Effect of Phytochrome and Kinetin on Nitrite Reductase Activity in Zea mays

Red light and kinetin (10 µm) increased nitrite reductase(NIR) activity by 85 and 47% respectively in excised leavesof etiolated Zea mays. The stimulatory effect of kinetin decayedslower than that of red light. Indoleacetic acid (10 µm)had no effect on NIR activity. In the presence of abscisic acid(10 µm), the kinetin stimulated increase in NIR activitywas totally nullified, however, the red light irradiated plantsretained 20–25% increase in NIR activity over the darkcontrol. If ABA was given 2 h after kinetin treatment or redlight irradiation, it totally blocked kinetin stimulation asnoticed earlier, but red light stimulation was inhibited byonly 11%. Kinetin-treated and the red light irradiated leavesshowed 20–25% increase in nitrate accumulation, whichwas totally nullified by ABA. The experiments presented suggestan independent mode of signal transduction by kinetin and phytochromein stimulating NIR activity. (Received December 2, 1986; Accepted February 7, 1987)