The stability and biological activity of cytokinin metabolites in soybean callus tissue

The activity, uptake and metabolism of cytokinin metabolites was determined in soybean (Glycine max (L.) Merr.) callus tissue. The following activity sequence was established: zeatin riboside (ZR)>zeatin (Z)>O-glucosides of Z, ZR and their dihydro derivatives>lupinic acid (an alanine conjugate of Z)>7- and 9-glucosides of Z which were almost inactive. The 7- and 9-glucosides and lupinic acid were taken up very slowly by the callus tissue and showed great metabolic stability, but some degradation to 7-glucosyladenine, 9-glucosyladenine and the 9-alanine conjugate of adenine occurred. Compared with its aglycone, O-glucosyl-ZR exhibited slow uptake and greatly enhanced stability but gas chromatographic-mass spectrometric analysis showed that appreciable amounts were hydrolyzed to ZR in the tissue. Both ZR and O-glucosyl-ZR were metabolised extensively, with adenine, adenosine, and adenine nucleotide(s) as the major metabolites. A diversity of minor metabolites of ZR were identified, including O-glucosides, lupinic acid and dihydrolupinic acid. The metabolism of ZR was suppressed by 3-isobutyl-1-methylxanthine. When compared with the soybean callus line normally used for cytokinin bioassays (cv. Acme, cotyledonary callus), related callus lines exhibited greatly differing growth responses to cytokinin: however, these were not reflected in marked differences in metabolism.Abbreviations GC-MS gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - LA lupinic acid - OGZR O--D-glucopyranosylzeatin riboside - TLC thin-layer chromatography - IMX 3-isobutyl-1-methylxanthine - Z zeatin - ZR zeatin riboside     

Production of 1,2-Diacylglycerol in PC12 Cells by Nerve Growth Factor and Basic Fibroblast Growth Factor

The addition of nerve growth factor (NGF) or basic fibroblast growth factor (bFGF) to PC12 cells prelabeled with [3H]inositol and preincubated for 15 min in the presence of 10 mM LiCl stimulated the production of inositol phosphates with maximal increases of 120-180% in inositol monophosphate (IP), 130-200% in inositol bisphosphate (IP2), and 45-50% in inositol trisphosphate (IP3) within 30 min. The majority of the overall increase (approximately 85%) was in IP; the remainder was recovered as IP2 and IP3 (approximately 10% as IP2 and 5% as IP3). Under similar conditions, carbachol (0.5 mM) stimulated about a 10-fold increase in IP, a sixfold increase in IP2, and a fourfold increase in IP3. The mass level of 1,2-diacylglycerol (DG) in PC12 cells was found to be dependent on the incubation conditions; in growth medium [Dulbecco's modified Eagle's medium (DME) plus serum], it was around 6.2 mol %, in DME without serum, 2.5 mol %, and after a 15-min incubation in Dulbecco's phosphate-buffered saline, 0.62 mol %. The addition of NGF and bFGF induced an increase in the mass level of DG of about twofold within 1-2 min, often rising to two- to threefold by 15 min, and then decreasing slightly by 30 min. This increase was dependent on the presence of extracellular Ca2+, and was inhibited by both phenylarsine oxide (25 microM) and 5'-deoxy-5'-methylthioadenosine (3 mM). Under similar conditions, 0.5 mM carbachol stimulated the production of DG to the same extent as 200 ng/ml NGF and 50 ng/ml bFGF. Because carbachol is much more effective in stimulating the production of inositol phosphates, the results suggest that both NGF and bFGF stimulate the production of DG primarily from phospholipids other than the phosphoinositides.     

