Effects of gene expressions in companion cells on the growth of higher plants

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Phloem is a route for long distance transport of metabolites and signals in higher plants. Sieve elements, the individual cell components of sieve tubes, are highly specialized for assimilate translocation, and lose most of their intracellular organelles, such as nuclei, vacuoles, Golgi bodies, and most ribosomes during the course of differentiation. However, proteins are thought to be required for the maintenance of the physiological functions of sieve tubes, and are presumed to be supplied from neighboring companion cells through plasmodesmata. Proteins detected in sieve element-companion cell complexes have been categorized by function, such as structural proteins, maintenance proteins involved in redox regulation, proteins related to signal transduction, and others (Hayashi et al. 2000 for review). However, most of the soluble proteins detected in phloem sap have not yet been identified or characterized.In this experiments, we identified a rice sieve-tube protein with a molecular mass of 31 kDa, RPP31, as a glutathione S-transferase (GST). And we analyzed the detailed chemical composition of rice phloem sap together with the gene expressions in the vascular tissues such as, thoredoxtn h, GST, GS, GOGAT etc..