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Showing papers in "Plant Physiology in 1981"


Journal ArticleDOI
TL;DR: It is proposed that, under low phosphorus nutrition, increased root membrane permeability leads to net loss of metabolites at sufficient levels to sustain the germination and growth of the mycorrhizal fungus during pre- and postinfection.
Abstract: The mechanism responsible for phosphorus inhibition of vesicular-arbuscular mycorrhiza formation in sudangrass (Sorghum vulgare Pers.) was investigated in a phosphorus-deficient sandy soil (0.5 micrograms phosphorus per gram soil) amended with increasing levels of phosphorus as superphosphate (0, 28, 56, 228 micrograms per gram soil). The root phosphorus content of 4-week-old plants was correlated with the amount of phosphorus added to the soil. Root exudation of amino acids and reducing sugars was greater for plants grown in phosphorus-deficient soil than for those grown in the phosphorus-treated soils. The increase in exudation corresponded with changes in membrane permeability of phosphorus-deficient roots, as measured by K+ (86Rb) efflux, rather than with changes in root content of reducing sugars and amino acids. The roots of phosphorus-deficient plants inoculated at 4 weeks with Glomus fasciculatus were 88% infected after 9 weeks as compared to less than 25% infection in phosphorus-sufficient roots; these differences were correlated with root exudation at the time of inoculation. For plants grown in phosphorus-deficient soil, infection by vesicular-arbuscular mycorrhizae increased root phosphorus which resulted in a decrease in root membrane permeability and exudation compared to nonmycorrhizal plants. It is proposed that, under low phosphorus nutrition, increased root membrane permeability leads to net loss of metabolites at sufficient levels to sustain the germination and growth of the mycorrhizal fungus during pre- and postinfection. Subsequently, mycorrhizal infection leads to improvement of root phosphorus nutrition and a reduction in membrane-mediated loss of root metabolites.

470 citations


Journal ArticleDOI
TL;DR: Endogenous elicitors were also solubilized by partial hydrolysis from cell walls of suspension-cultured tobacco, sycamore, and wheat cells, suggesting that galacturonic acid is an essential constituent of the elicitor-active wall fragments.
Abstract: An elicitor of phytoalexin accumulation (endogenous elicitor) is solubilized from purified cell walls of soybean (Glycine max [L.] Merr., cv. Wayne) by extracting the walls with hot water or by subjecting the walls to partial acid hydrolysis. The endogenous elicitor obtained from soybean cell walls binds to an anion exchange resin. The elicitor-active material released from the resin contains oligosaccharides rich in galacturonic acid; small amounts of rhamnose and xylose are also present. The preponderance of galacturonic acid in the elicitor-active fragments suggests that the elicitor is, in fact, a fragment of a pectic polysaccharide. This possibility is supported by the observation that treatment of the wall fragments with a highly purified endopolygalacturonase destroys their ability to elicit phytoalexin accumulation. This observation, together with other evidence presented in this paper, suggests that galacturonic acid is an essential constituent of the elicitor-active wall fragments. Endogenous elicitors were also solubilized by partial hydrolysis from cell walls of suspension-cultured tobacco, sycamore, and wheat cells.

325 citations


Journal ArticleDOI
TL;DR: Root cells of four common legumes were found to remain susceptible to nodulation by rhizobia for only a short period of time, suggesting the existence of a fast-acting regulatory mechanism in these hosts that prevents overnodulation.
Abstract: Root cells of four common legumes were found to remain susceptible to nodulation by rhizobia for only a short period of time. Delayed inoculation experiments conducted with these legume hosts indicated that the initially susceptible region of the root became progressively less susceptible if inoculations were delayed by a few hours. Profiles of the frequency of nodule formation relative to marks indicating the regions of root and root hair development at the time of inoculation indicated that nodulation of Vigna sinensis (L.) Endl. cv California Black Eye and Medicago sativa L. cvs Moapa and Vernal roots was inhibited just below the region that was most susceptible at the time of inoculation. This result suggests the existence of a fast-acting regulatory mechanism in these hosts that prevents overnodulation. Nodulation in white clover may occur in two distinct phases. In addition to the transient susceptibility of preemergent and developing root hair cells, there appeared to be an induced susceptibility of mature clover root hair cells. A cell-free bacterial exudate preparation from Rhizobium trifolii cells was found to render mature root hair cells of white clover more rapidly susceptible to nodulation.

290 citations


Journal ArticleDOI
TL;DR: The phenolic compounds salicylic acid and ferulic acid inhibited K(+) ((86)Rb(+)) absorption in excised oat root tissue and the degree of inhibition was both concentration- and pH-dependent.
Abstract: The phenolic compounds salicylic acid (o-hydroxybenzoic acid) and ferulic acid (4-hydroxy-3-methoxycinnamic acid) inhibited K(+) ((86)Rb(+)) absorption in excised oat (Avena sativa L. cv. Goodfield) root tissue. Salicylic acid was the most inhibitory. The degree of inhibition was both concentration- and pH-dependent. With decreasing pH, the inhibitory effect of the phenolic increased. During the early stages of incubation, the time required to inhibit K(+) absorption was also pH- and concentration-dependent. At pH 4.0, 5x10(-4) molar salicylic acid inhibited K(+) absorption about 60% within 1 minute; whereas, at pH 6.5, this concentration affected absorption only after 10 to 15 minutes. However, at 5 x 10(-3) molar and pH 6.5, salicylic acid was inhibitory within 1 minute. The capacity of the tissue to recover following a 1-hour treatment in 5 x 10(-4) molar salicylic acid ranged from no recovery at pH 4.5 to complete recovery at pH 7.5. The absorption of salicylic acid was pH-dependent, also. As pH decreased, more of the phenolic compound was absorbed by the tissue. The increased absorption of the compound at low pH most likely contributed to apparent tissue damage at pH 4.5 and might have accounted for the lack of recovery of K(+) absorption as pH decreased.Under the proper conditions of pH and concentration, phenolic acids such as salicylic acid could significantly affect mineral absorption by plants in the field.