Electrical properties of soybean plasma membrane measured in heterotrophic suspension callus

Previous work on heterotrophic suspension-cultured cells has failed to detect the electrogenic processes normally associated with the plasma membranes of non-animal cells. This study reports measurements on heterotrophic cells from soybean (Glycine max L.) suspension cultures, which are shown to be amenable to impalement with microelectrodes. The plasma membrane clearly exhibits fundamental characteristics which are common to many other plant cell types: (i) a resting membrane potential significantly more negative than-100mV (measured value:121±4mV); (ii) obvious electrogenic activity, as evidenced by the marked depolarization of the membrane (87±6mV) by cyanide, and by the fact the membrane potential was frequently more negative than the equilibrium potential for K⁺; (iii) a finite permeability to K⁺ ions; (iv) electrophoretic transport of glucose. The development of a recording medium consisting primarily of 1:5 diluted growth medium was critical for successful impalement of these cells. It is proposed that the novel identification of electrogenic processes in heterotrophic suspension-cultured cells results from the deployment of electrodes with relatively dilute filling solutions, thus avoiding substantial changes in intracellular ion concentrations.The overwhelming majority of cells in soybean suspension cultures exist in small clusters, and the possibility of intercellular coupling potentially precludes assessment of membrane specific resistance and current density. Furthermore, as with most higher-plant cells, the vacuole occupies a large fraction of the intracellular volume. However, a model in which the measuring electrode is cytosolically located and the cells are electrically well-coupled is the only one which satisfactorily generates values for membrane specific resistance in a manner which is not strongly dependent on the number of cells in the cluster: other models in which the electrode tip is located in the vacuole and-or the impaled cell is electrically isolated from the others do not seem to apply. The measured values of membrane specific resistance are in the range 5.4 to 8.4 ·m², which is in excellent agreement with comparable measurements on other plant and fungal cells. The results are discussed with respect to mechanisms of transmembrane signalling in soybean, as well as to general electrophysiological studies on higher-plant cells in suspension culture and in tissues.Abbreviations and symbols R_m membrane resistance - r_p plasma-membrane resistivity - SRB Soybean Recording Buffer - V_m membrane potential     

Astroglial Phosphoinositide Hydrolysis During Combined Glucose-Oxygen Deprivation: Role of the Metabotropic Glutamate Receptor

Abstract: Phosphatidylinositol bisphosphate hydrolysis, leading to the production of myo -inositol trisphosphate and diacylglycerol, may play a significant role in the pathogenesis of hypoxic-ischemic brain injury. We used tritiated myo -inositol phosphate (³H-IP) accumulation as a means to quantitate phosphoinositide hydrolysis in prelabeled astroglial cultures subjected to combined glucose-oxygen deprivation. Astroglial cultures exposed to combined glucose-oxygen deprivation had significantly greater ³H-IP accumulation compared with cultures exposed to control conditions. To delineate the role of the metabotropic glutamate receptor in astroglial phosphoinositide hydrolysis during combined glucose-oxygen deprivation, we studied the effects of two metabotropic glutamate receptor antagonists, 2-amino-3-phosphonopropionic acid and (+)-methyl-4-carboxyphenylglycine. 2-Amino-3-phosphonopropionic acid attenuated the accumulation of ³H-IP during combined glucose-oxygen deprivation but acted as an agonist under control conditions. (+)-Methyl-4-carboxyphenylglycine had no effect on ³H-IP accumulation during combined glucose-oxygen deprivation or under control conditions. These results suggest that activation of astroglial phosphoinositide hydrolysis during combined glucose-oxygen deprivation may be mediated, at least in part, by the metabotropic glutamate receptor.     

Variation in nicotine content of tobacco callus cultures

Plants ofNicotiana tabacum L. cv. Burley 21 which showed no difference in nicotine content were used to establish callus cultures. Cultures were initiated from different plants and from different leaves within each plant. The nicotine content of the calli was determined, and the results subjected to an analysis of variance. Differences between plants and differences within plants significantly affected the nicotine content of the cultures. The differences between plants were transmitted sexually and asexually, providing evidence that they are genetically determined. No such differences in nicotine content were found between the plants from which the cultures were established, indicating that nicotine production in vitro involves additional genes to those which are needed for nicotine production in the plant. The differences within plants were further investigated by establishing callus cultures from pith explants taken from different parts of the stem. Explants from apical pith tissue gave calli having far more nicotine and more roots than cultures derived from basal pith explants. This results may reflect the proximity of the apical pith explants to the site of auxin synthesis in the stem apex. Callus cultures derived from pith explants showed greater growth and nicotine production than those derived from leaf explants when the calli were induced on Murashige-Skoog medium containing -naphthalene acetic acid. This result is in conflict with the widely held belief that explants from different parts of the plant give cultures with similar yields of species-specific compounds.Abbreviations HN High nicotine - LN low nicotine     

