Sulfur dioxide improves the thermotolerance of maize seedlings by regulating salicylic acid biosynthesis.

Heat stress (HS) has become a serious threat to crop growth and yield. Sulfur dioxide (SO 2) is being verified as a signal molecule in regulating the plant stress response. However, it is unknown whether SO 2 plays a significant role in the plant heat stress response (HSR). Herein, maize seedlings were pretreated with various concentrations of SO 2 and then kept at 45 °C for heat stress treatment, aiming to study the effect of SO 2 pretreatment on HSR in maize by phenotypic, physiological, and biochemical analyses. It was found that SO 2 pretreatment greatly improved the thermotolerance of maize seedlings. The SO 2 -pretreated seedlings showed 30–40% lower ROS accumulation and membrane peroxidation, but 55–110% higher activities of antioxidant enzymes than the distilled water-pretreated seedlings under heat stress. Interestingly, endogenous salicylic acid (SA) levels were increased by ∼85% in SO 2 -pretreated seedlings, as revealed by phytohormone analyses. Furthermore, the SA biosynthesis inhibitor paclobutrazol markedly reduced SA levels and attenuated SO 2 -triggered thermotolerance of maize seedlings. Meanwhile, transcripts of several SA biosynthesis and signaling, and heat stress-responsive genes in SO 2 -pretreated seedlings were significantly elevated under HS. These data have demonstrated that SO 2 pretreatment increased endogenous SA levels, which activated the antioxidant machinery and strengthened the stress defense system, thereby improving the thermotolerance of maize seedlings under HS. Our current study provides a new strategy for mitigating heat stress damage for safe crop production. [Display omitted] • SO 2 pretreatment significantly improved the thermotolerance of maize seedlings. • SO 2 -pretreated seedlings had higher salicylic acid (SA) content under heat stress. • The SA inhibitor markedly attenuated the SO 2 -triggered thermotolerance. • Heat-related genes in SO 2 - pretreated seedlings were transcriptionally activated. • SO 2 may be a new signal molecule in mediating plant thermotolerance. [ABSTRACT FROM AUTHOR]