247 citations


Journal ArticleDOI
TL;DR: The inhibition of stem elongation in dark-grown seedlings by blue light was studied with marking techniques and with a high-resolution, growth-measuring apparatus to show that, after a short lag period, the growth rate declines in an exponential fashion to a lower rate.
Abstract: The inhibition of stem elongation in dark-grown seedlings by blue light was studied with marking techniques and with a high-resolution, growth-measuring apparatus. Blue light rapidly suppresses growth in a variety of cultivated species. In some species, the inhibition persists only during the period of irradiation, after which time growth quickly returns to the high dark rate, whereas, in other species, the light response has an additional long-term component which lasts for at least several hours in the dark. The long-term inhibition may be mediated by phytochrome, whereas the rapid, short-term component is specific to a blue-light receptor.The rapid inhibition of growth in cucumber (Cucumis sativus L.) requires high-energy blue irradiation, which is perceived directly by the growing region of the hypocotyl and inhibits all regions below the hook to the same extent. Detailed investigation of the kinetics of the inhibition in cucumber and in sunflower (Helianthus annuus L.) shows that, after a short lag period (20 to 30 seconds in cucumber, 60 to 70 seconds in sunflower), the growth rate declines in an exponential fashion to a lower rate, with a half-time of 15 to 25 seconds in cucumber and 90 to 150 seconds in sunflower. Excision of the hypocotyl greatly reduces the sensitivity of the growth rate to blue-light inhibition. Because of the rapid kinetics, the blue-light photoreceptor cannot affect cell enlargement by altering the supply of growth hormone or the sensitivity to hormones but probably operates more directly either on the biochemical process which loosens cell walls or on cell turgor.

245 citations


Journal ArticleDOI
TL;DR: The data indicate that host plant glutamine synthetase and NADh-glutamate synthase function to assimilate symbiotically fixed N and that NADH-dependent glutamate dehydrogenase may function in ammonia assimilation during senescence in alfalfa nodules.
Abstract: Nitrogenase-dependent acetylene reduction activity of glasshouse-grown alfalfa (Medicago sativa L.) decreased rapidly in response both to harvesting (80% shoot removal) and applied NO(3) (-) at 40 and 80 kilograms N per hectare. Acetylene reduction activity of harvested plants grown on 0 kilogram N per hectare began to recover by day 15 as shoot regrowth became significant. In contrast, acetylene reduction activity of all plants treated with 80 kilograms NO(3) (-)-N per hectare and harvested plants treated with 40 kilograms NO(3) (-)-N per hectare remained low for the duration of the experiment. Acetylene reduction of unharvested alfalfa treated with 40 kilograms N per hectare declined to an intermediate level and appeared to recover slightly by day 15. Changes in N(2)-fixing capacity were accompanied by similar changes in levels of nodule soluble protein.After an initial lag of 24 hours, specific activities of alfalfa nodule glutamine synthetase, NADH-glutamate synthase, and NAD-glutamate dehydrogenase (oxidative amination) decreased similar to but less rapidly than acetylene reduction activity. Increased specific activities of these nodule enzymes occurred as acetylene reduction activity increased and shoot growth resumed. The observed rates of glutamine synthetase and glutamate synthase were sufficient to assimilate ammonia produced via symbiotic N(2) fixation. Nodule NADH-dependent glutamate dehydrogenase (reductive amination) specific activity was not associated with changes in acetylene reduction activity.The data indicate that host plant glutamine synthetase and NADH-glutamate synthase function to assimilate symbiotically fixed N and that NADH-dependent glutamate dehydrogenase may function in ammonia assimilation during senescence in alfalfa nodules.

238 citations


Journal ArticleDOI
TL;DR: Cells of two species of single-celled marine algae, the diatom Skeletonema costatum (Greve), Cleve, and the chlorophyte Dunaliella tertiolecta Butcher, were cultured in white light and in neither organism did photosynthetic capacity correlate with changes in cellular content of PSI or PSII reaction centers.
Abstract: Cells of two species of single-celled marine algae, the diatom Skeletonema costatum (Greve), Cleve, and the chlorophyte Dunaliella tertiolecta Butcher, were cultured in white light of high (500-600 microeinsteins per square meter per second) and low (30 microeinsteins per square meter per second) intensity. For both algal species, cells grown at low light levels contained more chlorophyll a and had a lower ratio of chlorophyll a to chlorophylls b or c than did cells grown at high light levels. When photosynthetic unit sizes were measured on the basis of either oxygen flash yields or P700 photooxidation, different results were obtained with the different species. In the chlorophyte, the cellular content of photosystem I (PSI) and photosystem II (PSII) reaction centers increased in tandem as chlorophyll a content increased so that photosynthetic unit sizes changed only slightly and the ratio PSI:PSII reaction centers remained constant at about 1.1. In the diatom, as the chlorophyll content of the cells increased, the number of PSI reaction centers decreased and the number of PSII reaction centers increased so that the ratio of PSI:PSII reaction centers decreased from about unity to 0.44. In neither organism did photosynthetic capacity correlate with changes in cellular content of PSI or PSII reaction centers. The results are discussed in relationship to the physical and biological significance of the photosynthetic unit concept.

