Higher cadmium and zinc accumulation in parsley (Petroselinum crispum) roots activates its antioxidants defense system

Parsley (Petroselinum crispum) is herb with many biological and medicinal benefits for humans. However, growth on zinc (Zn) and cadmium (Cd) contaminated sites might get severely affected due to over accumulation of heavy metals (HM) in different plant tissues. Antioxidants play a crucial role in minimizing the negative effects of HM. The present study investigates the effects of Zn and Cd stress on P. crispum morphological parameters, enzymatic/non-enzymatic antioxidant profiling and metal accumulation in shoot/root. Plants were exposed to different concentrations of Zn (50, 100, 150 and 200 µM) and Cd (10, 20, 40 and 80 µM) along with control (no stress), in soil-less Hoagland's solution. The results showed that Zn and Cd substantially decrease the growth parameters with increased contents of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and electrolyte leakage (EL). Non-enzymatic antioxidant activities, like total phenolic contents (TPC) and ferric reducing antioxidant power (FRAP), were induced high in leaves only upon Cd stress and contrarily decreased upon Zn stress. Total flavonoid contents (TFC) were decreased under Zn and Cd stress. Enzymatic antioxidant activities like superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were also strongly induced upon Cd stress. At the same time, SOD and guaiacol peroxidase (GPX) activity was induced significantly upon Zn stress. Cd uptake and accumulation was notably high in roots as compared to shoots, which suggests P. crispum have a reduced ability to translocate Cd towards aboveground parts (leaves). Additionally, strong induction of antioxidants by P. crispum under Cd stress might indicate the capacity to effectively re-modulate its physiological response. However, further investigations regarding other HMs and experiments at the molecular level are still needed.