摘要:

A study has been made of the effects of the inhibitors carbonylcyanidem-chlorophenylhydrazone (CCCP), 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), and of anoxia on the light-sensitive membrane potential ofVallisnerialeaf cells. The present results are compared with the known effects of these inhibitors on ion transport and photosynthesis (Prins 1974 Ph.D thesis). The membrane potential is composed of a diffusion potential plus an electrogenic component. The electrogenic potential is about−13 millivolts in the dark and−80 millivolts in the light. The inhibitory effect of DCMU and CCCP on the electrogenic mechanisms strongly depends on the light intensity used, the inhibition being less at a higher light intensity. This is of significance in view of the often conflicting results obtained with these inhibitors. With ion transport inVallisneriathe electrogenic pump derives its energy from phosphorylation; however, the process which causes the initial light-induced hyperpolarization and the process that keeps the membrane potential at a steady hyperpolarized state in the light have different energy requirements. The action of photosystem I alone is sufficient to induce the initial hyperpolarization. For continuous operation in the light the activity of photosystem II also is nee

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

Several lines of evidence indicate that allophycocyanin is the previously unidentified“phycochrome”observed in extracts of blue-green algae.Fractions containing phycoerythrin, phycocyanin, and allophycocyanin and exhibiting light-induced absorbance changes were prepared from extracts ofNostoc muscorumandFremyella diplosiphonby isoelectric focusing. Illumination of such fractions with red light (650 nanometers) causes a reduction in absorbance at 620 nm (≃1 to 2%) and an increase at 560 nm. The effect, (previously observed by Björn and Björn [1976 Physiol Plant 36: 297-304]) is reversible, upon illumination with green light (550 nm). Selective immunoprecipitation of the phycobiliproteins indicates that allophycocyanin is the photoresponsive pigment.At pH 4.0 to 4.2, allophycocyanin purified from the same algae or fromPhormidium luridumexhibits a light-induced absorbance change at 620 nm, which coincides with its absorption maximum at this pH; the fluorescence emission of allophycocyanin under these conditions is at 647 nm and its S20,wis 2.28, compatible with anα1β1polypeptide composition. At neutral pH (5.8 to 7.0), allophycocyanin aggregates have a sedimentation coefficient of 4.8 (≃α3β3) and an additional absorption peak at 640 nm appears while that at 620 nm remains unaffected. The fluorescence emission maximum of the larger aggregate is at 667 nm and the light-induced change in its absorption is shifted to 650 nm. The effect of pH changes in the range 4.0 to 7.0 on the spectral and aggregation properties of allophycocyanin is completely reversible. Changes in pH which affect allophycocyanin aggregation have parallel effects on absorption and fluorescence maxima as well as on the light-induced absorbance changes of the biliprotein.No evidence is provided to resolve whether this phycochrome plays the role of an

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

Large doses ofγ-irradiation, given to air-dried pea seeds, inhibit the endomitotic DNA synthesis in pea epicotyls during germination in darkness. The cortex cells of the etiolated epicotyls reach only the 4 C DNA level, whereas cortex cells of unirradiated seeds reach the 8 C DNA level. Epicotyl elongation and cell elongation are also reduced.Application of gibberellic acid restores the endomitotic DNA synthesis and the cell elongation in epicotyls of irradiated seeds. The cortex cells reach again the 8 C DNA level in darkness.The results suggest thatγ-irradiation blocks endomitotic DNA synthesis and cell elongation by lowering the concentration of endogenous gibberellin

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

The phenylalanine ammonia-lyase (PAL) inhibitorl-α-aminooxy-β-phenylpropionic acid (AOPP) was root-fed to light-exposed soybean seedlings alone or with glyphosate [N-(phosphonomethyl)glycine] to test further the hypothesis that PAL activity is involved in the mode of action of glyphosate. Extractable PAL activity was increased by 0.01 and 0.1 millimolar AOPP. AOPP reduced total soluble hydroxyphenolic compound levels and increased phenylalanine and tyrosine levels, indicating thatin vivoPAL activity was inhibited by AOPP. The increase in extractable PAL caused by AOPP may be a result of decreased feedback inhibition of PAL synthesis by cinnamic acid and/or its derivatives. AOPP alone had no effect on growth (fresh weight and elongation) at either concentration, but at 0.1 millimolar it slightly alleviated growth (fresh weight) inhibition caused by 0.5 millimolar glyphosate after 4 days. Reduction of the free pool of phenylalanine by glyphosate was reversed by AOPP. These results indicate that glyphosate exerts some of its effects through reduction of aromatic amino acid pools through increases in PAL activity and that not all growth effects of glyphosate are due to reductions of aromatic amino acid

