Plant Physiology

Lauer, Michael J.; Pallardy, Stephen G.; Blevins, Dale G.; Randall, Douglas D.

doi: 10.1104/pp.91.3.848pmid: 16667147

Abstract Low phosphate nutrition results in increased chlorophyll fluorescence, reduced photosynthetic rate, accumulation of starch and sucrose in leaves, and low crop yields. This study investigated physiological responses of soybean (Glycine max [L.] Merr.) leaves to low inorganic phosphate (Pi) conditions. Responses of photosynthesis to light and CO2 were examined for leaves of soybean grown at high (0.50 millimolar) or low (0.05 millimolar) Pi. Leaves of low Pi plants exhibited paraheliotropic orientation on bright sunny days rather than the normal diaheliotropic orientation exhibited by leaves of high Pi soybeans. Leaves of plants grown at high Pi had significantly higher light saturation points (1000 versus 630 micromole photons [400-700 nanometers] per square meter per second) and higher apparent quantum efficiency (0.062 versus 0.044 mole CO2 per mole photons) at ambient (34 pascals) CO2 than did low Pi leaves, yet stomatal conductances were similar. High Pi leaves also had significantly higher carboxylation efficiency (2.90 versus 0.49 micromole CO2 per square meter per second per pascal), a lower CO2 compensation point (6.9 versus 11.9 pascals), and a higher photosynthetic rate at 34 pascals CO2 (19.5 versus 6.7 micromoles CO2 per square meter per second) than did low Pi leaves. Soluble protein (0.94 versus 0.73 milligram per square centimeter), ribulose-1,5-bisphosphate carboxylase/oxygenase content (0.33 versus 0.25 milligram per square centimeter), and ribulose-1,5-bisphosphate carboxylase/oxygenase specific activity (25.0 versus 16.7 micromoles per square meter per second) were significantly greater in leaves of plants in the high Pi treatment. The data indicate that Pi stress alters the plant's CO2 reduction characteristics, which may in turn affect the plant's capacity to accommodate normal radiation loads. 2 Present address: College of Marine Studies, Lewes Complex, University of Delaware, Lewes, DE 19958. 1 Supported by the Missouri Agricultural Experiment Station and by a grant from the U.S. Department of Agriculture National Needs Fellowship Program, grant 84-GRAD-9-0033. This research is a contribution of the Missouri Agricultural Experiment Station Journal Series No. 10,777. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

LaRosa, P. Christopher; Singh, Narendra K.; Hasegawa, Paul M.; Bressan, Ray A.

doi: 10.1104/pp.91.3.855pmid: 16667148

Abstract Osmotin is a major protein which accumulates in tobacco cells (Nicotiana tabacum L. var Wisconsin 38) adapted to low water potentials. Quantitation of osmotin levels by immunoblots indicated that cells adapted to 428 millimolar NaCl contained 4 to 30 times the level of osmotin found in unadapted cells, depending on the stage of growth. Unadapted cells accumulated low levels of osmotin with apparent isoelectric points, (pl) of 7.8 and >8.2. Upon transfer of NaCl-adapted cells to medium without NaCl and subsequent growth for many cell generations, the amount of osmotin declined gradually to a level intermediate between that found in adapted and unadapted cells. NaCl-adapted cells grown in the absence of NaCl accumulated both pl forms; however, the form accumulated by cells adapted to NaCl (pl > 8.2) was most abundant. Adapted cells grown in the absence of NaCl exhibited absolute growth rates and NaCl tolerance levels which were intermediate to those of NaCl-adapted and unadapted cells. The association between osmotin accumulation and stable NaCl tolerance indicates that cells with a stable genetic change affecting the accumulation of osmotin are selected during prolonged exposure to high levels of NaCl. This stable alteration in gene expression probably affects salt tolerance. 1 Supported by Purdue University Agricultural Experiment Station Program Funds, U.S. Department of Agriculture grant No. 86-CRCR-1-12064 and U.S. Department of Energy grant No. DE1309. Journal Paper No. 11963, Purdue University Agricultural Experiment Station. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Westgate, Mark E.; Grant, Debra L. Thomson

