摘要:

The effect of a number of physiological variables on the secretion of polysaccharide-degrading enzymes by culture-grownColletotrichum lindemuthianum(Saccardo and Magnus) Scribner was determined. The number of spores used to inoculate cultures grown on isolated bean hypocotyl cell walls affects the time after inoculation at which enzyme secretion occurs, but has no significant effect on the maximal amount of enzyme ultimately secreted. Cell walls isolated from bean leaves, first internodes, or hypocotyls (susceptible toC. lindemuthianuminfection), when used as carbon source forC. lindemuthianumgrowth, stimulate the fungus to secrete moreα-galactosidase than do cell walls isolated from roots (resistant to infection). The concentration of carbon source used for fungal growth determines the final level of enzyme activity in the culture fluid. The level of enzyme secretion is not proportional to fungal growth; rather, enzyme secretion is induced. Maximalα-galactosidase activity in the culture medium is found when the concentration of cell walls used as carbon source is 1% or greater. A higher concentration of cell walls is necessary for maximalα-arabinosidase activity. Galactose, when used as the carbon source, stimulatesα-galactosidase secretion but, at comparable concentrations, is less effective in doing so than are cell walls. Polysaccharide-degrading enzymes are secreted byC. lindemuthianumat different times during growth of the pathogen on isolated cell walls. Pectinase andα-arabinosidase are secreted first, followed byβ-xylosidase and cellulase, thenβ-glucosidase, and, finally,α-galact

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

The role of ethylene in the aging of bean (Phaseolus vulgarisL. cv. Red Kidney) petiole abscission zone explants was examined. The data indicate that ethylene does accelerate aging in addition to inducing changes in break strength. Application of ethylene during the aging stage (stage 1) promoted abscission when followed by a second ethylene treatment during the cell separating stage (stage 2). The half-maximal effective concentration of ethylene to induce aging was around 0.3 microliter per liter; 10 microliters per liter was a saturating dose. CO2reversal of ethylene action during stage 1 was incomplete and gave ambiguous results. CO2(10%) reversed the effect of 10 microliters per liter ethylene but not 1 microliter per liter ethylene. The possibility that ethylene not only accelerated aging but was also a requirement for it was tested, and experimental evidence in favor of this idea was obtained. It was concluded that ethylene plays a dual role in the abscission of bean petiole explants: a phytogerontological effect and a cellulase-inducing effect.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

The primary factor for atrazine selectivity in corn (Zea mays) is the activity of a soluble enzyme, glutathione S-transferase, which detoxifies atrazine by catalyzing the formation of an atrazine-glutathione conjugate (GS-atrazine). The nonenzymatic, benzoxazinone-catalyzed hydrolysis of atrazine to hydroxyatrazine contributed to the total resistance of corn to atrazine, but the nonenzymatic detoxication pathway does not seem to be essential for resistance. All corn lines investigated, except for susceptible GT112, rapidly detoxified atrazine by glutathione conjugation. Only GT112 had low glutathione S-transferase activity. Hydroxyatrazine was found in significant quantities only when atrazine was introduced initially into the roots. The amount of hydroxyatrazine formed was nearly equal for susceptible GT112 and most of the resistant corn lines investigated. This investigation indicates that some plants protect themselves against toxic organic halide compounds with a mechanism similar to that known to exist in animals.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

The ultrastructure and distribution of chloroplasts, mitochondria, peroxisomes, and other cellular constituents have been examined in cross sections of leaves from plants with either high or low photosynthetic capacity. Photosynthetic capacity of a given plant cannot be correlated with the presence or absence of grana in bundle sheath cell chloroplasts, the presence or absence of starch grains in bundle sheath or mesophyll cell chloroplasts, the chloroplast size in bundle sheath or mesophyll cells, or the location of chloroplasts within bundle sheath cells. We conclude that the number and concentration of chloroplasts, mitochondria, and peroxisomes in bundle sheath cells is the most reliable anatomical criterion presently available for determining the photosynthetic capacity of a given plant.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

A cell free system prepared from etiolated cucumber (Cucumis sativus, L) in tris-sucrose buffer is able to incorporateδ-aminolevulinic acid-4-14C into the two components of protochlorophyll: protochlorophyllide and protochlorophyllide ester. The activity is associated with the etioplasts. Optimal incorporation is obtained at pH 7.7. For the formation of protochlorphyllide ester, oxygen, reduced glutathione, methyl alcohol, magnesium, inorganic phosphate, and nicotinamide adenine dinucleotide are required. For the formation of14C-protochlorophyllide, adenosine triphosphate, and coenzyme A are required in addition to the above. The requirement for methyl alcohol is highly specific, and the methyl group appears to be incorporated into the protochlorophyll molecules. A biosynthetic scheme resulting in the parallel production of14C-protochlorophyllide and14C-protochlorophyllide ester from14C-Mg protoporphyrin monoester is presented

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

A crude homogenate obtained from greening cucumber (Cucumis sativus, L.) cotyledons in tris-sucrose, pH 7.7, containing coenzyme A, glutathione, potassium phosphate, pH 7.7, methyl alcohol, magnesium, nicotinamide adenine dinucleotide, and adenosine triphosphate, is able to incorporate 4-14C-δ-aminolevulinic acid into chlorophyllaandbin the presence of oxygen. If the homogenates are prepared from etiolated cotyledons which have been exposed to light for two and one-half hours,14C-chlorophyllais synthesized. However, when the homogenates are prepared from cotyledons illuminated for four and one-half hours, both14C-chlorophyllaandbare produced

