Roles of Antioxidant Enzymes, Secondary Metabolites, and Lipids in Light Adaption of Tea-Oil Plant (Camellia oleifera Abel)

Tea-oil (Camellia oleifera Abel) is an important woody crop for producing high-quality edible oil, which has been extensively cultivated in an unattended manner and exposed to various light stresses. To gain insights into the tea-oil plant’s adaption to different light environments, leaf anatomical characteristics, chlorophyll fluorescence quenching kinetics, and antioxidant enzyme activities were investigated under high (HL), medium (ML), and low light intensity (LL) conditions. Metabolomic and transcriptomic analyses were also performed to reveal the changes in secondary metabolites and lipid profiles. The results showed that HL and ML had a rapid NPQ relaxation compared to LL. As light intensity decreased, the chlorophyll fluorescence yields and PSII photochemical efficiency improved during both the light-adapted steady-state and dark relaxation phases. ML and LL exhibited lower PSII activity and higher NPQ compared to HL, as instantaneous light intensity increased. The increased leaf thickness, elevated CAT activity, and the up-regulated synthetic pathways of flavonoids, lignans, tannins, and triterpenoids helped tea-oil plants survive under HL and ML. SOD and POD played an important role in acclimation to LL, resulting in a lower level of lipid oxidation. HL and ML promoted lipid biosynthesis, while LL inhibited fatty acid elongation, enhanced degradation pathways of triacylglycerol and fatty acids, and facilized sphingolipid metabolism. These findings shed light on the adaptive mechanism of tea-oil plant to varying light intensity environments. To further unravel the complex interactions among lipids, secondary metabolites and the antioxidant system, future study should focus on verifying the functions of differentially expressed genes identified in this study.