A feedback inhibition between nitric oxide and hydrogen peroxide in the heat shock pathway in Arabidopsis seedlings

We even reported that hydrogen peroxide (H2O2) acts upstream of nitric oxide (NO) in the heat shock (HS) pathway in Arabidopsis (Arabidopsis thaliana) seedlings. In this work, we found a strange phenomenon that exogenous application of high concentration of H2O2 could not elevate internal H2O2 level under HS. NO donors sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) intensified this trend, whereas a special NO scavenger, 2-(4-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxyde (cPTIO) counteracted it, suggesting NO effects on reducing H2O2 accumulation. Western blotting and real-time reverse transcription-polymerase chain reaction demonstrated that NO eliminated H2O2 effects on the DNA-binding activity of HS factors and the accumulation of HS proteins. Subsequent experiments revealed that under HS, SNP and SNAP enhanced the activities of antioxidant enzymes catalase, ascorbate peroxidase and glutathione reductase, whereas c-PTIO inhibited them. Collectively, H2O2-induced NO stimulated the activities of antioxidant enzymes so as to eliminate excessive H2O2 in plant and then inhibit HS factor DNA-binding activity and HS protein accumulation, indicating a feedback inhibition between NO and H2O2 in thermotolerance.