Effects of simulated drought stress on carotenoid contents and expression of related genes in carrot taproots.

Carotenoids are liposoluble pigments found in plant chromoplasts that are responsible for the yellow, orange, and red colors of carrot taproots. Drought is one of the main stress factors affecting carrot growth. Carotenoids play important roles in drought resistance in higher plants. In the present work, the carotenoid contents in three different-colored carrot cultivars, 'Kurodagosun' (orange), 'Benhongjinshi' (red), and 'Qitouhuang' (yellow), were determined by ultra-high-performance liquid chromatography (UPLC) after 15% polyethylene glycol (PEG) 6000 treatment. Real-time fluorescence quantitative PCR (RT-qPCR) was then used to determine the expression levels of carotenoid synthesis- and degradation-related genes. Increases in β-carotene content in 'Qitouhuang' taproots under drought stress were found to be related to the expression levels of DcPSY2 and DcLCYB. Increases in lutein and decreases in α-carotene content in 'Qitouhuang' and 'Kurodagosun' under PEG treatment may be related to the expression levels of DcCYP97A3, DcCHXE, and DcCHXB1. The expression levels of DcNCED1 and DcNCED2 in the three cultivars significantly increased, thus suggesting that NCED genes could respond to drought stress. Analysis of the growth status and carotenoid contents of carrots under PEG treatment indicated that the orange cultivar 'Kurodagosun' has better adaptability to drought stress than the other cultivars and that β-carotene and lutein may be involved in the stress resistance process of carrot.