Salicylic acid stimulates secretion of the normally symplastic enzyme mannitol dehydrogenase: a possible defense against mannitol-secreting fungal pathogens.

The sugar alcohol mannitol is an important carbohydrate with well-documented roles in both metabolism and osmoprotection in many plants and fungi. In addition to these traditionally recognized roles, mannitol is reported to be an antioxidant and as such may play a role in host-pathogen interactions. Current research suggests that pathogenic fungi can secrete mannitol into the apoplast to suppress reactive oxygen-mediated host defenses.

Cloning and expression analysis of a UDP-galactose/glucose pyrophosphorylase from melon fruit provides evidence for the major metabolic pathway of galactose metabolism in raffinose oligosaccharide metabolizing plants.

The Cucurbitaceae translocate a significant portion of their photosynthate as raffinose and stachyose, which are galactosyl derivatives of sucrose. These are initially hydrolyzed by alpha-galactosidase to yield free galactose (Gal) and, accordingly, Gal metabolism is an important pathway in Cucurbitaceae sink tissue. We report here on a novel plant-specific enzyme responsible for the nucleotide activation of phosphorylated Gal and the subsequent entry of Gal into sink metabolism.

The effect of heat stress on tomato pollen characteristics is associated with changes in carbohydrate concentration in the developing anthers.

Continuous exposure of tomato 'Trust' to high temperatures (day/night temperatures of 32/26 degrees C) markedly reduced the number of pollen grains per flower and decreased viability. The effect of heat stress on pollen viability was associated with alterations in carbohydrate metabolism in various parts of the anther during its development. Under control, favourable temperature conditions (28/22 degrees C), starch accumulated in the pollen grains, where it reached a maximum value 3 d before anthesis; it then diminished towards anthesis.

Constitutive expression of a celery mannitol dehydrogenase in tobacco enhances resistance to the mannitol-secreting fungal pathogen Alternaria alternata.

Our previous observation that host plant extracts induce production and secretion of mannitol in the tobacco pathogen Alternaria alternata suggested that, like their animal counterparts, plant pathogenic fungi might produce the reactive oxygen quencher mannitol as a means of suppressing reactive oxygen-mediated plant defenses. The concurrent discovery that pathogen attack induced mannitol dehydrogenase (MTD) expression in the non-mannitol-containing host tobacco suggested that plants, unlike animals, might be able to counter this fungal suppressive mechanism by catabolizing mannitol of fungal origin. To test this hypothesis, transgenic tobacco plants constitutively expressing a celery Mtd cDNA were produced and evaluated for potential changes in resistance to both mannitol- and non-mannitol-secreting pathogens.

Analysis of celery (Apium graveolens) mannitol dehydrogenase (Mtd) promoter regulation in Arabidopsis suggests roles for MTD in key environmental and metabolic responses.

Of the growing list of promising genes for plant improvement, some of the most versatile appear to be those involved in sugar alcohol metabolism. Mannitol, one of the best characterized sugar alcohols, is a significant photosynthetic product in many higher plants. The roles of mannitol as both a metabolite and an osmoprotectant in celery (Apium graveolens) are well documented.

Roles for mannitol and mannitol dehydrogenase in active oxygen-mediated plant defense.

Reactive oxygen species (ROS) are both signal molecules and direct participants in plant defense against pathogens. Many fungi synthesize mannitol, a potent quencher of ROS, and there is growing evidence that at least some phytopathogenic fungi use mannitol to suppress ROS-mediated plant defenses. Here we show induction of mannitol production and secretion in the phytopathogenic fungus Alternaria alternata in the presence of host-plant extracts.

Subcellular localization of celery mannitol dehydrogenase. A cytosolic metabolic enzyme in nuclei.

Mannitol dehydrogenase (MTD) is the first enzyme in mannitol catabolism in celery (Apium graveolens L. var dulce [Mill] Pers. cv Florida 638).

Sugar Repression of Mannitol Dehydrogenase Activity in Celery Cells.

We present evidence that the activity of the mannitol-catabolizing enzyme mannitol dehydrogenase (MTD) is repressed by sugars in cultured celery (Apium graveolens L.) cells. Furthermore, this sugar repression appears to be mediated by hexokinases (HKs) in a manner comparable to the reported sugar repression of photosynthetic genes.

Immunolocalization of mannitol dehydrogenase in celery plants and cells.

Immunolocalization of mannitol dehydrogenase (MTD) in celery (Apium graveolens L.) suspension cells and plants showed that MTD is a cytoplasmic enzyme. MTD was found in the meristems of celery root apices, in young expanding leaves, in the vascular cambium, and in the phloem, including sieve-element/companion cell complexes, parenchyma, and in the exuding phloem sap of cut petioles.

Sequence analysis of a mannitol dehydrogenase cDNA from plants reveals a function for the pathogenesis-related protein ELI3.

Mannitol is the most abundant sugar alcohol in nature, occurring in bacteria, fungi, lichens, and many species of vascular plants. Celery (Apium graveolens L.), a plant that forms mannitol photosynthetically, has high photosynthetic rates thought to results from intrinsic differences in the biosynthesis of hexitols vs.

Purification of NAD-dependent mannitol dehydrogenase from celery suspension cultures.

Mannitol dehydrogenase, a mannitol:mannose 1-oxidoreductase, constitutes the first enzymatic step in the catabolism of mannitol in nonphotosynthetic tissues of celery (Apium graveolens L.). Endogenous regulation on the enzyme activity in response to environmental cues is critical in modulating tissue concentration of mannitol, which, importantly, contribute to stress tolerance of celery.