doi: 10.1104/pp.91.3.862pmid: 16667149

Abstract Reproductive development in maize (Zea mays L.) is vulnerable to plant water deficits during anthesis but becomes less sensitive as reproduction progresses. To determine whether changes in tissue water status correlated with the change in sensitivity, we examined the water potential (Ψw), osmotic potential (Ψs), and turgor of reproductive tissues during a short-term water deficit imposed at anthesis or mid-grain fill. Plants were grown in controlled environments in soil. At anthesis, leaf, husk, silk, and ovary Ψw of control plants was similar (−0.5 to −0.65 megapascal) at midday. When water was withheld, Ψw decreased to −1.75, −1.3, −1.2, and −1.0 megapascal in these tissues. Net water uptake by the ovaries was inhibited, but final dry weight, solute content, and total extractable carbohydrates were similar to the controls. At mid-grain fill, leaf, husk, grain, and embryo Ψw of control plants were −0.55, −0.35, −0.75, and −0.80 megapascal at midday. When water was withheld, leaf and husk Ψw decreased to −2.4 and −1.4 megapascal within 6 days. However, grain and embryo Ψw remained within 0.15 megapascal of control values. The grain continued to accumulate dry matter despite a net loss of water and a reduction in total solute content. These results indicate that the response of the reproductive tissues to plant water deficits varies with stage of grain development. The maintenance of a favorable water status only after grain filling is under way may explain, at least in part, the high sensitivity to plant water deficits early in reproductive development and the decrease in sensitivity as reproduction progresses. 1 Supported in part by U.S. Department of Agriculture Competitive Grant No. 86-CRCR-1-2055 to M.E.W. Contribution from USDA-Agricultural Research Service-MWA, Morris, MN, in cooperation with the University of Minnesota West Central Experiment Station, Journal Series No. 16,397. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Muhitch, Michael J.

doi: 10.1104/pp.91.3.868pmid: 16667150

Abstract Maize (Zea mays L.) kernel pedicels, including vascular tissues, pedicel parenchyma, placento-chalazal tissue, and the surrounding pericarp, contained two forms of glutamine synthetase (EC 6.3.1.2), separable by anion exchange chromatography under mildly acidic conditions. The earlier-eluting activity (GSp1), but not the later-eluting activity (GSp2), was chromatographically distinct from the maize leaf and root glutamine synthetases. The level of GSp1 activity changed in a developmentally dependent manner while GSp2 activity was constitutive. GSp1 and GSp2 exhibited distinct ratios of transferase to hydroxylamine-dependent synthetase activities (5 and 23, respectively), which did not change with kernel age. Purified pedicel glutamine synthetases had native relative molecular masses of 340,000, while the subunit relative molecular masses differed slightly at 38,900 and 40,500 for GSp1 and GSp2, respectively. Both GS forms required free Mg2+ with apparent K ms = 2.0 and 0.19 millimolar for GSp1 and GSp2, respectively. GSp1 had an apparent K m for glutamate of 35 millimolar and exhibited substrate inhibition at glutamate concentrations greater than 90 millimolar. In contrast, GSp2 exhibited simple Michaelis-Menten kinetics for glutamate with a K m value of 3.4 millimolar. Both isozymes exhibited positive cooperativity for ammonia, with S0.5 values of 100 and 45 micromolar, respectively. GSp1 appears to be a unique, kernel-specific form of plant glutamine synthetase. Possible functions for the pedicel GS isozymes in kernel nitrogen metabolism are discussed. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Kokubo, Akira; Kuraishi, Susumu; Sakurai, Naoki

doi: 10.1104/pp.91.3.876pmid: 16667151

Abstract Grass culms are known to differ in breaking strength, but there is little physicochemical data to explain the response. The fourth internode of four brittle and two nonbrittle barley (Hordeum vulgare L.) strains were used for physical and chemical studies of culm strength. Inner and outer culm diameters of brittle strains (3.6 ± 0.2 and 5.0 ± 0.1 millimeters) were not significantly different from those of nonbrittle strains (3.9 ± 0.2 and 5.2 ± 0.2 millimeters). Maximum bending stress, at which the culm was broken, was 192 ± 34 g/mm2 for brittle and 490 ± 38 g/mm2 for nonbrittle strains. Wall thickness and cell dimensions of epidermal, sclerenchyma, and parenchyma cells were measured in culm cross sections. The area of cell wall per unit cell area for each tissue was significantly correlated with the maximum bending stress (r = 0.93 for epidermis, 0.90 for sclerenchyma, and 0.84 for parenchyma). Cell walls of brittle culms had 6 to 64% as much cellulose content as those of nonbrittle culms. Maximum bending stress correlated significantly with cellulose content of the cell walls (r = 0.93), but not with the contents of noncellulosic compounds. The lower cellulose content of the brittle culm was significantly correlated with brittleness. 1 Supported by a Grant-in-Aid for Science Research (No. 63110007) from the Ministry of Education, Science and Culture of Japan. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Kenis, Juana D.; Campbell, Wilbur H.

