Showing papers in "Plant Physiology in 1969"
TL;DR: The energy balance and the diffusion porometer measurements indicate that the boundary layer resistances of leaves in the field are substantially less than those predicted from heat transport formulas based on wind flow and leaf size.
Abstract: Modifications of the design and calibration procedure of a diffusion porometer permit determinations of stomatal resistance which agree well with results obtained by leaf energy balance. The energy balance and the diffusion porometer measurements indicate that the boundary layer resistances of leaves in the field are substantially less than those predicted from heat transport formulas based on wind flow and leaf size.
266 citations
TL;DR: The amount of callose in sieve tube cells correlated with levels of β-1, 3-glucanase, suggesting that this enzyme played a role in the degradation ofβ-1- 3- glucans.
Abstract: The endo-beta-1, 3-glucanase (beta-1, 3-glucan 3-glucanhydrolase, EC 3216) extracted from Phaseolus vulgaris L cv Red Kidney had a pH optimum of 5 and a temperature optimum of 50 C Excision of plant tissue resulted in an increase in beta-1, 3-glucanase activity after a 6-hour lag period The increase could be prevented by indole-3-acetic acid, gibberellic acid, and cytokinins Ethylene (half-maximal concentration = 01 microliter/liter) promoted the synthesis of beta-1, 3-glucanase, and 10% CO(2) overcame some of the ethylene effect Cycloheximide prevented the induction of beta-1, 3-glucanase, but actinomycin D and chromomycin A(3) had only a partial effect The amount of callose in sieve tube cells correlated with levels of beta-1, 3-glucanase, suggesting that this enzyme played a role in the degradation of beta-1, 3-glucans
199 citations
TL;DR: The use of diphenylcarbazide as an electron donor coupled to the photoreduction of 2,6-dichlorophenolindophenol by tris-washed chloroplasts or subchloroplast fragments provides a simple and sensitive assay for photosystem 2 of chloroplast.
Abstract: The use of diphenylcarbazide as an electron donor coupled to the photoreduction of 2,6-dichlorophenolindophenol by tris-washed chloroplasts or subchloroplast fragments provides a simple and sensitive assay for photosystem 2 of chloroplasts. By varying the concentration of tris buffer at pH 8.0 during an incubation period it is shown that the destruction of oxygen evolution activity is accompanied by a corresponding emergence of an ability to photooxidize diphenylcarbazide, as evidenced by absorbance changes due to diphenylcarbazide at 300 nm. The temperature-sensitive oxidation of diphenylcarbazide is inhibited by DCMU and by high ionic strengths. This activity appears to measure the primary photochemical reaction of photosystem 2.
187 citations
TL;DR: The chemical mechanism of ethylene production from CEPA involves the nucleophilic attack on -the phosphonate dianion by a water molecule and the concerted elimination of chlorine, leading to direct formation of phosphate and chloride as shown in equation (I).
Abstract: 2-Chloroethylphosphonic acid (CEPA. "Amchem 66-329", "Ethrel"; ref. 1), a new plant growth regulator, degrades to yield ethylene in an alkaline solution. When applied to plants, it has been very effective in causing responses characteristic of ethylene treatment (3, 4, 6, 7). The formation of ethvlene or its alkene homologs from CEPA or its homologs was studied and deFcribed in detail in 1963 by Maynard and Swan (5) including the probable reaction mechanism. Nevertheless, several reports have since appeared describing the same reaction wi.thout citing (4, 8) or properly acknowledging (3) their work. Some investigators (7) have since suggested that the growth regulatory action of CEPA is due to the stimulation of ethylene production within the plant tissues without discussing the fact that CEPA itself is the ethylene producer. The chemical mechanism of ethylene production from CEPA suggested by Maynard and Swan (5) involves the nucleophilic attack on -the phosphonate dianion by a water molecule and the concerted elimination of chlorine, leading to direct formation of phosphate and chloride as shown in equation (I). Probably the OH-ion may also serve as an nucleophile in the reaction.
182 citations
TL;DR: Evidence is provided that 2-chloroethylphosphonic acid breaks down in the presence of a base to form ethylene with an apparent release of chloride and phosphonate with a second-order reaction, possibly involving the alkali in reaction with CEPA.
