Concentration-dependent effects of tungstate on germination, growth, lignification-related enzymes, antioxidants, and reactive oxygen species in broccoli (Brassica oleracea var. italica L.).

The phyto-impact of tungstate is not frequently studied like other heavy metals especially in the sight of continuous accumulation of tungstate in the agriculture soils and water. Thus, the present study was aimed to investigate the supplementation of various tungstate concentrations (0, 1, 5, 10, 50, and 100) to germination water (mg L-1) or clay soil (mg kg-1) on germination and metabolism of broccoli. Lower concentrations (1-10 mg L-1) accelerated germination process and reciprocally were recorded at the highest one (100 mg L-1). The promoter effect of lower concentrations on seedlings growing on tungstate contaminated soil was underpinned from enhancement of pigments, metabolites, enzymatic and non-enzymatic antioxidants, and nitrate reductase. However, the highest concentration-noxious impacts perceived from oxidative damage and membrane integrity deregulation accompanied with no gain from increment of proline, superoxide dismutase, and glutathione-S-transferase. The depletion of phytochelatins and nitric oxide jointed with the enhancement of peroxidases, polyphenol oxidase, and phenylalanine ammonia-lyase at higher concentration reinforced lignin production which restricted plant growth. The results supported the hormetic effects of tungstate (beneficial at low concentrations and noxious at high concentration) on morphological and physiological parameters of broccoli seedlings. The stimulatory effect of tungstate on metabolic activities could serve as important components of antioxidative defense mechanism against tungstate toxicity.