Sugar Leakage Research Articles

Industrial Distillation Fractions of Garlic Essential Oil, Design, Synthesis, and Antifungal Activity Evaluation of Aliphatic Substituted Trisulfide Derivatives.

Garlic oil has a wide range of biological activities, and its broad-spectrum activity against phytopathogenic fungi still has the potential to be explored. In this study, enzymatic treatment of garlic resulted in an increase of approximately 50 % in the yield of essential oil, a feasible GC-MS analytical program for garlic oil was provided. Vacuum fractionation of the volatile oil and determination of its inhibitory activity against 10 fungi demonstrated that garlic oil has good antifungal activity. The antifungal activity levels were ranked as diallyl trisulfide (S-3)>diallyl disulfide (S-2)>diallyl monosulfide (S-1), with an EC50 value of S-3 against Botrytis cinerea reached 8.16 mg/L. Following the structural modification of compound S-3, a series of derivatives, including compounds S-4~7, were synthesized and screened for their antifungal activity. The findings unequivocally demonstrated that the compound dimethyl trisulfide (S-4) exhibited exceptional antifungal activity. The EC50 of S-4 against Sclerotinia sclerotiorum reached 6.83 mg/L. SEM, In vivo experiments, and changes in mycelial nucleic acids, soluble proteins and soluble sugar leakage further confirmed its antifungal activity. The study indicated that the trisulfide bond structure was the key to good antifungal activity, which can be developed into a new type of green plant-derived fungicide for plant protection.

Plackett–Burman screening of physico-chemical variables affecting Citrus peel-mediated synthesis of silver nanoparticles and their antimicrobial activity

With the growing resistance of pathogenic microbes to traditional drugs, biogenic silver nanoparticles (SNPs) have recently drawn attention as potent antimicrobial agents. In the present study, SNPs synthesized with the aid of orange (Citrus sinensis) peel were engineered by screening variables affecting their properties via Plackett–Burman design. Among the variables screened (temperature, pH, shaking speed, incubation time, peel extract concentration, AgNO3 concentration and extract/AgNO3 volume ratio), pH was the only variable with significant effect on SNPs synthesis. Therefore, SNPs properties could be enhanced to possess highly regular shape with zeta size of 11.44 nm and zeta potential of − 23.7 mV. SNPs purified, capped and stabilized by cloud point extraction technique were then checked for their antimicrobial activity against Bacillus cereus, Listeria innocua, Listeria monocytogenes, Staphylococcus aureus, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhimurium and Candida albicans. The maximum antimicrobial activity of SNPs was recorded against E. coli, L. monocytogenes and C. albicans with clear zone diameter of 33.2, 31.8 and 31.7 mm, respectively. Based on minimum inhibition concentration and minimum bactericidal concentration of SNPs (300 mg/l) as well as their effect on respiratory chain dehydrogenases, cellular sugar leakage, protein leakage and lipid peroxidation of microbial cells, E. coli was the most affected. Scanning electron microscopy, protein banding and DNA fragmentation proved obvious ultrastructural and molecular alterations of E. coli treated with SNPs. Thus, biogenic SNPs with enhanced properties can be synthesized with the aid of Citrus peel; and such engineered nanoparticles can be used as potent antimicrobial drug against E. coli.

The Antifungal Activity and Action Mechanism of Lemongrass (Cymbopogon flexuosus) Essential Oil Against Fusarium avenaceum

Fusarium avenaceum is distributed worldwide and directly causes considerable crop losses. The compositions of lemongrass essential oils (EOs) were analysed by gas chromatography-mass spectrometry (GC-MS). The antifungal activity of lemongrass essential oils (EOs) and the main compounds against F. avenaceum were evaluated in vitro, and the underlying mechanism was investigated. Geranial, geranyl acetate, β-citronellol, citronellal, limonene, and citral were demonstrated to be the major constituents of the EOs. Lemongrass EOs and the main compounds possessed the antifungal effect against F. avenaceum, and citral exerted the strongest antifungal effects against F. avenaceum compared with other compounds, with IC50 values of 0.087 µl/mL. Lemongrass EOs and their major constituents increased the permeability of the F. avenaceum plasma membrane, resulting in increased conductivity, protein and soluble sugar leakage. The activity of pectin methyl galacturonase (PMG) in F. avenaceum was suppressed after treatment with lemongrass EOs. The results indicated that lemongrass EOs inhibited F. avenaceum growth by targeting its plasma membrane and reduced its pathogenicity by inhibiting enzyme activity.

