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Host-Pathogen Interactions: XII. Response of Suspension-cultured Soybean Cells to the Elicitor Isolated from Phytophthora megasperma var. sojae, a Fungal Pathogen of Soybeans 1

Ebel, Jürgen; Ayers, Arthur R.; Albersheim, Peter
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1976 EN
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The glucan elicitor isolated from the mycelial walls of Phytophthora megasperma var. sojae, the fungus which causes stem and root rot in soybeans, stimulates the activity of phenylalanine ammonia-lyase and the accumulation of glyceollin in suspension-cultured soybean cells. Nigeran, a commercially available fungal wall glucan, was the only other compound tested which has any activity in this system. Glyceollin is a phenylpropanoid-derived phytoalexin which is toxic to P. megasperma var. sojae. Evidence is presented to support the hypothesis that the action of elicitors in stimulating phytoalexin synthesis is not species or variety specific but, rather, is part of a general defensive response of plants.

Nitrate Reductase Activity in Soybeans (Glycine max [L.] Merr.): II. Energy Limitations 1

Nicholas, Joseph C.; Harper, James E.; Hageman, Richard H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1976 EN
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Growth chamber studies with soybeans (Glycine max [L.] Merr.) were designed to determine the relative limitations of NO3−, NADH, and nitrate reductase (NR) per se on nitrate metabolism as affected by light and temperature. Three NR enzyme assays (+NO3−in vivo, −NO3−in vivo, and in vitro) were compared. NR activity decreased with all assays when plants were exposed to dark. Addition of NO3− to the in vivo NR assay medium increased activity (over that of the −NO3−in vivo assay) at all sampling periods of a normal day-night sequence (14 hr-30 C day; 10 hr-20 C night), indicating that NO3− was rate-limiting. The stimulation of in vivo NR activity by NO3− was not seen in plants exposed to extended dark periods at elevated temperatures (16 hr-30 C), indicating that under those conditions, NO3− was not the limiting factor. Under the latter condition, in vitro NR activity was appreciable (19 μmol NO2− [g fresh weight, hr]−1) suggesting that enzyme level per se was not the limiting factor and that reductant energy might be limiting.

Studies on the Behavior of the Senescence Signal in Anoka Soybeans 1

Lindoo, Susan J.; Noodén, Larry D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1977 EN
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Soybean, a monocarpic plant, has been found to undergo rapid senescence as its fruits mature. In soybeans (Glycine max[L.] Merrill) cv. Anoka, foliar senescence begins during the period of most rapid pod-fill (seed growth), and it can be eliminated by surgical removal of the seeds at an early stage of their growth. Experiments in which fruits are removed from some regions of the plant but allowed to remain on other regions have established that the transmission of the senescence signal is limited; it affects mainly those leaves nearest to the nodes bearing the fruits. The implications of this localized signal movement are discussed.

Partitioning of 14C-Photosynthate, and Long Distance Translocation of Amino Acids in Preflowering and Flowering, Nodulated and Nonnodulated Soybeans 1

Housley, Thomas L.; Schrader, Larry E.; Miller, Marna; Setter, Timothy L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1979 EN
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The influence of stage of development (preflowering versus flowering) in nodulated and nonnodulated soybeans (Glycine max [L.] Merr. cv. Wells) on partitioning of 14C into assimilates following exposure of a soybean leaf to 14CO2 by both steady-state and pulse-labeling techniques was studied. Blades on the second fully expanded leaf from the stem apex were exposed to 14CO2. Radioactive assimilates were extracted from source leaf blades, petioles, and stems (both the path up and path down from source leaf), were separated into neutral (sugars), basic (amino acids), and acidic (organic acids, sugar phosphates) fractions by ion exchange chromatography. The basic fraction was further resolved using thin layer chromatography and the percentage of radioactivity recovered in each amino acid was determined.

