Synergistic role of exogenous proline and hydrogen sulfide in improving zinc stress tolerance in safflower (Carthamus tinctorius L.) seedlings

Abstract

Excess zinc (Zn), primarily resulting from anthropogenic sources, poses serious threats to plant health and food safety. This study explored the potential synergistic effects of exogenous proline (100 µM L-proline, Pro) and hydrogen sulfide (100 µM NaHS as an H₂S donor) in mitigating Zn toxicity in safflower (Carthamus tinctorius L.) seedlings exposed to 500 µM ZnSO₄·7 H₂O. Zn stress markedly reduced biomass accumulation and chlorophyll content, while elevating oxidative stress indicators, endogenous proline, methylglyoxal (MG), and H₂S levels. Interestingly, H₂S content increased not only under Zn stress alone but was further enhanced when Pro or NaHS were applied, suggesting a role for both compounds in modulating H₂S homeostasis. Co-application of Pro and NaHS significantly restored plant growth and chlorophyll content, accompanied by strengthened antioxidant defense and glyoxalase systems. The combined treatment also reduced Zn uptake and translocation, and more effectively scavenged MG through enhanced glyoxalase enzyme activity, likely due to a reinforced glutathione (GSH) pool. These results highlight the pronounced synergistic action of Pro and H₂S in alleviating Zn-induced oxidative damage, underscoring their potential as complementary agents in improving metal stress tolerance.

Graphical Abstract

Graphic presentation of possible effects of proline (Pro) and NaHS (as H₂S donors) on reducing Zn toxicity by strengthening ascorbate-glutathione (AsA-GSH) cycle, improving glyoxalase system performance and stimulating endogenous proline production based on the data of present study.