Changes in Ascorbate, Non-Protein Thiols-Cysteine in Linseed Seedlings Subjected to Boron Stress

To determine the effect of boron (B) on growth and ascorbate-non-protein thiols-cysteine in the leaves and roots of linseed (Linum usitatissimum L. var R-552), seedlings were raised in solution culture with variable boron supply (0.0033, 0.33 and 33 mg B L⁻¹) under controlled conditions in green house. Optimum seedling growth was observed at 0.33 mg B L⁻¹ supply whereas below and above this level seedlings showed growth retardation. Photosynthetic pigments were found to decrease more under excess boron (33 mg B L⁻¹) than deficient (0.0033 mg B L⁻¹). Accumulation of proline, hydrogen peroxide (H₂O₂) and lipid peroxidation was observed in both leaves and roots under deficient and excess boron supply. The concentration of ascorbate and non-protein thiols decreased with increased activity of ascorbate peroxidase (APX) and glutathione reductase (GR) enzymes was observed in both parts under boron stress. Cysteine concentration was elevated in leaves and decreased in roots.