Antifungal action and induction of resistance by β-aminobutyric acid against Penicillium digitatum to control green mold in orange fruit

Green mold, caused by Penicillium digitatum, is the most economically important postharvest disease of orange fruit worldwide. The aim of this study was to evaluate the effect of β-aminobutyric acid (BABA) treatment on the inhibition of P. digitatum both in orange fruit and in vitro as well as the possible mechanisms of action. BABA at 125 mM significantly inhibited mycelial growth, spore germination, and germ tube elongation of P. digitatum by 93.3, 90.3, and 90.5%, respectively. The relative electrical conductivity of mycelium was increased for a period of 0–36 h after treated with BABA at 125 mM. Furthermore, BABA caused a high level of malondialdehyde (MDA) in P. digitatum mycelia during four days of incubation. The ergosterol content in the plasma membrane of P. digitatum was significantly lower in BABA-treated mycelia. Also, protein and sugar leakage were increased with BABA treatment compared with that in the control. Besides, BABA caused a considerable reduction in the total lipid content of P. digitatum mycelia at 125 mM. Scanning electron microscopy (SEM) of P. digitatum treated with BABA at 125 mM showed shrunken, distorted, and collapsed mycelia. The application of BABA at 125 mM in orange fruit inoculated with P. digitatum suppressed disease incidence and disease severity by 74.6 and 77.3%, respectively, compared to untreated fruit. Moreover, the activity of defense-related enzymes, including peroxidase (POD), polyphenoloxidase (PPO), and phenylalanine ammonia-lyase (PAL) were significantly enhanced in the orange fruit treated with BABA at 125 mM.

Re-evaluating the role of bacteria in gerbera vase life

The relation between bacteria numbers in vase water and vase life of gerbera cut flowers has recently been challenged because of reported negative effects of bactericidal compounds. This relation is investigated using two types of experiments that do not rely on antimicrobial compounds. The first type controls vase water temperature (4, 15, 22 or 28 °C) independently from air temperature (15, 22 or 28 °C) to investigate whether fresh weight behavior for two mini gerbera cultivars (‘Okidoki’ and ‘Kimsey’) is affected by bacterial growth and leaking of soluble sugars in the vase water, or by senescence of the flower head. Fresh weight loss, when compared at constant water temperatures, was higher at higher air temperatures. At higher water temperatures and constant air temperatures fresh weight loss was not higher, although bacterial levels were high enough to expect water uptake issues. Also sugar consumption in the vase water depended on water temperature. This indicates that senescence was the main reason for the decline in fresh weight for these flowers, not bacterial growth. The second type of experiments was based on adding predetermined levels of bacteria (0, 103 or 105 CFU mL−1) and sugars (0.1% glucose or 0.2% sucrose) into vase water of flowers of three large-bloomed (‘Carambole’, ‘Candela’ and ‘Iceberg’) cultivars harvested with closed stem-ends and had their scapes sterilized before the start of vase life. When bacteria were added varying types of responses were observed. ‘Carambole’ flowers showed lower water uptake and lower transpiration and, early scape bending. Petal wilting was observed for ‘Candela’ flowers. ‘Carambole’ flowers showed higher scape sugar leakage levels in the vase water while ‘Candela’ flowers had higher scape firmness. ‘Iceberg’ flowers were also affected by bacteria, resulting in early scape bending, although sugar levels in the vase water were low. Furthermore, adding sucrose and/or bacteria in the vase water of one ‘Iceberg’ and one ‘Carambole’ flower in the same flask resulted in later scape bending for ‘Iceberg’ flowers compared to having two ‘Carambole’ or two ‘Iceberg’ flowers. The results indicate that bacteria interactions with gerbera flowers depend strongly on genotype.

Effects of Nonionic Surfactants on Xanthan Gum Production: a Survey on Cellular Interactions.