229 citations


Journal ArticleDOI
TL;DR: Determination of flux response curves on leaves in the normal position or in the inverted position led to the conclusion that the photoreceptors for blue as well as for red light are located on or near the surfaces of the leaves; presumably they are in the guard cells themselves.
Abstract: Flux response curves were determined at 16 wavelengths of light for the conductance for water vapor of the lower epidermis of detached leaves of Xanthium strumarium L An action spectrum of stomatal opening resulted in which blue light (wavelengths between 430 and 460 nanometers) was nearly ten times more effective than red light (wavelengths between 630 and 680 nanometers) in producing a conductance of 15 centimoles per square meter per second Stomata responded only slightly to green light An action spectrum of stomatal responses to red light corresponded to that of CO2 assimilation; the inhibitors of photosynthetic electron transport, cyanazine (2-chloro-4[1-cyano-1-methylethylamino]-6-ethylamino-s-triazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, eliminated the response to red light This indicates that light absorption by chlorophyll is the cause of stomatal sensitivity to red light Determination of flux response curves on leaves in the normal position (upper epidermis facing the light) or in the inverted position (lower epidermis facing the light) led to the conclusion that the photoreceptors for blue as well as for red light are located on or near the surfaces of the leaves; presumably they are in the guard cells themselves

228 citations


Journal ArticleDOI
TL;DR: Water potential (Psiomega) values were determined for aqueous colloids of four molecular sizes of polyethylene glycol (PEG) using freezing-point depression and vapor-pressure deficit methods and it is suggested that the Psiomega of PEG in water may be controlled primarily by the matric forces of ethylene oxide subunits of the PEG polymer.
Abstract: Water potential (Psiomega) values were determined for aqueous colloids of four molecular sizes of polyethylene glycol (PEG) using freezing-point depression and vapor-pressure deficit methods. A significant third-order interaction exists between the method used to determine Psiomega, PEG molecular size, and concentration. At low PEG concentrations, freezing-point depression measurements result in higher (less negative) values for Psiomega than do vapor-pressure deficit measurements. The reverse is true at high concentrations. PEG in water does not behave according to van't Hoff's law. Psiomega is related to molality for a given PEG but not linearly. Moreover, Psiomega varies with the molecular size of the PEG. It is suggested that the Psiomega of PEG in water may be controlled primarily by the matric forces of ethylene oxide subunits of the PEG polymer. The term matricum is proposed for PEG in soil-plant-water relation studies.

226 citations


Journal ArticleDOI
TL;DR: Polyamines, as well as putrescine, inhibited auxin-induced ethylene production and the conversion of methionine and 1-aminocyclopropane-1-carboxylic acid to ethylene.
Abstract: Ethylene production in apple fruit and protoplasts and in leaf tissue was inhibited by spermidine or spermine. These polyamines, as well as putrescine, inhibited auxin-induced ethylene production and the conversion of methionine and 1-aminocyclopropane-1-carboxylic acid to ethylene. Polyamines were more effective as inhibitors of ethylene synthesis at the early, rather than at the late, stages of fruit ripening. Ca2+ in the incubation medium reduced the inhibitory effect caused by the amines. A possible mode of action by which polyamines inhibit ethylene production is discussed.

224 citations


Journal ArticleDOI
TL;DR: Cycloheximide, an inhibitor of protein synthesis, effectively blocked both ethylene production and ACC formation, suggesting that water stress induces de novo synthesis of ACC synthase, which is the rate-controlling enzyme in the pathway of ethylene biosynthesis.
Abstract: Wheat leaves normally produced very little ethylene, but following a water deficit stress which caused a loss of 9% initial fresh weight, ethylene production increased more than 30-fold within 4 hours and declined rapidly thereafter. The changes in ethylene production were paralleled by an increase and subsequent decrease in 1-aminocyclopropanecarboxylic acid (ACC) content. The level of S-adenosylmethionine was unaffected, suggesting that the conversion of S-adenosylmethionine to ACC is a key reaction in the production of water stress-induced ethylene. This view was further supported by the observation that application of ACC to nonstressed leaf tissue caused a 70-fold increase in ethylene production, while aminoethoxyvinylglycine, a known inhibitor of the conversion of S-adenosylmethionine to ACC, inhibited ACC accumulation as well as the surge in ethylene production if the inhibitor was applied prior to the stress treatment. Cycloheximide, an inhibitor of protein synthesis, effectively blocked both ethylene production and ACC formation, suggesting that water stress induces de novo synthesis of ACC synthase, which is the rate-controlling enzyme in the pathway of ethylene biosynthesis.

