Showing papers in "Plant Physiology in 1975"

Water uptake, diameter change, and nonlinear diffusion in tree stems.

Abstract: A diffusion model for phloem swelling and contraction is proposed in which the rate of water movement changes markedly with moisture content. Good agreement between the actual swelling of the phloem of cotton stems and that predicted by the model was obtained. This result implies that water moves more readily into the phloem when it becomes wetter. This model also explains the lag of shrinkage of pine stems behind the water potential of the foliage and predicts that the lag is related to the thickness of the phloem.

Relation between Mesophyll Surface Area, Photosynthetic Rate, and Illumination Level during Development for Leaves of Plectranthus parviflorus Henckel

Abstract: The influence of illumination level during leaf development on the mesophyll cell surface area per unit leaf area (A(mes)/A), CO(2) resistances, and the photosynthetic rate was determined for leaves of Plectranthus parviflorus Henckel. The relative importance of A(mes)/A versus CO(2) resistances in accounting for observed changes in photosynthesis was quantitatively evaluated using equations based on analogies to electrical circuits.When the illumination during development was raised from 900 to 42,000 lux, the leaves more than tripled in thickness as the mesophyll cells increased in size and frequency, which caused A(mes)/A to go from 11 to 50. The net rate of photosynthesis at light saturation concomitantly increased 4-fold, reflecting a corresponding decrease in the total resistance for CO(2) movement per unit leaf area. However, the CO(2) resistance per unit area of mesophyll cells remained about 580 seconds per centimeter for leaves grown under 900 to 42,000 lux. Thus, for P. parviflorus, the increased photosynthetic rate for leaves developing under higher illuminations resulted from a higher A(mes)/A, not from changes in the CO(2) resistances within individual mesophyll cells, expressed per unit area of cell surface. Results are discussed in terms of previously observed increases in thickness, internal leaf area, and photosynthetic rates for sun versus shade leaves on various plant species.

The Interaction between Osmotic- and Pressure-induced Water Flow in Plant Roots.

Abstract: This paper presents a general model for coupled solute and water flow through plant roots based on the thermodynamics of irreversible processes. The model explains in a straight-forward manner such experimentally observed phenomena as changes in root resistance, increased solute flux, and apparent negative resistance, which have been reported for root systems under the influence of a hydrostatic pressure gradient. These apparent anomalies are explained on the basis of the interaction between the osmotic and hydrostatic driving forces and the well known "sweeping away" or dilution effect. We show that with a constant hydraulic conductivity the only features necessary to explain these phenomena are some type of membrane or membranelike structure and a mechanism for actively accumulating solutes.

Relationships between Leaf Water Status, Abscisic Acid Levels, and Stomatal Resistance in Maize and Sorghum

Abstract: A new method for abscisic acid extraction and purification was developed to handle large numbers of small (about 125 milligrams fresh weight) samples of leaf discs. This method enabled short term changes in abscisic acid to be followed in single leaves.Water potentials, stomatal diffusion resistance, and abscisic acid levels were measured in the leaves of maize (Zea mays L. var. Wisconsin 575) and sorghum (Sorghum bicolor, hybrid NK 145) plants subjected to a drought-recovery cycle under controlled environmental conditions. The levels of abscisic acid began to rise, and the stomata closed, over a narrow range of water potential (-8 to -10 bars) in both species. Abscisic acid levels continued to rise after the stomata closed. The maximum amount of abscisic acid extracted from maize leaves was about twice that from sorghum, but this represented a similar proportional increase over the control level.In excised leaves little or no change in abscisic acid levels was found within 60 to 120 minutes after stress was applied (phase I). Subsequently abscisic acid levels rose rapidly to about 20 times the prestress level (phase II). Stomatal closure always preceded the phase II increase in abscisic acid.The aftereffects of stress differed in the two species. In sorghum control levels of both abscisic acid and stomatal resistance were regained within 24 hours of rewatering. In maize abscisic acid levels also fell rapidly, but regained control levels only after 48 hours. The resumption of normal stomatal functioning occurred after a further 24 hours.Impaired stomatal functioning after stress does not appear to be associated with high residual levels of abscisic acid in the leaf.

Photocontrol of Anthocyanin Synthesis: III. The Action of Streptomycin on the Synthesis of Chlorophyll and Anthocyanin.