BackgroundXanthomonas campestris is a biopolymer producing gram negative bacterium. Production of xanthan biopolymer can be affected by different extrinsic factors as well as surfactants. Hitherto, effects of nonionic surfactants on xanthan production have been studied in a limited number of articles.ObjectiveIn the present study, nonionic surfactants were used to pursue their effects on improvement of xanthan production. Moreover, a number of cellular consequences upon the treatment were investigated with impacts on gum production.Materials and MethodsEffects of different nonionic surfactants (Tween 20, Tween 80 and Triton X100) on xanthan production and Xanthomonas campestris cells were assessed by ultramicroscopy (SEM), changes in culture turbidity, leakage of sugars and ATP, and quality of xanthan (i.e. pyruvate content and determination of polymer molecular weight).ResultsThe nonionic surfactant Tween 20 increased ATP (3.2 folds) and sugar leakage (3.1 folds). Furthermore, they caused cell shape alteration. Tween 80 improved both xanthan production (11 g.L-1) and viscosity of the product (1368 cP), while the total biomass remained unchanged (2.2 g.L-1). Molecular weight of xanthan was enhanced (from 23 to 59 million Da). Toxic effect of 5% (v/v) Triton X 100 decreased the turbidity of culture to 120 NTU and total biomass was diminished to 1 g.L-1. Tween 20 caused the loss of ATP and sugar leakage and led to lower xanthan production. It had no effect on biomass content.ConclusionsIn general, amounts of surfactants that bacterial cells can tolerate seem to be helpful in substrate and metabolite transportation, and enzyme activities involved in xanthan biosynthesis and release. Surfactants induce harsh damages to cell barriers, preventing the growth and adversely affecting quantity and quality of xanthan gum.

Silver nanoparticles as an antimicrobial agent: A case study on Staphylococcus aureus and Escherichia coli as models for Gram-positive and Gram-negative bacteria.

The current research was focused on the characterization and antimicrobial activity of silver nanoparticles (AgNPs) produced by Bacillus licheniformis NM120-17. The synthesis was initially observed by a colour change from pale yellow to brown which was further confirmed by UV-Vis spectroscopy. The AgNPs were characterized using TEM, EDAX and FTIR. The synthesized nanoparticles were found to be spherical and uniformly distributed with a size in the range of 9-27.5 nm. The antibacterial activities and acting mechanism of AgNPs were studied with respect to Staphylococcus aureus and Escherichia coli by measuring the growth curves, protein and reducing sugar leakage, respiratory chain dehydrogenase activity, as well as the formation of bactericidal reactive oxygen species (ROS). The experimental results indicated that 50 mg/ml AgNPs could completely inhibit the growth of bacterial cells and destroy the permeability of bacterial membranes and depress the activity of some membranous enzymes, which cause bacteria to die eventually. These nontoxic nanomaterials, which can be prepared in a simple and cost-effective manner, may be suitable for the formulation of new types of bactericidal materials.

Structure of a eukaryotic SWEET transporter in a homotrimeric complex.

Eukaryotes rely on efficient distribution of energy and carbon skeletons between organs in the form of sugars. Glucose in animals and sucrose in plants serve as the dominant distribution forms. Cellular sugar uptake and release require vesicular and/or plasma membrane transport proteins. Humans and plants use proteins from three superfamilies for sugar translocation: the major facilitator superfamily (MFS), the sodium solute symporter family (SSF; only in the animal kingdom), and SWEETs. SWEETs carry mono- and disaccharides across vacuolar or plasma membranes. Plant SWEETs play key roles in sugar translocation between compartments, cells, and organs, notably in nectar secretion, phloem loading for long distance translocation, pollen nutrition, and seed filling. Plant SWEETs cause pathogen susceptibility possibly by sugar leakage from infected cells. The vacuolar Arabidopsis thaliana AtSWEET2 sequesters sugars in root vacuoles; loss-of-function mutants show increased susceptibility to Pythium infection. Here we show that its orthologue, the vacuolar glucose transporter OsSWEET2b from rice (Oryza sativa), consists of an asymmetrical pair of triple-helix bundles, connected by an inversion linker transmembrane helix (TM4) to create the translocation pathway. Structural and biochemical analyses show OsSWEET2b in an apparent inward (cytosolic) open state forming homomeric trimers. TM4 tightly interacts with the first triple-helix bundle within a protomer and mediates key contacts among protomers. Structure-guided mutagenesis of the close paralogue SWEET1 from Arabidopsis identified key residues in substrate translocation and protomer crosstalk. Insights into the structure-function relationship of SWEETs are valuable for understanding the transport mechanism of eukaryotic SWEETs and may be useful for engineering sugar flux.

