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A novel methyl transferase induced by osmotic stress in the facultative halophyte Mesembryanthemum crystallinum.

ABSTRACT: Molecular mechanisms of osmotic stress tolerance were studied in Mesembryanthemum crystallinum (ice plant), a facultative halophyte capable of adjusting to and surviving in highly saline conditions. We screened a subtracted cDNA library enriched for salt stress-induced mRNAs to identify transcripts involved in this plant's adaptation to salinity. One mRNA, Imt1, was found to be up-regulated in leaves and, transiently, in roots. Nuclear run-on assays indicated that this mRNA is transcriptionally regulated. Imt1 encoded a predicted polypeptide of M(r) 40,250 which exhibited sequence similarity to several hydroxymethyl transferases. Expression of the protein in Escherichia coli and subsequent activity assays identified the protein as a novel myoinositol O-methyl transferase which catalyzes the first step in the biosynthesis of the cyclic sugar alcohol pinitol. Pinitol accumulates in salt-stressed M.crystallinum and is abundant in a number of salt- and drought-tolerant plants. The presence of high levels of sugar alcohols correlates with osmotolerance in a diverse range of organisms, including bacteria, fungi and algae, as well as higher plants. The stress-initiated transcriptional induction of IMT1 expression in a facultative halophyte provides strong support for the importance of sugar alcohols in establishing tolerance to osmotic stress in higher plants.

SUBMITTER: Vernon DM

PROVIDER: S-EPMC556674 | biostudies-other | 1992 Jun

REPOSITORIES: biostudies-other

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A novel methyl transferase induced by osmotic stress in the facultative halophyte Mesembryanthemum crystallinum.

Vernon D M DM Bohnert H J HJ

The EMBO journal 19920601 6

Molecular mechanisms of osmotic stress tolerance were studied in Mesembryanthemum crystallinum (ice plant), a facultative halophyte capable of adjusting to and surviving in highly saline conditions. We screened a subtracted cDNA library enriched for salt stress-induced mRNAs to identify transcripts involved in this plant's adaptation to salinity. One mRNA, Imt1, was found to be up-regulated in leaves and, transiently, in roots. Nuclear run-on assays indicated that this mRNA is transcriptionally ...[more]

PMID: 1600940

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Project description:Many environmental stresses cause osmotic stress which induces several metabolic changes in plants. These changes often vary depending on the genotype, type and intensity of stress or the environmental conditions. In the current experiments, metabolic responses of wheat to osmotic stress induced by different kinds of osmolytes were studied under iso-osmotic stress conditions. A single wheat genotypes was treated with PEG-6000, mannitol, sorbitol or NaCl at such concentrations which reduce the osmotic potential of the culture media to the same level (-0.8MPa). The metabolic changes, including the accumulation of proline, glycine betaine (GB) and sugar metabolites (glucose, fructose, galactose, maltose and sucrose) were studied both in the leaves and roots together with monitoring the plant growth, changes in the photosynthetic activity and chlorophyll content of the leaves. In addition, the polyamine metabolism was also investigated. Although all osmolytes inhibited growth similarly, they induced different physiological and metabolic responses: the CO2 assimilation capacity, RWC content and the osmotic potential (??) of the leaves decreased intensively, especially after mannitol and sorbitol treatments, followed by NaCl treatment, while PEG caused only a slight modification in these parameters. In the roots, the most pronounced decrease of ?? was found after salt-treatments, followed by PEG treatment. Osmotic stress induced the accumulation of proline, glycine betaine and soluble sugars, such as fructose, glucose, sucrose and galactose in both the root and leaf sap. Specific metabolic response of roots and leaves under PEG included accumulation of glucose, fructose and GB (in the roots); sucrose, galactose and proline synthesis were dominant under NaCl stress while exposure to mannitol and sorbitol triggered polyamine metabolism and overproduction of maltose. The amount of those metabolites was time-dependent in the manner that longer exposure to iso-osmotic stress conditions stimulated the sugar metabolic routes. Our results showed that the various osmolytes activated different metabolic processes even under iso-osmotic stress conditions and these changes also differed in the leaves and roots.

Dataset Information

A novel methyl transferase induced by osmotic stress in the facultative halophyte Mesembryanthemum crystallinum.

Publications

A novel methyl transferase induced by osmotic stress in the facultative halophyte Mesembryanthemum crystallinum.

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