Respiratory Changes with Chilling Injury of Soybeans

Leopold, A. Carl; Musgrave, Mary E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1979 EN
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The leakage of solutes from cotyledons of soybeans (cv. Chippewa 64) was markedly stimulated by a chilling treatment (1 to 4 C) during the 1st minute of imbibition, but chilling after even 1 minute of water uptake resulted in little or no leakage increase. The respiratory rate of soybean particles was reduced more than 60% if a chilling treatment (15 minutes at 1 to 4 C) was given during the first minutes of imbibition, and little or no reduction was obtained if the chilling treatment was begun at 5 to 15 minutes after the start of imbibition. Using KCN as an inhibitor of cytochrome oxidase pathway of respiration and salicylhydroxamic acid as an inhibitor of the alternative pathway, it was found that the chilling injury involved a major reduction in the cytochrome pathway in whole axes and cotyledons and an engagement of the alternative pathway of respiration in cotyledon tissue. The suggestion is made that the chilling injury involves lesions resulting from temperature stress during the reorganization of membranes with water entry, and that both the leakage and the respiratory effects are consequences of these membrane lesions.

Ureide Catabolism in Soybeans 1: III. Ureidoglycolate Amidohydrolase and Allantoate Amidohydrolase Are Activities of an Allantoate Degrading Enzyme Complex

Winkler, Rodney G.; Blevins, Dale G.; Randall, Douglas D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1988 EN
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We demonstrate that allantoate is catabolized in soybean seedcoat extracts by an enzyme complex that has allantoate amidohydrolase and ureidoglycolate amidohydrolase activities. Soybean seedcoat extracts released 14CO2 from [ureido-14C]ureidoglycolate under conditions in which urease is not detectable. CO2 and glyoxylate are enzymically released in a one to one ratio indicating that ureidoglycolate amidohydrolase is the responsible activity. Ureidoglycolate amidohydrolase has a Km of 85 micromolar for ureidoglycolate. Glyoxylate and CO2 are enzymically released from allantoate at linear rates in a one to 2.3 ratio from 5 to 30 min. This ratio is consistent with the degradation of allantoate to two CO2 and one glyoxylate with approximately 23% of the allantoate degraded reacting with 2-mercaptoethanol to yield 2-hydroxyethylthio, 2′-ureido, acetate (RG Winkler, JC Polacco, DG Blevins, DD Randall 1985 Plant Physiol 79: 787-793). That [14C]urea production from [2,7-14C]allantoate is not detectable indicates that allantoate-dependent glyoxylate production is enzymic and not a result of nonenzymic hydrolysis of a ureido intermediate (nonenzymic hydrolysis releases urea). These results and those from intact tissue studies (RG Winkler DG Blevins...

Abscisic Acid Suppression of Phenylalanine Ammonia-Lyase Activity and mRNA, and Resistance of Soybeans to Phytophthora megasperma f.sp. glycinea1

Ward, Edmund W. B.; Cahill, David M.; Bhattacharyya, Madan K.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1989 EN
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Etiolated hypocotyls of the resistant soybean (Glycine max [L.] Merr.) cultivar Harosoy 63 became susceptible to Phytophthora megasperma (Drechs.) f.sp. glycinea (Hildeb.) Kuan and Erwin race 1 after treatment with abscisic acid. Susceptibility was expressed by increases in lesion size and a major decrease in accumulation of the isoflavonoid phytoalexin, glyceollin. In untreated hypocotyls, activity of phenylalanine ammonia-lyase and accumulation of mRNA for this enzyme increased rapidly after infection, but these increases were suppressed in abscisic acid-treated hypocotyls. The results suggest the possibility that biosynthesis of glyceollin in the resistance response of soybeans may be controlled at the transcriptional level by changes in abscisic acid concentrations caused by infection.

Accumulation of Apoplastic Iron in Plant Roots 1: A Factor in the Resistance of Soybeans to Iron-Deficiency Induced Chlorosis?