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

Asparaginase (EC3.5.1.1) was isolated from the developing seed ofPisum sativum.The enzyme is dependent upon the presence of K+for activity, although Na+and Rb+may substitute to a lesser extent. Maximum activity was obtained at K+concentrations above 20 millimolar. Potassium ions protected the enzyme against heat denaturation. The enzyme has a molecular weight of 68,300.Asparaginase activity developed initially in the testa, with maximum activity (3.6 micromoles per hour per seed) being present 13 days after flowering. Maximum activity (1.2 micromoles per hour per seed) did not develop in the cotyledon until 21 days after flowering. Glutamine synthetase and glutamate dehydrogenase were also present in the testae and cotyledons but maximum activity developed later than that of asparaginase.Potassium-dependent asparaginase activity was also detected in the developing seeds ofVicia faba, Phaseolus multiflorus, Zea mays, Hordeum vulgare,and twoLupinusvarieties. No stimulation of activity was detected with the enzyme isolated fromLupinus polyphyllus,which has previously been shown to contain a K+-independent enzyme.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

Experiments were carried out to clarify problems encountered in measuring metabolic and storage pool sizes of nitrate in wheat leaf sections with anin vivonitrate reductase assay. The leaf sections were from seedlings grown on 15 millimolar nitrate. Data obtained show that the cessation of nitrite accumulation, used as an index of the active nitrate pool size, could be caused by lack of anaerobiosis in the assay system, the lack of energy for nitrate reduction, or a loss of nitrate reductase activity. Availability of nitrate was never the limiting factor in this system. It is concluded that pool sizes of nitrate cannot be determined in wheat leaves with thein vivoassays employed.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

Knowledge of the location and magnitude of the resistance to water flow in a plant is fundamental for describing whole plant response to water stress. The reported magnitudes of these resistances vary widely, principally because of the difficulty of measuring water potential within the plant. A number of interrelated experiments are described in which the water potential of a covered, nontranspiring leaf attached to a transpiring sorghum plant (Sorghum bicolor[L.] Moench) was used as a measure of the potential at the root-shoot junction. This allowed a descriptive evaluation of plant resistance to be made.The water potentials of a covered, nontranspiring leaf and a nonabsorbing root in solution, both attached to an otherwise actively transpiring and absorbing plant, were found to be similar. This supported the hypothesis that covered leaf water potential was equilibrating at a point shared by the vascular connections of both leaves and roots,i.e.the nodal complex of the root-shoot junction or crown. The difference in potential between a covered and exposed leaf together with calculated individual leaf transpiration rates were used to evaluate the resistance between the plant crown and the exposed leaf lamina called the connection resistance. There was an apparent decrease in the connection resistance as the transpiration rate increased; this is qualitatively explained as plant capacitance.Assuming that the covered leaf water potential was equal to that in the root xylem at the point of water absorption in the experimental plants with relatively short root axes, calculated radial root resistances were strongly dependent on the transpiration rate. For plants with moderate to high transpiration rates the roots had a slightly larger resistance than the shoots.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