Detection of lectins in nodulated peanut and soybean plants

The direct double-antibody enzymelinked immunosorbent assay system was used in the detection and measurement of seed lectins from peanut (Arachis hypogaea L.) and soybean (Glycine max L.) plants (PSL and SBL, respectively) that had been inoculated with their respective rhizobia. Concentrations of PSL dropped to undetectable levels in peanut roots at 9 d and stems and leaves at 27 d after planting; SBL could no longer be detected in soybean roots at 9 d and in stems and leaves at 12 d. A lectin antigenically similar to PSL was first detected in root nodules of peanuts at 21 d reaching a maximum of 8 g/g at 29 d then decreasing to 2.5 g/g at 60 d. There was no evidence of a corresponding lectin in soybean nodules.Sugar haemagglutination inhibition tests with neuraminidase-treated human blood cells established that PSL and the peanut nodule lectin were both galactose/lactose-specific. Further tests with rabbit blood cells demonstrated a second mannosespecific lectin in peanut nodule extracts that was not detected in root extracts of four-week-old inoculated plants or six-week-old uninoculated plants, although six-week-old root extracts from inoculated plants showed weak lectin activity. The root extracts from both nodulated and uninoculated plants contained another peanut lectin that agglutinated rabbit but not human blood cells. Haemagglutination by this lectin was, however, not inhibited by simple sugars but a glycoprotein, asialothyroglobulin, was effective in this respect.Abbreviations DAS double antibody sandwich - ELISA enzyme-linked immunosorbent assay - PBS phosphate-buffered saline - PSL peanut seed lectin - SBL soybean lectin     

Plant regeneration from callus cultures of several soybean genotypes via embryogenesis and organogenesis

Using callus derived from immature embryos, regeneration of viable plants was obtained in soybean (Glycine max (L.) Merr.). Depending on the composition of the medium, regeneration occurred via embryogenesis or via organogenesis. Embryogenesis resulted when embryos were plated on Murashige and Skoog (MS) medium containing 43 M -naphthaleneacetic acid. In work with the cultivar Williams 82, the addition of 5.0 M thiamine HCl increased embryogenesis from 33% to 58% of the embryos plated. Addition of 30 M nicotinic acid to the MS medium enhanced embryogenesis further to 76%. Organogenesis was obtained when medium containing 13.3 M 6-benzylaminopurine, 0.2 M and -naphthaleneacetic acid and four times the normal concentration of MS minor salts was used. Histological studies of these cultures confirmed the organogenic and embryogenic nature of the cultures, by demonstrating the formation of shoot buds and somatic embryos, respectively. Similar responses were obtained in all 54 genotypes tested in this manner. The cultures retained the ability to regenerate complete plants for at least 12 months and 12–15 subcultures. Seeds have been obtained from several regenerated plants and when grown in the field these produced normal-appearing fertile plants.Abbreviations BAP 6-benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetio acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid - MS Murashige and Shoog (1962) medium - NAA -naphthaleneacetic acid - picloram 4-amino-3,5,6-trichloropicolinic acid     

Changes in the pattern of phospholipid synthesis during the induction by cytokinin of cell division in soybean suspension cultures

