Ultra-low concentration of chlorine dioxide regulates stress-caused premature leaf senescence in tobacco by modulating auxin, ethylene, and chlorophyll biosynthesis.

Exploring novel growth regulators for premature senescence regulation is important for tobacco production. In the present study, chlorine dioxide (ClO) was explored as a novel plant growth regulator for tobacco growth, particularly its effect on leaf senescence and root development. The results showed that 0.15 μM ClO maintained the lushness of detached leaves and whole plants. Also, the leaves of ClO-treated plants exhibited a chlorophyll content of 58% higher than in CK (control) plants (P < 0.05). Besides, ClO treatment increased the biomass of roots and aboveground parts by 54 and 16%, respectively. The ClO-treated plants also showed enhanced activities of antioxidant enzymes and significantly reduced malondialdehyde contents (P < 0.05). Moreover, ClO treatment remarkably alleviated drought-caused premature senescence in the tobacco plants and partly rescued the exogenous ethylene-caused plant dwarfism. The indole-3-acetic acid content in ClO-treated plants was higher than in non-treated plants (P < 0.05), but ethylene content was significantly lower (P < 0.05). Gene expression analysis showed that ClO treatment remarkably suppressed ethylene synthase genes. However, the auxin biosynthesis and transport genes were up-regulated, with NtIAA17 increasing by five folds (P < 0.05). Further, ClO remarkably up-regulated the expression of chlorophyll biosynthesis genes, with a >20-fold increase in NtHEMA1 and NtCHLH expressions. These results designate ClO as a potential regulator for improving tobacco productivity by retaining higher chlorophyll content and promoting root growth.