Abstract: Strong growth regulating properties have been observed for 2-chloroethylphosphonic acid (Amchem 66-329) when applied to plants, and the regulatory effects have been attributed to the liberation of ethylene within plants (5). Many regulatory effects of this chemical resemble the effects of ethylene, including the induction of ripening in bananas and tomatoes (4), flowering in pineapple, and abscission and various epinastic responses (1). The present report provides evidence that 2-chloroethylphosphonic acid (CEPA) breaks down in the presence of a base to form ethylene with an apparent release of chloride and phosphonate. To illustrate the decomposition reaction, 5 ml of CEPA at 2 X 10-4 M in a 1000 ml reaction flask, with either NaOH (8 X 10-4 M) or 500 mg of etiolated pea epicotyls, evolve ethylene as shown in figure 1. The production of ethylene occurs not only in the presence of the plant tissue, but also in the presence of added base. In this experiment 1.0 jumole of CEPA was present initially and 0.98 ,tmole of ethylene had been produced 48 hr after addition of NaOH, indicating essentially complete conversion of the CEPA to ethylene. The logarithmic type of time curve in the presence of added base suggests a second-order reaction, possibly involving the alkali in reaction with CEPA. The rate of the reaction is increased by higher levels of added alkali. That the gas involved is ethylene was determined by gas chromatography (2) and its identity was confirmed by reaction with mercury perchlorate (6). The gas chromatographic peak considered to be ethylene was 99.2 % removed by introduction into the reaction flask of a paper wick moistened with Hg(C104)2. The decomposition of CEPA to ethylene should bring about the release of phosphonate and chloride. As an indication of phosphonate formation, in a test run concurrently with the experiment in figure 1 phosphate was measured by Allen's molybdate color test, assuming a fairly ready oxidation of the phos-
180 citations
TL;DR: It is suggested that monoterpenes may serve as substrates for energy metabolism in the secretory cells after other stored substrates have been depleted.
Abstract: Two types of experimental evidence are presented which suggest that the monoterpenes of peppermint (Mentha piperita L.) are subject to metabolic turnover. In kinetic studies with 14CO2, peppermint cuttings rapidly incorporate label into the monoterpenes and then lose most of the label from the monoterpenes, without corresponding changes in the amount of monoterpenes present. When peppermint plants are grown in a controlled environment (16-hr photoperiod, 24° day, 8° night) and analyzed at intervals leaf pair by leaf pair, there is a steady increase in monoterpenes until the time of floral initiation, followed by a rapid decrease. It is suggested that monoterpenes may serve as substrates for energy metabolism in the secretory cells after other stored substrates have been depleted.
176 citations
TL;DR: Absorption of Cu(2+), Zn( 2+), and Mn(2+) was concluded to be coupled to oxidative phosphorylation, and specifically to energy-conservation Site I.
Abstract: The absorption of Cu2+, Zn2+, and Mn2+ by leaf tissue of 4-month old sugarcane plants (Saccharum officinarum L., var. H53-263) has been investigated. After the “apparent free space” fraction was desorbed, the absorption of Cu2+, Mn2+, and Zn2+ yielded a curve typical of many ion uptake processes when measured as a function of the external concentration. However, only 1 absorption mechanism was evident for each cation. The pH optimum for Cu2+ and Zn2+ uptake was 5.0 to 6.0, whereas that for Mn2+ absorption was 4.5 to 6.0. Absorption was competitively inhibited by H+, and this inhibition was reversible when 0.5 mm Ca2+ was present. Cu2+ and Zn2+ were absorbed through the same carrier sites, as concluded from their mutually competitive activities. Mn2+ was absorbed through a second, independent mechanism. Uptake of each cation was strongly inhibited by uncouplers of oxidative phosphorylation, by Amytal and Nembutal2, by 5 × 10−2m succinate, and by ADP and Pi. Absorption of Cu2+, Zn2+, and Mn2+ was concluded to be coupled to oxidative phosphorylation, and specifically to energy-conservation Site I.
167 citations
TL;DR: Low levels of ADP-glucose pyrophosphorylase activity in the maize mutants correlate well with the low levels of starch found in the endosperm of these mutants.
Abstract: ADP-Glucose pyrophosphorylase activity has been detected in relatively low amounts in the embryos and endosperms of sh(2) and bt(2) mutant maize seeds. The total enzyme activities in sh(2) and bt(2) were about 12% and 17% respectively, of that found in starchy maize seeds (Dekalb 805). The ADP-glucose pyrophosphorylases from the starchy and mutant maize seeds were activated by 3-phosphoglycerate. However, the extent of the activation of the sh(2) enzyme was not as great as that observed with the bt(2) and Dekalb 805 enzymes. The low levels of ADP-glucose pyrophosphorylase activity in the maize mutants correlate well with the low levels of starch found in the endosperm of these mutants.
164 citations
TL;DR: Experiments in which chloroplasts were washed with tris and tricine buffers at different pH's indicated that the non-protonated (uncharged) form of tris was inhibitory to the Hill reaction while the protonated form oftris and the zwitterionic forms oftricine were non-inhibitory.
