Regulatory effects of exogenous melatonin and salicylic acid on low temperature induced-early flowering in tobacco

Low temperature not only inhibits tobacco growth but also leads to early flowering, significantly affecting the yield and quality. Melatonin (MLT) and salicylic acid (SA) play important roles in plant growth, development and stress response. However, limited research has determined the impact of MLT and SA on tobacco cold-stress response, especially cold-induced flowering. In this study, phenotypic and biochemical assays and gene expression analysis were conducted on tobacco cultivar ‘Yunyan 87’ under cold-stress with exogenous application of MLT and SA. The results showed that MLT and SA significantly reduced the accumulation of H 2 O 2 , increased the activity of antioxidant enzymes, and changed osmotic adjustment substances in tobacco under low-temperature stress. Besides, the application of exogenous SA significantly increased the expression levels of flower-positive factors NtFT4 , NtFT5 , and NtSOC1 ; however, no obvious effect was observed in the application of exogenous MLT. Consistently, exogenous SA aggravated low temperature-induced early flowering and reduction in the number of leaves; whereas MLT had no significant effect on these traits. In summary, both MLT and SA could enhance cold tolerance of tobacco. Furthermore, SA promotes low temperature-induced early flowering in tobacco, but MLT has no significant effect on tobacco flowering.