The Effect of Exogenously Applied Dicarboxylic Acids (Photon) on the Maize (Zea mays) Metabolite Profile

Maize is an important crop worldwide with approximately 1200 million tons consumed and a market size worth $143 billion. Environmental stress influence production of crops and mitigating these ensures optimum production. Dicarboxylic acids are known as emulsifying agents that mitigate various stresses in plants. Previous reports have shown that mixtures of dicarboxylic acids like azelaic and sebacic acid are equally important for plants and have improved plant resistance to stress by directly or indirectly affecting metabolic components. In this study, maize plants in their six-leaf (V6) growth stage were sprayed with a mixture of dicarboxylic acids (photon) to investigate the effect of priming on the metabolic profile of maize. A nontargeted ¹H-NMR-based metabolic approach was used to determine the metabolic responses of maize sprayed with photon and grown under the same conditions. Leaf samples were collected at various time points (1 h, 2 h, 12 h, 24 h, 1 week, 2 weeks, and 3 weeks) after application of photon. Orthogonal partial least squares-discriminant analysis (OPLS-DA) revealed various metabolites that were involved in tolerance to plant stress. A significant increase in salicylic acid (SA) and azelaic acid (AzA) was observed in photon-treated samples compared to the controls, and it was also responsible for an increase in amino acids (GABA, alanine, and asparagine) and sugars (sucrose, maltose, and trehalose). In addition, malate and aconitate accumulated after 2 h of treatment and were found to be present in higher concentrations in the treated maize leaf extracts. Since SA was identified as one of the major compounds in treated plants, the enzymatic antioxidants (SOD, CAT, and SOD) were further evaluated. Limited SOD and CAT activity at concentrations ranging from 16.63 to 3.91 µg/mL was detected. The POD showed the lowest activity with no significant differences between photon-treated and untreated extracts. The results indicate that maize plants treated with photon showed appreciable changes in various metabolites, although no significant priming effect on antioxidant enzyme activities was detected. Therefore, the priming effect is proposed to involve the SAR in maize.