Abstract: Experiments in which chloroplasts were washed with tris and tricine buffers at different pH's indicated that the non-protonated (uncharged) form of tris was inhibitory to the Hill reaction while the protonated form of tris and the zwitterionic forms of tricine were non-inhibitory. Buffers analogous to tris and tricine gave similar results. Photoreduction of NADP could be restored to the inhibited chloroplasts by adding the reduced forms of p-hydroquinone, p-aminophenol, p-phenylenediamine, benzidine, semicarbazide, and dihydroxydiphenyl, all of which donated electrons to photosystem II. Photoreduction of ferricyanide was shown with those donor systems (benzidine and semicarbazide) which did not react chemically with ferricyanide. Photophosphorylation was also restored with all of the electron donors except semicarbazide.
158 citations
TL;DR: The mechanism of stomatal opening in leaves is studied in this paper, where the primlary solute accumulating in the light was soluble carbohydrate produced during photosynthesis, because guard cells possess chloroplasts and other epidermal cells do not.
Abstract: Understanding the mechanism of stomatal opening in leaves is important because stomata are the avenues for CO, and H.,O diffusion. Stomata in most species open in the light when the guard cells that encompass the pores take up water and increase in turgor relative to adjacent epidermal cells (1). Thus stomatal opening is likely an osmotic phenomenon that depends upon the accumulation of solute in the guard cells, and during opening tllis accumulation has been reported to range from 0.: M to 0.5 M in various experiments (2). For over 100 years botanists have believed that the primlary solute accumulating in the light was soluble carbohydrate produced during photosynthesis, because guard cells possess chloroplasts and other epidermal cells do not. However careful quantitative work [reviewed in (3)] failed to provide strong support for this view.
156 citations
TL;DR: It will be shown that the fluorescence yield can be changed at will simply by varying the composition of the suspension medium, and may possibly be governed not only by the oxidation state olf the Q-pool, but also by ion induced structural changes.
Abstract: At room temperature, the fluorescence of chloroplasts in vivo and in vitro originates nearly exclusively from the chlorophyll of the oxygen evolving system II of the photosynthetic apparatus. The yield and the kinetics of this light emission are closely coupled to the primary photochemical events of photosystem II. Fluorescence studies, therefore, have contributed much to our knowledge about the water oxidizing photoact. According to Duysens and Sweers i(3) the fluorescence yield is determined by the oxidation state of the primary electron acceptor Q: when Q is oxidized, the fluorescence is quenched and, consequently, a low yield is observed; since reduced Q1(Q-) does not quench, a maximal fluorescence yield indicates a complete reduction of the electron acceptor pools containing Q. Several anomalies in the fluorescence kinetics of intact algae have led to the assumption of an non-homogeneous pool Q containing, even after the primary activation step (8), active and inactive oxidants Qa and Qi' (1,2, 4,12). Both forms of Q are thought to quench the fluorescence in their oxidized states, albeit with slightly different effectiveness. A photoreduction of the total pool Q requires an activation of any Qi' to Qa, which according to some authors (1,4,12) is sensitized by photosystem I. In this communication, we wish to report on an overriding influence of the ionic environment on the fluorescence yield of isolated chloroplasts. It will be shown that the fluorescence yield can be changed at will simply by varying the composition of the suspension medium. Accordingly, the fluorescence yield may possibly be governed not only by the oxidation state olf the Q-pool, but also by ion induced structural changes.
TL;DR: The distribution pattern for glycolate oxidase, glyoxylate reductase, catalase, and part of the malate dehydrogenase indicated that these enzymes exist together in this organelle, and this is inconsistent with current hypotheses about the mechanism of photorespiration.
Abstract: Leaves of 10 plant species, 7 with photorespiration (spinach, sunflower, tobacco, pea, wheat, bean, and Swiss chard) and 3 without photorespiration (corn, sugarcane, and pigweed), were surveyed for peroxisomes. The distribution pattern for glycolate oxidase, glyoxylate reductase, catalase, and part of the malate dehydrogenase indicated that these enzymes exist together in this organelle. The peroxisomes were isolated at the interface between layers of 1.8 to 2.3 m sucrose by isopycnic nonlinear sucrose density gradient centrifugation or in 1.95 m sucrose on a linear gradient. Chloroplasts, located by chlorophyll, and mitochondria by cytochrome c oxidase, were in 1.3 to 1.8 m sucrose. In leaf homogenates from the first 7 species with photorespiration, glycolate oxidase activity ranged from 0.5 to 1.5 mumoles x min(-1) x g(-1) wet weight or a specific activity of 0.02 to 0.05 mumole x min(-1) x mg(-1) protein. Glyoxylate reductase activity was comparable with glycolate oxidase. Catalase activity in the homogenates ranged from 4000 to 12,000 mumoles x min(-1) x g(-1) wet weight or 90 to 300 mumoles x min(-1) x mg(-1) protein. Specific activities of malate dehydrogenase and cytochrome oxidase are also reported. In contrast, homogenates of corn and sugarcane leaves, without photorespiration, had 2 to 5% as much glycolate oxidase, glyoxylate reductase, and catalase activity. These amounts of activity, though lower than in plants with photorespiration, are, nevertheless, substantial. Peroxisomes were detected in leaf homogenates of all plants tested; however, significant yields were obtained only from the first 5 species mentioned above. From spinach and sunflower leaves, a maximum of about 50% of the marker enzyme activities was found to be in these microbodies after homogenization. The specific activity for peroxisomal glycolate oxidase and glyoxylate reductase was about 1 mumole x min(-1) x mg(-1) protein; for catalase. 