Growth, physiological, and antioxidant characteristics in green and red Perilla frutescens varieties as affected by temperature- and water-stressed conditions

The objective of this study was to investigate the growth, photochemical reflectance, and antioxidant properties of P. frutescens species in response to temperature- and water-stress conditions. Two independent experiments were carried out in growth chambers and an environmentally controlled greenhouse for periods of five weeks in each experiment. Pots of red and green Perilla cultivars were planted under day/night temperatures of 15/10 °C, 20/15 °C, 25/20 °C (control), 30/25 °C, and 35/30 °C. Moreover, plants were subjected to four irrigation levels as measured by volumetric water content (VWC): 65 % (control), 40 %, 30 %, and 15 %. Changes in plant height and fresh and dry weights of shoots and leaves indicated that those at 10 °C suffered more severely than at 35 °C. When plants were treated with 15 °C and 15 % VWC stressing for five weeks, all plants exhibited harmful effects to their leaves compared to 25 °C and 65 % VWC treatments (control). The maximal quantum yield of PSII photochemistry values of all plants displayed significant decreases in severe-stress treatments (35 °C, 15 °C, and 15 % VWC) compared to controls, indicating that this parameter is suitable for evaluating the growth of these plants under temperature and water stressing sufficient to result in photoinhibitory effects. The normalized difference vegetation index values of all plants in 35 °C and 15 % VWC treatments were significantly lower than controls. In addition, red Perilla plants exhibited better temperature and drought tolerance than green plants due to their higher soil-plant analysis development values under the same temperature and VWC treatments. Therefore, these indices can be used as indicators to characterize the physiology of these plants. The increases in 2,2-diphenyl-1- picrylhydrazyl radical scavenging activity and total phenolics (TP) content of green Perilla leaf extract (PLE) were clearly manifested with 35 °C treatment compared to controls. However, there were clear increases in the TP content of all PLE with 15 % VWC treatment compared to controls. Thus, Perilla plants subjected to heat and water stresses can be used as a health food and for medicinal purposes due to high TP content, but the use of stressed plants for food purposes would be limited due to low marketability. Green- and red-leaf Perilla contained higher rosmarinic acid (RA) and caffeic acid (CA) content, respectively, in each VWC treatment, implying that their genotypes exhibited different abilities and specificities of photosynthetic metabolites.