Variation in nitrate nutrition leads to changes in the performance of the V-ATPase and immunological differences of proteolipid subunit c in tobacco (Nicotiana tabacum) leaves

Abstract

The tonoplast V-type H ⁺-ATPase (V-ATPase; EC 3.6.1.34) of higher plants responds by its activity and molecular-subunit fine structure to environmental parameters, such as temperature and salinity, or to the mode of photosynthesis in C₃–CAM intermediate plants. To test the hypothesis that the enzyme is responding to varied mineral nutrition in similar ways, tobacco plants were grown at low (2 mM) and high (40 mM) nitrate supply, and a group of plants was also transferred from the low to the high nitrate concentration for 48 h before analysis. Direct correlation of V-ATPase properties with nitrate regimes and leaf nitrate content were not found, but indirect effects related to nitrate-affected growth were obtained. Although the ATP-hydrolysis of isolated tonoplast vesicles was similar under all three conditions, H ⁺ -transport activity and hence the apparent H ⁺ -transport activity/ATP-hydrolysis coupling ratio of the V-ATPase in native tonoplast vesicles was high at low growth-limiting nitrate supply and after growth acceleration following the transfer of plants from low to high nitrate. Immunological differences of the V-ATPase suggested that the membrane-integral proteolipid subunit c showed structural differences related to nitrate nutrition. These differences were revealed by differential cross-reactions with two polyclonal antisera directed against the V-ATPase of Kalanchoë daigremontiana, respectively. The immunological differences could possibly be due to the expression of different forms of subunit c correlated with actual growth rates of leaves, which were high at 40 mM and after the transfer from 2 mM to 40 mM, and low at 2 mM nitrate. These complex responses to variation in nitrogen nutrition of plants are consistent with the notion in the literature that nitrate is both a nutrient and a signal for plant growth.