BIOLOGIA PLANTARUM(PRAHA) 24 (3) : 183--187, 1982 Regulation of Nitrate Reductase by Chloramphenicol in the Leaves of Vigna mungo (L.) HEPPER (Black-gram) R. C. SRIVASTAVA, BANDANA BOSE, R. D. TRIPATHI, D. MUKERJI**, and S. N. MATHUR Department of Botany, University of Gorakhpur* Abstract. Chloramphenicol has been found to inhibit nitrate reduetase activity in black-gram leaves. It inhibits in vivo nitrate reduetase activity up to 50--67%, and the catalytic property of the enzyme up to a maximum of 70--98%. Modulators, such as KNOs, NADH and HCOs- could not protect enzymeinhibitionby ehloramphenicol.It is suggested that the chloramphenicol inhibition is mainly through its effect on the catalytic process of the enzyme. Much work has been done on the effect of chloramphenicol (CP) on nitrate reductase (NR) activity. Though CP has no effect on NR activity in cucumber cotyledons (H~.wIT~ 1975), most of the workers reported a strong stimulatory effect in different plant species (ScHRADER et al. 1967, SRIVASTAVA 1976), however, there are a few demonstrations of its inhibitory action also under certain conditions (BE~.VERS et al. 1965, SAWHNEY and NAIK 1972). Recently, TRIPATHI et a~. (1977) demonstrated a marked inhibition of NR activity by CP in maize leaf tissue in light and proposed the possibility of a feed-back operation but further elucidation of this inhibitory effect seems important. In the present investigation CP responses in relation to age of the plant, regulators of 1NR such as KNO3, NADH, HCO3-, NAN02, and NaC1 on in vivo and in vitro NR activity has been studied in Vigna mungo (Black-gram). MATERIAL AND METHODS Seeds of black-gram (Vigna mungo cv. Type-9) were purchased from the National Seed Corporation of India, New Delhi; culture of Rhizobium legu- minosarum from the Division of Microbiology, Indian Agricultural Research Institute, New Delhi, and chemicals from I~I/S, B.D.H., M/S, Sarabhai M., and Chloramphenicol (Parke Davis Co., U.S.A.) from a local Drug Store. Received March 24, 1981; accepted October 5, 1981 * Addresa: Plant Physiology Research Laboratory, Department of Botany, University of Gorakhpur-273001, India. ** Present address: Department of Botany, Zambia University, P.O. Box 32379, Ltmaka Zambia (Central Africa). 183