TISSUE-SPECIFIC ACCUMULATION OF TRANSCRIPT ENCODING DELTA(1)-PYRROLINE-5-CARBOXYLATE REDUCTASE IN ARABIDOPSIS-THALIANA

Delta(1)-pyrroline-5-carboxylate reductase (EC 1.5.1.2; PSCR) catalyse s the final step in proline biosynthesis from glutamate and ornithine, where Delta(1)-pyrroline-5-carboxylate acts as an intermediate. In th is study, differential accumulation of mRNA transcript encoding PSCR w as investigated in tissues of the flowering stem of mature Arabidopsis thaliana (L.) Heynh. In situ hybridisation indicated that under norma l growth conditions, the highest concentration of PSCR transcripts occ urs in the cortical parenchyma, phloem, vascular cambium and pith pare nchyma in the vicinity of the protoxylem. Levels of signal generated i n these tissues increased in plants deprived of water for eight days. Genomic Southern analysis suggests the existence of only a single copy of the gene encoding P5CR in Arabidopsis. This conclusion eliminates the possibility that different genes encoding PSCR may exhibit differe nt tissue-specific patterns of transcript accumulation. Our findings s uggest that the upregulation of proline biosynthesis in response to wa ter-deprivation stress may be regulated in a tissue-specific manner. T he tissue-specific nature of proline biosynthesis suggests that this m ay be an important consideration in the production of transgenic plant s capable of synthesising elevated levels of proline. It is possible t hat differential expression of P5CR may in part be due to differences in the water status of different tissues. The latter explanation for t he patterns of expression observed would suggest that proline accumula tion is strictly a cellular response to water deficit.