Seed Vigor, Aging, and Osmopriming Affect Anion and Sugar Leakage during Imbibition of Maize (Zea mays L.) Caryopses

Conductivity was significantly increased by aging and decreased by osmopriming of maize (Zea mays L.) caryopses. Chloride, phosphate, and sulfate were the main anions that leaked out of maize seeds; their leakage was closely related to conductivity, increased by aging, and decreased by osmopriming. The anion leakage of isolated embryos correlated closely to seed vigor and was more sensitive to aging and priming than that of the whole seed. Anion leakage may be a more sensitive measure for seed vigor than bulk conductivity readings. Aging did not increase the sugar leakage of whole seeds but significantly increased the sugar leakage of isolated embryos. Sugar leakage was not closely related to total soluble sugar content of seeds. While priming decreased seed conductivity, the decreased anion and sugar leakage of the primed seeds was mainly caused by the washing effect during priming. The total anions or sugars left in the polyethylene glycol (PEG) solution after priming and in the conductivity solution of the primed seeds was almost the same as in the conductivity solution of the unprimed seeds alone.

Extracellular melibiose and fructose are intermediates in raffinose catabolism during fermentation to ethanol by engineered enteric bacteria.

Contrary to general concepts of bacterial saccharide metabolism, melibiose (25 to 32 g/liter) and fructose (5 to 14 g/liter) accumulated as extracellular intermediates during the catabolism of raffinose (O-alpha-D-galactopyranosyl-1, 6-alpha-D-glucopyranosyl-beta-D-fructofuranoside) (90 g/liter) by ethanologenic recombinants of Escherichia coli B, Klebsiella oxytoca M5A1, and Erwinia chrysanthemi EC16. Both hydrolysis products (melibiose and fructose) were subsequently transported and further metabolized by all three organisms. Raffinose catabolism was initiated by beta-fructosidase; melibiose was subsequently hydrolyzed to galactose and glucose by alpha-galactosidase. Glucose and fructose were completely metabolized by all three organisms, but galactose accumulated in the fermentation broth with EC16(pLOI555) and P2. MM2 (a raffinose-positive E. coli mutant) was the most effective biocatalyst for ethanol production (38 g/liter) from raffinose. All organisms rapidly fermented sucrose (90 g/liter) to ethanol (48 g/liter) at more than 90% of the theoretical yield. During sucrose catabolism, both hydrolysis products (glucose and fructose) were metabolized concurrently by EC16(pLOI555) and P2 without sugar leakage. However, fructose accumulated extracellularly (27 to 28 g/liter) at early stages of fermentation with KO11 and MM2. Sequential utilization of glucose and fructose correlated with a diauxie in base utilization (pH maintenance). The mechanism of sugar escape remains unknown but may involve downhill leakage via permease which transports precursor saccharides or novel sugar export proteins. If sugar escape occurs in nature with wild organisms, it could facilitate the development of complex bacterial communities which are based on the sequence of saccharide catabolism and the hierarchy of sugar utilization.

Net sugar transport is a multistep process. Evidence for cytosolic sugar binding sites in erythrocytes.