Abstract: Streptomycin enhances the synthesis of anthocyanins and inhibits the synthesis of chlorophylls and the development of chloroplasts in dark-grown seedlings of cabbage (Brassica oleracea), mustard (Sinapis alba), tomato (Lycopersicon esculentum), and turnip (Brassica rapa) exposed to prolonged periods of irradiation in various spectral regions. These results suggest that the contribution of photosynthesis to light-dependent high irradiance reaction anthocyanin synthesis in seedlings of cabbage, mustard, tomato, and turnip is minimal, if any at all. So far, phytochrome is the only photoreceptor whose action in the control of light-dependent anthocyanin synthesis in seedlings of cabbage, mustard, tomato, and turnip has been satisfactorily demonstrated.

Oxygen availability in polyethylene glycol solutions and its implications in plant-water relations.

Abstract: The solubility of O(2) in polyethylene glycol 4000 and 6000 solutions of varying concentrations was determined iodimetrically (titrimetrically) and electrochemically using a rotating glassy carbon electrode and a PAR Model 174 Polarograph. The titrimetric determination resulted in the formation of an unexpected precipitate at 2% (w/v) polyethylene glycol corresponding to the approximate critical micelle concentration of the two polyethylene glycol homologs. Beyond 5% polyethylene glycol, O(2) concentration was inversely proportional to polyethylene glycol concentration, and was higher in polyethylene glycol 4000 solutions than in polyethylene glycol 6000. The electrochemical data are a direct measure of O(2) transport to the electrode surface, rather than O(2) activity or concentration. Results indicate that even at relatively high H(2)O potentials, the transport of O(2) to the root surface might be insufficient to meet the plant's respiratory requirements.

Identification of plant hormones from cotton ovules.

Abstract: An extract from 8-day-old cotton ovules (Gossypium hirsutum L.) was partitioned into three fractions and each fraction was derivatized and analyzed separately. Gas-liquid chromatography and computer-controlled gas-liquid chromatography-mass spectrometry were used to separate, measure, and identify the naturally occurring plant hormones. A single extract contained abscisic acid, indoleacetic acid, and gibberellins A(1), A(3), A(4), A(7), A(9), and A(13) in the first fraction; ethyl indole-3-acetate and indole-3-aldehyde in the second fraction; and the cytokinins 6-(3-methyl-4-hydroxybutylamino)purine (dihydrozeatin), 6-(4-hydroxy-3-methyl-2-trans-butenylamino) purine (zeatin), 6-(3-methyl-2-butenylamino)purine(2iP), 6-(3-methyl-2-butenylamino)-9-beta-d-ribofuranosylpurine(2iPA), and 6-(4-hydroxy-3-methyl-2-trans-butenylamino)-9-beta-d- ribofuranosylpurine (zeatin riboside) in the third fraction.

The Relationship between Satellite Deoxyribonucleic Acid, Ribosomal Ribonucleic Acid Gene Redundancy, and Genome Size in Plants.

Abstract: The buoyant density of ribosomal DNA is similar in species with or without satellite DNA, and in all species examined was distinguishable from that of the satellite DNA. In melon tissues (Cucumus melo) the percentage satellite DNA is not correlated with the percentage hybridization to ribosomal RNA. Satellite DNA sequences do not appear to be dispersed between those coding for ribosomal RNA. There is no correlation between the presence of satellite DNA and high ribosomal RNA gene redundancy, but there is a correlation between satellite DNA and small genome size, which results in a correlation between satellite DNA and a high percentage hybridization to ribosomal RNA. Satellite DNAs are defined as minor components after CsCI centrifugation.

Loss of Ribulose 1,5-Diphosphate Carboxylase and Increase in Proteolytic Activity during Senescence of Detached Primary Barley Leaves

