Chromium interference in iron nutrition and water relations of cabbage

Cabbage (Brassica oleracea var. capitata cv. Snowball), known to be responsive to potentially toxic elements, was investigated for chromium (Cr³⁺) effect on iron metabolism and water relations. After 6 weeks growth in sand culture, a set of plants was supplied with 500 μM Cr³⁺ (CrCl₃), superimposed over the full nutrient solution (control). Exposure to excess Cr³⁺ led to increased accumulation of Cr, more in roots than in leaves, and to the development of toxicity symptoms. In decreasing chlorophyll concentration and the activities of heme enzymes, catalase and peroxidase, the excess Cr³⁺ effect resembled Fe deficiency. These changes, associated with decrease in Fe accumulation in Cr³⁺ treated plants, indicate that by reducing absorption of Fe, Cr³⁺ impairs the Fe requiring steps of chlorophyll and heme biosynthesis. In spite of lower water saturation deficit, the leaves of Cr³⁺ treated plants showed decrease in leaf water potential, associated with increase in diffusive resistance and lowering of transpiration rate, indicating development of water stress. Enhanced accumulation of proline in Cr³⁺ treated plants also suggested this. Observed changes in water stress parameters in Cr³⁺ stressed plants indicate that plant exposure to excess supply of Cr³⁺ reduces the physiological availability of water.