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PubMed1981

L-Lactate dehydrogenase from leaves of higher plants. Kinetics and regulation of the enzyme from lettuce (Lactuca sativa L).

1. L-Lactate dehydrogenase from lettuce (Lactuca sativa) leaves was purified to electrophoretic homogeneity by affinity chromatography. 2. In addition to its NAD(H)-dependent activity with L-lactate and pyruvate, the enzyme also catalyses the reduction of hydroxypyruvate and glyoxylate. The latter activities are not due to a contamination of the enzyme preparations with hydroxypyruvate reductase. 3. The enzyme shows allosteric properties that are markedly by the pH. 4. ATP is a potent inhibitor of the enzyme. The kinetic data suggest that the inhibition by ATP is competitive with respect to NADH at pH 7.0 and 6.2. The existence of regulatory binding sites for ATP and NADH is discussed. 5. Bivalent metal cations and fructose 6-phosphate relieve the ATP inhibition of the enzyme. 6. A function of leaf L-lactate dehydrogenase is proposed as a component of the systems regulating the cellular pH and/or controlling the concentration of reducing equivalents in the cytoplasm of leaf cells.

Adenosine Triphosphate↗
PubMed2000

Phylogenetic relationship and antifouling activity of bacterial epiphytes from the marine alga Ulva lactuca.

It is widely accepted that bacterial epiphytes can inhibit the colonization of surfaces by common fouling organisms. However, little information is available regarding the diversity and properties of these antifouling bacteria. This study assessed the antifouling traits of five epiphytes of the common green alga, Ulva lactuca. All isolates were capable of preventing the settlement of invertebrate larvae and germination of algal spores. Three of the isolates also inhibited the growth of a variety of bacteria and fungi. Their phylogenetic positions were determined by 16S ribosomal subunit DNA sequencing. All isolates showed a close affiliation with the genus Pseudoalteromonas and, in particular, with the species P. tunicata. Strains of this bacterial species also display a variety of antifouling activities, suggesting that antifouling ability may be an important trait for members of this genus to be highly successful colonizers of animate surfaces and for such species to protect their host against fouling.

Animals↗
PubMed1991

Guaianolides from Lactuca saligna.

The phytochemical investigation of the aerial parts of LACTUCA SALIGNA L. revealed the presence of lactucin, lactucopicrin, and a new guaianolide named 11beta,13-dihydrolactucopicrin. The structural configuration was established through spectral data.

Journal Article↗
PubMed1994

Isolation of a polysaccharide with antiviral effect from Ulva lactuca.

A polysaccharide from the green marine algae Ulva lactuca has been isolated. The substance has been investigated after acid hydrolysis by thin-layer and gas chromatography. The following carbohydrate components have been found: arabinose-xylose-rhamnose-galactose-mannose-glucose in ratio 1:1:9:5:2.5:16 respectively. One unidentified sugar has been demonstrated too. The polysaccharide has been studied for antiviral activity in vitro against a number of human and avian influenza viruses. A considerable inhibition of the viral reproduction was found. The effect was dose-dependent, strain-specific and selective.

Antiviral Agents↗
PubMed1953

Metabolic factors influencing the sodium and potassium distribution in Ulva lactuca.

1. Methods for the use of the marine green alga, Ulva lactuca, in studies on electrolyte metabolism are described. 2. The effect of illumination and iodoacetate on the potassium and sodium content, as well as the influence of light and running sea water on the iodoacetate effect was investigated. The rate of exchange of cellular potassium ion for K(42) under conditions of light and dark at 20 and 30 degrees C. was studied. 3. Ulva maintained in the dark for long periods loses some potassium and gains sodium, both effects being reversed upon illumination. The presence of 0.001 M iodoacetate in the dark causes a marked progressive loss of potassium and gain of sodium, phenomena which do not occur when the alga is illuminated. Evidence for the penetration of the inhibitor into the cell in the presence of light is presented. The iodoacetate effect on potassium and sodium content, once established, can be "washed out" of the alga when the plant is placed in light and running sea water without the inhibitor. Illumination and increased temperature each favor a more rapid exchange of tissue for environmental potassium ion. 4. In the interpretation of these findings it is emphasized that metabolic work, perhaps in the form of ion transports, must be done by the cell to compensate for the continual flow of potassium ion and sodium ion with their respective concentration gradients and thus maintain homeostasis within the cell. Evidence is presented which indicates separate mechanisms for the distribution of sodium and potassium in this organism. It is further suggested that the degradation of phosphoglyceric acid, an important glycolytic and photosynthetic intermediate, or one of the products of its metabolism supplied the energy for these ion transports(s). The role of permeability per se is considered.