8000 mumoles x min(-1) x mg(-1) protein, and for malate dehydrogenase, 40 mumoles x min(-1) x mg(-1) protein. Only small to trace amounts of marker enzymes for leaf peroxisomes were recovered on the sucrose gradients from the last 5 species of plants. Bean leaves, with photorespiration, had large amounts of these enzymes (0.57 mumole of glycolate oxidase x min(-1) x g(-1) tissue) in the soluble fraction, but only traces of activity in the peroxisomal fraction. Low peroxisome recovery from certain plants was attributed to particle fragility or loss of protein as well as to small numbers of particles in such plants as corn and sugarcane. Homogenates of pigweed leaves (no photorespiration) contained from one-third to one-half the activity of the glycolate pathway enzymes as found in comparable preparations from spinach leaves which exhibit photorespiration. However, only traces of peroxisomal enzymes were separated by sucrose gradient centrifugation of particles from pigweed. Data from pigweed on the absence of photorespiration yet abundance of enzymes associated with glycolate metabolism is inconsistent with current hypotheses about the mechanism of photorespiration. Most of the catalase and part of the malate dehydrogenase activity was located in the peroxisomes. Contrary to previous reports, the chloroplast fractions from plants with photo-respiration did not contain a concentration of these 2 enzymes, after removal of peroxisomes by isopycnic sucrose gradient centrifugation.
TL;DR: A scheme for the distribution of enzymes associated with glycolate metabolism and photorespiration is presented and it is possible that excess glyoxylate from the peroxisomes could return to the chloroplasts to be reduced to glycolates or oxidized to account for part of the CO(2) loss during photore Spiration.
Abstract: Chloroplasts, mitochondria, and peroxisomes from leaves were separated by isopycnic sucrose density gradient centrifugation. The peroxisomes converted glycolate-(14)C or glyoxylate-(14)C to glycine, and contained a glutamate: glyoxylate aminotransferase as indicated by an investigation of substrate specificity. The pH optimum for the aminotransferase was between 7.0 and 7.5, and the Km for l-glutamate was 3.6 mm and for glyoxylate, 4.4 mm. The reaction of glutamate plus glyoxylate was not reversible. The isolated peroxisomes did not convert glycine to glyoxylate nor glycine to serine.Peroxisomes did not oxidize glycolate or glyoxylate to CO(2). Chloroplasts could very slowly oxidize glyoxylate, but not glycolate, to CO(2). Chloroplast oxidation of glyoxylate was heat labile and widely distributed among plants. Oxidation was stimulated by light and oxygen. but was not inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU).A scheme for the distribution of enzymes associated with glycolate metabolism and photorespiration is presented. Glycolate biosynthesis occurs in the chloroplasts. In the peroxisomes, glycolate is oxidized with O(2) uptake to glyoxylate by glycolate oxidase, and the glyoxylate is converted to glycine by glutamate:glyoxylate aminotransferase. Further metabolism of glycine does not occur in the peroxisomes. It is possible that excess glyoxylate from the peroxisomes could return to the chloroplasts to be reduced to glycolate or oxidized to account for part of the CO(2) loss during photorespiration.
TL;DR: It is concluded that alpha-amylase is the major enzyme involved in the initial degradation of starch into more soluble forms while phosphorylase and beta-amymylase assist in the further conversion to free sugars.
Abstract: Starch, total α- and β-amylase, and phosphorylase levels and the zymogram patterns of these 3 starch-degrading enzymes were determined in the cotyledons of smooth pea (Pisum sativum L.) during the first 15 days of germination. Starch is degraded slowly in the first 6 days; during this time, α-amylase is very low, β-amylase is present at a constant level while phosphorylase gradually increases and reaches a peak on the fifth day. Beginning on the sixth day there is a more rapid degradation of starch which coincides with α-amylase production. One phosphorylase band and 2 β-amylase bands are present in the zymogram of the imbibed cotyledon. An additional phosphorylase band and 1 α-amylase band appear during germination. Seeds imbibed in benzyladenine, chloramphenicol, and in cycloheximide show retarded growth and slower starch degradation and enzyme production than the controls. We conclude that α-amylase is the major enzyme involved in the initial degradation of starch into more soluble forms while phosphorylase and β-amylase assist in the further conversion to free sugars.
TL;DR: It was shown that per gram fresh weight of roots, approximately 0.7 to 0.8 mumoles of K(+) were absorbed per mumole ofK(+) stimulated ATP hydrolysis, which was taken to mean that sufficient membrane associated ATPase exists to account for K(-) transport in the oat roots.