Longnecker, Nancy; Welch, Ross M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1990 EN
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We hypothesized that the resistance of Hawkeye (HA) soybean (Glycine max L.) to iron-deficiency induced chlorosis (IDC) is correlated to an ability to accumulate a large pool of extracellular-root iron which can be mobilized to shoots as the plants become iron deficient. Iron in the root apoplast was assayed after efflux from the roots of intact plants in nutrient solution treated with sodium dithionite added under anaerobic conditions. Young seedlings of HA soybean accumulated a significantly larger amount of extracellular iron in their roots than did either IDC-susceptible PI-54619 (PI) soybean or IDC-resistant IS-8001 (IS) sunflower (Helianthus annus L.). Concurrently, HA soybean had much higher concentrations of iron in their shoots than either PI soybean or IS sunflower. The concentration of iron in the root apoplast and in shoots of HA soybean decreased sharply within days after the first measurements of extracellular root iron were made, in both +Fe and −Fe treatments. The accumulation of short-term iron reserves in the root apoplast and translocation of iron in large quantities to the shoot may be important characteristics of IDC resistance in soybeans.

Foliar Sterols in Soybeans Exposed to Chronic Levels of Ozone 1

Grunwald, Claus; Endress, Anton G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1985 EN
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Soybeans (Glycine max) exposed to chronic levels of ozone showed a linear decrease in biomass with increasing concentration. The foliar free sterols increased while the steryl ester, and the steryl glycosides, a minor component, decreased with increasing pollutant concentration. Of the free sterols, stigmasterol showed the largest increase, followed by sitosterol; campesterol, however, decreased. All steryl esters decreased; sitosterol showed the largest decrease and campesterol the least.

Response to Drought Stress of Nitrogen Fixation (Acetylene Reduction) Rates by Field-Grown Soybeans

Weisz, P. Randall; Denison, Robert F.; Sinclair, Thomas R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1985 EN
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The effects of drought stress on soybean nodule conductance and the maximum rate of acetylene reduction were studied with in situ experiments performed during two seasons and under differing field conditions. In both years drought resulted in decreased nodule conductances which could be detected as early as three days after water was withheld. The maximum rate of acetylene reduction was also decreased by drought and was highly correlated with nodule conductance (r = 0.95). Since nodule conductance is equal to the nodule surface area times the permeability, the relationship of these variables to both whole-plant and unit-nodule nitrogenase activity was explored. Drought stress resulted in a decrease in nodule gas permeability followed by decreases in nodule surface area when drought was prolonged. Under all conditions studied acetylene reduction on a unit-nodule surface area basis was highly correlated with nodule gas permeability (r = 0.92). A short-term oxygen enrichment study demonstrated nodule gas permeability may limit oxygen flux into both drought-stressed and well-watered nodules of these field-grown soybeans.

Effect of Pod Removal on Leaf Photosynthesis and Soluble Protein Composition of Field-Grown Soybeans 1

Wittenbach, Vernon A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1983 EN
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Well nodulated, field-grown soybeans (Glycine max [L.] Merr. var Williams) were depodded just prior to seed development and near mid pod-fill. Both treatments caused a considerable increase in leaf dry weight, suggesting continued photosynthate production following pod removal. Moreover, depodding had a marked effect on leaf soluble protein without affecting total proteolytic activity. Early depodding caused a 50% increase in leaf protein, and both early and late depodding caused the retention of protein for several weeks following the decline in control leaves. But despite this retention of protein, leaves of depodded plants showed no difference in the onset of the irreversible decline in photosynthesis. Therefore, although depodding delayed the loss of leaf chlorophyll and protein, it did not delay the onset of functional leaf senescence and in fact, actually appeared to enhance the rate of decline in photosynthesis. There was a good correlation between the irreversible decline in ribulose bisphosphate carboxylase (activity and amount) and that of photosynthesis. In contrast, the correlation did not seem as good between stomatal closure and the onset of the irreversible decline in photosynthesis. The reason total soluble protein remained high following depodding while carboxylase...

