Abiotic stress induces differential expression of genes responsible for the synthesis of raffinose family of oligosaccharides (RFOs) in plants. RFOs are described as the most widespread D-galactose containing oligosaccharides in higher plants. Biosynthesis of RFOs begin with the activity of galactinol synthase (GolS; EC 2.4.1.123), a GT8 family glycosyltransferase that galactosylates myo-inositol to produce galactinol. Raffinose and the subsequent higher molecular weight RFOs (Stachyose, Verbascose, and Ajugose) are synthesized from sucrose by the subsequent addition of activated galactose moieties donated by Galactinol. Interestingly, GolS, the key enzyme of this pathway is functional only in the flowering plants. It is thus assumed that RFO synthesis is a specialized metabolic event in higher plants; although it is not known whether lower plant groups synthesize any galactinol or RFOs. In higher plants, several functional importance of RFOs have been reported, e.g., RFOs protect the embryo from maturation associated desiccation, are predominant transport carbohydrates in some plant families, act as signaling molecule following pathogen attack and wounding and accumulate in vegetative tissues in response to a range of abiotic stresses. However, the loss-of-function mutants reported so far fail to show any perturbation in those biological functions. The role of RFOs in biotic and abiotic stress is therefore still in debate and their specificity and related components remains to be demonstrated. The present review discusses the biology and stress-linked regulation of this less studied extension of inositol metabolic pathway.

The pathway from glucose 6-phosphate (G 6-P) to myoinositol 1-phosphate (Ins 1-P) and myo-inositol (Ins) is essential for the synthesis of various metabolites. In the halophyte Mesembryanthemum crystallinum (common ice plant), two enzymes, myo-inositol O-methyltransferase (IMT1) and ononitol epimerase (OEP1), extend this pathway and lead to the accumulation of methylated inositols, D-ononitol and D-pinitol, which serve as osmoprotectants. This paper describes transcripts for the enzyme, Inps1, encoding myo-inositol 1-phosphate synthase (INPS1), from the ice plant. Two Inps-like sequences are present in the genome. The deduced amino acid sequences of the cloned transcript are 49.5% and 87-90%, respectively, identical to those of yeast and other higher plant sequences. Inps1 RNA amounts are upregulated at least fivefold and amounts of free Ins accumulate approximately 10-fold during salinity stress. Inps1 induction is by transcription, similar to the induction of Imt1. In contrast, Arabidopsis thaliana does not show upregulation of Inps1 or increased amounts of Ins when salt-stressed. The lack of Inps1 induction in Arabidopsis exemplifies differences in glycophytic and halophytic regulation of gene expression at the point of entry into a pathway that leads to osmoprotection. The stress-induced coordinate upregulation of this pathway and its extension by novel enzymes in the ice plant also highlights biochemical differences.

Recent research in the area of importance of microbes has revealed the immense industrial potential of exopolysaccharides and their derivative oligosaccharides from lactic acid bacteria. However, due to lack of adequate technological knowledge, the exopolysaccharides have remained largely under exploited. In the present review, the enormous potentials of different types of exopolysaccharides from lactic acid bacteria are described. This also summarizes the recent advances in the applications of exopolysaccharides, certain problems associated with their commercial production and the remedies.

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L-myo-Inositol 1-phosphate synthase (MIPS, EC 5.5.1.4), the key enzyme in the inositol and phosphoinositide biosynthetic pathway, is present throughout evolutionarily diverse organisms and is considered an ancient protein/gene. Analysis by multiple sequence alignment, phylogenetic tree generation and comparison of newly determined crystal structures provides new insight into the origin and evolutionary relationships among the various MIPS proteins/genes. The evolution of the MIPS protein/gene among the prokaryotes seems more diverse and complex than amongst the eukaryotes. However, conservation of a 'core catalytic structure' among the MIPS proteins implies an essential function of the enzyme in cellular metabolism throughout the biological kingdom. ß

Salinity poses a serious threat to yield performance of cultivated rice in South Asian countries. To understand the mechanism of salt-tolerance of the wild halophytic rice, Porteresia coarctata in contrast to the salt-sensitive domesticated rice Oryza sativa, we have compared P. coarctata with the domesticated O. sativa rice varieties under salinity stress with respect to several physiological parameters and changes in leaf protein expression. P. coarctata showed a better growth performance and biomass under salinity stress. Relative water content was conserved in Porteresia during stress and sodium ion accumulation in leaves was comparatively lesser. Scanning electron microscopy revealed presence of two types of salt hairs on two leaf surfaces, each showing a different behaviour under stress. High salt stress for prolonged period also revealed accumulation of extruded NaCl crystals on leaf surface. Changes induced in leaf proteins were studied by two-dimensional gel electrophoresis and subsequent quantitative image analysis. Out of more than 700 protein spots reproducibly detected and analyzed, 60% spots showed significant changes under salinity. Many proteins showed steady patterns of up- or downregulation in response to salinity stress. Twenty protein spots were analyzed by MALDI-TOF, leading to identification of 16 proteins involved in osmolyte synthesis, photosystem functioning, RubisCO activation, cell wall synthesis and chaperone functions. We hypothesize that some of these proteins confer a physiological advantage on Porteresia under salinity, and suggest a pattern of salt tolerance strategies operative in salt-marsh grasses. In addition, such proteins may turn out to be potential targets for recombinant cloning and introgression in salt-sensitive plants.