Abstract: Monovalent ion stimulated ATPase activity from oat (Avena sativa) roots has been found to be associated with various membrane fractions (cell wall, mitochondrial and microsomal) of oat roots. The ATPase requires Mg(2+) (or Mn(+2)) but is further stimulated by K(+) and other monovalent ions. The monovalent ions are ineffective in the absence of the divalent activating cation. The ATPase has been described with respect to monovalent ion specificity, temperature, pH, substrate specificity, and Mg(2+) and K(+) concentrations. It was further shown that oligomycin inhibits a part of the total ATPase activity and on the basis of the oligomycin sensitivity it appears that at least 2 membrane associated ATPases are being measured. The mitochondrial fraction is most sensitive to oligomycin and the microsomal fraction is least sensitive to oligomycin. The oligomycin insensitive ATPase appears to be stimulated more by K(+) than the oligomycin sensitive ATPase.It was further shown that per gram fresh weight of roots, approximately 0.7 to 0.8 mumoles of K(+) were absorbed per mumole of K(+) stimulated ATP hydrolysis. This result was obtained for a variety of K(+) concentrations and was taken to mean that sufficient membrane associated ATPase exists to account for K(+) transport in the oat roots.
TL;DR: The activity of pectin esterase and cellulase in abscission of citrus explants was studied and it was established that application of cycloheximide during the lag period and before cellulase activity can be measured inhibits to a certain extent the formation of cellulase.
Abstract: The activity of pectin esterase and cellulase in abscission of citrus explants was studied No relation was established between pectin esterase and abscission, while cellulase activity was markedly increased before abscission and for a certain period after excision IAA and cycloheximide delay abscission and cellulase activity, while ethylene and, to a lesser extent, GA3 accelerate them Application of cycloheximide during the lag period and before cellulase activity can be measured, inhibits to a certain extent the formation of cellulase An escape from the inhibitory effect of cycloheximide is detected when inhibitor is supplied at the end of the lag period
TL;DR: The average stomatal resistance for both surfaces of the leaf, which is the major diffusive resistance to water vapor, to a first approximation acts as an on-off switch and helps prevent further decline in leaf-water potential.
Abstract: Concurrent measurements of abaxial and adaxial stomatal resistance and leaf-water potentials of snap beans (Phaseolus vulgaris L.) in the field and growth chamber show that the stomata on the 2 surfaces of the leaflet react differently to water deficit. The stomata on the abaxial surface, which are about 7 times more numerous than on the adaxial surface, are not significantly affected at leaf-water potentials greater than —11 bars, but with further decrease in leaf-water potential, the resistance rapidly increases. On the other hand, the resistance of the adaxial stomata increases sharply at a leaf-water potential of about —8 bars and is constant at higher water potentials. The average stomatal resistance for both surfaces of the leaf, which is the major diffusive resistance to water vapor, to a first approximation acts as an on-off switch and helps prevent further decline in leaf-water potential. The relation between the leaf-water potential and the stomatal resistance links the soil-water potential to the transpiration stream as needed for soil-plant-atmosphere models.
TL;DR: This work demonstrates, for the first time, a physiological process specifically requiring K(+), and assuming that ion uptake is an integral part of stomatal opening, guard cells would appear to have an ion uptake mechanism of a degree of specificity previously unknown in higher plants.
Abstract: The effect of various ions on stomatal opening was studied in isolated epidermal strips of Vicia faba L. Stomata in strips floating on 10 mm KCl and in CO(2)-free air opened in light, closed in subsequent darkness, then opened fully again when illuminated. A light-activated highly specific effect of K(-) (and Rb(+)) on opening was found. When strips were floated on high concentrations (50 or 100 meq/liter) of Li(+), Na(+) or Cs(+), stomata opened but light had very little effect on the concentrations required for opening. With K(+), the opening produced in the dark was the same as with the other alkali ions. Light, however, lowered more than 100-fold the concentration of K(+) required for maximal opening. Thus only the effect of K(+) (and Rb(+)) was greatly accentuated by light. NH(4) (+) and Mg(2+) did not produce opening.No specific anion is required in association with K(+). Opening was the same when Cl(-), Br, and NO(3) (-) were used as counter ions, but was less when SO(4) (2-) was used, particularly at higher concentrations and in the dark.The results are discussed in relation to the recent proposal that the basis for stomatal opening is K(+) uptake in amounts sufficient to act as an osmotic agent. This work also demonstrates, for the first time, a physiological process specifically requiring K(+). Assuming that ion uptake is an integral part of stomatal opening, guard cells would appear to have an ion uptake mechanism of a degree of specificity previously unknown in higher plants.
