An Inclusive Insight into leaf Metabolome Reveals Substantial Metabolic flux in Maize Seedlings Subjected to Boron (B) Toxicity.

Plants require boron for normal growth and metabolism. The presence of boron above threshold levels causes significant alterations in normal physiological, cellular, and metabolic functions in plants. The present study examines the impact of boron stress on the growth of maize seedlings and their leaf metabolome. Boron toxicity led to a significant decline in root and leaf growth and in fresh and dry biomass compared to the control in maize seedlings. Boron stress also resulted in a significant decline in pigment content, including chlorophyll a, chlorophyll b, and total chlorophyll. The GC-MS and ¹H-NMR-based metabolic analysis of the aqueous (80% v/v) methanolic extract of maize leaves revealed that boron stress caused significant disparity in metabolites, which includes changes in the abundance of amino acids, carbohydrates, fatty acids, sugar alcohols, and secondary metabolites, compared to the control. The GC-MS-based analysis showed significantly higher levels of metabolites such as L-ascorbic acid, morpholine, docosanoic acid, and glutaric acid, while moderately higher levels of D-mannitol, stearic acid, dodecane, glycine, decalin, thiourea, and D-glucitol were observed in maize leaves under boron stress compared to the control. Among the identified metabolites using GC-MS, L-ascorbic acid showed the highest fold increase under boron stress compared to the control. The metabolic profile obtained using ¹H-NMR-based analysis showed a significant accumulation of sucrose, followed by isoleucine and ethanol, in leaves under boron stress compared to the control. Additionally, metabolites such as arginine, lactate, proline, and tyrosine showed moderately higher levels in leaves under boron stress than in the control. The results clearly indicate that boron stress causes substantial damage to maize seedlings by inhibiting plant growth, reducing biomass, and decreasing photosynthetic pigment content, while inducing a significant metabolic imbalance in leaves.