Localization of nitrite and sulfite reductase in bundle sheath and mesophyll cells of maize leaves

Abstract

The distribution of nitrite reductase (EC 1.7.7.1) and sulfite reductase (EC 1.8.7.1) between mesophyll ceils and bundle sheath cells of maize (Zea mays L. cv. Seneca 60) leaves was examined. This examination was complicated by the fact that both of these enzymes can reduce both NO‐2 and SO2‐3 In crude extracts from whole leaves, nitrite reductase activity was 6 to 10 times higher than sulfite reductase activity. Heat treatment (10 min at 55°C) caused a 55% decrease in salfite reductase activity in extracts from bundle sheath cells and mesophyll cells, whereas the loss in nitrite reductase activity was 58 and 82% in bundle sheath cells and mesophyll cell extracts, respectively. This result was explained, together with results from the literature, by the hypothesis that sulfite reductase is present in both bundle sheath cells and mesophyll cells, and that nitrite reductase is restricted to the mesophyll cells. This hypothesis was tested i) by comparing the distribution of nitrite reductase activity and sulfite reductase activity between bundle sheath and mesophyll cells with the presence of the marker enzymes ribulose‐l, 5‐bisphosphate carboxylase (EC 4.1.1.39) and phosphoe‐nolpyruvate carboxylase (EC 4.1.1.32), ii) by examining the effect of cultivation of maize plants in the dark without a nitrogen source on nitrite reductase activity and sulfite reductase activity in the two types of cells, and iii) by studying the action of S2‐on the two enzyme activities in extracts from bundle sheath and mesophyll cells. The results from these experiments are consistent with the above hypothesis.