Nitrate Reduction and ¹⁴CO₂ Incorporation in the Developing Leaves of Plants Differing in Photosynthetic Pathways

Nitrate reductase (NR) and nitrite reductase (NiR) in vivo in the developing leaves of Cestrum noctirnum, L., Dodonaea viscosa L. (C₃ dicote), Aptenia cordifolia Brown (facultative CAM); Kalan-choe pinnatum Lam. Pers. (CAM succulent); Trianthema monogyna L., Portulaca quadrifida L. (C₄ succulent dicots) and Setaria italica Beauv. Agrest., Pennisetum purpureum Schumach. (C₄ monocots) have beeninvestigated. C₃ plants showed higher NRA (Nitrate reductase activity) while, NiRA (Nitrite reductase activity) was higher in C₄ plants. NRA reached it's maximum before full expansion of the leaves of all the plants studied except T. monogyna. NiRA showed almost a similar trend in both C₃ and C₄ type of plants. However, the youngest leaves of CAM plants showed maximum activity of this enzyme. NiRA decreased m the leaf of succulents and P. purpureum plants along with the age. Chlorophyll content and the carbon fixation in the leaves at all the developmental stages in most of the plants correlated more with the level of NiR than NR.