Abstract: Symptoms typical of senescence occurred in green detached primary barley ( Hordeum vulgare L.) leaves placed in darkness and in light. Chlorophyll, total soluble protein, ribulose 1,5-diphosphate carboxylase protein and activity each progressively decreased in darkness and to a lesser extent in light. In all treatments most of the total soluble protein lost was accounted for by a decrease in ribulose 1,5-diphosphate carboxylase protein, suggesting that the chloroplast was a major site of degradation early in senescence. Loss of ribulose 1,5-diphosphate carboxylase protein was negatively correlated with an increase in proteolytic activity measured against azocasein. Both rates were exponential, with about a 30% difference in apparent rate constants. Cycloheximide essentially prevented the loss of chlorophyll, ribulose 1,5-diphosphate carboxylase protein, and activity and completely inhibited the increase in proteolytic activity against azocasein. Since chloramphenicol had little effect on the loss of ribulose 1,5-diphosphate carboxylase protein or chlorophyll, or on proteolytic activity against azocasein, it is suggested that the proteolytic activity was developed on cytoplasmic 80 S ribosomes. Kinetin greatly retarded the onset of such symptoms of senescence by inhibiting the losses of chlorophyll and ribulose 1,5-diphosphate carboxylase protein and protected against inactivation of enzymic activity. It also prevented the increase in proteolytic activity measured against azocasein. Incorporation of labeled amino acids into ribulose 1,5-diphosphate carboxylase during its rapid degradation showed that the enzyme was under turnover. The changes in ribulose 1,5-diphosphate carboxylase protein and activity, chlorophyll, soluble protein other than ribulose 1,5-diphosphate carboxylase, proteolytic and esterolytic activity during senescence indicate that senescence is a selective, sequential process.

Asparagine Metabolism—Key to the Nitrogen Nutrition of Developing Legume Seeds

Abstract: Asparagine accounted for 50 to 70% of the nitrogen carried in translocatory channels serving fruit and seed of white lupin (Lupinus albus L.). Rates of supply of the amide always greatly exceeded its incorporation as such into protein. An asparaginase (l-asparagine amido hydrolase EC 3.5.1.1) was demonstrated in crude extracts of seeds. In vitro activity was up to 5 mumoles of aspartate formed per hour per gram fresh weight at the apparent Km(Asn) value of 10 mM, and this more than accounted for the estimated rates of asparagine utilization in vivo. Asparaginase activity per seed increased 10-fold in the period 5 to 7 weeks after anthesis, coinciding with early stages of storage protein synthesis in the cotyledons.Double labeled ((14)C (U), (15)N (amide)) asparagine was fed to fruiting shoots through the transpiration steram. Fruit phloem sap analysis indicated that virtually all of the label was translocated to seeds in the form of asparagine. In young seeds (15)N from asparagine breakdown was traced to the ammonia, glutamine, and alanine of endospermic fluid, the (14)C appearing mainly in nonamino compounds. In the cotyledon-filling stage the C and N of asparagine was contributed to a variety of amino acid residues of protein.

Control of Storage Protein Metabolism in the Cotyledons of Germinating Mung Beans: Role of Endopeptidase

Abstract: The autodigestive proteolytic activity of extracts of cotyledons of mung beans (Phaseolus aureus Roxb.) increased 4- to 5-fold during germination. A similar increase was found in the ability of these extracts to digest added casein or mung bean globulins. The increase occurred after a 2-day lag during the next 2 to 3 days of germination and coincided with the period of rapid storage protein breakdown. To understand which enzyme(s) may be responsible for this increase in proteolytic activity, the hydrolytic activity of cotyledon extracts toward a number of synthetic substrates and proteins was measured. Germination was accompanied by a marked decline in leucine aminopeptidase, while carboxypeptidase increased about 50%. There were no dramatic changes in either α-mannosidase or N-acetyl-β-glucosaminidase, enzymes which may be involved in the metabolism of the carbohydrate moieties of the reserve glycoproteins. The increase in general proteolytic activity was closely paralleled by a 10-fold increase in endopeptidase activity. This activity was inhibited by sulfhydryl reagents such as N-ethylmaleimide. Studies with inhibitors of proteolytic enzymes showed that reagents which blocked sulfhydryl groups also inhibited the rise in general proteolytic activity. Our results suggest that the appearance of a sulfhydryl-type endopeptidase activity is a necessary prerequisite for the rapid metabolism of the reserve proteins which accompanies germination.

Photoreceptor Pigment for Blue Light in Neurospora crassa

Abstract: Irradiating the mycelium of Neurospora crassa with moderate intensities of blue light causes a reversible photoreduction of a b-type cytochrome. The action spectrum for the photoreduction of cytochrome b is very similar to the absorption spectrum of flavin pigments. Prolonged irradiation of the mycelium with strong blue light irreversibly bleaches flavin-like pigments and as these pigments are bleached the photoresponse of cytochrome b is lost. We conclude from these and other data that a flavin is the photoreceptor pigment for the photoreduction of cytochrome b. The close similarity between the action spectrum for the photoreduction of cytochrome b and action spectra for a number of physiological photoresponses suggests that this photoreceptor pigment controls a wide variety of photobiological processes in a wide diversity of organisms.

