Abstract
Melatonin (MT) plays integral roles in regulating several biological processes including plant growth, seed germination, flowering, senescence, and stress responses. This study investigated the effects of MT on adventitious root formation (ARF) of de-rooted tomato seedlings. Exogenous MT positively or negatively influenced ARF, which was dependent on the concentration of MT application. In the present experiment, 50 ÎŒM MT showed the best effect on inducing ARF. Interestingly, exogenous MT promoted the accumulation of endogenous nitric oxide (NO) by down-regulating the expression of S-nitrosoglutathione reductase (GSNOR). To determine the interaction of MT and NO in ARF, MT synthesis inhibitor p-chlorophenylalanine, NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt as well as GSNOR-overexpression plants with low NO levels were used. The function of MT was removed by NO scavenger or GSNOR-overexpression plants. However, application of MT synthesis inhibitor did little to abolish the function of NO. These results indicate that NO, as a downstream signal, was involved in the MT-induced ARF. Concentrations of indole-3-acetic acid and indole-3-butyric acid, as well as the expression of several genes related to the auxin signaling pathway (PIN1, PIN3, PIN7, IAA19, and IAA24), showed that MT influenced auxin transport and signal transduction as well as auxin accumulation through the NO signaling pathway. Collectively, these strongly suggest that elevated NO levels resulting from inhibited GSNOR activity and auxin signaling were involved in the MT-induced ARF in tomato plants. This can be applied in basic research and breeding.
Highlights
Melatonin (N-acetyl-5-methoxytryptamine) was discovered in the bovine pineal gland in 1958 (Lerner et al, 1958), and MT was identified in plants by Dubbels et al (1995)
Levels of auxin efflux genes (PIN1, PIN3 and PIN7) and auxin signaling transduction genes (IAA19 and IAA24) were significantly increased by exogenous MT application. These results strongly suggest that nitric oxide (NO) may act as a downstream signal of MT to enhance auxin signaling that induces the adventitious root formation (ARF) of de-rooted tomato explants
Compared with no MT treatment, treatment with exogenous MT significantly enhanced the numbers of adventitious roots for the concentrations applied (p < 0.05)
Summary
Melatonin (N-acetyl-5-methoxytryptamine) was discovered in the bovine pineal gland in 1958 (Lerner et al, 1958), and MT was identified in plants by Dubbels et al (1995). Roles of Melatonin in Adventitious Root Formation (Arnao and HernĂĄndez-Ruiz, 2015), organ development (Arnao and HernĂĄndez-Ruiz, 2014), root system architecture (PelagioFlores et al, 2012; Zhang et al, 2014), senescence (Byeon et al, 2012; Wang et al, 2013a,b; Shi et al, 2015b), defense (Weeda et al, 2014), and stress response (Pape and LĂŒning, 2006; Posmyk et al, 2009; Byeon and Back, 2014; Kostopoulou et al, 2015; Liu et al, 2015b; Zhang et al, 2015) in plants. The major questions that remain unanswered concern how MT functions in plants, and whether it depends on auxin signaling. Does MT share similar functions to auxin in plants, in relation to its second messenger? These issues stimulated us to study the relationship of MT, auxin and their second messenger based on currently available literature and emerging considerations Does MT share similar functions to auxin in plants, in relation to its second messenger? If so, what acts as the second messenger? These issues stimulated us to study the relationship of MT, auxin and their second messenger based on currently available literature and emerging considerations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
