Department of Life Sciences, University of Indore, Indore-452001, India
Enclosing nitrate grown maize (Zea mays L. cv. GS-2) seedlings in a chamber containing 50 ppm H2S, increased nitrate reductase activity after a lag of ether 30 min in primary leaves or of 60 min in secondary leaves and this increase continued for the duration of experiment which was 4 h. In the seedlings raised without nitrate, the enzyme activity declined due to exposure to H2S. When additional dosage of H2S were injected in the chamber after every 30 min, the enzyme activity declined after the third dose in both leaves. The enzyme activity increased in response to H2S, only when the seedlings were raised with low levels of sulphur. When the seedlings were raised with 5 or 10 mM sulphur in the nutrient solution, H2S inhibited enzyme activity in both leaves. Exogenous supply of cysteine, a possible product of H2S assimilation, also increased nitrate reductase activity in the presence of nitrate. It is postulated that increase in nitrate reductase activity during H2S supply is due to its assimilation into sulphur containing amino acids.
