Effect of chromium on some enzyme activities in the wheat rhizosphere

Abstract

We investigated the effect of Cr(Vl) on the rhizosphere enzymes of wheat seedlings by using the rhizobox setup developed by Youssef and Chino (1988). In this system, 20 mg Cr(Vl) kg^<-1> soil as K_2Cr_2O_7 was placed in several compartments separated from each other by a 500 mesh nylon cloth. Wheat seedlings were transplanted, was placed in a growth chamber under 33.6 μ mol m^<-2> S^<-1> light and 24/20℃ day/night, for one month. Plant growth, plant height, total root weight, total shoot weight and number of total tillers were lower, but the root/shoot ratio was higher in the Cr treatment than in the control, indicating that the addition of Cr(Vl) exerted an adverse effect on plant growth, especially on roots. There was a decrease in the pH across the rhizosphere within a range of 5 mm wide from the rhizoplane, which was most pronounced in the central compartment (C.C.) in both the control (1.25 unit) and Cr treatment (1.86 unit), i.e. the Cr treatment further decreased the pH (0.61 unit) within a range of 2 mm from the rhizoplane. Phosphomonoesterase, phosphodiesterase, exocellulase and β-glucosidase activities were much higher in the C.C. with a negligible or no rhizospheric effect in other compartments both in the control and Cr treatment. However, the Cr treatment enhanced the activities of exocellulase and β-glucosidase, but decreased the activities of phosphomonoesterase and phosphodiesterase in the C.C. The findings obtained in the current studies was analyzed in terms of possible application to the development of phytoremediation technology.