摘要:

Effects of high light and temperature stress on the structure and function of the photosynthetic apparatus of wheat (Triticum aestivum) were studied. There was a decrease in the electron transport activity of chloroplasts isolated from photoinhibited and heat-stressed leaves. Chlorophyll fluorescence was measured in photoinhibited and heat-stressed leaves and the decrease in variable fluorescence and variable to maximum fluorescence ratio of the stressed leaves indicated a loss in the quantum yield of photosynthesis. The decrease in electron transport activity was accompanied by an increase in peroxidation of thylakoid lipids. Lipid peroxidation indicated the oxidative degradation of polyunsaturated fatty acyl residues of the thylakoid lipids. A negative correlation was observed between electron transport activity and lipid peroxidation. The electron transport activity was completely lost as the peroxidation level reached a threshold equivalent to 0.6 micromoles malondialdehyde. The threshold of lipid peroxidation for complete loss of activity was the same for both photoinhibition and heat treatment, suggesting that the nature of the environmental stress may be less important with respect to the relationship between electron transport and lipid peroxidation. Thus, it seems likely that lipids are required for sustaining the photosynthetic activity under environmental stress, and a loss in activity is observed as the lipids are degraded either by high light or high temperature stress.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

Cucumber (Cucumis sativusL., cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid and then incubated in the dark for 14 hours. The intact chloroplasts were isolated from the above plants in the dark and were exposed to weak light (250 micromoles per square meter per second). Within 30 minutes, photosystem II activity was reduced by 50%. The singlet oxygen (1O2) scavengers, histidine and sodium azide (NaN3) significantly protected against the damage caused to photosystem II. The hydroxyl radical scavenger formate failed to protect the thylakoid membranes. The production of1O2monitored asN,N-dimethylp-nitrosoaniline bleaching increased as a function of light exposure time of treated chloroplasts and was abolished by the1O2quencher, NaN3. Membrane lipid peroxidation monitored as malondialdehyde production was also significantly reduced when chloroplasts were illuminated in the presence of NaN3and histidine. Protochlorophyllide was the most abundant pigment accumulated in intact chloroplasts isolated from 5-aminolevulinic acid-treated plants and was probably acting as type II photosensitizer.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

Cinnamyl alcohol dehydrogenase (CAD) is an enzyme involved in lignin biosynthesis. In this paper, we report the purification of CAD to homogeneity from tobacco (Nicotiana tabacum) stems. The enzyme is low in abundance, comprising approximately 0.05% of total soluble cell protein. A simple and efficient purification procedure for CAD was developed. It employs three chromatography steps, including two affinity matrices, Blue Sepharose and 2′5′ADP-Sepharose. The purified enzyme has a specific cofactor requirement for NADP and has high affinity for coniferyl alcohol (Km= 12 micromolar) and coniferaldehyde (Km= 0.3 micromolar). Two different sized polypeptide subunits of 42.5 and 44 kilodaltons were identified and separated by reverse-phase HPLC. Peptide mapping and amino acid composition analysis of the polypeptides showed that they are closely related, although not identi

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

Several polyclonal sera were raised in rabbits and in mice against putative sucrose carrier proteins,i.e.a 42 kilodalton (O Gallet, R Lemoine, C Larsson, S Delrot [1989] Biochim Biophys Acta 978: 56-64) and a 62 kD (KG Ripp, PV Viitanen, WD Hitz, VR Fransceschi [1988]Plant Physiol 88: 1435-1445) polypeptide of the plasma membrane. The effects of these sera on the active uptake of sucrose and of valine into purified plasma membrane vesicles from sugar beet (Beta vulgarisL.) leaves and roots were studied. At a dilution of 1/50, the anti-42 kilodalton sera consistently inhibited sucrose uptake in plasma membranes from leaves or from roots. They had no effect on valine uptake. Under the same experimental conditions, the anti-62 kilodalton sera had no effect on active uptake of sucrose. The data further support the view that a 42 kilodalton polypeptide is a component of the transport system mediating sucrose uptake across the plasma membrane of plant cells.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

An immunoglobulin Mkmonoclonal (F8IVE9) antibody raised against oat (Avena sativacv Garry) root homogenate has been produced and characterized. The predominant target bound by this antibody is a 62-kilodalton protein (p62) that is expressed in both oat root and oat shoot cells. Treatment of the oat antigen with periodate, or with recombinant N-glycanase, affects the F8IVE9 binding to the antigen, suggesting that the specific epitope for this monoclonal antibody involves a carbohydrate determinant. Levels of p62 present in cells of the oat root increase approximately twofold as the root tissue matures during the first 11 days postgermination. In contrast, levels of expression in shoot tissue remain relatively constant during the same period. The p62 antigen has been shown to be expressed at the plasma membrane by immunohistochemical means, by immunofluorescent labeling of protoplasts, and by enzyme-linked immunosorbent assay analysis of purified plasma membrane. The F8IVE9 antigenic target appears to be uniformly distributed through root tissue but is differentially expressed in specific sections of the shoot. F8IVE9 antibody also binds to antigens expressed in a number of other species, including clover, corn, pea, broccoli, mustard, and bean, and has been shown to bind toSamaneaprotoplast plasma membranes. This monoclonal antibody may prove to be useful for a variety of investigations, including an analysis of the specific patterns of cellular differentiation that occur during early morphogenesis, and the characterization of plasma membrane-associated elements in plants.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

