Exogenous nitric oxide delays salt-induced leaf senescence in cotton (Gossypium hirsutum L.)

Abstract

Nitric oxide (NO) is a signaling molecule which plays an important role in delaying leaf senescence and increasing abiotic stress tolerance, but it is not clear if and how exogenous NO delays salt-induced leaf senescence in cotton. In this study, uniform cotton seedlings with five true main-stem leaves were cultured in hydroponics for 20 days and subjected to 150 mM NaCl. Seedlings were then treated with foliar spray of 300 μM sodium nitroprusside (SNP), a nitric oxide donor, and those with water spray were used as control. The effects of SNP on leaf senescence and expression of senescence-related genes were examined. Foliar spray with SNP significantly delayed leaf senescence in terms of the increased chlorophyll (Chl) content, photosynthetic (Pn) rate and expression of LHCB gene at 22 days after salt stress (DAS). The SNP significantly (p < 0.05) increased the expression of SOS1 and NHX1 genes and K+ content in leaves, but decreased leaf Na+ content. It also reduced (p < 0.05) the expression of ABA biosynthesis genes, NCED2, NCED9, and ABA content but increased the expression of cytokinin biosynthesis gene, IPT1 and ZR and iPA contents at 22 DAS. The overall results suggest that the delay in salt-induced leaf senescence by SNP was due to marked decrease in Na+ and ABA contents and increase in K+ and cytokinin through regulation of the expression of SOS1, NHX1, NCED2, NCED9 and IPT1 genes under salt stress. Foliar spray with SNP can be potentially useful in delaying leaf senescence, thereby increasing the economic yield of cotton under salt stress.