The Plasmalemma and the Tonoplast of plant cells as targets to increase plant productivity

Crop productivity depends on the ability of the plant to transport the assimilates from the leaf blade to the receiving organs harvested for human consumption. This transport is controlled by the distribution and the activity of specific membrane transporters. The objective of the project is to characterize and identify plant plasmalemma transporters and tonoplast transporters, and to clone the corresponding genes. Sucrose is the major mobile carbohydrate in the plant and may be finally stored as sucrose or as starch in fruits. Amino acid transport is necessary for the synthesis of storage proteins found in cereals and legumes. Malate is one of the major solutes accumulated in vacuoles of higher plants, being involved in transient storage of carbon, charge balance, cytoplasmic homeostasis and turgor maintenance. Ion transport across the plasmalemma is necessary for the mainteance of cell metabolism. Significant work to date includes: reconstitution procedures for the sucrose carrier and amino acid carriers; complementation studies with yeasts; the first demonstration that a plant membrane protein can be successfully synthesized and targeted to the oocyte plasma membrane; isolation of Arabidopsis mutants for K plus uptake; identification of a novel malate selective ion channel in the tonoplast of CAM plants; establishment of a library of monoclonal antibodies against the native tonoplast membrane of Kalancthoe; development of a protocol for isolation of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) from Kalanchoe mesophyll cells. From current progress it may be foreseen that geneticengineering of transport proteins in plants will be possible in the near future. This opens new insights on possible manipulation of the plant content and on its stress tolerance.