Interaction of nitrate and sulfate reduction in tobacco

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Abstract
A series of experiments was conducted to study the interrelationship of SO42- and NO3- reduction in ''Ky14'' tobacco plants (N. tabacum L.) as influenced by NO3- and SO42- availability. The activities of ATP sulfurylase and nitrate reductase, the first steps of SO42- and NO3- reduction, respectively, were used as indicators of the state of regulation of the assimilatory pathways of SO42- and NO3-. ATP sulfurylase activity was derepressed when SO42- was limited in the nutrient solution, provided that there was a net accumulation of reduced N in the tissue. The availability of SO42- or the lack of N resulted in repressed activity of ATP sulfurylase. Nitrate reductase activity was induced when NO3- was available in the nutrient solution, provided that there was a net accumulation of reduced S in the tissue. When NO3- was limited in the nutrient solution or there was a lack of S, nitrate reductase activity was repressed.