L-myo-Inositol-1-phosphate synthase (EC 5.5.1.4, MIPS), an evolutionarily conserved enzyme protein, catalyzes the synthesis of inositol, which is implicated in a number of metabolic reactions in the biological kingdom. Here we report on the isolation of the gene (PINO1) for a novel salt-tolerant MIPS from the wild halophytic rice, Porteresia coarctata (Roxb.) Tateoka. Identity of the PINO1 gene was confirmed by functional complementation in a yeast inositol auxotrophic strain. Comparison of the nucleotide and deduced amino acid sequences of PINO1 with that of the homologous gene from Oryza sativa L. (RINO1) revealed distinct differences in a stretch of 37 amino acids, between amino acids 174 and 210. Purified bacterially expressed PINO1 protein demonstrated a salt-tolerant character in vitro compared with the salt-sensitive RINO1 protein as with those purified from the native source or an expressed salt-sensitive mutant PINO1 protein wherein amino acids 174 -210 have been deleted. Analysis of the salt effect on oligomerization and tryptophan fluorescence of the RINO1 and PINO1 proteins revealed that the structure of PINO1 protein is stable toward salt environment. Furthermore, introgression of PINO1 rendered transgenic tobacco plants capable of growth in 200 -300 mM NaCl with retention of ϳ40 -80% of the photosynthetic competence with concomitant increased inositol production compared with unstressed control. MIPS protein isolated from PINO1 transgenics showed salt-tolerant property in vitro confirming functional expression in planta of the PINO1 gene. To our knowledge, this is the first report of a salt-tolerant MIPS from any source.Inositols are six-carbon cyclohexane hexitols found ubiquitously in the biological kingdom, and its metabolism plays a vital role in growth regulation, membrane biogenesis, osmotolerance, and in many other processes. As phosphorylated derivatives, its role as a phosphorus store and as a "second messenger" in signal transduction pathways has long been recognized. myo-Inositol, physiologically the most favored stereoisomer among the eight possible geometric isomers of inositol, also enters into an array of biochemical reactions having diverse functions in cellular metabolism both as free and conjugated and phosphorylated or methylated forms (1-3).The primary enzyme for the synthesis of L-myo-inositol 1-phosphate from glucose 6-phosphate is L-myo-inositol-1-phosphate synthase (EC 5.5.1.4; referred to as MIPS), 1 which synthesizes L-myo-inositol 1-phosphate through an internal oxidoreduction reaction involving NAD ϩ . Free inositol is generated by dephosphorylation of the MIPS product by a specific Mg 2ϩ -dependent inositol-1-phosphate phosphatase (EC 3.1.3.25). This mechanism is followed by all myo-inositolproducing organisms throughout the phylogenetic lines, and MIPS has been identified as an evolutionarily conserved protein (4). The structural gene coding for cytosolic MIPS, termed INO1, was first identified in yeast, Saccharomyces cerevisiae (5, 6) and cloned by Klig and Henry (7)....

We have previously demonstrated that introgression of PcINO1 gene from Porteresia coarctata (Roxb.) Tateoka, coding for a novel salt-tolerant L-myo-inositol 1-phosphate synthase (MIPS) protein, confers salt tolerance to transgenic tobacco plants (Majee, M., Maitra, S., Dastidar, K.G., Pattnaik, S., Chatterjee, A., Hait, N.C., Das, K.P. and Majumder, A.L. (2004) A novel salt-tolerant L-myo-inositol-1-phosphate synthase from Porteresia coarctata (Roxb.) Tateoka, a halophytic wild rice: molecular cloning, bacterial overexpression, characterization, and functional introgression into tobacco-conferring salt-tolerance phenotype. J. Biol. Chem. 279, 28539-28552). In this communication we have shown that functional introgression of the PcINO1 gene confers salt-tolerance to evolutionary diverse organisms from prokaryotes to eukaryotes including crop plants albeit to a variable extent. A direct correlation between unabated increased synthesis of inositol under salinity stress by the PcINO1 gene product and salt tolerance has been demonstrated for all the systems pointing towards the universality of the application across evolutionary divergent taxa.