Salt stress increases the expression of p5cs gene and induces proline accumulation in cactus pear
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Proline (Pro) is one of the most accumulated osmolytes in salinity and water deficit conditions in plants. In the present study, we measured the Pro content, the activity and the expression level of delta 1-pyrroline-5-carboxylate synthetase (P5CS: γ-glutamyl kinase, EC 2.7.2.11 and glutamate-5-semialdehyde dehydrogenase, EC 1.2.1.41), a key regulatory enzyme involved in the biosynthesis of Pro, in cactus pear (Opuntia streptacantha) subjected to 6, 9 and 11 days of salt stress. Treatment with NaCl of O. streptacantha young plants resulted in a decrease in the cladode thickness and root length, and in a significant and gradual accumulation of Pro in young cladodes, in a time- and concentration-dependent manner. P5CS activity, studied as γ-glutamyl kinase, was reduced at all times as a consequence of salt treatment, except at the sixth day at 75 and 150 mM of NaCl, where a slight increase was observed. We isolated an open reading frame (ORF) fragment of p5cs gene. The deduced amino acid sequence of the P5CS protein exhibited 90.4%25 of identity with the P5CS protein from Mesembryanthemum crystallinum. RT-PCR analysis revealed that the Osp5cs gene of O. streptacantha was induced by salt stress at 9 and 11 days of treatment. Furthermore, ABA-induced Osp5cs gene expression was observed in cladodes of cactus pear young plants. We observed an evident correlation between the transcript up-regulation and the Pro accumulation under salt stress; however, these results do not parallel with the changes in P5CS enzymatic activity. This Pro accumulation might function as an osmolyte for the intracellular osmotic adjustment and might be playing a critical role in protecting photosynthetic activity in O. streptacantha plants under salt stress. © 2007 Elsevier Masson SAS. All rights reserved.
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Abscisic acid; Delta 1-pyrroline-5-carboxylate synthetase; Opuntia streptacantha; Proline; Salt stress abscisic acid; glutamate 5 kinase; glutamate 5-kinase; glutamate gamma semialdehyde dehydrogenase; phosphotransferase; proline; sodium chloride; unclassified drug; vegetable protein; amino acid sequence; article; biosynthesis; dose response; drug effect; gene expression regulation; genetics; Mesembryanthemum; metabolism; molecular genetics; nucleotide sequence; Opuntia; osmotic pressure; photosynthesis; physiology; time; Abscisic Acid; Amino Acid Sequence; Dose-Response Relationship, Drug; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Glutamate-5-Semialdehyde Dehydrogenase; Mesembryanthemum; Molecular Sequence Data; Opuntia; Osmotic Pressure; Phosphotransferases (Carboxyl Group Acceptor); Photosynthesis; Plant Proteins; Proline; Sodium Chloride; Time Factors; Cactaceae; Mesembryanthemum; Mesembryanthemum crystallinum; Opuntia; Opuntia streptacantha; Pyrus
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