Cysteine proteinases and programmed cell death in tomato

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The controlled suicide, or programmed death, of particular cells and tissues is a natural part of development in most multicellular organisms. In plants, the formation of the water conducting tissue, the "wood" in trees,  is absolutely dependent on the programmed death of the cells that will be directly involved in water conduction. The process is also important in the formation of supportive tissues, the protective bark of trees, and in the response of plants to pathogen invasion. Senescence, the processes leading to leaf fall in autumn is also a consequence of programmed cell death. How the process is controlled in plants, however, is not fully understood. We are investigating the role of a group of particular enzymes involved in separate occurrences of programmed cell in various plants, using tomato as our model system. The various protein digesting enzymes have key roles in  both early and late stages of the death process. Understanding of how the cells and the plant control where and when the enzymes appear and how they are activated should allow us to gain a more complete understanding of the entire program controlling the plant cell death process.     One of the enzymes that we have found in tomato is common to the death of nutritive cells in the germinating seed and to the death of cells that allows for release of pollen from the flowers.  This enzyme works late in the program. A second and a third enzyme we have isolated both seem to work earlier in the death program, but all are common to a number of cell death events.  In each case there is only one copy of the gene coding for the enzyme, so all of them seem to be extremely important to the plant. Very similar enzymes exist in very distantly related pea and castor bean plant. Our continued experiments will attempt to determine just how important these, and related enzymes, are in the life of the plant.   Future implications of the research would be to fine tune the timing of events involving programmed cell, such as fruit drop, plant senescence during seed filling, fruit ripening, wood formation, etc., to assist in harvest, improve crop yield, extend fruit shelf-life and improve wood production and quality.