry fruit is an aggregate fruit and falls under the category of berries.During the later stage of its growth and development,the hardness of the fruit decreases dramatically,making it extremely susceptible to decay,which severely affects its storage quality and market value.Putrescine（Put）and Spermidine（Spd）as important amines of polyamines（PAs）,can regulate fruit ripening and maintain pre-harvest fruit hardness and quality.This study used’Hong Yan’strawberries as the experimental material,and treated strawberry plants with Put+Ca²⁺,Spd+Ca²⁺,D-Arg+Ca²⁺,and dd H₂O+Ca²⁺（control group）.We studied the effects of different treatments on fruit quality,cell wall metabolism,cell wall related enzyme activity,and calcium morphology transformation at ripening,to clarify the physiological mechanism of polyamine and calcium co-treatment on strawberry fruit softening during ripening.Furthermore,we explored the molecular mechanism of polyamine synthesis genes on strawberry fruit softening using a transient transformation system.The main research results are as follows:（1）Compared with the control group,Put+Ca²⁺treatment of’Hong Yan’strawberries can improve the hardness,TSS,TA and ASR quality indexes of the fruit at maturity,inhibit the activity of PG and PL cell wall enzymes,reduce the content of WSP and SH in the cell wall,and increase the content of ISP and CSP;D-Arg+Ca²⁺and Spd+Ca²⁺treatments can reduce fruit hardness and related quality,among which Spd+Ca²⁺treatment promotes fruit ripening and softening most significantly.（2）Compared with the control group,Put+Ca²⁺treatment can promote the increase of water-soluble calcium,pectin calcium and oxalate calcium content in the fruit,and reduce the content of phosphate calcium;D-Arg+Ca²⁺and Spd+Ca²⁺treatments can reduce the content of water-soluble calcium and oxalate calcium in strawberry fruit,and increase the content of phosphate calcium.（3）Compared with the empty vector,overexpression of the FaSAMDC5 gene can promote strawberry ripening,advance the ripening period of strawberry fruit,and reduce fruit hardness,pectin calcium,oxalate calcium,and phosphate calcium content,as well as increase the activity of PL and PG cell wall enzymes;however,overexpression of FaADC4inhibits strawberry fruit ripening,increases fruit hardness,promotes fruit conversion to pectin calcium,and significantly reduces PL enzyme activity;after overexpression of FaSAMDC5 and FaADC4 genes,they upregulate and downregulate the expression of FaPL4,FaCEL24,and FaPG1 genes,respectively.