Effect of melatonin on propyzamide-induced stress tolerance in Vigna radiata (L.) R. Wilczek seedlings

Background Melatonin (MEL) is a plant hormone with broad biological activity that also affects microtubules, which are essential for cell division and plant growth. This study investigated the relationship between MEL application and vegetative development in mung bean ( Vigna radiata (L.) R. Wilczek) seedlings exposed to propyzamide (PROP), a herbicidal inhibitor of microtubule polymerisation. It also examined whether melatonin exerts a protective effect on this development and to what extent this effect is associated with cortical microtubules. Results Morphometric and morphological analyses showed that PROP markedly inhibited seedling growth by approximately 25% compared with the control, primarily due to cell cycle arrest in prophase. In contrast, MEL alone stimulated growth by 10–20%. Immunofluorescence analysis of β -tubulin localisation demonstrated that MEL, when applied in combination with PROP, partially counteracted PROP-induced microtubule disorganisation, as evidenced by a twofold increase in fluorescence intensity and reduced growth inhibition. The strongest protective effect was observed with 20 µM MEL, which increased seedling length by 22% relative to PROP alone and reduced growth inhibition by 17% relative to the control. However, 30 µM MEL in combination with PROP was less effective (approximately 5% stimulation), confirming the dose-dependent effect. Conclusions These findings provide new insights into the protective role of melatonin against microtubule-disrupting herbicides and demonstrate, for the first time, its mitigating effect on propyzamide-induced stress in V. radiata seedlings. This highlights the potential of melatonin as a safener and contributes to a better understanding of its role in regulating growth under stress conditions.