The intercellular compartmentation of metabolites in leaves of Zea mays L

Abstract

Sap extracted from attached leaves of two-to three-week-old maize plants witt the aid of a roller device was almost devoid of bundle-sheath contamination as judged by the distribution of mesophyll and bundle-sheath markers. The extraction could be done very rapidly (less than 1 s) and the extract immediately quenched in HClO4 or reserved for enzyme assay. Comparison of the contents of metabolites in intact leaves and in the leaf extract allowed estimation of the distribution of metabolites between the bundle-sheath and the mesophyll compartments. Substantial amounts of metabolites such as malate and amino acids were present in the non-photosynthetic cells of the midrib. In the illuminated leaf, triose phosphate was predominantly located outside the bundle-sheath while the major part of the 3-phosphoglycerate was in the bundle sheath. The results indicate the existence of concentration gradients of triose phosphate and 3-phosphoglycerate in the leaf which are capable of maintaining carbon flow between the mesophyll and bundle-sheath cells during photosynthesis. There was no evidence for the existence of a gradient of pyruvate between the bundle-sheath and the mesophyll cells.