Human erythrocyte net sugar transport is hypothesized to be rate-limited by reduced cytosolic diffusion of sugars and/or by reversible sugar association with intracellular macromolecules [Naftalin, R.J., Smith, P.M., & Roselaar, S.E. (1985) Biochim. Biophys. Acta 820, 235-249]. The present study examines these hypotheses. Protein-mediated 3-O-methylglucose uptake at 4 degrees C by human erythrocytes and by resealed, hypotonically lysed erythrocytes (ghosts) is inhibited by increasing solvent viscosity. Protein-mediated transport and transbilayer diffusion of the slowly transported substrate 6-NBD glucosamine are unaffected by increasing solvent viscosity. These findings suggest that protein-mediated 3-O-methylglucose transport is diffusion-limited in erythrocytes. More detailed analyses of red cell 3-O-methylglucose uptake (at 4 degrees C and at limiting extracellular sugar levels) reveal that net influx is a biexponential process characterized by rapid filling of a small compartment (C1 = 29 +/- 6% total cell volume; k1 = 7.4 +/- 1.7 min-1) and slow filling of a larger compartment (C2 = 71 +/- 6% total cell volume k2 = 0.56 +/- 0.11 min-1). Erythrocyte D-glucose net uptake at 4 degrees C is also a biphasic process. Transmembrane sugar leakage is a monoexponential process indicating that multicomponent, protein-mediated uptake does not result from sugar uptake by two cell populations of differing cellular volume. Sugar exit at limiting 3-O-methylglucose concentrations is described by single exponential kinetics. This demonstrates that multicomponent sugar uptake does not result from influx into two populations of cells with widely different sugar transporter content. We conclude that biexponential sugar uptake results from slow (relative to transport) exchange of sugars between serial, intracellular sugar compartments. Biexponential sugar uptake is observed under equilibrium exchange conditions (intracellular sugar concentration = extracellular sugar concentration) but only at 3-O-methylglucose concentrations of less than 1 mM. Above this sugar concentration, exchange uptake is a monoexponential process. Because diffusion rates are independent of diffusant concentration, this suggests that multicomponent uptake results from high-affinity sugar binding within the cell. The concentration of cytosolic binding sites (30 microM, Kd(app) = 400 microM) was estimated from the equilibrium cellular 3-O-methylglucose space. Biexponential net 3-O-methylglucose uptake is also observed in human erythrocyte ghosts, in control human K562 cells, and in K562 cells induced to synthesize hemoglobin by prolonged exposure to hemin. This demonstrates that neither membrane-bound nor free cytosolic hemoglobin forms the sugar-binding complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Seed Vigor and Sugar Leakage for Isolines of Sweet Corn with Traditional vs. shrunken-2 Endosperm

Supersweet corn has problems establishing a stand, a problem that is related to a damaged pericarp that allows leakage from seeds during imbibition. This study compared seed vigor and sugar leakage of sweet corn isolines with different endosperms. Isoline pairs (C68, IaS125, Ia453, Il442a, and Oh43) of sweet corn (Zea mays L. var. rugosa) with two endosperms (sul or sh2) were used. Seeds were germinated at 10, 15, or 20C. Seeds also were planted in Urbana, Ill., where seedling growth was measured. Seeds also were soaked in water for 24 h, and then leachate was analyzed for sugars (anthrone method) and for sucrose, fructose, and glucose (HPLC). No seeds germinated at 10C. At 15 and 20C, more sul seeds germinated than sh2 seeds in most cases. In fields, sul plants were more vigorous than sh2 plants based on emergence, plant height, leaf number, weight, and leaf area. More sugars leaked from sh2 than sul seeds. More sucrose leaked from sh2 than sul seeds in all but two isolines, where none leaked. More fructose leaked from sh2 than sul seeds in all but two isolines, where no differences occurred. More glucose leaked from sh2 than sul seeds only in Oh43.

Effects of Ca2+- and Mg2+-enriched germination media on germination and sugar leakage of Ca-deficient soybean seed

Inadequate seed Ca concentrations are associated with reduced seed quality of soybean [Glycine max (L.) Merr.]. Standard germination and sugar leakage tests were conducted to determine the effect of seed Ca content and exogenous Ca2+ or Mg2+ on seed quality and seed leakage. Soybean seeds containing different Ca levels were germinated in rolled towels that had been soaked in distilled water, 0.01 M Ca(NO3)2, or 0.01 M Mg(NO3)2. Sugar leakage was measured by soaking seed containing 1.10, 1.72 or 2.36 mg g−1 Ca in distilled water, 0.01 M Ca (NO3)2, 0.01 M Mg(NO3)2 or polyethylene glycol (PEG). An aliquot of the bathing solution was analyzed for sugar content after 6, 12 and 24 h of soaking, by using high-performance liquid chromatography. As seed Ca content decreased from 2.36 to 1.10 mg g−1, germination in distilled water decreased from 87 to 56%. Addition of either Ca(NO3)2 or Mg(NO3)2 to the medium resulted in increased germination of low-Ca seed, but Ca(NO3)2 was more effective in improving germination of low-Ca seed than Mg(NO3)2. Total sugar leakage was significantly greater in low-Ca seed than in high-Ca seed. Bathing solutions of Ca(NO3)2 or Mg(NO3)2 significantly decreased sugar leakage, compared with distilled water or PEG. These results suggest that the role of Ca in seed germination may involve membrane stabilization. They also indicate that the addition of Ca(NO3)2 or Mg(NO3)2 to the germination medium may improve germination of Ca-deficient seed. Key words: Soybean, germination, calcium, magnesium, sugar leakage, membrane integrity

