Effects of plant growth regulators on mitigating water deficit stress in young yellow passion fruit plants

Water deficit significantly affects the growth and survival of young plants following transplantation. We performed morphophysiological and biochemical analyses on young yellow passion fruit (Passiflora edulis Sims) plants under well-watered and water-deficit irrigation regimes and pre-treated with three plant growth regulators (PGRs) application-an agrochemical composed of auxins, gibberellins, and cytokinins; salicylic acid (SA); and sodium nitroprusside (SNP), a nitric oxide donor-and a control group with no PGRs. Results showed significant damage by water restriction on biometric attributes; however, the application of PGRs mitigated these effects, reducing growth inhibition processes. In terms of water stress mitigation, differences were observed between PGRs, depending on the morphophysiological or biochemical characteristic. The effectiveness of SNP was higher than the other PGRs in preventing stomatal conductance reduction and maintaining CO2 assimilation, while the agrochemical was the most effective in preventing photosynthetic pigments content decrease. All PGRs promoted osmoregulation in plants subjected to water deficit, thus helping to preserve cell turgor. Furthermore, PGRs application attenuated oxidative stress, either by increasing antioxidant enzymes activity, or by preventing or decreasing the content of thiobarbituric acid-reactive substances, thus preventing lipid peroxidation. These findings suggest that the application of PGRs can be a useful strategy to improve young passion fruit plants tolerance to water restriction following transplantation. The multiple beneficial effects do not allow us to indicate the only one most effective PGR; however, a chemical constituents-related principal component analysis suggests that the agrochemical and SA are the most effective PGRs on mitigating water deficit stress.