Exogenous salicylic acid promotes carotenoid accumulation and antioxidant capacity in germinated maize kernels by regulating carotenoid biosynthetic pathway

Salicylic acid (SA), as an endogenous plant growth regulator, plays a crucial role in growth and development of plants. This study investigated the influence of varying concentrations of exogenous SA on the physiological and biochemical properties, antioxidant capacity, carotenoid content, and gene expression levels of germinated maize kernels. The results showed that the highest total phenolic and vitamin C contents were found with 0.10 mmol/L of SA, while the highest soluble protein, free amino acid and proline contents were found with 0.50 mmol/L of SA. The content of lutein and zeaxanthin reached the highest under 0.05 mmol/L of SA treatment, which were 18% and 22% higher than that of the control group, respectively. Meanwhile, the expression of seven key genes involved in carotenoid synthesis exhibited different degrees of up-regulation or down-regulation, which may be the reason for promoting carotenoid enrichment in germinated maize kernels. In addition, the antioxidant enzyme activities and antioxidant capacity in germinated maize kernels reached the highest value under the 0.1 mmol/L of SA treatment. Moreover, the correlation analysis results showed the transcription levels of some carotenogenic genes were significantly correlated with carotenoid content or antioxidant capacity. In summary, exogenous SA increased the content of bioactive components, especially carotenoids, and enhanced the antioxidant activity of germinated maize. Therefore, exogenous SA treatment may be used as an efficient germination method to improve the quality of germinated maize.