The Inducible Formation and Stability of Nitrate Reductase in Higher Plants

Abstract

The induction of nitrate reductase by molybdenum or nitrate in excised tissues of cauliflower leaf was dependent on temperature; for the range 2^° to 12^° C, Q₁₀ was about 2; for the range 12^° to 22^° C, Q₁₀ was greater than 3. Enzyme formation was initially most rapid at 32^° C but did not continue for as long as it did at 22^° or 24^° C. Decreased oxygen supply lessened the rate of enzyme formation. The effects on enzyme formation of a wide range of natural and synthetic antimetabolites were tested with respect to induction by either nitrate or molybdenum, when introduced at the same time by infiltration. Actidione (cycloheximide), patulin, cycloserine, polymyxin B, L-2-thiolhistidine D-methionine, L-dihydroxyphenylalanine, D,L-α-methylglutamic acid, sarcosine and 1 ,2-dichloro-4-(p-nitrobenzenesulphonylamido)-5-nitrobenzene (DCDNS) were the most inhibitory compounds tested. Serine stimulated production of enzyme activity; kinetin, benzimidazole, and p-fluorophenylalanine, 3-α-methyltryptophane and the 4- isomer, chloramphenicol, gramicidin, and several thio- and^aza- derivatives of purines or pyrimidines were practically without effect. Differential effects of inhibitors on enzyme formation in response to nitrate or molybdenum were rarely observed, and no deductions regarding the possible sequence in which the substrate and prosthetic metal induce activity could be inferred from the results.