This work was undertaken to study the effects of abscisic acid (ABA) and sodium tungstate (Na₂WoO₄) as an ABA synthesis inhibitor on carotenoid synthesis in germinated maize. Yellow maize kernels (cv. ‘Suyu 29’) was soaked in different concentrations of exogenous ABA and germinated. The contents of soluble protein, free amino acids, proline, vitamin C, total phenols and carotenoid, antioxidant enzyme activity, antioxidant capacity, and the expression of the genes associated with carotenoid synthesis in germinated maize were determined. The results showed that ABA increased the contents of soluble protein, free amino acids, proline, vitamin C, total phenols and endogenous ABA in germinated maize compared with the untreated control group. At an ABA concentration of 5 mg/L, the carotenoid content reached the highest level, and the levels of lutein and zeaxanthin increased by 27.6% and 20.1%, respectively, compared with the control group. However, Na₂WoO₄ inhibited the synthesis of endogenous ABA and reduced the content of carotenoids. Quantitative fluorescence polymerase chain reaction (PCR) results showed that ABA treatment could significantly increase the expression of the genes associated with carotenoid synthesis in germinated maize. Meanwhile, the antioxidant enzyme activity and antioxidant capacity were significantly enhanced. In summary, exogenous ABA treatment can promote endogenous ABA synthesis in germinated maize, and increase the expression of the genes associated with carotenoid synthesis and antioxidant capacity, thus improving nutritional quality.

In this study, the lycopene β-cyclase (LCYb) and lycopene ε-cyclase (LCYe) genes were cloned from maize, and the encoded products were analyzed by bioinformatics methods. After expression in Escherichia coli, the catalytic properties of LCYb and LCYe from maize were explored by color complementation and product analysis experiments. The results of sequence analysis showed that the full-length cDNA of maize LCYb and LCYe were 1470 and 1611 bp, respectively, which were more than 90% homologous to those of sorghum and millet. LCYe and LCYb proteins were successfully purified by fusion expression with glutathione thiotransferase tags. The results of color complementation test and high performance liquid chromatography (HPLC) analysis showed that maize LCYb had catalytic activity on β-ring, could cyclize both ends of lycopene to form β-carotene, and had very weak ε-ring catalytic activity, which could form α-carotene through the intermediate γ-carotene. Maize LCYe was also found to able to catalyze both ends of lycopene to form ε-carotene. This study can lay a foundation for exploring the molecular mechanism of the regulation of maize carotenoid.