Journal ArticleDOI
TL;DR: Results add support to the proposal that R. leguminosarum and R. trifolii have a particularly close genetic relationship.
Abstract: The sequence of the glycosyl residues and the anomeric configurations of the glycosyl linkages of the acidic polysaccharides secreted by Rhizobium leguminosarum 128c53, Rhizobium leguminosarum 128c63, Rhizobium trifolii NA30, and Rhizobium trifolii 0403 have been determined. All four polysaccharides were found to have the following glycosyl repeating-unit structure, where galactosyl is Gal, glucosyl is Glc, glucuronosyl is GlcA, and pyruvyl is Pyr: [Formula: see text] Each of the glycosyl residues of these polysaccharides was determined to be in the d configuration and in the pyranose ring form. These results add support to the proposal that R. leguminosarum and R. trifolii have a particularly close genetic relationship. The significance of these results with regard to the possible function of these polysaccharides in the nodulation process is discussed.

Journal ArticleDOI
TL;DR: Cotton plants subjected to a series of water deficits exhibited stress adaptation in the form of osmoregulation when plants were subjected toA subsequent drying cycle, and cells of adapted leaves appeared to have smaller vacuoles and greater nonosmotic cell volume than did control plants.
Abstract: Cotton plants subjected to a series of water deficits exhibited stress adaptation in the form of osmoregulation when plants were subjected to a subsequent drying cycle. After adaptation, the leaf water potential coinciding with zero turgor was considerably lower than in plants that had never experienced a water stress. The relationship between leaf turgor and leaf water potential depended on leaf age.Nonstomatal factors severely limited photosynthesis in adapted plants at high leaf water potential. Nonetheless, adapted plants maintained photosynthesis to a much lower leaf water potential than did control plants, in part because of increased stomatal conductance at low leaf water potentials. Furthermore, adapted plants continued to translocate recently derived photosynthate to lower leaf water potentials, compared with control plants.Stress preconditioning modified cellular ultrastructure. Chloroplasts of fully turgid adapted leaves contained extremely large starch granules, seemed swollen, and had some breakdown of thylakoid membrane structure. In addition, cells of adapted leaves appeared to have smaller vacuoles and greater nonosmotic cell volume than did control plants.

Journal ArticleDOI
TL;DR: The normal growth of the mutants under nonphotorespiratory atmospheric conditions indicates that mitochondrial serine transhydroxymethylase is not required in C(3) plants for any function unrelated to photorespiration, and it is suggested that glycine decarboxylation is the sole site of photorespiratories CO(2) release in wild-type plants.
Abstract: Three allelic mutants of Arabidopsis thaliana which lack mitochondrial serine transhydroxymethylase activity due to a recessive nuclear mutation have been characterized. The mutants were shown to be deficient both in glycine decarboxylation and in the conversion of glycine to serine. Glycine accumulated as an end product of photosynthesis in the mutants, largely at the expense of serine, starch, and sucrose formation. The mutants photorespired CO(2) at low rates in the light, but this evolution of photorespiratory CO(2) was abolished by provision of exogenous NH(3). Exogenous NH(3) was required by the mutants for continued synthesis of glycine under photorespiratory conditions. These and related results with wild-type Arabidopsis suggested that glycine decarboxylation is the sole site of photorespiratory CO(2) release in wild-type plants but that depletion of the amino donors required for glyoxylate amination may lead to CO(2) release from direct decarboxylation of glyoxylate. Photosynthetic CO(2) fixation was inhibited in the mutants under atmospheric conditions which promote photorespiration but could be partially restored by exogenous NH(3). The magnitude of the NH(3) stimulation of photosynthesis indicated that the increase was due to the suppression of glyoxylate decarboxylation. The normal growth of the mutants under nonphotorespiratory atmospheric conditions indicates that mitochondrial serine transhydroxymethylase is not required in C(3) plants for any function unrelated to photorespiration.

Journal ArticleDOI
TL;DR: A computer program (CHELATE) to calculate all equilibrium species (free metal ions, metal complexes, etc.) in any user-defined system, such as xylem fluid was used to calculate the distribution of six metals in 0- to 1-hour exudate from soybean and tomato plants grown in normal and Zn-phytotoxic nutrient solutions.
Abstract: Theoretical considerations of metal complex formation in aqueous solutions were used to develop a computer program (CHELATE) to calculate all equilibrium species (free metal ions, metal complexes, etc.) in any user-defined system, such as xylem fluid. Mass-balance equations were established to describe each free metal ion and each free ligand concentration as a function of solution pH, total metal or total ligand, hydrogen-association constants, and the stability constants of known metal complexes. A default data base can be altered by the user to define any desired system covered by the stored equilibrium data. The program can currently handle nine metal ions, 35 ligands, and 500 complex species. The validity of the program was confirmed by using experimental test systems in which free-metal ion activity measurements were made with ion-selective electrodes. Program CHELATE was used to calculate the distribution of six metals in 0- to 1-hour exudate from soybean ( Glycine max L. Merr.) and tomato ( Lycopersicon esculentum Mill.) plants grown in normal and Zn-phytotoxic nutrient solutions. The results indicated that Fe is bound by citric acid, and Cu is bound by several amino acids in the normal-Zn exudate. Most of the Cu in soybean exudate is bound to asparagine and histidine. In tomato, Cu is bound to histidine, glutamine, and asparagine. Zinc, Mn, Ca, and Mg are bound primarily by citric acid and malic acid in both species; the per cent bound for these metals is lower than that for Fe and Cu. Zinc phytotoxicity caused equilibrium concentration shifts and resulted in the formation of several additional metal complexes not found in the normal-Zn exudate.

