ABSTRACT
This study was conducted to investigate the role of phenolic compounds in the antioxidant defense system in Malva parviflora L. plants treated with cadmium (Cd). After surface sterilization, the seeds were sown on seedling trays. Forty-day-old plants were then transferred to hydroponic cultures with Cd (40⯵M) or without Cd (control). Some biochemical and physiological parameters were assayed on the sixth day after Cd treatment. Based on the results, the plants showed an increase in leaf soluble carbohydrates, total phenolic compounds, total flavonoids, and phenylalanine ammonia-lyase (PAL) activity at the end of the exposure period. However, length, fresh weight, chlorophyll (Chl) b, total Chl, stomatal conductance and starch content decreased under Cd treatment. There was no significant difference between the plants exposed to Cd and the control group for Chl a, SPAD index, carotenoids, and anthocyanins as well as the H2O2 content six days after treatment. The Cd content in the roots was considerably higher than that in the shoots. In assessing the antioxidant capacity of plant extracts, different results were observed using 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) test and beta-carotene/linoleic acid bleaching assay. According to the results of this study, it seems that increased activity of PAL enzyme leads to an increase in biosynthesis of phenolic compounds in M. parviflora. This mechanism probably increases the antioxidant capacity of the plant to suppress Cd-induced toxicity and oxidative stress.