Effect of seed treatment emulsifiers on seed quality and membrane function in maize

Abstract Three commonly used seed treatment emulsifiers, Triton X-100, Proprietary-adjuvant A and Proprietary-adjuvant B, were applied to four seed lots differing in genotype, and seed vigor. Seed quality was measured by cold germination test, leachate conductivity, and sugar leakage. Membrane repair capacity during imbibition, and also membrane lipid composition and thermal properties, were determined. Seed and seedling performance as indicated by germination tests showed no significant difference between control and treated seed in the two high-vigor seed lots. All three emulsifiers, especially at high treatment rates, significantly reduced the performance of the two low-vigor seed lots. Conductivity and cold test germination were not related. However, a high correlation was found between sugar leakage and cold test germination following emulsifier treatment. The occurrence of membrane repair and the associated changes in phospholipid composition and thermal properties in the emulsifier-treated seed indicate a modification of the membrane function due to the emulsifier or adjuvant treatments.

Effects of Anoxia on Uptake and Loss of Solutes in Roots of Wheat

This paper reports on leakage of K+, Cl-, free amino acids and soluble sugars from roots of 4-5-day-old intact wheat seedlings, exposed to anoxia. Leakages were slower from hypoxically than from aerobically pretreated roots. For the first 24 h of anoxia, leakage of K+ and free amino acids was similar, while sugar leakage was slow. Subsequently, leakage of all three solutes usually increased with time. Net losses of K+ and Cl-, after 48 or 72 h exposure of intact seedlings to anoxia, were faster, and/or occurred earlier: (i) in expanding than in expanded root tissues; (ii) at 25� than at 15�C. Re-aeration showed that expanded root tissues retained their capacity to take up K+ and accumulate Cl-, for at least 12 h after the root tips had lost their ability to elongate. Roots which had lost their elongation potential after 20 h of anoxia, as diagnosed by microscopic observation, still had high solute concentrations in the 1-5 mm and 10-20 mm segments from the root tip, but the 0-1 mm apices had lost 70-90% of their K+, free amino acids and soluble sugars. In contrast, solute concentrations were still high in 0-1 mm tips which had not yet lost their elongation potential. Thus, either irreversible injury of the apices is caused by sudden loss of membrane integrity, or there is another cause of death leading to rapid leakage.

Heat shock tolerance and antioxidant activity in moth bean seedlings treated with tetcyclacis

Moth bean (Vigna aconitifolia (Jacq.) Marechal cv. Jaadia) seeds were germinated in the presence of 0, 18, or 36 μM solutions of the gibberellin biosynthesis inhibitor, tetcyclacis. After 72 h, seedlings were exposed to 22 or 48°C for 90 min. The 48°C temperature dramatically increased total electrolyte and sugar leakage from the seedlings, particularly in the controls. Tetcyclacis reduced electrolyte and sugar leakage at 48°C by 15–35% compared to the 48°C controls. High temperature increased malondialdehyde concentration in control seedlings but not in treated seedlings indicating that tetcyclacis inhibited high temperature-induced lipid peroxidation. Relative to the control, tetcyclacis tended to increase the total activities of catalase and peroxidase in the seedlings. In contrast, tetcyclacis tended to decrease ascorbic acid oxidase activity, particularly at 48°C. These results suggest that tetcyclacis conferred at least some heat shock tolerance to moth bean seedlings. This increased tolerance was correlated with increased activities of some antioxidant systems.

