Photosynthetic Carbon Metabolism in the Palisade Parenchyma and Spongy Parenchyma of Vicia faba L.

Abstract

Palisade parenchyma cells and spongy parenchyma cells were isolated separately from Vicia faba L. leaflets. Extracts of the cell isolates were assayed for several enzymes involved in CO₂ fixation and photorespiration. When compared on a chlorophyll basis, the levels of enzyme activities either were equal in the different cell types or were greater in the spongy parenchyma; this difference is a reflection, perhaps, of the higher protein-chlorophyll ratio in the latter tissue. The distribution of radioactivity in the products of photosynthesis by each cell type was the same at various times after exposure to NaH¹⁴CO₃, and the kinetics of ¹⁴C incorporation into these compounds was similar. However, a larger percentage of radioactivity was incorporated by the cell isolates into the 80% ethanol-insoluble fraction and correspondingly less into the neutral fraction as compared to whole leaf. It was concluded that photosynthetic CO₂ fixation is similar in the different mesophyll tissues from which these cells were derived.