Chloroplast Ultrastructure, Chlorophyll Fluorescence, and Pigment Composition in Chilling-Stressed Soybeans 1

Musser, Robert L.; Thomas, Shirley A.; Wise, Robert R.; Peeler, Thomas C.; Naylor, Aubrey W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1984 EN
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Shoots of 16-day-old soybeans (Glycine max L. Merr. cv Ransom) were chilled to 10°C for 7 days and monitored for visible signs of damage, ultrastructural changes, perturbations in fluorescence of chlorophyll (Chl), and quantitative changes in Chl a and b and associated pigments. Precautions were taken to prevent the confounding effects of water stress. A technique for the separation of lutein and zeaxanthin was developed utilizing a step gradient with the high performance liquid chromatograph. Visible losses in Chl were detectable within the first day of chilling, and regreening did not occur until the shoots were returned to 25°C. Ultrastructurally, unstacking of chloroplast grana occurred, and the envelope membranes developed protrusions. Furthermore, the lipids were altered to the point that the membranes were poorly stabilized by a glutaraldehyde/osmium double-fixation procedure. Chl fluorescence rates were greatly reduced within 2 hours after chilling began and returned to normal only after rewarming. The rapid loss of Chl that occurred during chilling was accompanied by the appearance of zeaxanthin and a decline in violaxanthin. Apparently a zeaxanthin-violaxanthin epoxidation/de-epoxidation cycle was operating. When only the roots were chilled...

Alteration of 14C-Assimilate Partitioning in Leaves of Soybeans Having Increased Reproductive Loads at One Node 1

Carlson, Dale R.; Brun, William A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1984 EN
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The objectives of this study were to determine if the partitioning of recently fixed carbon between starch and water-soluble compounds could be altered by increasing the pod load in the leaf axil, and if the presence of source leaves acropetal to such a node would influence the partitioning of carbon within the subtending leaf. Soybeans (Glycine max L. Merr. cv Hodgson 78) were grown to full-bloom in a controlled environment chamber, and then deflowered at all nodes except the eighth. This treatment resulted in an 83% increase in the number of pods at the eighth node. At 24 days after flowering, one-half of the treated plants were girdled above the untreated node. Forty-two hours later, the eighth trifoliolate was pulsed with 14CO2 and sampled for radiolabeled starch and water-soluble compounds (WSC) at 0.5, 2, 4, 8, 12, and 24th after labeling.

Effects of CO2 Enrichment and Carbohydrate Content on the Dark Respiration of Soybeans 1

Hrubec, Terry C.; Robinson, J. Michael; Donaldson, Robert P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1985 EN
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26.63%
During the period of most active leaf expansion, the foliar dark respiration rate of soybeans (Glycine max cv Williams), grown for 2 weeks in 1000 microliters CO2 per liter air, was 1.45 milligrams CO2 evolved per hour leaf density thickness, and this was twice the rate displayed by leaves of control plants (350 microliters CO2 per liter air). There was a higher foliar nonstructural carbohydrate level (e.g. sucrose and starch) in the CO2 enriched compared with CO2 normal plants. For example, leaves of enriched plants displayed levels of nonstructural carbohydrate equivalent to 174 milligrams glucose per gram dry weight compared to the 84 milligrams glucose per gram dry weight found in control plant leaves. As the leaves of CO2 enriched plants approached full expansion, both the foliar respiration rate and carbohydrate content of the CO2 enriched leaves decreased until they were equivalent with those same parameters in the leaves of control plants. A strong positive correlation between respiration rate and carbohydrate content was seen in high CO2 adapted plants, but not in the control plants.