Evidence for Covalently Attached p-Coumaric Acid and Ferulic Acid in Cutins and Suberins

Abstract: p-Coumaric acid (4-hydroxycinnamic acid) and ferulic acid (4-hydroxy-3-methoxycinnamic acid) have been identified as constituents of cutin. Their reduction products were isolated from a phenolic fraction released from the cutin of the fruits of apple, peach, pear, and two varieties of tomato and apple leaf by treatment with LiAlH(4) or LiAlD(4). They were identified by combined gas chromatography and mass spectrometry. p-Coumaric acid was present in all samples of cutin (0.07-0.53% by weight), whereas only peach and pear cutin contained measurable amounts of ferulic acid (0.007% and 0.035%, respectively). Both p-coumaric acid and ferulic acid were identified to be constituents of the insoluble material recovered after partial hydrolysis (12-42% loss) of cutin in 1 m NaOH at 80 C. A significant part (48%) of the p-coumaric acid contained in tomato cutin was contained in the insoluble material recovered after partial degradation (7.4%) of this cutin with 0.01 m NaOH. These data indicate that these phenolic components are tightly (possibly covalently) bound to cutin. Similar analysis of the phenolic fractions from the suberins of potato, sweet potato, turnip, rutabaga, carrot, and red beet revealed that they contained only ferulic acid (0.05-0.22%). Ferulic acid was identified as a constituent of the insoluble material recovered after partial hydrolysis of potato and beet suberins (34% and 32% loss, respectively) in 1 m NaOH at 80 C. A major part (65%) of the ferulic acid contained in potato suberin was contained in the insoluble material recovered after partial (26.8% loss) degradation of this suberin with 0.01 m NaOH. Ferulic acid appears to be tightly (probably covalently) bound to suberin.

The Structure of Plant Cell Walls: VII. Barley Aleurone Cells

Abstract: The walls of barley (Hordeum vulgare var. Himalaya) aleurone cells are composed of two major polysaccharides, arabinoxylan (85%) and cellulose (8%). The cell wall preparations contain 6% protein, but this protein does not contain detectable amounts of hydroxyproline. The arabinoxylan has a linear 1,4-xylan backbone; 33% of the xylosyl residues are substituted at the 2 and/or 3 position with single arabinofuranosyl residues. The results of in vitro cellulose binding experiments support the hypothesis that noncovalent bonds between the arabinoxylan chains and cellulose fibers play a part in maintaining wall structure. It is suggested that bonding between the arabinoxylan chains themselves is also utilized in forming the walls.

Host-Pathogen Interactions: VIII. Isolation of a Pathogen-synthesized Fraction Rich in Glucan That Elicits a Defense Response in the Pathogen's Host.

Abstract: A polysaccharide from the fungal pathogen Colletotrichum lindemuthianum causes browning and phytoalexin production when applied to the cut surfaces of bean (Phaseolus vulgaris) cotyledons and hypocotyls. The application of an amount of polysaccharide equivalent to less than 100 ng of glucose will elicit this response in the bean tissues. The polysaccharide has been isolated both from culture filtrates and from the mycelial walls of the fungus. Purification of the polysaccharide involved anion and cation exchange chromatography and gel filtration. The polysaccharide has an apparent molecular weight between 1,000,000 and 5,000,000 daltons, and consists predominantly of 3- and 4-linked glucosyl residues.

Photosynthetic Action Spectra of Trees: II. The Relationship of Cuticle Structure to the Visible and Ultraviolet Spectral Properties of Needles from Four Coniferous Species.