Mannitol Metabolism in Celery Stressed by Excess Macronutrients.

The effect of excess macronutrients in the root environment on mannitol and sucrose metabolism was investigated in celery (Apium graveolens L. var dulce [Mill.] Pers.

Effect of Different Carbon Sources on Relative Growth Rate, Internal Carbohydrates, and Mannitol 1-Oxidoreductase Activity in Celery Suspension Cultures.

Little information exists concerning the biochemical route of mannitol catabolism in higher plant cells. In this study, the role of a recently discovered mannitol 1-oxidoreductase (MDH) in mannitol catabolism was investigated. Suspension cultures of celery (Apium graveolens L.

Partial purification and characterization of mannitol: mannose 1-oxidoreductase from celeriac (Apium graveolens var. rapaceum) roots.

A mannitol:mannose 1-oxidoreductase was isolated from celeriac (Apium graveolens var. rapaceum) root tips by fractionation with (NH4)2SO4, followed by chromatography on a Fractogel DEAE column and then concentration with (NH4)2SO4. This newly discovered mannitol dehydrogenase catalyzes the NAD-dependent oxidation of mannitol to mannose, not mannitol to fructose.

CO(2)-Enhanced Yield and Foliar Deformation among Tomato Genotypes in Elevated CO(2) Environments.

Yield increases observed among eight genotypes of tomato (Lycopersicon esculentum Mill.) grown at ambient CO(2) (about 350) or 1000 microliters per liter CO(2) were not due to carbon exchange rate increases. Yield varied among genotypes while carbon exchange rate did not.

Role of sucrose phosphate synthase in sucrose biosynthesis in ripening bananas and its relationship to the respiratory climacteric.

During ripening of bananas (Musa spp. [AAA group, Cavendish subgroup]), there is a massive conversion of starch to sucrose. Also during ripening there is a rise in respiration known as the respiratory climacteric.

Sucrose Phosphate Synthase and Acid Invertase as Determinants of Sucrose Concentration in Developing Muskmelon (Cucumis melo L.) Fruits.

Fruits of orange-fleshed and green-fleshed muskmelon (Cucumis melo L.) were harvested at different times throughout development to evaluate changes in metabolism which lead to sucrose accumulation, and to determine the basis of differences in fruit sucrose accumulation among genotypes. Concentrations of sucrose, raffinose saccharides, hexoses and starch, as well as activities of the sucrose metabolizing enzymes sucrose phosphate synthase (SPS) (EC 2.

Effect of Restricted Root Growth on Carbohydrate Metabolism and Whole Plant Growth of Cucumis sativus L.

The effects of varied rooting volumes on root growth and source leaf carbohydrate metabolism were studied in greenhouse-grown cucumber (Cucumis sativus L cv Calypso) plants. Plants were grown for 7 weeks in container volumes that ranged from 0.4 to 5.

Regulation of photosynthetic carbon metabolism in cucumber by light intensity and photosynthetic period.

The effects of photosynthetic periods and light intensity on cucumber (Cucumis sativus L.) carbon exchange rates and photoassimilate partitioning were determined in relation to the activities of galactinol synthase and sucrose-phosphate synthase. Carbon assimilation and partitioning appeared to be controlled by different mechanisms.

Galactinol synthase activity and soluble sugars in developing seeds of four soybean genotypes.

Galactinol synthase (UDP-galactose:inositol galactosyltransferase) is the first unique enzyme in the biosynthetic pathway of raffinose saccharides. Its role as a regulator of carbon partitioning between sucrose and raffinose saccharides in developing soybean (Glycine max L. Merrill) seeds was examined.

Leaf Carbohydrate Status and Enzymes of Translocate Synthesis in Fruiting and Vegetative Plants of Cucumis sativus L.

Carbon partitioning in the leaves of Cucumis sativus L., a stachyose translocating plant, was influenced by the presence or absence of a single growing fruit on the plant. Fruit growth was very rapid with rates of fresh weight gain as high as 3.

Carbohydrate Changes during Maturation of Cucumber Fruit : Implications for Sugar Metabolism and Transport.

Changes in the carbohydrate profiles in the mesocarp, endocarp, and seeds of maturing cucumber (Cucumis sativus, L.) fruit were analyzed. Fruit maturity was measured by a decrease in endocarp pH, which was found to correlate with a loss in peel chlorophyll and an increase in citric acid content.

Carbon dioxide effects on ethanol production, pyruvate decarboxylase, and alcohol dehydrogenase activities in anaerobic sweet potato roots.

The effect of varied anaerobic atmospheres on the metabolism of sweet potato (Ipomoea batatas [L.] Lam.) roots was studied.

A Potential Pathway for Galactose Metabolism in Cucumis sativus L., A Stachyose Transporting Species.

Conversion of [(14)C]galactose (Gal) 1-P, UDP-[(14)C]Gal, or UDP-[(14)C]glucose to [(14)C]sucrose was observed when cell-free homogenates of cucumber (Cucumis sativus L.) fruit peduncles were incubated with individual (14)C-labeled substrates, appropriate cofactors, and fructose. The sucrose product was labeled only in the glucose moiety.

Separation and characteristics of galactose-1-phosphate and glucose-1-phosphate uridyltransferase from fruit peduncles of cucumber.

Galactose-1-phosphate uridyltransferase (EC 2.7.7.