Enzymic Degradation of Allantoate in Developing Soybeans 1

Winkler, Rodney G.; Polacco, Joseph C.; Blevins, Dale G.; Randall, Douglas D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1985 EN
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A Mn2+-dependent enzymic breakdown of allantoate has been detected in crude and partially purified extracts of developing soybeans. The products detected were CO2, NH3, glyoxylate, labile glyoxylate derivatives, and low levels of urea. Urea is initially produced at less than 10% the rate of urease-independent CO2 release indicating that the activity is not allantoate amidinohydrolase (i.e. urea is not directly cleaved off allantoate). The urease-independent CO2 releasing activity has an apparent Km of 1.0 millimolar for allantoate. Ethylenediaminetetraacetate, borate, and acetohydroxamate (all at 10 millimolar) inhibit the enzymic production of NH3, CO2, and labile glyoxylate derivatives from allantoate. However, the potent urease inhibitor, phenyl phosphordiamidate does not inhibit CO2 and NH3 release indicating that the action of acetohydroxamate is not due to its inhibition of urease. That the allantoatedegrading activity was more than 5-fold greater in seed coats than in embryos is consistent with the data of Rainbird et al. (Plant Physiol 1984 74: 329-334) which indicate that available ureides are metabolized before reaching the embryo. 2-Ethanolthio, 2′ureido, acetic acid (NH2COHNCHCO2HSCH2CH2OH), the first allantoate-derived product detected by HPLC analysis...

Carbon and Nitrogen Assimilation and Partitioning in Soybeans Exposed to Low Root Temperatures 1

Walsh, Kerry B.; Layzell, David B.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1986 EN
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Low root temperature effects on vegetative growth of soybean (Harosoy 63 × Rhizobium japonicum USDA 16) were examined in 35 day old plants exposed to temperatures of 15°C (shoots at 25°C) for an 11 day period. Duing this period various aspects of C and N assimilation and partitioning were monitored including shoot night and nodulated root respiration, C and N partitioning to six plant parts, C2H2 reduction, H2 evolution, leaf area, transpiration, net photosynthesis, and N2 fixation. The low temperature treatment resulted in a decrease in the net rate of N2 fixation but nitrogenase relative efficiency increased. In response, the plant retained N in the tissues of the nodulated root and decreased N partitioning to young shoot tissues, thereby inducing the remobilization of N from older leaves, and reducing leaf area development. The leaf area specific rate of net photosynthesis was not affected over the study period; however, shoot and nodulated root respiration declined. Consequently, C accumulated in mature leaves and stems, partly in the form of increased starch reserves. Three possibilities were considered for increasing low temperature tolerance in nodulated soybeans: (a) decrease in temperature optima for nitrogenase, (b) increased development of nodules and N2 fixation capacity at low temperature...

Remobilization Patterns of C and N in Soybeans with Different Sink-Source Ratios Induced by Various Night Temperatures 1

Seddigh, Majid; Jolliff, Gary D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1986 EN
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26.63%
The effects of increased sink-source ratios, induced by elevating night temperatures, on remobilization of 14C-assimilates and N within field-grown soybeans (Glycine max [L.] Merr.) was investigated from preflowering to maturity. Raising the mean minimum night temperature for the entire growing season from 10 (check, uncontrolled) to 16°C increased seed growth without appreciable effect on final leaf area. Increasing this temperature to 24°C increased seed growth and reduced final leaf area. Leaves, stems, petioles, and pods acted as intermediate storage sites for 14C assimilates. Only plants with higher night temperatures remobilized some of the stored assimilates during the period of rapid seed growth. Even the seeds in the 24°C plants with the largest sink-source ratios did not utilize all the C-assimilates potentially available for remobilization. Nitrogen was readily remobilized from petioles, stems, and pods of all treatments as early as the beginning of seed development, but from the leaves only during late seed-filling. However, only plants with elevated night temperatures tended to remobilize all of the available N from vegetative tissues and pods. We concluded that a larger portion of stored assimilates may be remobilized to the seed if a strong seed sink can be sustained. It also appeared that with increasing sink-source ratios...