Eukaryota↗
PubMed1994

Analysis of a detailed genetic linkage map of Lactuca sativa (lettuce) constructed from RFLP and RAPD markers.

A detailed genetic map has been constructed from the F2 population of a single intraspecific cross of Lactuca sativa (n = 9). It comprises 319 loci, including 152 restriction fragment length polymorphism (RFLP), 130 random amplified polymorphic DNA (RAPD), 7 isozyme, 19 disease resistance, and 11 morphological markers. Thirteen major, four minor linkage groups and several unlinked markers are identified for this genome which is estimated to be approximately 1950 cM. RFLP and RAPD markers show similar distributions throughout the genome and identified similar levels of polymorphism. RAPD loci were much quicker to identify but more difficult to order. Procedures for generating accurate genetic maps and their limitations are described.

Chromosome Mapping↗
PubMed1994

Mutants of downy mildew resistance in Lactuca sativa (lettuce).

As part of our investigation of disease resistance in lettuce, we generated mutants that have lost resistance to Bremia lactucae, the casual fungus of downy mildew. Using a rapid and reliable screen, we identified 16 distinct mutants of Latuca sativa that have lost activity of one of four different downy mildew resistance genes (Dm). In all mutants, only a single Dm specificity was affected. Genetic analysis indicated that the lesions segregated as single, recessive mutations at the Dm loci. Dm3 was inactivated in nine of the mutants. One of five Dm 1 mutants was selected from a population of untreated seeds and therefore carried a spontaneous mutation. All other Dm1, Dm3, Dm5/8 and Dm7 mutants were derived from gamma- or fast neutron-irradiated seed. In two separate Dm 1 mutants and in each of the eight Dm3 mutants analyzed, at least one closely linked molecular marker was absent. Also, high molecular weight genomic DNA fragments that hybridized to a tightly linked molecular marker in wild type were either missing entirely or were truncated in two of the Dm3 mutants, providing additional evidence that deletions had occurred in these mutants. Absence of mutations at loci epistatic to the Dm genes suggested that such loci were either members of multigene families, were critical for plant survival, or encoded components of duplicated pathways for resistance; alternatively, the genes determining downy mildew resistance might be limited to the Dm loci.

Chromosome Mapping↗
PubMed1994

Cell-Wall Autohydrolysis in Isolated Endosperms of Lettuce (Lactuca sativa L.).

Cell walls prepared from the endosperm tissue of hydrated lettuce (Lactuca sativa L.) seeds undergo autohydrolysis. Release of carbohydrates is most rapid (0.4-0.6 [mu]g per endosperm) within the 1st h of incubation in buffer, but substantial autolysis is sustained for at least 10 h. Autolysis is temperature sensitive, and the optimum rate occurs at pH 5. The rate of autolysis increases markedly in the period just prior to radicle emergence. The cell-wall polysaccharide composition in micropylar and lateral endosperm regions differs significantly; the micropylar walls are rich in arabinose and glucose with substantially lower amounts of mannose. Although walls prepared from both micropylar and lateral regions undergo autolysis, micropylar walls release carbohydrates at a higher rate than lateral walls. Autolysis products elute as large polymers when subjected to size-exclusion chromatography, suggesting that endo-enzyme activity is responsible for release of fragments containing arabinose, galactose, mannose, and uronic acids. Arabinose, galactose, mannose, and glucose are also released as monomers. As a function of time, the ratio of polymers to monomers decreases, indicating that exo-enzyme activity is also present. Thermoinhibition or treatment with abscisic acid suppresses germination and reduces the rates of autolysis of walls isolated from the endosperm by about 25%. Treatments that alleviate thermoinhibition (kinetin and gibberellic acid) increase the rates of autolysis by 20 to 30% when compared to thermoinhibited controls.

Journal Article↗
PubMed1973

The Effect of Arsenate and Other Inhibitors on Early Events during the Germination of Lettuce Seeds (Lactuca sativa L.).