A method is described for preparing fully viable, cytokinin-starved soybean (Glycine max (L.) Merr. cv. Acme) cells from a suspension-culture of callus tissue. The cells respond to kinetin treatment by re-initiating cell division. We present evidence, from the pattern of incorporation of ³²P-labelled inorganic phosphate into individual phospholipids during the first hour of this response, that the synthesis of phosphatidylinositol (PI) and of phosphatidic-acid head-groups is affected within 15 min. The polyphosphoinositide phosphatidylinositol 4-phosphate, but not phosphatidylinositol 4,5-bisphosphate, was detected in the tissue. The characteristics of cytokinin-induced PI synthesis in cytokinin-starved soybean cells appear to resemble the PI response of animal cells.Abbreviations DPG diphosphatidylglycerol - PA phosphatidic acid - PC phosphatidylcholine - PE phosphatidylethanolamine - PG phosphatidylglycerol - PI phosphatidylinositol - PIP phosphatidylinositol 4-phosphate - PIP₂ phosphatidylinositol 4,5-bisphosphate - PS phosphatidylserine - Pi inorganic phosphate - TLC thin-layer chromatography     

High-performance liquid chromatographic assay with ultraviolet spectrometric detection for the evaluation of inhibitors of phosphatidylinositol-specific phospholipase C

A nonradioactive spectrometric assay for the evaluation of inhibitors of phosphatidylinositol-specific phospholipase C (PI-PLC) is described. l-alpha-Phosphatidylinositol from bovine liver was used as substrate in the presence of the micelle-forming detergent deoxycholic acid. PI-PLC isolated from Bacillus cereus and crude cytosol fractions from porcine brain were used as enzyme sources. PI-PLC activity was determined by measuring the release of 1-stearoyl-2-arachidonoyl-sn-glycerol with reversed-phase HPLC and UV detection at 200 nm. PI-PLC from B. cereus was not inhibited by the putative PI-PLC inhibitors U-73122 and ET-18-OCH(3) at 100 microM, whereas the isobenzofuranone derivative 5 blocked the enzyme with an IC(50) of 75 microM. PI-PLC activity present in porcine brain cytosol was decreased by all three test compounds at 100 microM to approximately 30 to 50%.     

Phosphoenolpyruvate carboxylase in soybean root nodules: An immunochemical study

The activity of phosphoenolpyruvate carboxylase (E.C. 4.1.1.31) strongly increased during the maturation of soybean (Glycine max L. Weber) root-nodules. By using a specific immune serum it was shown that this increase was the consequence of an elevated population of enzyme molecules whose appearance preceded the emergence of nitrogen fixing capacity. Whether or not the phenomenon could be ascribed to the formation of a specific isoenzyme is not known. The location of the enzyme was also investigated. Immunocyto-fluorescence experiments established that phosphoenolpyruvate carboxylase was present in the cytoplasmic compartment of both infected and uninfected cells of nodules.Abbreviation PEPCase phosphoenolpyruvate carboxylase     

Inositol Pyrophosphates Modulate S Phase Progression after Pheromone-induced Arrest in Saccharomyces cerevisiae

Several studies have demonstrated the activation of phosphoinositide-specific phospholipase C (Plc) in nuclei of mammalian cells during synchronous progression through the cell cycle, but the downstream targets of Plc-generated inositol 1,4,5-trisphosphate are poorly described. Phospholipid signaling in the budding yeast Saccharomyces cerevisiae shares similarities with endonuclear phospholipid signaling in mammals, and many recent studies point to a role for inositol phosphates, including InsP₅, InsP₆, and inositol pyrophosphates, in mediating the action of Plc. In this study, we investigated the changes in inositol phosphate levels in α-factor-treated S. cerevisiae, which allows cells to progress synchronously through the cell cycle after release from a G₁ block. We found an increase in the activity of Plc1 early after release from the block with a concomitant increase in the levels of InsP₇ and InsP₈. Treatment of cells with the Plc inhibitor {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075","term_text":"U73122"}}U73122 prevented increases in inositol phosphate levels and blocked progression of cells through S phase after pheromone arrest. The enzymatic activity of Kcs1 in vitro and HPLC analysis of [³H]inositol-labeled kcs1Δ cells confirmed that Kcs1 is the principal kinase responsible for generation of pyrophosphates in synchronously progressing cells. Analysis of plc1Δ, kcs1Δ, and ddp1Δ yeast mutants further confirmed the role that a Plc1- and Kcs1-mediated increase in pyrophosphates may have in progression through S phase. Our data provide genetic, metabolic, and biochemical evidence that synthesis of inositol pyrophosphates through activation of Plc1 and Kcs1 plays an important role in the signaling response required for cell cycle progression after mating pheromone arrest.     

