Unraveling early redox responses and secondary metabolite accumulation in garlic under drought and high temperature

Garlic (Allium sativum L.) is valued for its nutritional, economic, and bioactive properties, yet its secondary metabolic responses to concurrent water-availability and temperature conditions remain poorly understood. This study investigated the temporal metabolic responses of garlic plants to drought and high temperature, applied individually and in combination, over an 8-day period, using univariate and multivariate approaches. Drought emerged as the dominant factor influencing plant redox status, leading to a pronounced shift in glutathione redox status by day 8, characterized by increased content of oxidized glutathione (GSSG), proportion of oxidized glutathione within the total glutathione pool (%GSSG), and a decreased reduced-to-oxidized glutathione ratio (GSH/GSSG). These changes indicate enhanced oxidative pressure and activation of redox-associated signaling pathways. Methyl jasmonate (MeJA) accumulation, particularly under co-occurring drought and high temperature, was temporally associated with increased contents of several flavonoid glycosides, suggesting a link between jasmonate-related signaling and phenylpropanoid-derived antioxidant responses. Conversely, organosulfur metabolites displayed variable responses, reflecting complex regulation and potential sensitivity to temperature. Multivariate analysis further revealed a time- and treatment-dependent shift in metabolic response, with water availability becoming the primary source of data variation towards the end of the experiment. These findings highlight the importance of stress interactions and temporal dynamics in shaping plant early metabolic responses, and point to glutathione redox parameters and MeJA as candidate metabolite-level indicators warranting further validation for stress monitoring.