Regulation of tocopherol (vitamin E) biosynthesis by abscisic acid-dependent and -independent pathways during abiotic stress in Arabidopsis

The increase in tocopherol (vitamin E) biosynthesis in Arabidopsis during drought and osmotic stress, but not during high light or nitrogen deprivation, is mediated by abscisic acid. Plants increase the production of antioxidants including tocochromanols (vitamin E) during stress. To study the regulation of tocochromanol synthesis, Arabidopsis plants were exposed to drought, osmotic stress stimulated by polyethylene glycol, abscisic acid (ABA), nitrogen deprivation, and high light. ABA treatment resulted in increased contents of tocochromanols, and expression of the key tocopherol biosynthesis genes VTE2 and HPPD was upregulated, indicating that tocochromanol accumulation was regulated by ABA. Under drought and osmotic stress, the ABA and tocochromanol contents as well as VTE2 and HPPD expression were also increased. ABA levels did not change during nitrogen deprivation or high light treatment, indicating that tocochromanol accumulation under these conditions was ABA-independent. Tocochromanol accumulation during drought or osmotic stress was not compromised in the ABA-deficient aba1-6, aba2-1 and aba3-2 mutants, suggesting that tocochromanol synthesis under these conditions was mostly regulated in an ABA-independent way. Therefore, the accumulation of tocochromanols in Arabidopsis can be regulated by ABA-dependent and ABA-independent signaling pathways, based on the specific conditions.