TL;DR: Evidence is provided that the interaction of soybean and R. japonicum in some way controls nitrogenase activity, which results in a particular growth response in the plant.
Abstract: Highly efficient nitrogen fixation by nodulating bacteria is required for maximum production by leguminous plants. The symbiotic relationship between nodulating bacteria and legumes in nodule formation and nitrogen fixation is complex and variable (2). The Rhizobium and legume genotypes (strains and varieties) exert influences which determine the growth response of the host (3,4, 10, 11). The growth response may be poor or moderate to luxuriant, and these symbioses are referred to as ineffective and effective, respectively. Three ranges of effectiveness based on nitrogen content were used by Parker and Allen (12) to compare the growth response of clover inoculated with 35 strains of R. trifolii. Abel and Erdman (1) evaluated the response of field grown Lee soybeans to different strains of R. japonicum and concluded that some symbioses exhibited more effectiveness than others in increasing seed yield, protein percentage of seed, nodulation,, plant appearance and fresh plant weight. Effectiveness in nodulated soybean has not been compared with activity of the nitrogen fixing enzyme. Nitrogen fixing activity ini nodulated leguminous plants can be estimated rapidly and conveniently by the acetylene reduction assay using gas chromatographic techniques (7). Requirements for the reduction of acetylene and molecular nitrogen have been shown to be the same for intact soybean nodules (9) and for partially purified cell-free extracts of bacteroids (8). Using this assay would indirectly determine nitrogenase activity for particular soybeanRhizobium symblioses exhibiting ineffectiveness or effectiveness. The present report provides evidence that the interaction of soybean and R. japonicum in some way controls nitrogenase activity, which results in a particular growth response in the plant.
TL;DR: Phenylalanine ammonia-lyase activity is low in the external layers of intact mature grapefruit peel, and protein synthesis seems to be needed at both levels of ethylene evolution and enhancement of PAL activity.
Abstract: l-Phenylalanine ammonia-lyase (PAL) activity is low in the external layers (flavedo) of intact mature grapefruit peel. Flavedo discs evince upon incubation increasing PAL activity and ethylene production. Light has no effect in enhancing PAL activity in discs. Exogenous ethylene stimulates PAL activity in the flavedo of intact mature grapefruits (half maximum stimulation at 15 ppm); such activity rapidly decreases when fruit is removed from the ethylene containing atmosphere. Carbon dioxide inhibits both ethylene production and PAL activity of discs; exogenous ethylene only partly relieves PAL inhibition. Cycloheximide inhibits both PAL activity and ethylene production by flavedo discs. The same concentration of cycloheximide also inhibits PAL activity of discs in the presence of exogenous ethylene. Protein synthesis seems therefore to be needed at both levels of ethylene evolution and enhancement of PAL activity.
TL;DR: It was concluded that 1 of the roles of ethylene in abscission is to regulate the production of cellulase which in turn is required for cell separation.
Abstract: Cellulase (beta-1,4-glucan-glucanohydrolase EC 3.2.1.4) activity increased during abscission and was localized in the cell separation layer of Phaseolus vulgaris L. cv. Red Kidney (bean), Gossypium hirsutum L. cv. Acala 4-42 (Cotton) and Coleus blumei Benth. Princeton strain (Coleus) abscission zone explants. Cellulase activity was optimum at pH 7, was reduced by one-half after heating to 55 degrees for 10 min, and was associated with the soluble components of the cell. Explants treated with aging retardants (indoleacetic acid, (6)N-benzyladenine, and coumarin), CO(2), actinomycin D or cycloheximide had less cellulase activity than untreated controls. Ethylene increased cellulase activity of aged explants after a 3-hr lag period but had no effect on cellulase activity of freshly excised explants. It was concluded that 1 of the roles of ethylene in abscission is to regulate the production of cellulase which in turn is required for cell separation.
TL;DR: The efflux of K(+) from the pulvinar cells of Mimosa pudica was shown to increase substantially during the seismonastic reaction, and this result is shown to indicate a decrease in sigma (reflection coefficient) of pulpvinar cell membrane for potassium salts which could account for the pulvini cell turgor decrease.
Abstract: The efflux of K + from the pulvinar cells of Mimosa pudica was shown to increase substantially during the seismonastic reaction. This result is shown to indicate a decrease in σ (reflection coefficient) of pulvinar cell membrane for potassium salts which could account for the pulvinar cell turgor decrease during the seismonastic reaction. Membrane potentials and concentrations of Ca 2+ , K + , Cl - , S, and P were measured in the top and bottom halves of pulvini. Pulvinar cells showed a large negative membrane potential, cell vacuole relative to external solution, but no significant difference in membrane potential could be detected between upper and lower pulvinar cells. A large difference in K + and Cl - concentration between top and bottom pulvinar halves was evident in reactive pulvini but not in unreactive pulvini. The effect of K + concentration on plant growth and leaf reactivity was also investigated.
