Journal of Food, Agriculture & Environment Vol.9 (3&4) : 2 7 9 - 2 8 4 . 2 0 1 1 www.world-food.net

Received 26 April 2011, accepted 29 September 2011.

Abstract

A central enzyme in the proline biosynthesis is the bifunctional enzyme Ä1- pyrroline-5-carboxylate synthase (P5CS) that includes two functional catalytic domains: the ã-glutamyl kinase and the glutamic-ã-semialdehyde dehydrogenase. This enzyme catalyzes the first two steps of the proline biosynthetic pathway and plays a central role in the regulation of this process in plants. A full-length cDNA denominated HvP5CS for Ä1-pyrroline-

5-carboxylate synthetase (P5CS) was cloned from barley. HvP5CS contains an open reading frame encoding a 716 amino acid polypeptide. Sequence analysis showed that HvP5CS shares 95% identity in nucleotide sequence and 97.3% identity in amino acid sequence with the wheat P5CS. Semiquantitative reverse transcription-PCR analysis was used here to investigate the expression patterns of HvP5CS in response to drought, salt stress, and after treatment with abscisic acid (ABA). The expression of HvP5CS in leaves was up-regulated under these conditions, and was higher under drought and salt stress compared to its induction in response to ABA treatment. The  corresponding mRNA transcripts started to increase after 4 days under drought stress, while a rapid up-regulation of HvP5CS was noticed under salt stress at 2 hours post treatment. In all cases, the induction of HvP5CS expression preceded the proline accumulation. These results suggest that HvP5CS was one of the stress-inducible genes regulating the accumulation of proline in plants subjected to stress.