Journal ArticleDOI
TL;DR: The results show that N nutrition and water stress interact to control ABA accumulation and the events regulated by that accumulation.
Abstract: Nitrogen nutrition exerted a strong effect on stomatal sensitivity to water stress in cotton. In well-watered plants grown with 0.31 millimolar N in the nutrient solution, stomata closed at a water potential of -9 bars even though the wilting point was below -15 bars. For each doubling of nutrient N level, the water potential for stomatal closure decreased by about 2 bars. Elevated intercellular CO(2) concentrations caused only slight stomatal closure regardless of N nutrition. Exogenous abscisic acid (ABA) greatly increased stomatal sensitivity to elevated CO(2) concentrations.PLANTS SUBJECTED TO WATER STRESS GAVE THE FOLLOWING RESPONSES: (a) decreased stomatal conductance at ambient external CO(2) concentration; (b) increased stomatal sensitivity to elevated CO(2) concentrations; (c) decreased mesophyll conductance to CO(2); and (d) increased endogenous ABA content. All of these responses to stress occurred at a higher water potential in N-deficient plants than in normal plants. The results show that N nutrition and water stress interact to control ABA accumulation and the events regulated by that accumulation.

Journal ArticleDOI
TL;DR: Analysis of extracts from kernels of the double mutant ae du indicated that the two mutants act independently, suggesting that the alterations of the starch may be accounted for by changes in the soluble synthase and branching enzyme fractions.
Abstract: Soluble starch synthase and starch-branching enzymes in extracts from kernels of four maize genotypes were compared. Extracts from normal (nonmutant) maize were found to contain two starch synthases and three branching enzyme fractions. The different fractions could be distinguished by chromatographic properties and kinetic properties under various assay conditions. Kernels homozygous for the recessive amylose-extender (ae) allele were missing branching enzyme IIb. In addition, the citrate-stimulated activity of starch synthase I was reduced. This activity could be regenerated by the addition of branching enzyme to this fraction. No other starch synthase fractions were different from normal enzymes. Extracts from kernels homozygous for the recessive dull (du) allele were found to contain lower branching enzyme IIa and starch synthase II activities. Other fractions were not different from the normal enzymes. Analysis of extracts from kernels of the double mutant ae du indicated that the two mutants act independently. Branching enzyme IIb was absent and the citrate-stimulated reaction of starch synthase I was reduced but could be regenerated by the addition of branching enzyme (ae properties) and both branching enzyme IIa and starch synthase II were greatly reduced (du properties). Starch from ae and du endosperms contains higher amylose (66 and 42%, respectively) than normal endosperm (26%). In addition, the amylopectin fraction of ae starch is less highly branched than amylopectin from normal or du starch. The above observations suggest that the alterations of the starch may be accounted for by changes in the soluble synthase and branching enzyme fractions.

Journal ArticleDOI
TL;DR: Studies of ribulose-1,5-bisphosphate (RuBP) carboxylase from taxonomically diverse plants show that the enzyme from C(3) and crassulacean acid metabolism pathway species exhibits lower K(m)(CO(2)) values than does that from C (4) species.
Abstract: Studies of ribulose-1,5-bisphosphate (RuBP) carboxylase from taxonomically diverse plants show that the enzyme from C3 and crassulacean acid metabolism pathway species exhibits lower Km(CO2) values (12-25 micromolar) than does that from C4 species (28-34 micromolar). RuBP carboxylase from aquatic angiosperms, an aquatic bryophyte, fresh water and marine algae has yielded consistently high Km(CO2) values (30-70 micromolar), similar in range to that of the enzyme from C4 terrestrial plants. This variation in Km(CO2) is discussed in relation to the correlation between the existence of CO2-concentrating mechanisms for photosynthesis and the affinity of the enzyme for CO2. The Km(RuBP) of the enzyme from various sources ranges from 10 to 136 micromolar; mean ± sd = 36 ± 20 micromolar. This variation in Km(RuBP) does not correlate with different photosynthetic pathways, but shows taxonomic patterns. Among the dicotyledons, the enzyme from crassinucellate species exhibits lower Km(RuBP) (18 ± 4 micromolar) than does that from tenuinucellate species (25 ± 7 micromolar). Among the Poaceae, RuBP carboxylase from Triticeae, chloridoids, andropogonoids, Microlaena, and Tetrarrhena has yielded lower Km(RuBP) values (29 ± 11 micromolar) than has that from other members of the grass family (46 ± 10 micromolar).

Journal ArticleDOI
TL;DR: Temperature stress, like several other environmental stresses, induces the plant to produce high levels of ABA, and ABA may be a common mediator for all plant stresses.
Abstract: To investigate the abscisic acid (ABA) production of tomato (Mill.) plants in response to diurnal stressful temperatures, five-week old seedlings were exposed to day/night temperatures of 10/5, 15/10, 25/15, 35/25, or 45/35 C. The daylength was 16 hours with a light intensity of approximately 400 microeinsteins per meter per second. Plant tops were sampled at 12, 24, 48, and 72 hours. Free, alkaline-hydrolyzable (conjugated), and total ABA quantities were measured using standard gas chromatographic techniques. All temperature regimes significantly increased both free and conjugated ABA levels over concentrations in control plants (25/15 C). The highest ABA levels were observed in plants exposed to the coolest temperature of 10/5 C. Since normal water potentials were obtained in plants of all treatments, the observed ABA response was not due to temperature-induced water stress. Therefore, temperature stress, like several other environmental stresses, induces the plant to produce high levels of ABA. Because of the similar involvement of ABA in temperature-induced and other environmental stresses, ABA may be a common mediator for all plant stresses.