doi: 10.1104/pp.91.3.883pmid: 16667152

Abstract Detached first leaves of 3-day-old corn seedlings (Zea mays L. W64AxW183E) were incubated with nitrate in air or 100% O2 in the light. Nitrate accumulation in the leaves was not depressed by O2. NADH:nitrate reductase activity and enzyme protein, as measured with an enzyme-linked immunosorbent assay, increased in parallel during the 8 h nitrate treatment in air, but in O2 the levels of enzyme activity and protein were depressed. NADH:nitrate reductase mRNA levels were the same in the air-and O2-treated leaves. Total soluble protein levels in leaves were slightly depressed by O2 and shifting from O2 to an air environment increased the protein level. Incorporation of [35S]methionine during nitrate treatment revealed that total soluble protein and nitrate reductase protein synthesis were both depressed by the O2 environment relative to air, but both recovered when leaves were shifted from O2 to air. Although O2 accelerated inactivation of nitrate reductase in vitro, the in vivo inactivation rate appeared to be too low to account for the depressed level of nitrate reductase activity in O2-treated leaves. We concluded that O2 inhibition of nitrate reductase biosynthesis in detached corn leaves was largely due to inhibition of total soluble protein synthesis at the level of translation. 2 J. D. K. was a Visiting Research Scientist supported by a fellowship from the Consejo Nacional de Investigaciones Científicas y Técnicas de la Repüblica Argentina. Permanent address: Laboratorio de Fisiología Vegetal, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Casilla de Correo 395, 5000 Córdoba, Argentina. 1 Supported by grants 86-CRCR-11289 and 88-37262-3896 from the Competitive Research Grants Office of the U.S. Department of Agriculture and grants DMB 85-02672 and 88-03998 from the National Science Foundation. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Bruce, Robert J.; West, Charles A.

doi: 10.1104/pp.91.3.889pmid: 16667153

Abstract Suspension cultures of castor bean (Ricinus communis L.) which have been treated with pectic fragment elicitor rapidly accumulate lignin as measured by derivatization with thioglycolic acid. The responsiveness of cultured cells to elicitor is dependent on the stage of culture growth. In 6-day (maximally responsive) cultures, increases in lignin are first evident 3 hours after addition of pectic fragment elicitor with maximal rates of lignin synthesis between 4 and 10 hours. The abundance of lignin in cultures after 12 hours of elicitor treatment is 10- to 20-fold higher than in untreated control cultures and can thereby account for as much as 2% of the dry cell weight. Only intermediate sizes of pectic oligomer are active as elicitors of lignin. Half-maximal accumulation of lignin occurs at 250 to 300 micrograms per milliliter of an optimal elicitor preparation with an average degree of polymerization of seven. We consider the synthesis of lignin in elicited cultures to be a mechanism of plant disease resistance which is induced by the elicitor. Plant peroxidases have been proposed to catalyze the last enzymatic steps in the biosynthesis of both lignin and hydrogen peroxide. Six extracellular isoenzymes of peroxidase (two anionic, designated A1 and A2, and four cationic, designated C2, C3, C4, and C7) are detectable in healthy suspension cultures of castor bean by native gel electrophoresis. Treatment of cultures with elicitor causes substantial changes in the activity of four of these species (A1, C2, C3, and C7). Elicitor treatment also results in the appearance of three new peroxidase isoenzymes that are not readily detectable in healthy cultures (C1, C5, and C6). Increases in the activities of these isoenzymes are concurrent with or slightly precede the accumulation of lignin in elicited 6-day cultures. By 12 hours after addition of elicitor, C1 becomes the most abundant extracellular isoperoxidase. The differential regulation of expression of peroxidase isoenzymes following elicitor treatment suggests that individual isoenzymes of peroxidase may have specific functional roles in the biosynthesis of disease-lignin. 1 This work was partially supported by U.S. Department of Agriculture Competitive Research Grant 86 CRCR 12145. R. J. B. was partially supported as a Cellular and Molecular Biology Trainee by National Institutes of Health National Research Service Award GM 07185-07. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Egli, Margaret A.; Griffith, Stephen M.; Miller, Susan S.; Anderson, Michael P.; Vance, Carroll P.

