Phytotoxic effects of high chromium on oxidative stress and metabolic changes in Citrullus

Citrullus (Citrullus vulgaris cv Ludhiana) was grown in refined sand at ambient temperature in a glasshouse. Plants were maintained in complete nutrient solution for 24 days and on 25^th day chromium as dichromate was added at 0.05, 0.10, 0.20, 0.30 and 0.40 mM. Excess Cr reduced plant height, leaf area with loss of turgor and chlorosis of middle leaves. Later, chlorosis became severe and changed to necrosis in patches. Chromium accumulation reduced the biosynthesis of chlorophylls, catalase, protein, non-protein nitrogen, starch and increased the concentration of sugars, phenols, protein nitrogen, Hill reaction activity and activity of peroxidase and increased the activity of acid phosphatase. The translocation of iron, and chromium in different parts of citrullus were affected most significantly by excess chromium. The concentration of Cr, its uptake and translocation from roots to tops increased with excess Cr, whereas iron concentration increased in roots and decreased in stem and leaves of citrullus.