Biosynthesis of Ferredoxin-Nitrite Reductase in Rice Seedlings

Changes in ferredoxin-nitrite reductase [EC 1.7.7.1] in etiolated rice seedlings were followed during induction by nitrate and light. Etiolated seedlings showed maximal induction of the enzyme activity during greening with nitrate, while the enzyme activity in etiolated seedlings receiving nitrate in darkness increased half as much as that in nitrate-treated greening plants. The increase in nitrite reductase activity during induction coincided with an increase in the content of proteins immunoprecipitated by antibodies raised against spinach nitrite reductase. Light had no effect on the induction of the extractable nitrite reductase in the absence of nitrate. Poly(A)+-RNA extracted from nitrate-treated greening shoots directed the synthesis in a rabbit reticulocyte-lysate of polypeptides immunoprecipitated by spinach nitrite reductase antibodies. One major polypeptide larger than the native enzyme was found among the translation products, suggesting that nitrite reductases in greening rice shoots are synthesized as an precursor form. Analysis of two-dimensional electrophoretograms indicated the existence of isoforms of nitrite reductase in rice seedlings which had been immunoprecipitated with spinach nitrite reductase antibodies.