TL;DR: Neither NAA nor kinetin at any concentration tested stimulated tracheary element formation in the absence of an effective level of the other hormone, however, 2,4-D at 10(-7) or 10(-6)m promoted both cell proliferation and tracheARY element differentiation in the presence of an exogenous cytokinin.
Abstract: The relationship between tracheary element differentiation, cell proliferation and growth hormones was examined in agar-grown soybean callus. The time course of cell division and tracheary element formation in tissues grown on a medium containing 5 × 10−7m kinetin and 10−5m NAA was determined by means of maceration technique. After a slight lag period, a logarithmic increase in cell number was observed through the twelfth day of the culture period. Cell numbers increased at a considerably slower rate after the twelfth day. The rate of tracheary element formation varied with the rate of cell proliferation. Tracheary elements increased logarithmically during the log phase of growth. As the rate of cell division decreased after the twelfth day of culture, the rate of tracheary element formation also decreased. In the presence of 10−5m NAA, cell number increased as the kinetin concentration was increased between 10−9 and 10−6m. However, tracheary element formation was not initiated unless the kinetin concentration was 5 × 10−8m or above. When the Biloxi callus was subcultured repeatedly on media containing 10−8m kinetin, a tracheary element-free population of cells was obtained. This undifferentiated tissue produced tracheary elements upon transfer to a medium containing 5 × 10−7m kinetin. In the presence of 5 × 10−7m kinetin, NAA stimulated cell proliferation between 10−7 and 10−5m, but no tracheary elements were formed without auxin, or with 10−7m NAA. Neither NAA nor kinetin at any concentration tested stimulated tracheary element formation in the absence of an effective level of the other hormone. However, 2,4-D at 10−7 or 10−6m promoted both cell proliferation and tracheary element differentiation in the absence of an exogenous cytokinin.
TL;DR: While light doubled ethylene production from the lettuce seeds, its effect was not mediated by the phytochrome system since both red and far-red light had a similar effect.
Abstract: Ethylene increased the germination of freshly imbibed lettuce (Lactuca sativa L. var. Grand Rapids) seeds. Seeds receiving either red or far-red light or darkness all showed a positive response to the gas. However, ethylene was apparently without effect on dormant seeds, those which failed to germinate after an initial red or far-red treatment. Carbon dioxide, which often acts as a competitive inhibitor of ethylene, failed to clearly reverse ethylene-enhanced seed germination. While light doubled ethylene production from the lettuce seeds, its effect was not mediated by the phytochrome system since both red and far-red light had a similar effect.
TL;DR: Results of the chemical analyses of sugar constituents as well as the measurements of Sucrose synthetase activity show that the scutellum is the site of sucrose synthesis in the germinating rice seeds and it is supported that glucose derived from the reserve starch in endosperm is transported to scUTellum, where it is converted to sucrose.
Abstract: In a close parallel to the developmental pattern of α-amylase activity, a rapid increase of maltase activity occurred in the endosperm tissue of germinating rice seeds after about 4 days of the seed imbibition. The overall pattern of the 2 hydrolytic enzyme activities strongly suggest that amylolytic breakdown is the major metabolic route of starch utilization in the germinating rice seeds. Results of the chemical analyses of sugar constituents as well as the measurements of sucrose synthetase activity show that the scutellum is the site of sucrose synthesis in the germinating rice seeds. It is thus supported that glucose derived from the reserve starch in endosperm is transported to scutellum, where it is converted to sucrose. Sucrose is further mobilized to the growing tissues, shoots and roots.
TL;DR: Substrate specificity studies indicate that of several fatty acids, ricinoleate is oxidized most rapidly by the preparation from the maturing seed while palmitate and linoleate are oxidizedMost rapidly by extracts obtained from tissue germinated for 4 days.
Abstract: In the maturing castor bean seed (Ricinus communis), maximum beta-oxidation appears at 28 days after flowering and in the germinating seed, 4 days after germination. Highest specific activities for both beta-oxidation systems and their component enzymes are associated with cytosomal particles banding at a density of 1.25 g/ml in a sucrose gradient. Substrate specificity studies indicate that of several fatty acids, ricinoleate is oxidized most rapidly by the preparation from the maturing seed (28 days after flowering) while palmitate and linoleate are oxidized most rapidly by extracts obtained from tissue germinated for 4 days. The beta-oxidation activities observed in both systems reflect the expression of activity of at least 3 of the component enzymes, crotonase, beta-hydroxyacyl dehydrogenase and beta-keto-thiolase, which rise and fall co-ordinately. Acyl thiokinase does not appear to play a limiting role in regulating beta-oxidation per se under the conditions employed here.
TL;DR: Ca(2+) uptake was studied in short-term experiments using 5-day-old excised maize roots, and inhibition by dinitrophenol and low temperature shows that the process is metabolically mediated.