Pectins as mediators of wall porosity in soybean cells

The non-invasive technique of fluorescence redistribution after photobleaching was employed on soybean (Glycine max (L.) Merr.) root cells grown in suspension culture to examine macromolecular transport across plant cell walls. Using both fluorescently derivatized dextrans and proteins of graded size, a functional range of diameters for putative trans-wall channels was determined to be 6.6–8.6 nm. A mild treatment with pectinase apparently enlarged the channels, without adversely affecting cell viability, enabling significantly larger molecules to pass through the wall. Treatment of the cells with cellulysin or protease did not have this enlargement effect. It appears that the organization of pectic substances is a major control element in defining the sieving properties of the wall.Abbreviations EDTA ethylenediaminetetraacetic acid - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Fl-dextran fluorescein-derivatized dextran - FRAP fluorescence redistribution after photobleaching - kDa kilodalton     

Intracellular redistribution of phytochrome in etiolated soybean (Glycine max L.) seedlings

The intracellular distribution of phytochrome in hypocotyl hooks of etiolated soybean (Glycine max L.) has been examined by immunofluorescence using a newly produced monoclonal antibody (Soy-1) directed to phytochrome purified from etiolated soybean shoots. Cortical cells in the hook region exhibit the strongest phytochrome-associated fluorescence, which is diffusely distributed throughout the cytosol in unirradiated, etiolated seedlings. A redistribution of immunocytochemically detectable hytochrome to discrete areas (sequestering) following irradiation with red light requires a few minutes at room temperature in soybean, whereas this redistribution is reversed rapidly following irradiation with far-red light. In contrast, sequestering in oat (Avena sativa L.) occurs within a few seconds (D. McCurdy and L. Pratt, 1986, Planta 167, 330–336) while its reversal by far-red light requires hours (J. M. Mackenzie Jr. et al., 1975, Proc. Natl. Acad. Sci. USA 72, 799–803). The time courses, however, of red-light-enhanced phytochrome pelletability and sequestering are similar for soybean as they are for oat. Thus, while these observations made with a dicotyledon are consistent with the previous conclusion derived from work with oat, namely that sequestering and enhanced pelletability are different manifestations of the same intracellular event, they are inconsistent with the hypothesis that either is a primary step in the mode of action of phytochrome.Abbreviations DIC differential interference contrast - FR far-red light - Ig immunoglobulin - Pfr, P far-red- and red-absorbing form of phytochrome, respectively - R red light This work was supported by National Science Foundation grant No. DCB-8703057.     

The occurrence of leghemoglobin protein in the uninfected interstitial cells of soybean root nodules

The distribution of leghemoglobin (Lb) in resin-embedded root nodules of soybean (Glycine max (L.) Merr.) was investigated using immunogold labeling. Using anti-Lb immunoglobulin G and protein A-gold, Lb or its apoprotein was detected both in cells infected by Bradyrhizobium japonicum and in uninfected interstitial cells. Leghemoglobin was present in the cytoplasm, exclusive of the organelles, and in the nuclei of both cell types. In a comparison of the density of labeling in adjacent pairs of infected and uninfected cells, Lb was found to be about four times more concentrated in infected cells. This is the first report of Lb in uninfected cells of any legume nodule; it raises the possibility that this important nodule-specific protein may participate in mediating oxygen flow to host plant organelles throughout the infected region of the nodule.Abbreviations BSA bovine serum albumin - IgG immunoglobulin G - kDA kilodalton - Lb leghemoglobin - TBST Tris-buffered saline plus Tween 20     

Spatial relationships between uninfected and infected cells in root nodules of soybean