Journal ArticleDOI
TL;DR: Light-induced coleoptile stimulation and mesocotyl suppression in etiolated Avena sativa (cv. Lodi) has been quantitated and can be explained by the action of phytochrome.
Abstract: Light-induced coleoptile stimulation and mesocotyl suppression in etiolated Avena sativa (cv. Lodi) has been quantitated. Etiolated seedlings showed the greatest response to light when they were illuminated 48 to 56 hours after imbibition. Two low-irradiance photoresponses for each tissue have been described. Red light was 10 times more effective than green and 1,000 times more effective than far red light in evoking these responses. The first response, which resulted in a 45% mesocotyl suppression and 30% coleoptile stimulation, had a threshold at 10−14 einsteins per square centimeter and was saturated at 3.0 × 10−12 einsteins per square centimeter of red light. This very low-irradiance response could be induced by red, green, or far red light and was not photoreversible. Reciprocity failed if the duration of the red illumination exceeded 10 minutes. The low-irradiance response which resulted in 80% mesocotyl suppression and 60% coleoptile stimulation, had a threshold at 10−10 einsteins per square centimeter and was saturated at 3.0 × 10−8 einsteins per square centimeter of red light. A complete low-irradiance response could be induced by either red or green light but not by far red light. This response could be reversed by a far red dose 30 times greater than that of the initial red dose for both coleoptiles and mesocotyls. Reciprocity failed if the duration of the red illumination exceeded 170 minutes. Both of these responses can be explained by the action of phytochrome.

Journal ArticleDOI
TL;DR: A large seasonal variation in polyphenol oxidase activity may result from a decrease in enzyme content rather than inhibition of the enzyme present.
Abstract: Polyphenol oxidase activity (E.C. 1.14.18.1) has been found in two enzyme species isolated from thylakoid membranes of spinach chloroplasts. The proteins were released from the membrane by sonication and purified >900-fold by ammonium sulfate precipitation, gel filtration, and ion-exchange chromatography. The enzymes appear to be the tetramer and monomer of a subunit with a molecular weight of 42,500 as determined by lithium dodecyl sulfate gel electrophoresis. The higher molecular weight enzyme is the predominant form in freshly isolated preparations but on aging or further purification, the amount of lower molecular weight enzyme increases at the expense of the higher.Sonication releases polyphenol oxidase from the membrane largely in the latent state. C(18) fatty acids, especially linolenic acid, are potent activators of the enzymic activity. In the absence of added fatty acids, the isolated enzyme spontaneously, but slowly, activates with time.Purified polyphenol oxidase utilizes o-diphenols as substrates and shows no detectable levels of monophenol or p-diphenol oxidase activities. The K(m) values for 3,4-dihydroxyphenylalanine and O(2) are 6.5 and 0.065 millimolar, respectively. Suitable substrates include chlorogenic acid, catechol, caffeic acid, pyrogallol, and dopamine; however, the enzyme is substrate-inhibited by the last four at concentrations near their K(m) A large seasonal variation in polyphenol oxidase activity may result from a decrease in enzyme content rather than inhibition of the enzyme present.

Journal ArticleDOI
TL;DR: Xylem fluid was analyzed for numerous solutes to characterize chemically the sap as a medium for forming and transporting metal complexes, and it was demonstrated that extrapolation of xylem-fluid analyses to whole-plantxylem sap is valid only for sap samples collected shortly after topping a plant.
Abstract: Xylem fluid was analyzed for numerous solutes to characterize chemically the sap as a medium for forming and transporting metal complexes The stem exudate was collected hourly for 8 hours from topped 31-day-old soybean (Glycine max L Merr) and 46-day-old tomato (Lycopersicon esculentum Mill) plants grown in normal (05 micromolar) and Za-phytotoxic nutrient solutions Soybean plants were grown in the normal and high-Zn solutions for 24 days; tomato plants were grown for 32 days The exudate was analyzed for seven organic acids, 22 amino acids, eight inorganic solutes, apparent ionic strength, and pH Significant changes in many solutes occurred over the 8-hour sampling period These fluctuations depended on plant species, individual solute, and Zn treatment, and demonstrated that extrapolation of xylem-fluid analyses to whole-plant xylem sap is valid only for sap samples collected shortly after topping a plant Exudate pH decreased over the 8-hour period for both species; exudate ionic strength increased for tomato and decreased for soybean At the normal-Zn treatment (0 to 1 hour), the highest acid micromolar concentrations in soybean exudate were: asparagine, 2,583; citric, 1,706; malic, 890; and malonic, 264 Under the same conditions, the highest acid micromolar concentrations in tomato exudate were: maleic, 1,206; malic, 628; glutamine, 522; citric, 301; and asparagine, 242 Cysteine and methionine were above detection limits only in soybean exudate Zinc phytotoxicity caused significant changes in many solutes The analyses reported here provide a comprehensive data base for further studies on metal-complex equilibria in xylem fluid

