Role of light in the synthesis of nitrate reductase and nitrite reductase in rice seedlings

Abstract

1. In rice seedlings synthesis of methyl viologen-nitrite reductase was stimulated by light, as was that of NADH-nitrate oxidoreductase (EC 1.6.6.1). A small residual effect of light on the synthesis of the enzymes persisted in the dark for a short time. 2. In etiolated seedlings exposed to light and nitrate, a lag period of 3h was necessary before enzyme synthesis commenced, whereas in green seedlings kept in the dark for 36h, synthesis of both the enzymes started as soon as light and nitrate were provided. 3. Experiments with cycloheximide suggested that fresh protein synthesis in light was necessary for formation of active enzymes. Mere activation by light of inactive enzymes or their precursors, was not involved. 4. In green seedlings synthesis of nitrite reductase was more sensitive to chloramphenicol than that of nitrate reductase. In chloramphenicol-treated etiolated seedlings, however, synthesis of both the enzymes was inhibited to the same extent on subsequent light-treatment. 5. A close correlation was observed between inhibition of the Hill reaction by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and simazin [2-chloro-4,6-bis(ethylamino)-s-triazine] (at high concentration) and the inhibition of enzyme synthesis. At lower concentrations, however, simazin stimulated nitrate reductase. 6. In a single leaf synthesis of enzymes was observed only in portions exposed to light, whereas little activity was present in the dark covered part. 7. CO(2) deprivation severely inhibited the synthesis of enzymes in the light. Sucrose could not reverse this effect. 8. In excised embryos cultured in synthetic media containing sucrose, light was also essential for enzyme formation. 9. It is suggested that redox changes taking place in the green tissues as a result of the Hill reaction create conditions favourable for the induced synthesis of nitrate reductase and nitrite reductase.

Cerium Relieves the Inhibition of Nitrogen Metabolism of Spinach Caused by Magnesium Deficiency

“…In comparison to the control grown in the Mg 2+ -present media, the contents of free amino acid and soluble protein Fig. 1 20.51% and 61.97%, respectively, while those of Ce 3+ -treated group grown in the Mg 2+ -deficient media were alleviated by 7.69% and 13.36%, and in the Mg 2+ -present media were increased by 5.13% and 38.03%, respectively. We also observe that deprivation of Mg 2+ inhibited chlorophyll formation of spinach significantly, and Ce 3+ treatment could promote chlorophyll formation, particularly grown in the Mg 2+ -deficient media.…”

“…NiR activity was measured following the method of Sawhney and Naik [20]. The assay mixture in a final volume of 2 ml contained 100 μM phosphate buffer (pH 7.5), 1.0 μM NaNO 2 , 0.4 μM methylviologen, and 0.5 ml of enzyme extract.…”

Synthesis of wheat leaf nitrite reductase de novo following induction with nitrate and light

“…This was the conclusion drawn from experiments using protein synthesis inhibitors to prevent the appearance of nitrite reductase activity in Lemna [12] and bean leaves [15]. However in similar experiments with maize [ll] and rice [13], chloramphenicol prevented the appearance of nitrite reductase activity and it was suggested that the protein was synthesisied on chloroplast ribosomes [l 11. Our attempts to demonstrate the synthesis of nitrite reductase by isolated chloroplasts from pea and wheat (I. S. Small and A. L. Phillips, unpublished) and by the coupled transcriptiontranslation of chloroplast DNA from pea and wheat (A. K. Huttly, unpublished) have been unsuccessful, further suggesting that synthesis occurs outside the chloroplasts in vivo.…”

Effect of Mycorrhizal Colonization on Nitrogen and Phosphorous Metabolism in Wheat (Triticum aestivum L.) under Water Deficit Stress

“…Nitrate reductase activity was determined Invivo conditions (Sawhney and Naik, 1972). The enzyme was assayed colorimetrically by monitoring the amount of nitrite produced.…”