Exogenous phytosulfokine α application delays senescence and promotes antioxidant nutrient accumulation in strawberry fruit during cold storage by triggering endogenous phytosulfokine α signaling

In this study, the mechanism by which the exogenous application of 150 nM signaling bioactive peptide phytosulfokine alpha (PSK alpha) delays senescence and improves antioxidant nutrient accumulation in strawberry fruit during storage at 4 degrees C for 18 d was investigated. Results showed that the higher endogenous accumulation of PSK alpha in strawberry fruit treated with 150 nM PSK alpha may result from the higher expression of PSK3 and PSK6 genes. Besides, the higher endogenous accumulation of Ca(2 )in strawberry fruit treated with 150 nM PSK alpha may be ascribed to the higher cytosolic accumulation of cGMP, resulting from the triggering of endogenous PSK alpha signaling pathway, represented by higher expression of PSKR1 gene. Besides, the higher endogenous melatonin accumulation resulting from higher expression of TDC, T5H, SNAT, and ASMT genes in strawberry fruit treated with 150 nM PSK alpha may be ascribed to the higher endogenous accumulation of Ca2+. Moreover, the higher ABTS and DPPH scavenging capacity in strawberry fruit treated with 150 nM PSK alpha may be ascribed to the higher accumulation of phenols, flavonoids, and anthocyanins, resulting from higher gene expression and activities of PAL and CHS. Based on our findings, the exogenous application of PSK alpha could be employed as a beneficial procedure for delaying senescence and improving antioxidant nutrient accumulation in strawberry fruit during cold storage, by triggering endogenous PSK alpha signaling, promoting endogenous melatonin accumulation, and activating the phenylpropanoid pathway.