Abstract: The relative reflectance spectra for control and treated (surface wiped) current-year foliage of Douglas fir, and Sitka, Colorado, and Blue spruce ( Pseudotsuga menziesii [Mirb.] Franco, Picea sitchensis [Bong.] Carr., Picea pungens Engelm., and Picea pungens Engelm. var. hoopsii, respectively) were obtained from 220 to 700 nm. The green color of the control foliage of both Douglas fir and Sitka spruce was unaffected by the treatment whereas the blue-green and blue-white foliage of control Colorado and Blue spruce, respectively, became “green” as a result of the wiping. The relative reflectance curves for all green foliage, including the treated Colorado and Blue spruce, were all very similar with a peak in the green (540-560 nm), minima in the red (660-680 nm) and blue (450-500 nm), and very low reflectivities in the ultraviolet (λ Scanning electron microscope examination of the needles9 surfaces revealed a system of wax filaments whose complexity correlated with the degree of ultraviolet and blue reflectance. It is concluded that both the bluish appearance (glaucous bloom) and the low relative efficiencies of blue light in photosynthesis of Colorado and Blue spruce result from the selectively enhanced reflection of blue light caused by the presence of the epicuticular wax deposits. The enhanced blue light reflection was shown to be the shoulder of a scattering effect which appeared to peak in the short ultraviolet region below 200 nm. The ecological implications of the results are discussed.

Protoheme turnover and chlorophyll synthesis in greening barley tissue.

Abstract: Studies in which (14)C-labeled precursors were fed to etiolated barley leaves (Hordeum vulgare L. var. Proctor) yielded chlorophyll and protoheme having similar specific radioactivities. These findings indicate: (a) there appears to be a rapid turnover of protoheme in the absence of net synthesis; (b) both pigments probably originate from a single 5-aminolevulinic acid pool; (c) the efficient utilization of glutamate-1-(14)C and the relatively poor utilization of glycine-2-(14)C suggest that 5-aminolevulinic acid is probably synthesized by a pathway other than 5-aminolevulinic acid synthetase (succinyl CoA-glycine succinyltransferase) in agreement with previously published work; (d) protoheme turnover appears to be faster under conditions which allow for rapid chlorophyll accumulation; (e) difference spectra indicate that mitochondrial cytochromes make a relatively minor contribution to the total heme in barley leaves. These findings are discussed in the light of current knowledge about tetrapyrrole regulation in photosynthetic organisms.

Osmoregulation in Cotton Fiber: Accumulation of Potassium and Malate during Growth

Abstract: Kinetics and osmoregulation of cotton (Gossypium hirsutum L.) fiber growth (primarily extension) have been studied. Growth is dependent on turgor pressure in the fiber. It is inhibited when a decrease in the water potential of the culture medium due to an addition of Carbowax 6000, equals the turgor pressure of the fiber. Potassium and malate accumulate in the fiber and reach peak levels when the growth rate is highest. Maximum concentrations of potassium and malate reached in the fiber can account for over 50% of the osmotic potential of the fiber. As growth slows down, levels of potassium and malate decrease and turgor pressure declines. Cotton ovules are capable of fixing H(14)CO(3) (-) in the dark, predominantly into malate. Fiber growth is inhibited by the absence of potassium and/or atmospheric CO(2). We suggest that potassium and malate act as osmoregulatory solutes and that malate, at least in part, arises from dark CO(2) fixation reactions.

Cycloheximide Is Not a Specific Inhibitor of Protein Synthesis in Vivo

Abstract: Cycloheximide is frequently presumed to inhibit specifically the cytoplasmic protein synthesis of eukaryotes. Although previous investigators have shown that it had other effects on the cells of a variety of organisms, these results were frequently presumed to be secondary effects of the inhibition of protein synthesis. This paper shows that a wide range of deleterious effects are produced by cycloheximide on a single organism, Chlamydomonas reinhardi Dangeard. If, protein synthesis is inhibited by nonpermissive conditions in temperature-sensitive mutants or with other treatments these “secondary” effects are not produced. Instead, cycloheximide appears to have two or three independent inhibitory effects on the cell. Moreover, in contrast to a number of previous investigations, these results show that protein synthesis is not required for RNA synthesis. Instead the rate of RNA synthesis is actually increased by interference with protein synthesis.

Leaf water stress in engelmann spruce: influence of the root and shoot environments.