The effect of arsenate, arsenite, 2,4-dinitrophenol, and anaerobiosis on early events in seed germination was investigated using both intact and punched seeds of lettuce (Lactuca sativa L.). It was found that punching the seed removes penetration barriers to the entrance of inhibitors without an undue loss of germination or light responses. The kinetics of the action of germination inhibitors were established by 2-hour pulse experiments. Arsenate and 2, 4-dinitrophenol have very different kinetics. The inhibition of germination in punched seeds by arsenate given in conjunction with phosphate compared with the lack of inhibition of arsenate plus phosphate on the growing seedling, suggest a distinct metabolic change in the germinating embryo at some time between the onset of germination and subsequent seedling growth.

Journal Article↗
PubMed1973

Vanadium and plant nutrition: the growth of lettuce (lactuca sativa L.) and tomato (lycopersicon esculentum mill.) plants in nutrient solutions low in vanadium.

Lettuce (Lactuca sativa L.) and tomato (Lycopersicon esculentum Mill.) plants were grown in purified nutrient solutions with and without the addition of 50 nanograms per milliliter V. These experiments showed that lettuce and tomato plants can be grown to maturity on nutrient solutions containing less than 0.04 nanogram per milliliter V with tissue concentrations of less than 2 to 18 nanograms per gram V. Growth and dry matter yield were comparable to those of plants grown on nutrient solutions containing 50 nanograms per milliliter with tissue levels of V from 117 to 418 nanograms per gram. Thus if V is an essential element for lettuce and tomato plants, the adequate tissue level would be less than 2 nanograms per gram V derivable from a growth medium containing less than 0.04 nanogram per milliliter V.

Journal Article↗
PubMed1974

Effects of Germination-promoting Substances Given in Conjunction with Red Light on the Phytochrome-mediated Germination of Dormant Lettuce Seeds (Lactuca sativa L.).

Ethylene or thiourea can substitute for gibberellic acid but not for red light in breaking the secondary dormancy induced by extended dark storage of fully hydrated lettuce seeds (Lactuca sativa cv. Grand Rapids). After 10 days of storage, ethylene, thiourea, or gibberellic acid applied either separately or in any combination in conjunction with red light induced near maximal germination. When applied separately without red light, none of the substances promoted germination of seeds stored 10 days. Combinations of any two or all three of the substances in the absence of red light induced some germination but no combination was as effective as any single substance given with red light.

Journal Article↗
PubMed1975

Effect of Gibberellic Acid, Kinetin, and Ethylene plus Carbon Dioxide on the Thermodormancy of Lettuce Seed (Lactuca sativa L. cv. Mesa 659).

The effects of gibberellic acid and kinetin with ethylene plus carbon dioxide on the thermodormancy of lettuce seeds (Lactuca sativa L. cv. Mesa 659) at 35 C in the dark were studied. The combination of gibberellic acid plus kinetin with ethylene plus carbon dioxide was most effective in overcoming thermodormancy in these Great Lakes type seeds, alleviating any induced light requirement. Gibberellic acid action required at least a minimal level of ethylene plus carbon dioxide. Kinetin action was independent of ethylene plus carbon dioxide but interacted with the gases when the gases were added. A schematic representation of the interaction is presented.

Journal Article↗
PubMed1977

Release of Esterase Following Germination of Lettuce Seed (Lactuca sativa L.).

Light-insensitive lettuce seeds, Lactuca sativa L. cv. Great Lakes, release esterases for a period following radicle protrusion. Very little or no enzymes are released prior to 24 hours or after 48 hours of germination. As compared to intact seeds, half-seeds readily release esterases and the release is not affected by far red irradiation. Bulk of the released esterases are derived from the endosperm tissue and presumably exists in the intact seed as a component of the extraembryonic fluid.

Journal Article↗
PubMed1985

Blue and Green Light-Induced Phototropism in Arabidopsis thaliana and Lactuca sativa L. Seedlings.

Exposure time-response curves for blue and green light-induced phototropic bending in hypocotyls of Arabidopsis thaliana (L.) Heynh. and Lactuca sativa L. seedlings are presented. These seedlings show significant phototropic sensitivity up to 540 to 550 nanometers. Since wave-lengths longer than 560 nanometers do not induce phototropic bending, it is suggested that the response to 510 to 550 nanometers light is mediated by the specific blue light photoreceptor of phototropism. We advise care in the use of green ;safelights' for studies of phototropism.

Journal Article↗
PubMed1985

Interactions between Mild NaCl Stress and Red Light during Lettuce (Lactuca sativa L. cv Grand Rapids) Seed Germination.