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

Operational and constructional details are given of an apparatus which permits simultaneous enzyme extraction from up to 16 cell samples under standardized conditions. The main advantages of the method are: (a) individual samples remain in the same container throughout the whole operation; (b) the samples can be stirred continuously and uniformly during extraction; (c) rapid changes of extractant are facilitated by a simple draining operation; (d) the extraction temperature can be strictly controlled. The method is rapid, efficient, and reproducible in extracting a number of enzymes from cultured rose cells. Other uses of the apparatus are discussed, particularly in relation to the extraction of protein, nucleic acids, and some low molecular weight materials.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

Nicotinamide adenine dinucleotide phosphate-specific isocitrate dehydrogenase was extracted from etiolated pea (Pisum sativumL.) seedlings and was purified 65-fold. The purified enzyme exhibits one predominant protein band by polyacrylamide gel electrophoresis, which corresponds to the dehydrogenase activity as measured by the nitro blue tetrazolium technique. The reaction is readily reversible, the pH optima for the forward (nicotinamide adenine dinucleotide phosphate reduction) and reverse reactions being 8.4 and 6.0, respectively. The enzyme has different cofactor and inhibitor characteristics in the two directions. Manganese ions can be used as a cofactor for the reaction in each direction but magnesium ions only act as a cofactor in the forward reaction. Zinc ions, and to a lesser extent calcium ions, inhibit the enzyme at low concentrations when magnesium but not manganese is the metal activator. It is suggested that there is a fundamental difference between magnesium and manganese in the activation of the enzyme. The enzyme shows normal kinetics and the Michaelis contant for each substrate was determined. The inhibition by nucleotides, nucleosides, reaction products, and related compounds was studied. The enzyme shows a linear response to the mole fraction of reduced nicotinamide adenine dinucleotide phosphate when total nicotinamide adenine dinucleotide phosphate (nicotinamide adenine dinucleotide phosphate plus reduced nicotinamide adenine dinucleotide phosphate) is kept constant. Isocitrate in the presence of divalent metal ions will protect the enzyme from inactivation byp-chloromercuribenzoate. Protection is also afforded by manganese ions alone but not by magnesium ions alone There is a concerted inhibition of the enzyme by oxalacetate and glyoxylate.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

The control points of the Embden-Meyerhof-Parnas pathway in germinating castor bean (Ricinus communis) endosperms are sought in two ways: (a) by measuring the amounts of various glycolytic intermediates at intervals during the germination; (b) by determining the crossover points appearing during anoxia.A significant departure from thermodynamic equilibrium between substrates and products is found at the level of fructose 1,6-diphosphatase and phosphofructokinase. A definite shift of this ratio is observed at the onset of active gluconeogenesis. The concentrations of phosphoenolpyruvate and 3-phosphoglyceric acid increase at the same time. Another departure from the expected equilibrium is also observed at the level of the pyruvate kinase.The imposition of anoxia on 5-day-old endosperms reveals two crossover points, at the level of the same enzymes. It is therefore concluded that they regulate the glycolytic flow.The maximal glycolytic flow, however, is only 1/10 of the gluconeogenic one. To account for this high gluconeogenic efficiency, it is postulated that gluconeogenesis and glycolysis occur in separate intracellular regions. The consistent departure from equilibrium between adenylates observed during the early stages of anoxia supports the concepts that the pools of glycolytic and gluconeogenic intermediates are indeed compartmented and that the two processes are independently regulated.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB

摘要:

Effects of the R- and S-isomers and racemate of 1-(α-methylbenzyl)-3-(3,4-dichlorophenyl)urea (MBPU) were measured on phosphorylation and electron transport in mung bean (Phaseolus aureusL.) mitochondria and spinach (Spinacia oleraceaL.) chloroplasts.In chloroplasts, S-MBPU inhibited basal and methylamine-uncoupled electron transport with ferricyanide as the oxidant, both photoreduction and coupled photophosphorylation with water as the electron donor and with ferricyanide and nicotinamide adenine dinucleotide phosphate (NADP) as oxidants, and cyclic photophosphorylation with phenazine methosulfate as the electron mediator under an argon gas phase. With ascorbate 2,6-dichloro-phenolindophenol as the electron donor, phosphorylation coupled to NADP reduction was inhibited, but the reduction of NADP was not inhibited. The R-isomer of MBPU, like the S-isomer, inhibited all of the photophosphorylation reactions studied. However, unlike the S-isomer, the R-isomer either did not inhibit or was a very weak inhibitor of all photoreduction reactions. The effects of the MBPUs on the chloroplast reactions can be explained by action at two different sites: an optically specific site near photosystem II and the oxygen evolution pathway, and a second optically nonspecific site associated with the generation of ATP.In mitochondria, both the R- and S-isomers stimulated state 4 respiration, inhibited state 3 respiration, and released oligomycin-inhibited respiration with malate, succinate, and NADH as substrates. Both enantiomers were equally active in all studies with malate and succinate as substrates. However, with NADH as substrate, R-MBPU was a stronger inhibitor of state 3 respiration and a weaker stimulator of state 4 respiration than S-MBPU

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1971

数据来源: ASPB