Effects of chilling and high light stress on phenolic metabolism and antioxidant activity of Aloe vera L. plants

High light (HL) can limit plant photosynthetic activity, growth and productivity. The HL effect was more pronounced in plants grown at low temperature. In order to determine the effects of chilling stress (4 0C) and light intensities (450 and 850 µmol m-2 s-1) on antioxidant defense system and  phenolic metabolism of Aloe vera L., an experiment was  conducted in a randomized complete block design with four replications in a research greenhouse. The results indicated that the Aloe vera has a stronger HL tolerance. Increased tolerance in HL-treated plants was related to screening of photoradiation by phenolic compounds (but not the mechanism of ROS scavenging). Although total phenolics and flavonoids concentration as well as phenylalanine ammonia-lyase (PAL) and catalase (CAT) activity responded positively to the chilling treatment, but cold stress considerably increased the rise in malondialdehyde (MDA) content (as a marker of lipid peroxidation), suggesting that Aloe vera is sensitive to chilling treatment. Additionally, chilling raised free radical scavenging activities of Aloe vera leaf gel using DPPH radical-scavenging because of an enhancement of total phenolic, and may be recommended for increasing leaf gel quality.