Abstract: The response of xylem pressure potential of Engelmann spruce (Picea engelmannii Engelm.) to environmental factors was studied in the natural subalpine environment. Data were analyzed in the context of a leaf water potential model based upon the van den Honert model for water transport through the soil-plant-atmosphere continuum. At soil temperatures of 10 to 15 C, xylem pressure potential decreased to about −10 bars as the ratio of leaf to air absolute humidity difference to leaf diffusion resistance (an estimate of transpiration) increased. The potentials were slightly lower at all flux rates above zero when the soil temperature was 5 to 10 C, and at temperatures of 0 to 5 C the potentials decreased sharply to as low as −20.4 bars, even though the soil water supply was adequate. The relative viscosity of water and soil to leaf resistances for flow were compared for Engelmann spruce and citrus at low soil temperatures. These comparisons indicated that decreased root permeability was probably not an important factor causing higher stresses in spruce at 5 to 10 C, but for citrus, root permeability became limiting at soil temperatures as high as 13.5 C. Xylem pressure potential was correlated with net radiation during the daytime when soil temperature was above 7 C. Under other conditions, however, xylem potential and net radiation apparently had a different relationship. The relationship between flux density and potential was the same on unshaded and shaded portions of the crown, with differences in potential related to differences in flux density.

Histochemical and biochemical observations on storage protein metabolism and protein body autolysis in cotyledons of germinating mung beans.

Abstract: Storage protein hydrolysis in the cotyledons of germinating mung beans (Phaseolus aureus Roxb.) was examined by histochemical techniques, and the autolytic capacity of isolated protein bodies was studied with biochemical methods. The localization of endopeptidase activity within the cotyledons was studied using an India ink-gelatin film technique. After 24 hours of imbibition, a low level of endopeptidase activity was found throughout the storage tissues of the cotyledons. A marked increase in activity was noted in cells farthest from the vascular bundles 48 to 60 hours after the start of imbibition. The decrease in storage protein followed the same spatial distribution starting in the cells farthest from the bundles. The cotyledons contain a population of cells in various stages of endopeptidase activity enhancement and storage protein degradation. A wave of endopeptidase activity moves progressively through the cotyledons towards the vascular bundles leaving behind areas devoid of stored reserves and low in endopeptidase activity. Observations on the morphology of protein bodies during germination indicate that the membrane surrounding them remains intact, while the reserves disappear. This result suggests that the protein bodies may be undergoing autolysis. To determine whether this may indeed be the case, protein bodies were isolated from the meal of mung bean seeds using an aqueous medium containing 80% glycerol. The protein body preparations and the cytoplasm were assayed for the presence of a number of enzymes which may be involved in the breakdown of the storage proteins. The protein bodies contained all, or nearly all, of the carboxypeptidase, alpha-mannosidase, N-acetyl-beta-glucosaminidase, and caseolytic activity. The cytoplasm contained all, or most, of the leucine aminopeptidase and the trypsin-like activity (benzoyl arginine-p-nitroanalide as substrate). Incubation of the isolated protein bodies resulted in the release of amino acids. An analysis of the products of hydrolysis indicated that very little, if any, storage protein was being hydrolyzed during the incubation. Hydrolysis of the storage proteins present in the protein bodies was greatly accelerated by the addition of extracts from the cotyledons of 4-day-old seedlings. The results suggest that new enzymic activities not present in the protein bodies isolated from dry seeds must either be activated or synthesized and possibly added to the protein bodies before storage protein breakdown can begin.

Separation of Chlorophyll Degradation from Other Senescence Processes in Leaves of a Mutant Genotype of Meadow Fescue (Festuca pratensis L.)

Abstract: Chlorophyll levels in l-cm sections of the youngest fully expanded leaves of normal (Y) Festuca pratensis L. declined almost to zero over a period of 6 days after excision. Chlorophyll in a mutant genotype (NY) remained near the initial level for the whole of this period. Abscisic acid promoted pigment loss in Y but had no significant effect on chlorophyll in NY. Kinetin retarded pigment loss in Y but was ineffective in NY. Other biochemical changes associated with leaf senescence—reduction in protein content and the appearance of novel isoenzymes of α-naphthyl acetate esterases—occurred in both genotypes. Abscisic acid accelerated protein breakdown, whereas kinetin inhibited the loss of protein in both genotypes. The mutation thus appears to be expressed as a highly specific lesion in pigment metabolism. We concluded that pigment breakdown, which is widely used as an index of leaf senescence, may not be an inevitable part of the aging process.

Photocontrol of Anthocyanin Synthesis: IV. Dose Dependence and Reciprocity Relationships in Anthocyanin Synthesis.