The sensitivity of lettuce (Lactuca sativa L. cv Grand Rapids) seeds to red light was reduced by NaCl concentrations which had no effect upon the germination of continuously illuminated seeds. The germination capacity of the seeds was fully restored by increased red light exposures. Indirect evidence indicates that NaCl does not affect the photoconversion of red-absorbing form of phytochrome to the far-red absorbing form of phytochrome. Instead, the increased red light requirements are attributable to increases in the threshold levels of the far-red absorbing form of phytochrome necessary to induce germination and to changes in the slopes of the fluence-response curves. Results also show that the sensitivity of the seeds to NaCl decreased as the time between red light irradiation and the imposition of NaCl stress increased.

Journal Article↗
PubMed1986

Role of Ethylene in Lactuca sativa cv ;Grand Rapids' Seed Germination.

Promotion of thermoinhibited (30 degrees C) lettuce (Lactuca sativa cv ;Grand Rapids') seed germination by ethylene is similar to the action of the gas in other hormonal systems. Ethylene was more active than propylene and ethane was inactive. An inhibitor of ethylene production, aminoethoxy-vinylglycine, reduced ethylene evolution and germination. Inhibitors of ethylene action such as, 5-methyl-7-chloro-4-ethoxycarbonylmethoxy-2,1,3-benzothiadiazole, 2,5-norbornadiene, and silver thiosulfate inhibited germination and the effect was reversed by the addition of ethylene to the gas phase. The action of ethylene appears to be due to the promotion of radial cell expansion in the embryonic hypocotyl. The action of N6-benzyladenine and fusiccocin, which also overcome thermoinhibition, appears to be due to a promotion of hypocotyl elongation. None of the germination promoters studied appeared to function by lowering the mechanical resistance of the endosperm to embryonic growth. Data presented here are consistent with the view that ethylene plays a role in lettuce seed germination under thermoinhibited and normal conditions.

Journal Article↗
PubMed1988

Abscisic Acid Is an Endogenous Inhibitor in the Regulation of Mannanase Production by Isolated Lettuce (Lactuca sativa cv Grand Rapids) Endosperms.

The production of mannanase, a cell-wall-degrading carbohydrase, can be manipulated in isolated lettuce (Lactuca sativa cv Grand Rapids) endosperms by changes in the volume of buffer in which they are incubated. The enzyme is produced when endosperms are incubated in a large volume, but not when incubated in a small volume, which is suggestive that an endogenous, diffusible inhibitor of mannanase production is being lost from the endosperms in a large volume (JD Bewley, P Halmer 1980/1981 Israel J Bot 29: 118-132). We have investigated the possibility that the phytohormone abscisic acid (ABA) is involved in this regulation of mannanase production in isolated lettuce endosperms. We find several correlations between the presence of the endogenous inhibitor and of ABA, i.e. (a) a ;leachate' prepared from isolated lettuce endosperms induces synthesis of ABA-specific proteins in barley aleurone layers, indicating that incubation of endosperms in a large volume results in the diffusion of ABA therefrom into the surrounding medium; (b) fractionation of the components of a leachate by either polyvinylpyrrolidone-chromatography of C(18) reversed-phase high performance liquid chromatography fails to separate the endogenous inhibitor from authentic ABA; and (c) changes in the incubation volume of endosperms result in changes in the amount of extractable ABA in the endosperms, as detected by ELISA. These results are consistent with a role for endogenous ABA in the regulation of mannanase production in isolated lettuce endosperms.

Journal Article↗
PubMed1988

Isolation, molecular properties and kinetic studies of a strict beta-fucosidase from Lactuca sativa latex. Its possible role in the cell-wall degradation of articulated laticifers.

A beta-fucosidase located in the latex serum of Lactuca sativa has been isolated and purified to homogeneity. This enzyme greatly differs from the other fucosidases already known in that it is strictly specific for the fucosyl residue and for the anomeric beta carbon. It is the first time that such an enzyme is shown to exist. The enzyme is a monomer and its molecular mass is close to 37 kDa. Its sedimentation constant is equal to 2.8 S. It is very stable at pH 5.5 in citrate/phosphate buffer but extensive denaturation occurs up to pH 7.5. Kinetic studies have shown that two ionization steps probably control the rate of the enzymatic hydrolysis. No precise information could be obtained about the possible in vivo role of this beta-fucosidase. However, the pure enzyme can release fucose from the cell walls obtained from hypocotyls of L. sativa. This result may be taken as evidence for the presence of beta-fucosidic links in these walls so that the enzyme could be involved in the differentiation of articulated laticifers.

Amino Acids↗