Guard cell protoplasts fromCommelina communisL. illuminated with red light responded to a blue light pulse by an H+extrusion which lasted for about 10 minutes. This proton extrusion was accompanied by an O2uptake with a 4H+to O2ratio. The response to blue light was nil in darkness without a preillumination period of red light and increased with the duration of the red light illumination until about 40 minutes. However, acidification in response to a pulse of blue light was obtained in darkness when external NADH (1 millimolar) was added to the incubation medium, suggesting that redox equivalents necessary for the expression of the response to blue light in darkness may be supplied via red light. In accordance with this hypothesis, the photosystem II inhibitor 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (10 micromolar) decreased the acidification in response to blue light more efficiently when it was added before red light illumination than before the blue light pulse. In the presence of hexacyanoferrate, the acidification in response to a blue light pulse was partly inhibited (53% of control), suggesting a competition for reducing power between ferricyanide reduction and the response to blue light.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

Japanese black pine (Pinus thunbergii) cotyledons were found to synthesize chlorophylls in complete darkness during germination, although the synthesis was not as great as that in the light. The compositions of thylakoid components in plastids of cotyledons grown in the dark and light were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of polypeptides and spectroscopic determination of membrane redox components. All thylakoid membrane proteins found in preparations from light-grown cotyledons were also present in preparations from dark-grown cotyledons. However, levels of photosystem I, photosystem II, cytochromeb[ill]/f, and light-harvesting chlorophyll-protein complexes in dark-grown cotyledons were only one-fourth of those in light-grown cotyledons, on a fresh weight basis. These results suggest that the low abundance of thylakoid components in dark-grown cotyledons is associated with the limited supply of chlorophyll needed to assemble the two photosystem complexes and the light-harvesting chlorophyll-protein complex.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

The 2′,3′-dialdehyde derivative of ATP (dial-ATP) has been shown to be an affinity label for the ATP binding site of the H+-ATPase from tonoplast of etiolated mung bean seedlings (Vigna radiataL.). The dial-ATP caused marked inactivation of enzymatic activities of both membrane-bound and soluble ATPase and its associated proton translocation. The inactivation was reversible, but could be stabilized by NaBH4. The sodium dodecyl sulfatepolyacrylamide gel electrophoresis pattern revealed that the dial-ATP binding site was in the large (A) subunit of ATPase. The inhibition could be substantially protected by its physiological substrate ATP, pyrophosphate, and nucleotides in the decreasing order: ATP>pyrophosphate>ADP = AMP>GTP>CTP = UTP. A Lineweaver-Burk plot showed that the mode of inhibition was competitive with respect to ATP. Loss of ATPase activity followed pseudo-first order kinetics with aKiof 4.1 millimolar, a minimum inactivation half-time of 20 seconds, and a pseudo-first order rate constant of 0.035 s−1. The double logarithmic plot of apparent rate constantversusdial-ATP concentration gave a slope of 0.927, indicating that inactivation results from reaction of at least one lysine residue at the catalytic site of the large subunit. Labeling studies with [3H]dial-ATP indicate that the incorporation of approximately 1 mole of dial-ATP per mole ATPase is sufficient to completely inhibit the ATPase. A working model of nonequivalent subunits for enzymatic mechanism of vacuolar ATPase is sugg

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

To study gene regulation during the transition from late embryogeny to germination, we have analyzed the expression of a gene encoding the glyoxylate cycle enzyme malate synthase in transgenic tomato (Lycopersicon esculentum) plants. We have shown that although there are at least four classes of malate synthase genes inBrassica napusL., one gene is expressed at a high level during both late embryogeny and postgermination. Analyses of transgenic tomato plants containing the expressedB. napusgene along with 4.7 and 1.0 kilobase pairs of 5′and 3′flanking sequences, respectively, confirmed that a single gene is expressed at both stages of development. Furthermore, localization studies have shown that mRNA encoded by theB. napusgene is distributed throughout the tissues of a mature embryo but is not detected in the vascular cylinder of a seedling. We conclude that the sequences required to qualitatively regulate the gene correctly over the plant life cycle are present within the transferred gene and/or flanking regions. Moreover, the malate synthase gene is regulated differently during late embryogeny and postgermination in the developing vascular cylin

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB

摘要:

Phenylalanine ammonia-lyase (PAL, EC4.3.1.5) is involved in the lignification of pine suspension cultures in response to an elicitor prepared from an ectomycorrhizal fungus. To elucidate the molecular basis of this response, PAL was purified to homogeneity from jack pine (Pinus banksiana) suspension cultures using anion-exchange and chromatofocussing fast protein liquid chromatography. Physical characterization of the enzyme revealed that pine PAL was similar to PAL from other plant sources. Pine PAL had a pH optimum of 8.8, an isoelectric point of 5.75, and a native molecular mass of 340 kilodaltons. The enzyme appears to be a tetramer composed of 77 kilodalton subunits. Chromatographic and western blot analyses were used to identify possible isoenzymic changes in pine PAL in response to elicitation and to determine the nature of the increase in PAL activity associated with inducible lignification in these cultures. Only one species of PAL was detected inP. banksianacell cultures and increased quantities of this protein were correlated with the enhanced enzyme activity observed in elicited cultures.P. banksianaPAL was not feedback-inhibited by a wide range of phenolic compounds at micromolar concentrations, including the reaction product cinnamic acid. Our data suggest that a different set of metabolic and molecular controls must be in place for the regulation of PAL in pine.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1992

数据来源: ASPB