Journal ArticleDOI
TL;DR: A series of non-photoautotrophic mutants of Chlamydomonas reinhardii was isolated by replica-plating mutagenized cells which had been grown in the dark, finding that many of these acetate-requiring mutants are photosensitive, and 15 which show uniparental inheritance.
Abstract: A series of non-photoautotrophic mutants of Chlamydomonas reinhardii was isolated by replica-plating mutagenized cells which had been grown in the dark. Many of these acetate-requiring mutants are photosensitive, showing poor growth on acetate medium in the light, but normal growth in the dark. Biochemical characterization showed that the photosensitive mutants all had specific lesions in photosynthesis or photosynthetic pigment accumulation. The acetate-requiring mutants which were not photosensitive were all able to fix CO(2). Among the light-sensitive mutants are 15 which show uniparental inheritance. These include six with specific lesions in photosystem II and one with an altered large subunit of ribulose-1,5-bisphosphate carboxylase. Since these two classes of uniparental mutants have been rare or not previously reported, it seems likely that photosensitivity is an important factor which limited their detection in previous mutant isolation experiments.

Journal ArticleDOI
TL;DR: Of the 43 plant families investigated, the Fe-containing superoxide dismutase was found in three families: Gingkoaceae, Nymphaceae, and Cruciferae.
Abstract: Superoxide dismutases (EC 11511) in vascular plants representing different evolutionary levels were characterized using polyacrylamide gel electrophoresis The three forms of the enzyme were distinguished from each other based on the following criteria: a) the Cu-Zn enzyme is sensitive to cyanide wherease the Fe and Mn enzymes are not; and b) the Cu-Zn and Fe enzymes are inhibited by H2O2 whereas the Mn enzyme is H2O2-resistant Of the 43 plant families investigated, the Fe-containing superoxide dismutase was found in three families: Gingkoaceae, Nymphaceae, and Cruciferae

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TL;DR: It is established that the ability to tolerate and to circumvent the toxic effects of selenium, characteristic of the accumulator species of Astragalus, is associated with a reduced incorporation of this element into protein.
Abstract: Protein fractions from three selenium-tolerant and three selenium-sensitive Astragalus species, grown in the presence of [75Se]selenate, were analyzed for their selenium content. Though tolerant species are known to accumulate considerably more selenium than do sensitive plants, protein fractions from the three selenium accumulators were found to contain significantly less selenium (0.46 to 0.57 picomoles selenium per milligram protein) than did protein fractions from the three nonaccumulators (4.17 to 5.02 picomoles selenium per milligram protein). Under similar conditions, seedlings of Vigna radiata (L.) Wilczek had taken up selenium (6.31 picomoles selenium per milligram protein) at levels comparable to those observed in the proteins of the nonaccumulator Astragali. These results establish that the ability to tolerate and to circumvent the toxic effects of selenium, characteristic of the accumulator species of Astragalus, is associated with a reduced incorporation of this element into protein.

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TL;DR: It is found that rehydrating leaf discs of cowpea show increasing leakiness in proportion to the extent of prior desiccation, whereas Selaginella lepidophylla Spring.
Abstract: The leakage of solutes from foliar tissue is utilized as a dynamic measure of apparent changes in membrane integrity in response to desiccation. It is found that rehydrating leaf discs of cowpea (Vigna sinensis [L.] Endl.) show increasing leakiness in proportion to the extent of prior desiccation, whereas Selaginella lepidophylla Spring., a resurrection plant, does not. The elevated leakage rate of cowpea after desiccation recovers with time, and the passage of time in the stressed condition results in reduced subsequent leakiness. These characteristics are interpreted as suggesting that the leakage of solute reflects the condition of cellular membranes, and that desiccation stress leads to lesions in the membranes. The kinetics of solute leakage is suggested as a simple means of following changes in membrane lesions and associated features of membrane repair and hardening.

Journal ArticleDOI
TL;DR: The soluble enzyme fraction obtained from the albino-3 mutant was shown to be almost totally defective in enzyme activity required for the biosynthesis of [(14)C]geranylgeranyl pyrophosphate from [1-C]isopentenyl pyroph phosphate.
Abstract: The conversion of isopentenyl pyrophosphate to phytoene in Neurospora crassa requires both a soluble and a particulate fraction. Soluble and particulate enzyme fractions obtained from light-treated and dark-grown wild type, albino-1, albino-2, albino-3, and white collar-1 strains were mixed in various combinations, and the activity for conversion of [1-(14)C]isopentenyl pyrophosphate to phytoene was assayed. From such experiments it can be concluded that: (a) albino-3 is defective in the soluble fraction; (b) albino-2 is defective in the particulate fraction; (c) the in vivo light treatment increases the enzyme activity in the particulate fraction; (d) this light effect occurs in wild type, albino-1, and albino-3 strains; and (e) enzyme activity is present in the particulate fraction obtained from the white collar-1 mutant, but the in vivo light treatment does not cause an increase in this activity. To measure directly the level of particulate enzyme activity, [(14)C]geranylgeranyl pyrophosphate was used as a substrate. This compound, which is not available commercially, was synthesized enzymically using extracts of pea cotyledons. Particulate enzyme fractions obtained from wild type, albino-1, and albino-3 strains incorporate [(14)C]geranylgeranyl pyrophosphate into phytoene, and this activity is higher in extracts obtained from light-treated cultures. The particulate fraction obtained from the white collar-1 mutant also incorporates [(14)C]geranylgeranyl pyrophosphate into phytoene, but the in vivo light treatment does not cause an increase in this activity. No incorporation occurs when particulate fractions obtained from either dark-grown or light-treated albino-2 cultures are assayed. The soluble enzyme fraction obtained from the albino-3 mutant was shown to be almost totally defective in enzyme activity required for the biosynthesis of [(14)C]geranylgeranyl pyrophosphate from [1-(14)C]isopentenyl pyrophosphate. An in vivo light treatment increases the level of this activity in wild type, albino-1, albino-2, and albino-3 strains, but not in the white collar-1 mutant. A model is presented to account for all of the results obtained in this investigation. It is proposed that the white collar-1 strain is a regulatory mutant blocked in the light induction process, whereas the albino-1, albino-2, and albino-3 strains are each defective for a different enzyme in the carotenoid biosynthetic pathway.

