Spermine-priming restrained water relations and biochemical deteriorations prompted by water deficit on two soybean cultivars.

The outstanding role of spermine in eliciting defense adaptation of soybean to different levels of water deficit (0, -0.1, -0.5 and -1.1 MPa) was investigated by determining the changes in growth, photosynthetic pigments, osmolytes, water relations, and antioxidants. All the studied traits clearly revealed cultivar-dependent variation in response to water deficit where cv. Giza 111 was tolerant and cv. Giza 21 was sensitive. Both cultivars came in agreement that photosynthetic limitation (chlorophylls reduction) was the troubling shot induced by water deficit. Such limitation was reflected on three directions (a) disturbances of water relations (stomatal conductance, transpiration rate, relative water content and water use efficiency), (b) down regulation of metabolites which affect osmotic adjustment and (c) elevated reactive oxygen species (increased hydrogen peroxide) and destruction of membrane stability (increment of electrolyte leakage and lipid peroxidation). The damaging impacts of water deficit on these parameters were obviously coined for sensitive cultivar compared to tolerant one. Although spermine priming did not have apparent stimulatory role on well-watered plants, unequivocal inversion from a state of down regulation to up-regulation was distinct under water stress. In this regard, spermine enhanced pigments, osmolytes accumulation, up-regulated water relations and enhanced membrane stabilization. Furthermore, spermine pre-sowing decreased oxidative stress by lowering hydrogen peroxide via activation of anthocyanins, total antioxidants and phenolic compounds.