Asian Journal of Microbiology, Biotechnology & Environmental Sciences Paper

RESPONSE OF ENZYMZTIC PARAMETERS OF ELEUSINE CORACANA GAERTN. SEEDLINGS TO MERCURY AND ZINC STRESS

MANNA MILIAN, K. BIJAY KUMAR AND B.K. MOHANTY

Abstract

Tolerance response of Eleusine coracana (Finger millet) to enzymatic parameters were evaluated with the experimental treatments of Zinc Sulphate (ZnSO4.7H2O) and Mercuric Chloride ( HgCl2). The selected concentrations of both the metals were in the range of 0.1mg/L to 100mg/L since 1000mg/L showed zero percentage germination of seeds. Chlorophyllase, the enzyme that breaks the chlorophyll showed an increase in its activity with the rise in the levels of both the metals. Protease was induced to a milder or greater extent by both zinc and mercury. While zinc suppressed DNase in both the root and the shoot, mercury had an inductive and suppressive effect in the shoot and the root respectively. RNase was stable in the shoot in response to mercury but there was significant suppression in the root. Zinc also caused a decrease in RNase activity in the shoot. Both the metals induced the activities of catalase, peroxidase and polyphenol- oxidase enzymes both in the shoot and the root. The peroxisomal enzyme catalase responded well to the metal exposure in the roots, as well as in the shoots. The second peroxisomal enzymes, peroxidase showed consistent response to the metals. There was induction with the increase in metal concentration and suppressions in its activity at the peak of the metal level. Polyphenol oxidase followed rise in activity with the increase in concentration. The other enzyme that showed dose related to both the metals was acid phosphatase and this parameter can also be used as an index of zinc and mercury toxicity in Eleusine. In general there was an induction of Acid phosphatase and Acid inorganic pyrophosphatase activity with exception of the effects of zinc in the root. Both mercury and zinc were responsible for an increase in the activity of Alkaline inorganic pyrophosphatase enzyme. The trends in acid phosphatase activity in response to metals shows that the enzyme cannot be used as a general indicator of metal toxicity as its responses are dependent on species. It was found that at higher concentration alkaline inorganic pyrophosphatase activity is rapid in photosynthesizing tissue. Based on such findings they proposed that the pyrophosphate released during synthetic reactions may be removed by alkaline inorganic phosphatase.