Different modulation of the redox homeostasis and hormone levels by ascorbate, hydrogen peroxide and hydrogen sulfide in maize

Ascorbate, hydrogen peroxide and hydrogen sulfide affect the cellular redox homeostasis by distinct mechanisms. This work aimed to compare their relative effect (set against the control) on the redox and hormonal state of maize seedlings by the application of an oxidant (5 mM H₂O₂) and two reductants (5 mM ascorbate and 1 mM NaHS). Interestingly, NaHS significantly increased the reduced-to-oxidized glutathione ratio in shoots, resulting in a more reduced cellular environment. In contrast, Asc decreased this ratio, leading to oxidative stress, while H₂O₂ had no significant effect. Accordingly, the greatest increase in electrolyte leakage and lipid peroxidation was observed in Asc-treated seedlings. Among the enzymes participating in the removal of H₂O₂, the activity of dehydroascorbate reductase, monodehydroascorbate reductase, and catalase exhibited a great increase after 7 days of Asc treatment, while ascorbate peroxidase exhibited the highest activity after H₂O₂ application. Besides Asc, H₂O₂ also resulted in a great increase in the level of the stress hormones jasmonic acid, salicylic acid and abscisic acid compared to H₂S. These changes were accompanied by a great reduction of shoot fresh weight by Asc and H₂O₂ but not by NaHS. This inhibition of growth is an indicator of oxidative stress induced by Asc and H₂O₂ treatments. Interestingly, phenolic and flavonoid compounds varied significantly across treatments, suggesting redox regulation of their synthesis. The simultaneous changes in the studied parameters signify the crosstalk of hormones and antioxidants to regulate specific modifications in plant growth and metabolism via cellular redox regulation. The present results about the pivotal role of redox balance in maintaining physiological and biochemical processes offer insights into strategies for enhancing plant resilience and productivity.