Spermine alleviates heat-induced senescence in creeping bentgrass by regulating water and oxidative balance, photosynthesis, and heat shock proteins

Spermine (SPM) is involved in response to abiotic stress in plants, but the potential role of SPM in regulating senescence has not been well documented. Objectives of this study were to examine the effect of changes in endogenous polyamines (PAs) by SPM application on improving heat tolerance of creeping bentgrass (Agrostis stolonifera) and explore the SPM-regulated senescence associated with alterations of water and oxidative balance, photosynthesis, and heat shock proteins under heat stress. The results showed that persistent high temperature caused severe oxidative damage and significant decreases in chlorophyll (Chl) content, photosynthetic efficiency, and leaf water content leading to premature senescence in creeping bentgrass, as reflected by a significant upregulation of transcriptions of senescence-associated genes (AsSAG39, Ash36, and Asl20). The improvement of endogenous spermidine (SPD) and SPM content induced by SPM application could significantly alleviate heat stress damage to creeping bentgrass through maintaining higher Chl content, net photosynthetic rate, photochemical efficiency, and performance index on absorption basis, promoting osmotic adjustment ability and antioxidant enzyme (superoxid dismutase, catalase, peroxidase, and ascorbate peroxidase) activities to enhance the scavenging capacity of reactive oxygen species, and upregulating transcriptions of heat shock protein (HSP) genes (HSP90-5, HSP90.1-b1, HSP82, HSP70, HSP26.7, HSP17.8, and HSP12) helping to maintain normal synthesis and functions of proteins under high temperature stress, thereby delaying heat-induced leaf senescence. These findings reveal an important role of PAs in regulating senescence in perennial plants exposed to a high temperature environment.