Spermine mitigates the adverse effects of water deficit by strengthening antioxidant enzymes and anthocyanin pathway-related gene expressions

Abstract

Water deficit is regarded as one of the worst causes of low agricultural productivity. It disrupts morphophysiological and biochemical processes in plants. In the current research, spermine effectively induced defense responses to abiotic stresses. The foliar spray with spermine ameliorated the adverse impacts of water deficit on zinnia plants (Zinnia elegans L.). The aim of this study was to investigate the effects of foliar spraying of spermine on growth characteristics, enzyme antioxidants activity, gas exchange and genes expression related to the anthocyanin biosynthesis pathway (ABP) of zinnia plants grown under water-deficit treatments. The evaluations involved measuring growth characteristics (i.e. height, flower biomass, total plant biomass, fresh and dry plant weight, flower diameter, and vase life), photosynthesis and gas exchange (stomata conductivity, intracellular CO2, transpiration), water use efficiency (WUE), lipid peroxidation (MDA), enzymatic activity (POD and APX) and genes expression related to ABP (CHS, CHI, F3H, F3'H, ANS, 3GT, DFR and AT2). Spermine mitigated the adverse impacts of severe water-deficit on the growth characteristics, flower longevity, and WUE. Our results showed that spermine boosted antioxidant enzymes activity and reduced lipid peroxidation of zinnia under severe and moderate water-deficit. Real-time PCR analysis of genes related to ABP revealed that the early (CHI, CHS and F3H) and late (ANS and 3GT) biosynthetic genes were promptly induced by both water deficit and spermine treatments. We showed that DFR and AT2 genes were induced by different levels of drought stress, while the F3'H gene was expressed only by the exogenous application of spermine. Spermine decreased the MDA content and enhanced the water-deficit tolerance of zinnia plants by maintaining morphological integrity, gaseous exchange, chlorophyll index, WUE, APX, and POD enzyme activities, as well as gene expressions related to ABP. Spermine (3 mM) can be applied as a foliar treatment to alleviate the adverse impacts of water-deficit in zinnia plants.