Relationships Between Nitrate Reductase, Nitrite Reductase, and Ribulose Diphosphate Carboxylase Activities in Chlorophyll‐Deficient Mutants of Barley1

Abstract

The relationship between a photosynthetic enzyme localized within the chloroplast and the nitrate‐reducing enzymes was determined by assaying 5‐day‐old chlorophyll‐deficient mutants of ‘Himalaya’ barley (Hordeum vulgare L.) for ribulose diphosphate carboxylase, nitrate reductase, nitrite reductase, and glucose‐6‐phosphate dehydrogenase activities. The mutants varied from albino to nearly normal green and had carboxylase activities ranging from zero to slightly greater than the level in Himalaya seedlings. Carboxylase activity was significantly correlated with both nitrate reductase (r = 0.86) and nitrite reductase (r = 0.78) activities. Nitrite reductase and nitrate reductase activities were also significantly correlated (r = 0.92). Glucose‐6‐phosphate dehydrogenase was not significantly correlated with nitrate reductase (r = −0.11), nitrite reductase (r = −0.11, or carboxylase (r = −0.19). The close relationship between the nitrate‐reducing enzyme and ribulose diphosphate carboxylase may indicate that both nitrate and nitrite reductases are dependent upon chloroplast development or functional chloroplasts for activity in 5‐day‐old barley leaves.