Abstract: Under continuous far red light, anthocyanin synthesis in young, dark-grown cabbage seedlings (Brassica oleracea cv. Red Acre) is irradiance-dependent and fails to follow the reciprocity (irradiance × time = constant) relationships. Under intermittent far red treatments extended over a prolonged period of time, anthocyanin synthesis becomes dose dependent, and reciprocity relationships are valid. Intermittent far red treatments with short dark intervals between successive irradiations are as effective as continuous treatments, if the total radiation doses applied with the two types of treatments are equal and are applied over equally long periods of time. The high effectiveness of inter-mittent treatments, the dose dependence, and the validity of the reciprocity relationships suggest that cycling between red-absorbing form of phytochrome and far red-absorbing form of phytochrome and the formation of electronically excited far red-absorbing form of phytochrome, or the involvement of a second photoreactive system, besides phytochrome, may play only a minor role in high irradiance reaction anthocyanin synthesis brought about by prolonged exposures to far red irradiation.

Relationships between the Transition of the Physical Phase of Membrane Lipids and Photosynthetic Parameters in Anacystis nidulans and Lettuce and Spinach Chloroplasts.

Abstract: The transition of the physical phase of lipids in membrane fragments of a blue-green alga Anacystis nidulans was studied by a spin labeling technique. The maximum hyperfine splitting of the electron spin resonance spectrum of the N-oxyl-4', 4'-dimethyloxazolidine derivative of 5-ketostearic acid plotted against the reciprocal of the absolute temperature gave a discontinuity point that was characteristic of a transition of the physical phase of the hydrocarbon region of membrane lipids. The phase transition appeared at approximately 13 or 24 C in the organisms grown at 28 or 38 C, respectively.The temperature dependence curve of chlorophyll a fluorescence in intact cells, membrane fragments, and extracted lipids of Anacystis cells suspended in a buffer solution showed that the fluorescence yield became maximum near the phase transition temperatures. These findings suggest that chlorophyll a in the thylakoid membrane works as a native fluorescence probe for the detection of phase transition.The temperature dependence of photosynthetic electron transport reactions was studied by measuring the oxidoreductive reactions of P700 and by measuring O(2) evolution. Each of the Arrhenius plots of the reaction rates was composed of two straight lines with a break near the phase transition temperatures. The activation energy was always lower above than below the transition temperatures. It is proposed to explain these phenomena that a reaction involving plastoquinone is influenced by the physical state of membrane lipids.The shift between the pigment state 1 and state 2 measured by fluorescence transients also showed a characteristic break in the Arrhenius plots near the phase transition temperatures; below the transition temperatures the shift almost disappeared. This suggests that the configurational change of the thylakoid membrane related to the state 1 and state 2 shift is dependent on the physical state of membrane lipids. In the chloroplasts of lettuce and spinach, on the other hand, there was no break in the Arrhenius plot of the electron transport reactions or of Mg(2+)-induced changes of chlorophyll a fluorescence.It is suggested that the transitions of the hyperfine splitting of the ESR signal, electron transport, and the configurational change, as well as the appearance of the maximum of chlorophyll a fluorescence, in the thylakoid membranes of Anacystis nidulans are all related to the transition of the physical phase of membrane lipids between the liquid crystalline state and the mixed liquid crystal-solid state.

Carbon dioxide compensation points of flowering plants.

Abstract: Carbon dioxide compensation points of several hundred species of monocotyledons and dicotyledons have been measured during the course of various experiments in our laboratory over a period of several years. These have been classified into two groups: high, compensation points of 40 mul/l or greater; and low, compensation points of 10 mul/l or less. They are listed alphabetically both by families and species for monocotyledons and dicotyledons. Only two species did not unequivocally fit into the above established groups. These were Moricandia arvensis (L.) DC., which had an average compensation point of 26 mul/l and Panicum milioides Nees ex Trin., which was variable, but most often equilibrated between 12 to 20 mul/l CO(2).

