REGULATION OF NITRATE REDUCTASE IN SPORISORIUM-REILIANUM

The production and regulation of the enzyme nitrate reductase (NR; EC 1.6.6.2) was studied in Sporisorium reilianum which causes head smut i n sorghum. The fungus was grown in Czapek Dox broth containing sodium nitrate as the sole nitrogen source. Among the different forms of nitr ogen tested, only NO3 induced the NR whereas others such as ammonium, glutamate and urea repressed the NR activity. Complex media such as po tato dextrose broth and Sabouraud dextrose broth supported profuse gro wth but very little enzyme production. The results also indicate that NO, is essential for NR induction and when transferring the NO3 grown cells to ammonium, NR activity was repressed. On the other hand, repre ssion caused by ammonium could be derepressed by NO3.