In soybean (Glycine max (L.) Merr.) the uninfected cells of the root nodule are responsible for the final steps in ureide production from recently fixed nitrogen. Stereological methods and an original quantitative method were used to investigate the organization of these cells and their spatial relationships to infected cells in the central region of nodules of soybean inoculated with Rhizobium japonicum strain USDA 3I1B110 and grown with and without nitrogen (as nitrate) in the nutrient medium. The volume occupied by the uninfected tissue was 21% of the total volume of the central infected region for nodules of plants grown without nitrate, and 31% for nodules of plants grown with nitrate. Despite their low relative volume, the uninfected cells outnumbered the much larger infected cells in nodules of plants grown both without and with nitrate. The surface density of the interface between the ininfected and infected tissue in the infected region was similar for nodules in both cases also, the total range being from 24 to 26 mm²/mm³. In nodules of plants grown without nitrate, all sampled infected cells were found to be in contact with at least one uninfected cell. The study demonstrates that although the uninfected tissue in soybean nodules occupies a relatively small volume, it is organized so as to produce a large surface area for interaction with the infected tissue.     

Polyphosphoinositide phospholipase C and evidence for inositol-phosphate-hydrolysing activities in the plasma-membrane fraction from light-grown wheat (Triticum aestivum L.) leaves

The phospholipase C (PLC; EC 3.1.4.3) activity in isolated plasma membranes of light-grown wheat (Triticum aestivum L. cv. Prelude) leaves was investigated. The activity against the polyphosphoinositides was strongly dependent on Ca²⁺ and was affected by the anionic detergent deoxycholate (DOC). In the presence of 20 M Ca²⁺ the PLC activity preferred phosphatidylinositol 4,5-bisphosphate (PIP₂) over phosphatidylinositol 4-monophosphate (PIP) as a substrate. Instead, with 1 mM Ca²⁺ the enzyme clearly favoured PIP. In addition, the PIP₂-PLC activity was increased by Mg²⁺ and in the presence of GTP, guanosine 5-(-thio)-triphosphate as well as ATP, CTP, guanosine 5-diphosphate and guanosine 5-(-thio)-diphosphate. Further analysis showed that a molybdate-sensitive phosphatase activity catalysing the dephosphorylation of inositol 1,4,5-trisphosphate (Ins(1,4,5)P₃) is also associated with the plasma-membrane vesicles. Dephosphorylation of Ins(1,4,5)P₃ was reduced in the presence of GTP or by inclusion of the unspecific phosphatase inhibitor molybdate. The results indicate the presence of a PIP₂-PLC activity and the presence of a molybdate-sensitive phosphatase activity in wheat plasma-membrane vesicles.Abbreviations DOC deoxycholate - IDPase inosine 5-diphosphatase - InsP_s inositol phosphates, the numbering at the end indicates the number of phosphate residues and when their positions on the inositol ring are known they are indicated in parentheses, i.e. - Ins(1,4,5)P₃ inositol 1,4,5-trisphosphate - PIP phosphatidylinositol 4-monophosphate - PIP₂ phosphatidylinositol 4,5-bisphosphate - PLC phospholipase C This work was financially supported by grant from the Deutsche Forschungsgemeinschaft (DFG). M. C. Arz gratefully acknowledges the support of a Graduiertenstipendium des Landes Nordrhein-Westfalen (Germany). We wish to thank S. Laden and G.E. Grambow for assistance.     

Arabinogalactan proteins during the development of soybean root nodules

In soybean (Glycine max (L.) Merr.) root nodules the level of hydroxyproline-containing molecules is developmentally regulated. Hydroxyproline accumulates in both nodule cortex and medulla. In the cortex, the hydroxyproline is mainly localized in the cell wall, presumably as extensin, but in the medulla it is mainly in the soluble fraction as an arabinogalactan protein (AGP). Nodule-specific AGPs are present at early nodulation. The highest concentration of AGP is in the nodule medulla, followed by nodule cortex, uninfected roots, leaves, flowers, pods and seeds. Root nodules and all organs of the soybean plant that were tested were found to express a tissue-specific set of arabinogalactan proteins.Abbreviation AGP Arabinogalactan protein     