Epibrassinolide Does Not Enhance Heat Shock Tolerance and Antioxidant Activity in Moth Bean

Moth bean (Vigna aconitifolia Jacqu. Marecbal cv. Jaadia) seeds were germinated in 0, 0.1, 1, or 2 μm EBL. After 72 hours, seedlings were exposed to 22 or 48C for 90 minutes. At 48C, EBL increased total electrolyte, K+, and sugar leakage from the seedlings relative to the control. Following exposure to 48C, EBGtreated seedlings bad higher malondialdebyde concentrations than controls, indicating that EBL enhanced high-temperature-induced lipid peroxidation. At 48C, EBL increased ascorbic acid oxidase activity but decreased superoxide dismutase activity relative to the control. Taken collectively, these data do not support a hypothesis that brassinosteroids confer beat shock tolerance to moth bean. Chemical name used: 24-epibrassinolide (EBL).

Role of Carbohydrates in Desiccation Tolerance and Membrane Behavior in Maturing Maize Seed

Seed corn (Zea mays L.) ears harvested at seed moisture contents greater than 400 g H2O kg−1 fresh wt. (fw) are sensitive to rapid, high‐temperature (45–50 °C) drying, but tolerant to low‐temperature drying. A preconditioning process that precludes this injury without major moisture loss was used to study the nature of the drying damage and the role of soluble sugars in membrane stabilization during drying of two seed corn hybrids. Ears were harvested at moisture contents of 550, 450, and 400 g H2O kg−1 fw, and preconditioned at 35 °C for 6 to 48 h before drying at 50 °C. Seed germination was correlated with leachate conductivity (r = −0.79) and sugar leakage (r = −0.80) after different times of preconditioning indicating the involvement of membrane function in the damage caused by high temperature drying. Total soluble‐sugar concentration decreased during preconditioning with no significant change individual monosaccharide content. The percentage composition of sucrose and a larger oligosaccharide, raffinose, increased significantly during preconditioning. The high correlations between raffinose/sucrose and warm germination, conductivity, and sugar leakage (r = 0.83, −0.80, and −0.71 for A632, and 0.89, −0.78, and −0.79 for B73, respectively) indicates the added effect of raffinose on induced protection. These results suggest that soluble‐sugar compositional relationships rather than absolute content may play an important role in membrane stabilization. The presence of raffinose at certain levels also may be a key factor in protecting maturing seeds from high temperature drying damage. The results also indicate that the transition from desiccation intolerance to tolerance is metabolic and not necessarily related to moisture loss.

THERMOTOLERANCE AND ANTIOXIDANT ACTIVITY OF MOTH BEAN SEEDLINGS AS INFLUENCED BY 24-EPIBRASSINOLIDE

Seeds of moth bean (Vigna aconitifolia Jacqu. Marechal cv. Jaadia) were germinated in the presence of 0, 0.1, 1, or 2 μm 24-epibrassinolide (EBL). After 72 h, cotyledons were excised and the seedlings exposed to 22 or 48 °C for 90 min. At 48 °C EBL increased total electrolyte, K+, and sugar leakage relative to the untreated control. Following exposure to 48 °C, EBL-treated seedlings had higher malondialdehyde concentrations than controls indicating that EBL enhanced high temperature-induced lipid peroxidation. At 48 °C, EBL increased ascorbic acid oxidase activity and decreased superoxide dismutase activity relative to the control. Taken together, these data do not support the hypothesis that brassinosteroids confer thermotolerance to plants. On the contrary, EBL increased high temperature-induced damage and reduced the activity of some antioxidant systems that may protect against stress-induced cellular damage.

Effect of cations on invertase activity and sugar leakage of carrot slices

The presence of Na +, K +, Mg 2+, Ca 2+ or Sr 2+ in the ageing solutions of slices freshly excised from storage roots produces an immediate decrease in sugar loss when compared with water. Although this seems to be a general salt effect, specific differences between the cations could be detected as early as 10 min from the beginning of incubation. Ca 4 hr after excision the rate of sugar reabsorption by the slices equals that of sugar loss. This recovery process is prevented by cycloheximide (1 μM) and by Mg2 2+ at concentrations higher than 2–4 mM. Besides decreasing leakage the cations stimulate the rise in invertase activity. At concentrations higher than 2 mM this stimulation seems to be, essentially, of an osmotic nature. At concentrations lower than 2 mM the effect is probably related to increased invertase secretion to some extracytoplasmic compartment, e.g. the cell wall.