doi: 10.1104/pp.91.3.898pmid: 16667154

Abstract Effective (N2-fixing) alfalfa (Medicago sativa L.) and plant-controlled ineffective (non-N2-fixing) alfalfa recessive for the in 1 gene were compared to determine the effects of the in 1 gene on nodule development, acetylene reduction activity (ARA), and nodule enzymes associated with N assimilation and disease resistance. Effective nodule ARA reached a maximum before activities of glutamine synthetase (GS), glutamate synthase (GOGAT), aspartate aminotransferase (AAT), asparagine synthetase (AS), and phosphoenolpyruvate carboxylase (PEPC) peaked. Ineffective nodule ARA was only 5% of effective nodule ARA. Developmental profiles of GS, GOGAT, AAT, and PEPC activities were similar for effective and ineffective nodules, but activities in ineffective nodules were lower and declined earlier. Little AS activity was detected in developing ineffective nodules. Changes in GS, GOGAT, AAT, and PEPC activities in developing and senescent effective and ineffective nodules generally paralleled amounts of immunologically detectable enzyme polypeptides. Effective nodule GS, GOGAT, AAT, AS, and PEPC activities declined after defoliation. Activities of glutamate dehydrogenase, malate dehydrogenase, phenylalanine ammonia lyase, and caffeic acid-o-methyltransferase were unrelated to nodule effectiveness. Maximum expression of nodule N-assimilating enzymes appeared to require the continued presence of a product associated with effective bacteroids that was lacking in in 1 effective nodules. 1 This material is based upon work supported in part by grant 87-CRCR-1-2588 from the Competitive Research Grants Office of the U.S. Department of Agriculture (C. P. V.), and in part by the U.S. Department of Agriculture Food and Agricultural Sciences National Needs Graduate Fellowship Program under agreement No. 84-GRAD-9-0013 (M. A. E.). Cooperative investigation of USDA-ARS and the Minnesota Agricultural Experiment Station (Scientific Journal Series No. 16870). This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Labate, Carlos A.; Leegood, Richard C.

doi: 10.1104/pp.91.3.905pmid: 16667155

Abstract The aim of this work was to examine the effect of exposure of leaves to low temperatures (5°C) upon the contents of phosphorylated intermediates and respiration in darkened barley (Hordeum vulgare L.) plants which differed in their carbohydrate status. In leaves that had previously been illuminated for 24 hours, there was a large increase in amounts of phosphorylated metabolites at 5°C during the first 3 hours of darkness, compared with control plants kept at 30°C. Hexose phosphates accounted for about two-thirds of this increase, which reached a peak after about 3 hours. At higher temperatures, there was a peak in the amount of fructose 2,6-bisphosphate and the rate of respiration which accompanied the transient increase in phosphorylated intermediates. At 5°C the increase in phosphorylated intermediates was not accompanied by appreciable changes in fructose 2,6-bisphosphate, and there was a rapid decline in the rate of respiration. Leaves that had previously been darkened for 24 hours and that were low in carbohydrate failed to accumulate phosphorylated intermediates when exposed to low temperatures. The results are discussed with respect to the acclimation of carbohydrate metabolism to low temperatures. The results suggest that respiratory carbohydrate metabolism is strictly controlled even when the carbohydrate supply and glycolytic intermediates are abundant. The possibility that accumulation of hexose phosphates may be involved in acclimation of metabolism to low temperature is discussed. 2 Permanent address: Escola Superior de Agricultura “Luiz de Queiroz,” Departamento de Genética, Universidade de São Paulo, Piracicaba, C. P. 83, CEP 13400, Brazil. 1 Supported by the Agricultural and Food Research Council, U.K. (Research grant PG50/67) and by the Science and Engineering Research Council, U.K. C. A. L. was supported by the British Council, by an Overseas Research Student Award, and by CNPq Brazil. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Dhawale, Shree; Souciet, Ginette; Kuhn, David N.

doi: 10.1104/pp.91.3.911pmid: 16667156

Abstract Soybeans (Glycine max [L.] Merr.) respond to pathogens by producing isoflavonoid-derived phytoalexins. Chalcone synthase (CHS) is the first enzyme of the flavonoid/isoflavonoid biosynthetic pathway. We investigated changes in the steady state levels of CHS mRNA and other specific mRNAs at increasing times after inoculation in two different race-specific interactions, one between leaves and the bacterium Pseudomonas syringae pv glycinea (Psg), and one between roots and the fungus, Phytophthora megasperma f. sp. glycinea (Pmg). The amount of CHS mRNA increases significantly in soybean leaves inoculated with an avirulent race of Psg but not with a virulent race or water. In contrast, the increase in CHS mRNA is similar in roots inoculated with zoospores of either an avirulent or virulent race of Pmg. CHS mRNA increases significantly in pathogen inoculated roots but not in uninoculated controls. Hydroxyproline-rich glycoprotein (HRGP) has been observed by others to increase in wounded or pathogen-inoculated plants. We report here that HRGP mRNA levels are greater in roots inoculated with an avirulent Pmg race than with a virulent race, but inoculation with either race causes a significant increase in HRGP mRNA with respect to controls. Calmodulin or ubiquitin mRNA do not increase in either uninoculated or inoculated roots and leaves. The possibility that race-specific resistance in soybeans is expressed differently in different organs of the plant is discussed. 2 Present address: USDA, Regional Poultry Research Laboratory, East Lansing, MI 48823. 3 Present address: Institut de Biologie Moleculaire des Plantes du CNRS, Laboratoire de Biochimie, 67084 Strasbourg, France. 1 Supported by U.S. Department of Agriculture grant 83-CRCR-1-1209, National Science Foundation award 8316825, and the Purdue Agriculture Experiment Station, Purdue University, Journal Paper No. 11,382. This content is only available as a PDF. © 1989 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)