Characterization of a connexin homologue in cultured soybean cells and diverse plant organs

Antibodies were prepared against ratliver connexin (27-kDa polypeptide subunit of cell gap junctions found between contacting animal cells) and a putative soybean (Glycine max (L.) Merr.) connexin (29-kDa polypeptide) previously isolated from cultured soybean root cells (SB-1 cell line). The antibodies were utilized to examine the intracellular localization of soybean connexin in these cultured soybean cells and to probe for the presence of a soybean-type connexin in petals, fruits, and leaves from a variety of plants. As judged by specific reactivity on immunoblots, both antibodies against the 27-kDa polypeptide (ratliver connexin) and against the 29-kDa polypeptide (operationally termed soybean connexin) were utilized to demonstrate immunological relatedness of the 27-kDa (rat liver) and the 29-kDa (soybean) polypeptide. Immunofluorescent localization of the putative soybean connexin in cultured soybean cells utilizing these probes demonstrated a peripherally localized punctate pattern of labeling at areas of contact between cells. Use of antibody to the soybean connexin as a probe on immunoblots of extracts from petals, fruits and leaves demonstrated that the soybean-type connexin is present in a large number of different plants.Abbreviations kDa kilodalton - IgG immunoglobulin G - NEPHGE non-equilibrium pH gradient electrophoresis - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis     

Membrane organization in soybean seeds during hydration

The ability of seeds to withstand dehydration indicates that their membranes may maintain structural integrity even when dry. Analysis of polar lipids (the principal lipidic constituents of the membranes) from soybean seeds (Glycine-max (L.) Merr.) by X-ray diffraction indicated that even in the dehydrated state the lipids retained a lamellar (bilayer) configuration. As the degree of hydration was raised, evidence of some structural alteration (apparent as an abrupt increase in bilayer spacing) was obtained from diffraction patterns of both the extracted lipid and particles of seed tissue. In seed tissue this increase in bilayer spacing occurred at a hydration level just above that at which free water could be detected by nuclear-magnetic-resonance analysis. The water content at which the increase in bilayer spacing occurred was higher in the seed tissue than in the extracted polar lipids, probably because other cell components restricted the availability of free water in the seed.Abbreviation NMR nuclear-magnetic resonance     

Interactive effects of light,leaf temperature,CO2 and O2 on photosynthesis in soybean

A biochemical model of C ₃photosynthesis has been developed by G.D. Farquhar et al. (1980, Planta 149, 78–90) based on Michaelis-Menten kinetics of ribulose-1,5-bisphosphate (RuBP) carboxylase-oxygenase, with a potential RuBP limitation imposed via the Calvin cycle and rates of electron transport. The model presented here is slightly modified so that parameters may be estimated from whole-leaf gas-exchange measurements. Carbon-dioxide response curves of net photosynthesis obtained using soybean plants (Glycine max (L.) Merr.) at four partial pressures of oxygen and five leaf temperatures are presented, and a method for estimating the kinetic parameters of RuBP carboxylase-oxygenase, as manifested in vivo, is discussed. The kinetic parameters so obtained compare well with kinetic parameters obtained in vitro, and the model fits to the measured data give r ²values ranging from 0.87 to 0.98. In addition, equations developed by J.D. Tenhunen et al. (1976, Oecologia 26, 89–100, 101–109) to describe the light and temperature responses of measured CO₂-saturated photosynthetic rates are applied to data collected on soybean. Combining these equations with those describing the kinetics of RuBP carboxylase-oxygenase allows one to model successfully the interactive effects of incident irradiance, leaf temperature, CO₂ and O₂ on whole-leaf photosynthesis. This analytical model may become a useful tool for plant ecologists interested in comparing photosynthetic responses of different C₃ plants or of a single species grown in contrasting environments.Abbreviations PCO photorespiratory carbon oxidation - PCR photosynthetic carbon reduction - PPFD photosynthetic photon-flux density - RuBP ribulose bisphosphate