Abstract: Ca(2+) uptake was studied in short-term experiments using 5-day-old excised maize roots. This tissue readily absorbs Ca(2+), and inhibition by dinitrophenol and low temperature shows that the process is metabolically mediated. The uptake of Ca(2+), like that of other cations, is influenced by the counter ion, the pH and concentration of the ambient solution, and the presence of other cations. The rate of uptake from various salts decreases in the following order: NO(3) (-) > Cl(-) = Br(-) > SO(4) (2-). K(+) and H(+) greatly interfere with Ca(2+) absorption, while Li(+) and Na(+) have only slight effects.
TL;DR: When disks of carrot (Daucus carota) phloem parenchyma are incubated for 6 days there is a 10-fold increase in cell wall hydroxy Proline due to the synthesis and secretion of hydroxyproline-containing macromolecules.
Abstract: When disks of carrot (Daucus carota) phloem parenchyma are incubated for 6 days there is a 10-fold increase in cell wall hydroxyproline due to the synthesis and secretion of hydroxyproline-containing macromolecules. The synthesis of these molecules and their secretion are demonstrated by measuring the kinetics of incorporation and of chase of 14C-proline and hydroxyproline in different fractions of the cytoplasm and the cell wall. The hydroxyproline-containing molecules which are secreted are associated with the membranous organelles of the cytoplasm. They can be fractionated into trichloroacetic acid-soluble and trichloroacetic acid-precipitated fractions. The properties of the trichloroacetic acid-soluble fraction associated with the membranous organelles are consistent with its role as a cell wall precursor.
TL;DR: A cycloheximide-sensitive increase in the activity of phenylalanine ammonia-lyase occurs in Xanthium leaf disks exposed to light, indicating that photosynthesis is involved and that turnover, i.e., degradation as well as synthesis of lyase protein occurs is suggested by the apparent loss of radioactive ammonia-LYase from leaf disks placed in darkness.
Abstract: A cycloheximide-sensitive increase in the activity of phenylalanine ammonia-lyase (EC 4.3.1.5) occurs in Xanthium leaf disks exposed to light. Radioactive ammonia-lyase has been isolated by means of sucrose density gradient centrifugation and starch gel electrophoresis from disks fed l-isoleucine-U-(14)C or l-arginine-U-(14)C. The incorporation of radioactive amino acids into phenylalanine ammonia-lyase together with the inhibitory effects of cycloheximide indicate that the observed increase in enzyme activity involves the induction of lyase synthesis.The light-dependent synthesis of the ammonia-lyase is completely inhibited by 50 mum 3-(4-chlorophenyl)-1,1-dimethylurea (CMU) indicating that photosynthesis is involved. Only a trace quantity of some photosynthetic product must be needed because half light saturation occurs at very low intensity (ca. 30 ft-c). Exogenous carbohydrate is also required for continuing enzyme synthesis over a 72 hr period. But carbohydrate does not replace the photosynthetic requirement in darkness. Enzyme formed in light disappears rapidly from disks placed in the dark. The decay of ammonia-lyase activity follows first order kinetics. The half-life of the lyase ranged from 6 to 15 hr in leaf material used. Cyoloheximide inhibits the decay of lyase activity. Thus the maintenance of turnover in Xanthium leaf disks requires de novo synthesis of protein. That turnover, i.e., degradation as well as synthesis of lyase protein occurs is suggested by the apparent loss of radioactive ammonia-lyase from leaf disks placed in darkness. Light-induced synthesis coupled with rapid turnover can produce a diurnal fluctuation of ammonia-lyase activity in Xanthium leaf disks. Alternating periods of enzyme synthesis and degradation were observed in disks exposed to 24 hr cycles of light and dark. The average level of enzyme activity maintained in the tissue was directly related to the length of the light period. Induction of lyase synthesis was also observed in excised leaves and to a lesser extent in leaves of whole plants.
TL;DR: It was not possible to resolve the 2 activities of sucrose synthetase but their stabilities to partial thermal inactivation are identical, and their ratios are constant over a wide range of activities.
Abstract: Sucrose synthetase activity is high in young potato tubers but decreases markedly during maturation. The activity decreases rapidly after the tubers are harvested and remains low regardless of storage temperature. This enzyme was purified 34-fold from freshly harvested immature potatoes. It catalyzes both cleavage and synthesis of sucrose but the 2 activities differ in a number of ways. The pH optima are 6.6 and 8.8 for sucrose cleavage and synthesis. respectively. Sucrose cleavage is activated 4-fold by mercaptoethanol and is inhibited by Mn(2+). In contrast, sucrose synthesis is activated only slightly by either mercaptoethanol or Mn(2+) alone but 2-fold in the presence of both reagents. However, it was not possible to resolve the 2 activities, their stabilities to partial thermal inactivation are identical, and their ratios are constant over a wide range of activities.