Photosynthetic physiology of green and red Perilla frutescens varieties under drought conditions

The effects of water stress on photosynthetic pigments and secondary metabolites of two varieties of greenand purple-leaf Perilla frutescens plants were studied. Plants were grown in plastic pots for 14 days followed by water stress treatment for 10 days in a greenhouse. The trends and rates of soil water potential (SWP), leaf water content (LWC), and the maximum photochemical quantum yield (Fv/Fm) values in these two varieties were similar as the period of water stress increased from 1 to 8 days. The responses of SWP, LWC, and Fv/Fm values to water stress treatment of both varieties were adapted to a water stress period of 4 days. Purple plants exhibited significantly higher levels of anthocyanins and flavonoids than green plants under drought conditions. However, chlorophyll (Chl) a + b and carotenoids (Car) in the two varieties showed no significant differences in all water-depletion periods. The adjusted normalized difference vegetation index was significantly correlated with leaf Chl a+b, and the photochemical reflectance index was significantly correlated with Car in both species, and these can be used as indicators to characterize the physiology of these plants