Pyruvate, Pi Dikinase in Bundle Sheath Strands as Well as in Mesophyll Cells in Maize Leaves

Abstract

Mesophyll protoplasts and bundle sheath strands were isolated from maize leaves. Light microscopic observation showed the preparations were pure and without cross contamination. Protein blot analysis of mesophyll and bundle sheath cell soluble protein showed that the concentration of pyruvate orthophosphate dikinase (EC 2.7.9.1) is about one-tenth as much in the bundle sheath cells as in mesophyll cells, but about eight times greater than that found in wheat leaves, on the basis of soluble protein. Phosphoenolpyruvate carboxylase (EC 4.1.1.31) was barely detectable in the bundle sheath cells, while ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and NADP-dependent malic enzyme (EC 1.3.1.37) were exclusively present in the bundle sheath cells and were absent in the mesophyll cells. Whereas pyruvate, Pi dikinase was previously considered localized only in mesophyll cells of C₄ plants, these results clearly demonstrate the presence of appreciable quantities of the enzyme in the bundle sheath cells of the C₄ species maize.