Melatonin promotes seed germination under salinity and enhances the biosynthesis of steviol glycosides in Stevia rebaudiana Bertoni leaves

Abstract

Melatonin (MEL) can act as a plant growth regulator and biostimulator in stressful situations. Using MEL in seed pretreatment also affects the future growth of plants. Therefore, this research investigated the effects of MEL on seed germination and seedling growth under NaCl in in vitro conditions. The additional effects of MEL on the accumulation of steviol glycosides (SGs) and on the expression of appropriate genes were also studied. Five μM of MEL was the best concentration for seed germination, while 20 μM exerted a positive impact on the biomass of stevia plantlets. NaCl significantly decreased seed germination, but MEL alleviated this effect when seeds were germinated in 50 mM of NaCl. Under salinity, the values of almost all morphological traits decreased as MEL concentration increased. The highest amounts of stevioside and rebaudioside A (Reb A) were observed as a result of treating seeds with 5 and 20 μM of MEL, respectively. When adding NaCl, positive impacts of MEL on the accumulation of both SGs were also observed. Expression analyses of the genes involved in SGs biosynthesis was explored in seeds and leaves, and the transcripts of key enzymes occurred in both the tissues. However, quantitative polymerase chain reaction (qPCR) analysis showed that all tested genes were upregulated in younger leaves, contrary to older ones. Also in younger, rather than older, leaves SG gene expression varied according to MEL concentration. This study, therefore, presents the promising potential of MEL for improving stevia seed germination under salinity conditions and for enhancing the production of SGs in stevia plants.

Melatonin inhibits seed germination by crosstalk with abscisic acid, gibberellin, and auxin in Arabidopsis

“…For example, a higher level of germination post‐heat stress was obtained with the 1000 µM MT treatment 48 . Moreover, exogenous melatonin promoted seed germination under salt stress in cotton, cucumber, and Stevia rebaudiana Bertoni 49‐51 . These studies show that MT may be involved in seed germination.…”

Melatonin Alleviates Low-Temperature Stress via ABI5-Mediated Signals During Seed Germination in Rice (Oryza sativa L.)

“…Therefore, it was feasible to improve seed germination by using phytohormones, i.e., MT, in agricultural productions. Indeed, MT has been widely and effectively applied to alleviate the stress-induced delays of seed germination in various plants ( Posmyk et al, 2008 ; Zhang et al, 2013 , 2014 ; Hernández et al, 2015 ; Chen et al, 2020 ; Simlat et al, 2020 ). In this research, we found that the applications of exogenous MT significantly improved the germination rates ( Figures 1 , 2A,B and Supplementary Figures 3A,B ) and seedling performance ( Supplementary Figures 3C,D ), which were largely related to the recovery of water absorption ( Supplementary Figure 3D ) and membrane permeability ( Figure 3 ).…”

“…Exogenous applications of melatonin ( N -acetyl-5-methoxytryptamine, MT) have been determined as an effective way to improve seed germination under various stress conditions ( Hernández et al, 2015 ; Xiao et al, 2019 ; Simlat et al, 2020 ). For example, exogenous MT enabled the promotion of seed germination under salinity ( Zhang et al, 2014 ) and water stress ( Zhang et al, 2013 ) in cucumber ( Cucumis sativus L.) while high levels of germination under post-salt and toxic copper ion stress conditions were also observed in cotton ( Gossypium hirsutum L.) ( Chen et al, 2020 ) and in red cabbage ( Posmyk et al, 2008 ), respectively.…”

“…For example, exogenous MT enabled the promotion of seed germination under salinity ( Zhang et al, 2014 ) and water stress ( Zhang et al, 2013 ) in cucumber ( Cucumis sativus L.) while high levels of germination under post-salt and toxic copper ion stress conditions were also observed in cotton ( Gossypium hirsutum L.) ( Chen et al, 2020 ) and in red cabbage ( Posmyk et al, 2008 ), respectively. Moreover, MT treatments also protected seeds against heat stress in Arabidopsis ( Hernández et al, 2015 ) and salt stress in Stevia rebaudiana Bertoni ( Simlat et al, 2020 ). In addition, improvements of MT on seed germination have also been reported in maize under chilling stress ( Cao et al, 2019 ).…”

Recent Progress on Melatonin-Induced Salinity Tolerance in Plants: An Overview

“…The highest stevioside and rebaudioside A (Reb A) values were obtained from 5 and 20 µM MEL application of seeds, respectively. Steviol glycoside gene expression in young leaves varied according to MEL concentration (Simlat et al, 2020).…”