Relationship of Endogenous Abscisic Acid to Sucrose Level and Seed Growth Rate of Soybeans 1

Schussler, Jeffrey R.; Brenner, Mark L.; Brun, William A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1991 EN
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It has been proposed that abscisic acid (ABA) may stimulate sucrose transport into filling seeds of legumes, potentially regulating seed growth rate. The objective of this study was to determine whether the rate of dry matter accumulation in seeds of soybeans (Glycine max L.) is correlated with the endogenous levels of ABA and sucrose in those sinks. The levels of ABA and sucrose in seed tissues were compared in nine diverse Plant Introduction lines having seed growth rates ranging from 2.5 to 10.0 milligrams dry weight per seed per day. At 14 days after anthesis (DAA), seeds of all genotypes contained less than 2 micrograms of ABA per gram fresh weight. Levels of ABA increased rapidly, however, reaching maxima at 20 to 30 DAA, depending upon tissue type and genotype. ABA accumulated first in seed coats and then in embryos, and ABA maxima were higher in seed coats (8 to 20 micrograms per gram fresh weight) than in embryos (4 to 9 micrograms per gram fresh weight. From 30 to 50 DAA, ABA levels in both tissues decreased to less than 2 micrograms per gram fresh weight. Levels of sucrose were also low early in development, less than 10 milligrams per gram fresh weight at 14 DAA. However, by 30 DAA, sucrose levels in seed coats had increased to 20 milligrams per gram fresh weight and remained fairly constant for the remainder of the filling period. In contrast...

Rapid Release of Protease Inhibitors from Soybeans: Immunochemical Quantitation and Parallels with Lectins

Hwang, David L.; Yang, Wen-Kuang; Foard, Donald E.; Lin, K.-T. -Davis
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1978 EN
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Specific antisera were prepared against the Bowman-Birk trypsin inhibitor and four other trypsin inhibitors of low molecular weight isolated from soybeans (Glycine max L. cv. Tracy). These antisera were used to detect the presence and amount of the inhibitors in: (a) seeds and protein extracts of soybean meal; (b) seedlings; and (c) the water surrounding the seeds and roots of seedlings. Lectin activities in seeds, seedlings, and water were also determined at the same time as the protease inhibitor activities. By competitive inhibition of immunoprecipitation, the combined five low molecular weight protease inhibitors were found to constitute the following percentages of proteins (w/w): 6.3% in defatted soybean meal; 8.1% of the protein extracted from the meal by a buffer of pH 8.6; 8.3, 14.7, 15.2, 16.1, 17.2, and 18.9% of the protein in a lyophilisate of water in which seeds were incubated for 4, 8, 12, 16, 20, and 24 hours, respectively; 8.2% in a lyophilisate of water in which roots of seedlings grew for 20 days; 1.5% in cotyledons; and less than 0.1% in epicotyls, hypocotyls, and roots of 12-day-old seedlings. Hemagglutination activities, expressed as the lowest amount of protein required to give a positive agglutination of 0.2 ml of 2% rabbit red blood cells...

Studies on Genetic Male-Sterile Soybeans: I. Distribution of Plant Carbohydrate and Nitrogen during Development 1

Wilson, Richard F.; Burton, Joseph W.; Buck, Jamie A.; Brim, Charles A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1978 EN
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26.63%
Soybeans (Glycine max [L.] Merr. cv. NC 69-2774) were used to study the nonstructural carbohydrate and nitrogen content of plant tissues, and nitrogenase activity throughout the development of male-sterile and male-fertile plants. Male-sterile plants set approximately 85% fewer pods plus seed than the male-fertile siblings and retained green leaves until a killing frost at 145 days after emergence. Reduced pod set caused increased carbohydrate accumulation in the leaf and root systems of male-sterile plants. Total carbohydrate in roots of male-sterile plants increased from 1.7 to 7.6 times that in the male-fertile roots. A high proportion (60 to 70%) of the male-sterile root carbohydrate was starch. Apparently, root starch was not metabolized by the male-sterile plants. Late in plant development per cent nitrogen was higher in the male-sterile soybean tissues. However, no difference was found in the ability of the nodulated root systems from either genotype to fix nitrogen.