Paclobutrazol induced non-enzymatic antioxidants and polyamine levels in soybean plants grown under salinity stress

Paclobutrazol (PBZ) is a member of the triazole family of plant growth regulators and is known to protect crops from environmental stresses such as salinity and drought. It plays a role in maintaining water balance, photosynthesis capacity and enhancing antioxidant enzyme activities. Despite the well-documented effects of PBZ on antioxidant defence in soybean plants, the changes in non-enzymatic antioxidants and endogenous polyamines in the PBZ-treated plants grown under salinity stress are still not studied. Herewith, the study aimed to clarify the effects of PBZ on these molecules. For this purpose, the combined effect of salt (250 mM NaCl) and three different concentrations of PBZ (5, 10 and 20 ppm) on soybean (Glycine max L.) plants were studied. Proline, hydroxyl radical (OH.) scavenging capacity, non-enzymatic antioxidants (anthocyanin, flavonoid, phenolic and free thiol-containing compounds) and polyamines spermine, spermidine, and putrescine were investigated in the treated plants. We found that the PBZ (10 ppm) treatment was the most effective concentration to counteract oxidative stress due to NaCl in soybean seedlings. It significantly increased hydroxyl radical scavenging activity, proline, total phenolics, flavonoids, and conjugated polyamine content compared to those found in salt-treated plants only. For the first time, our study showed that PBZ could induce the non-enzymatic antioxidant defence in soybean plants grown under salt stress conditions.