Monospecific antibodies raised against four glyoxysomal enzymes (isocitrate lyase, catalase, malate synthase, and malate dehydrogenase) have been used to detect these proteins among the products ofin vitrotranslation in a wheat germ system programmed with cotyledonary RNA from cucumber seedlings.In vitroimmunoprecipitates were compared electrophoretically with the same enzymes labeledin vivoand also with the purified proteins. Isocitrate lyase yields two bands on sodium dodecyl sulfate-polyacrylamide gels, as synthesized bothin vitro(61.5K and 60K products) andin vivo(63K and 61.5K polypeptides). Both the 63K and 61.5K subunits can also be demonstrated for the isolated enzyme. The two subunits are antigenically cross-reactive and yield similar electrophoretic profiles upon partial proteolytic digestion. A larger subunit is seenin vitrothanin vivofor both malate dehydrogenase (38Kversus33K) and catalase (55Kversus54K); this suggests a need for processing which is often a characteristic of proteins that must be transported across or into membranes. Malate synthase has a molecular weight of 57K bothin vitroandin vivo,but the isolated enzyme is a glycoprotein, containingN-acetyl glucosamine, mannose, and possibly also fucose and xylose. This indicates that the polypeptide portion of the isolated enzyme is smaller than thein vitroproduct and suggests processing of malate synthase also. None of the other three enzymes appears to be glycosylated. The implications of these size differences for the compartmentalization of matrix and membrane-bound glyoxysomal enzymes are discussed.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

The effects of the diphenyl ether herbicides HOE 29152 (methyl-2[4-(4-trifluoromethoxy) phenoxy] propanoate) and nitrofluorfen (2-chloro-1-[4-nitrophenoxy]-4-[trifluoromethyl]benzene) on photosynthetic electron transport have been examined with pea seedling and spinach chloroplasts. Linear electron transport (water to ferricyanide or methylviologen) is inhibited in treated chloroplasts, but neither photosystem II activity (water to dimethylquinone plus dibromothymoquinone) nor photosystem I activity (diaminodurene to methylviologen) is affected. Cyclic electron flow, cata-lyzed by either phenazine methosulfate or diaminodurene, is resistant to inhibition by nitrofluorfen. In diphenyl ether-treated chloroplasts the half-time for the dark reduction of cytochromefis increased 5- to 15-fold. These data indicate that the site of inhibition for the diphenyl ethers is between the two photosystems in the plastoquinone-cytochromefregion.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB

摘要:

The objectives of this study were (a): to define the effects of light, dark, and temperature on nodule activity (acetylene reduction), and (b) to establish the contributions of reserve carbohydrate and recent photosynthate to the support of nodule function. Anin situassay of nodule activity was developed for use with intact, hydroponically grown soybeans (Glycine max[L.] Merr. cv. Calland).Nodule activity of 35-day-old plants grown in controlled environment chambers decreased during a 10-hour dark period at 18 C, compared with activity during the preceding and subsequent 14-hour light periods at 27 C. In contrast, plants that were maintained at a constant 27 C did not vary in nodule activity during diurnally varying dark and light exposure. Nodules of plants exposed to diurnal 18 and 27 in 24-hour continuous dark were less active at 18 C than at 27 C. At constant 27 C, nodule activity was sustained throughout the 24-hour dark period. Thus, nodule activity was independent of short term dark periods but dependent on temperature; nodule activity was decreased at the lower temperature.Temperature also affected the nodule activity of plants maintained in the light. Exposure of shoots and roots of intact plants to the lower temperature (5 hours at 18 C) during the light period resulted in a marked decrease in nodule activity, compared with that of plants maintained at 27 C. Exposure of only the shoot portion to 18 C (roots were maintained at 27 C) resulted in a similar decrease in nodule activity.Nodules of plants exposed to 10 days of diurnally variable dark, light, and temperature had high activity in the light at 27 C and low activity in the dark at 18 C. Nodule activity of plants at a constant 27 C was not affected by diurnally variable dark and light exposure throughout the 10-day period, although activity generally increased with time due to increased nodule mass. At a constant 27 C, nodules of intact plants in continuous dark sustained activity through 72 hours before declining to zero by 7 days. At diurnally varying 18 and 27 C in continuous dark, peak diurnal nodule activity was sustained through 5 days, and then declined to zero by 8 days. Analyses of the carbohydrate content of tissue harvested from this study suggested use of reserve photosynthate (primarily of shoot origin) in support of nodule activity in the absence of concurrent photosynthesis.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1980

数据来源: ASPB