Foliar 2,3-dihydroporphyrin iron (III) spray confers ameliorative antioxidation, ion redistribution and seed traits of salt-stressed soybean plants

Abstract: Dihydroporphyrin iron (III) chelates (also known as DHFe) have a role in plant growth regulation under normal and stressful conditions. In the present study, using Glycine max cultivars Jackson (the salt-sensitive) and Lee68 (the salt-tolerant) as the experimental materials, the physiological and molecular events contributing to the ameliorative effects of foliar DHFe spray on seedling growth; leaf photosynthetic parameters; reactive oxygen species (ROS) content; antioxidant enzyme activity; Na+, K+, and Cl- contents; and seed traits of soybean plants under control or salt-stressed conditions were investigated. The results showed that foliar spraying DHFe solution on soybean seedlings under NaCl treatment can significantly increase the leaf osmotic potential (ψs) and relative water content (RWC); reduce the Na+ and Cl- contents and Na+/K+ ratio; and simultaneously enhance the leaf antioxidant enzymes (CAT and APX, POD and SOD) activity, together with the mitigated ROS damage (lower H2O2 and MDA contents). Thus, it can apparently restore the salt stress-inhibited growth and photosynthetic capacity of Jackson and Lee68 seedlings, of which the salt-sensitive cv. Jackson displayed more pronounced effects. This may be related to the fact that, except for DHFe as a kind of antioxidant, foliar application of DHFe could enhance the transcription levels of GmCLC1 in roots and leaves and those of GmSOS1 in roots of Jackson plants under salt stress. When continuously cultivated to maturity, foliar spraying DHFe under salt stress could improve, to a certain extent, the seed traits (including the numbers of pods and seeds and seeds dry weight per plant) of both soybean cultivars. This approach may also provide a valuable theoretical basis and technical guidance for future practical application of DHFe as a type of plant growth promoter for the chemical regulation of foliar DHFe spray in mitigating salt injury to soybean and other crops under saline cultivation conditions.