CORRELATION BETWEEN THE INDUCTION OF A GENE FOR DELTA(1)-PYRROLINE-5-CARBOXYLATE SYNTHETASE AND THE ACCUMULATION OF PROLINE IN ARABIDOPSIS-THALIANA UNDER OSMOTIC-STRESS

The isolation and characterization is reported of a cDNA for Delta(1)- pyrroline-5-carboxylate (P5C) synthetase (cAtP5CS), an enzyme involved in the biosynthesis of proline, from a cDNA library prepared from a d ehydrated rosette plant of Arabidopsis thaliana. Southern blot analysi s suggested that only one copy of the corresponding gene (AtP5CS) is p resent, in A. thaliana. The deduced amino acid sequence of the P5CS pr otein (AtP5CS) from A. thaliana exhibited 74% homology to that of the P5CS from Vigna aconitifolia. Northern blot analysis;revealed that the gene for P5CS was induced by dehydration, high salt and treatment wit h ABA, while it was not induced by heat or cold treatment. Moreover, t he simultaneous accumulation of proline was observed as a result of th e former treatments in A. thaliana. A cDNA for P5C reductase (cAtP5CR) was also isolated from A. thaliana and Northern blot analysis was per formed. The AtP5CR gene was not induced to a significant extent by deh ydration or high-salt stress. These observations suggest that the AtP5 CS gene plays a principal role in the biosynthesis of proline in A. th aliana under osmotic stress.