Carbon Dioxide Assimilation by Leaves, Isolated Chloroplasts, and Ribulose Bisphosphate Carboxylase from Spinach

Abstract: The relationship between rate of photosynthesis and CO(2) concentration has been reinvestigated using isolated spinach (Spinacia oleracea) chloroplasts. The apparently low CO(2) concentration required for half-maximal photosynthesis is shown to result partly from a ceiling imposed by electron transport. In double reciprocal plots of rate against CO(2) concentration, this ceiling results in departures from linearity at high CO(2) concentrations. If these rate limitations are disregarded in extrapolation the "true" CO(2) concentration required for half maximal carboxylation by intact chloroplasts is approximately 46 mum (CO(2)).When assayed under comparable conditions, ribulose bisphosphate carboxylase from these chloroplasts also shows an apparent Km (CO(2)) of approximately 46 mum, suggesting that its characteristics are not modified by extraction. An improved assay for ribulose bisphosphate carboxylase yielded rates of carboxylation considerably higher than those previously reported, the highest maximal velocities recorded approaching 1000 mumoles CO(2) fixed mg(-1) chlorophyll hr(-1) at 20 C. With such Km and V(max), values the carboxylase would be able to achieve, at concentrations of CO(2) less than atmospheric, rates of CO(2) fixation equal to those displayed by the parent tissue or by the average plant under favorable conditions in its natural environment.

Glycosidases in Cell Wall-degrading Extracts of Ripening Tomato Fruits

Abstract: Enzyme preparations were obtained from cell wall debris of tomato (Lycopersicon esculentum L. cv. Tropic) fruits at various stages of ripeness and were assayed for glycosidase and polysaccharidase activities. In addition to polygalacturonase (mol wt 40,000), ripening fruits contain beta-galactosidase (mol wt 63,000) and beta-1, 3-glucanase (mol wt 12,000). The beta-glycosidases, unlike polygalacturonase, are active in extracts of green fruits. Placental tissue shows very low polygalacturonase but increasing beta-galactosidase and beta-1, 3-glucanase activities as ripening proceeds. A large change in the susceptibility of the walls to hydrolase action occurs before the stage in which the greatest polygalacturonase activity occurs. The possibility that the beta-glycosidases contribute to the wall modifications that lead to fruit softening is discussed.

Determination of Unfrozen Water in Winter Cereals at Subfreezing Temperatures

Abstract: The freezing of water in acclimated and nonacclimated cereals was studied using pulsed nuclear magnetic resonance spectroscopy. The quantity of unfreezable water per unit dry matter was not strongly dependent on the degree of cold acclimation. In contrast, the fraction of water frozen which was tolerated by nonacclimated winter cereals and by an acclimated spring wheat (Triticum aestivum L.) was less than in acclimated hardy cereals. The freezing curves had the following form:LT = L0ΔTm/T + KLT and L0 are liquid water per unit dry matter at T and 0 C, respectively. ΔTm is the melting point depression and K is the liquid water which does not freeze.

Nitrate uptake and induction of nitrate reductase in excised corn roots.

Abstract: The characteristics of nitrate uptake and induction of nitrate reductase were studied in excised roots of corn ( Zea mays L.). Upon initial exposure to nitrate, the low initial rate of nitrate uptake gradually increased until a steady uptake rate was achieved in 1 to 2 hours depending on the NO 3 − concentration. The pattern was observed over a wide range (0.2-5 mm) of nitrate concentrations and was independent of the accompanying cation. The nitrate uptake pattern as a function of increasing external nitrate concentrations (0.2-50 mm) followed saturation type kinetics. The reciprocal plot of the data was not linear but hyperbolic, indicating that more than one K m for nitrate uptake can be resolved from the data. This suggests the existence of either one carrier system with changing kinetic constants or the existence of dual uptake systems. The pattern of induction of nitrate reductase was coincident with the pattern of nitrate uptake as a function of time and increasing nitrate concentrations. The rate of induction of nitrate reductase was regulated by the rate of nitrate flux. Washing the roots for 2 hours enhances nitrate uptake by 2.5-fold over the nonwashed tissue. The presence of nitrate in the washing solution leads to further (3.5-fold over control) increases in the rate of nitrate uptake supporting the contention that nitrate plays a specific role in the induction of the inducible nitrate carrier independent of the washing effect.

Isolation and Characterization of the Multiple 7S Globulins of Soybean Proteins

Abstract: Two major proteins (the 7S and 11S globulins) of soybean (Glycine max) were simultaneously isolated by a simple method based on their different solubilities in dilute tris (hydroxymethyl) aminomethane buffers. The purified 7S globulins, which represented essentially the entire 7S soybean protein fraction capable of dimerization at 0.1 ionic strength, were fractionated into five components by diethylaminoethyl Sephadex A-50 column chromatography. The five 7S components were characterized by disc-electrophoresis.