Physio-Biochemical Response of Borago officinalis L. Roots to Cadmium Toxicity

Cadmium (Cd) has been highlighted as a major heavy metal pollutant that causes considerable damage to plants, animals and humans. The present study aimed to determine the effect of Cd exposure on the physiological, biochemical, and metabolic characteristics of Borago officinalis roots. Borage seedlings were exposed to different concentrations of Cd (0, 81, 162, 243, and 324 mu M) under hydroponic culture conditions and sampled at five-time points after treatment (12, 24, 48, 72, and 108 h). Cd accumulation, biochemical parameters (the content of total protein, proline, soluble sugars, hydrogen peroxide (H2O2), malondialdehyde (MDA), and antioxidant enzymes activity), and accumulation of secondary metabolites in borage roots were determined. The results indicated that Cd accumulation in roots increased significantly under Cd stress. Proline, soluble sugars, anthocyanin, phenolic compounds, and flavonoid content increased in borage roots with increasing Cd concentrations. The highest values were related to 324 mu M Cd treatment at 108 h after stress. Additionally, the activity of antioxidant enzymes, including catalase, peroxidase, and polyphenol oxidase enzymes, as well as H2O2 and MDA content, were considerably increased under Cd treatments, especially at the highest Cd concentration (324 mu M Cd). Furthermore, increasing the duration of Cd exposure intensified the effects of Cd stress on biochemical properties and secondary metabolite content. These findings enhance our insights about the detoxification strategies such as antioxidant systems in roots and open new approaches that can be useful for manipulating Cd tolerance in borage.