Journal ArticleDOI
TL;DR: It is suggested that uptake of monovalent phosphate in Lemna gibba proceeds by an H(+) cotransport dependent on the proton electrochemical potential difference and, hence, on the activity of an H (+) -extrusion pump.
Abstract: High rates of phosphate uptake into phosphate-starved Lemna gibba L. G1 were correlated with a high membrane potential (pd = −220 millivolts). In plants maintaining a low pd (−110 millivolts), the uptake rate was only 20% of that of high-pd plants. At the onset of phosphate transport, the membrane of high-pd plants was transiently depolarized. This effect was much smaller in low-pd plants. Light stimulated phosphate uptake and the repolarization upon phosphate-induced depolarization, especially in plants grown without sucrose. The phosphate uptake rate was optimal at pH 6 and decreased with increasing pH, corresponding to the phosphate-induced pd changes. Phosphate starvation stimulated the uptake and increased the phosphate-induced depolarization, thus indicating that phosphate uptake depends on the intracellular phosphate level. It is suggested that uptake of monovalent phosphate in Lemna gibba proceeds by an H+ cotransport dependent on the proton electrochemical potential difference and, hence, on the activity of an H+ -extrusion pump.

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TL;DR: Young barley seedlings were stressed using nutrient solutions containing NaCl or polyethylene glycol and measurements were made of leaf growth, water potential, osmotic potential and turgor values of both growing (basal) and nongrowing (blade) tissues, hypothesized that blades have high water potential values and are generally unresponsive to stress.
Abstract: Young barley seedlings were stressed using nutrient solutions containing NaCl or polyethylene glycol and measurements were made of leaf growth, water potential, osmotic potential and turgor values of both growing (basal) and nongrowing (blade) tissues. Rapid growth responses similar to those noted for corn (Plant Physiology 48: 631-636) were obtained using either NaCl or polyethylene glycol treatments by which exposure of seedlings to solutions with water potential values of −3 to −11 bars effected an immediate cessation of leaf elongation with growth resumption after several minutes or hours. Latent periods were increased and growth resumption rates were decreased as water potential values of nutrient solutions were lowered. In unstressed transpiring seedlings, water potential and osmotic potential values of leaf basal tissues were usually −6 to −8 bars, and −12 to −14 bars, respectively. These tissues began to adjust osmotically when exposed to any of the osmotic solutions, and hourly reductions of 1 to 2 bars in both water potential and osmotic potential values usually occurred for the first 2 to 4 hours, but reduction rates thereafter were lower. When seedlings were exposed to solutions with water potential values lower than those of the leaf basal tissues, growth resumed about the time water potential values of those tissues fell to that of the nutrient solution. After 1 to 3 days of seedling exposure to solutions with different water potential values, cumulative leaf elongation was reduced as the water potential values of the root medium were lowered. Reductions in water potential and osmotic potential values of tissues in leaf basal regions paralleled growth reductions, but turgor value was largely unaffected by stress. In contrast, water potential, osmotic potential, and turgor values of leaf blades were usually changed slightly regardless of the degree and duration of stress, and blade water potential values were always higher than water potential values of the basally located cells. It is hypothesized that blades have high water potential values and are generally unresponsive to stress because water in most of the mesophyll cells in this area does not exchange readily with water present in the transpiration stream.

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TL;DR: A model which describes the ionic atmosphere in the cell walls as a result of simultaneous electrostatic interactions between free ions (Donnan effect) and specific association equilibria, including acido-basic ones correctly accounted for the whole set of experimental results and predicted the values of the unmeasurable local concentrations and pH.
Abstract: Purified cell walls were prepared from roots of Horse bean (Vicia faba L., var. minor) and Yellow Lupine (Lupinus luteus L.). Two methods were used: (a) grinding and (b) lysis of the endocellular contents by Triton X-100. The Ca2+, Mg2+, and K+ contents were determined after incubation in various solutions in such a manner that the measurements gave access to the undisturbed equilibrium contents. The results were used to test a model which describes the ionic atmosphere in the cell walls as a result of simultaneous electrostatic interactions between free ions (Donnan effect) and specific association equilibria, including acido-basic ones. This model correctly accounted for the whole set of experimental results and predicted the values of the unmeasurable local concentrations and pH.