摘要:

Heat-labile elicitors of phytoalexin accumulation in soybeans (Glycine maxL. Merr. cv Wayne) were detected in culture filtrates ofErwinia carotovoragrown on a defined medium containing citrus pectin as the sole carbon source. The heat-labile elicitors were highly purified by cation-exchange chromatography on a CM-Sephadex (C-50) column, followed by agarose-affinity chromatography on a Bio-Gel A-0.5m gel filtration column. The heat-labile elicitor activity co-purified with twoα-1,4-endopolygalacturonic acid lyases (EC 4·2·2·2). Endopolygalacturonic acid lyase activity appeared to be necessary for elicitor activity because heat-inactivated enzyme preparations did not elicit phytoalexins. The purified endopolygalacturonic acid lyases elicited pterocarpan phytoalexins at microbial-inhibitory concentrations in the soybean-cotyledon bioassay when applied at a concentration of 55 nanograms per milliliter (1×10−9molar). One of these lyases released heat-stable elicitors from soybean cell walls, citrus pectin, and sodium polypectate. The heat-stable elicitor-active material solubilized from soybean cell walls by the lyase was composed of at least 90% (w/v) uronosyl residues. These results demonstrate that endopolygalacturonic acid lyase elicits phytoalexin accumulation by releasing fragments from pectic polysaccharides in plant cell

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Electrophysiological measurements on internodal cells ofChara corallinaKlein ex Willd., em. R.D.W. revealed that in the presence of (2-[4-(2′,4′-dichlorophenoxy)phenoxy]propionic acid) (diclofop) the membrane potential was very sensitive to the pH of the bathing medium. At pH 5.7, 100 micromolar diclofop caused a slow reduction in the electrogenic component of the membrane potential to the value of−123±5 millivolts. Membrane resistance initially decreased, recovered transiently, then stabilized at approximately 65% of the control value. At pH 7.0, the potential appeared to plateau around−200 millivolts before rapidly declining to−140±4 millivolts; removal of diclofop resulted in recovery of the electrogenic component. Diclofop reduced cytoplasmic ATP levels by 96.4% and 36.6% at pH 5.7 and 7.0, respectively. At pH 8.2, diclofop did not change the ATP concentration significantly, but induced a hyperpolarization of the membrane potential to near−250 millivolts, and also reduced or inhibited the dark-induced hyperpolarization; the light-induced depolarization was reduced to a lesser extent. DCMU applied in the light elicited the same response at the plasmalemma as placing cells in the dark. When K+channels were opened and cells depolarized with 10 millimolar K+, diclofop induced a further depolarization of approximately 30 millivolts. Cells decoupled with HPO4−2were still sensitive to diclofop. Currents associated with OH−efflux and HCO3−influx, as measured with a vibrating probe technique, became spatially destabilized and reduced in magnitude in the presence of diclofop. After 60 minutes, most of the cell surface was engaged in a low level of OH−efflux activity. The results indicate that diclofop may be a proton ionophore at pH 7.0 and 5.7. At pH 8.2, diclofop may inhibit the operation of the H+-ATPase and OH−efflux systems associated with HCO3−transport by perturbing the control processes that integrate the two, without a reduc

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Anacystis nidulanscells grown under high (3%) CO2partial pressure have greater phycocyanin to chlorophyll ratio (Phc/Chl) relative to cells grown under low (0.2%) CO2tension (Eley (1971) Plant Cell Physiol 12: 311-316). Absorbance difference spectrophotometry ofA. nidulansthylakoid membranes in the ultraviolet (ΔA320) and red (ΔA700) regions of the spectrum reveal photosystem II/photosystem I (PSII/PSI) reaction center ratio (RCII/RCI) changes that parallel those of Phc/Chl. For cells growing under 3% CO2, the Phc/Chl ratio was 0.48 and RCII/RCI = 0.40. At 0.2% CO2, Phc/Chl = 0.38 and RCII/RCI = 0.24. Excitation of intact cells at 620 nm sensitized RCII at a rate approximately 20 times faster than that of RCI, suggesting that Phc excitation is delivered to RCII only. In the presence of DCMU, excitation at 620 nm induced single exponential RCII photoconversion kinetics, suggesting a one-to-one structural-functional correspondance between phycobilisome and PSII complex in the thylakoid membrane. Therefore, phycobilisomes may serve as microscopic markers for the presence of PSII in the photosynthetic membrane ofA. nidulans. Neither the size of individual phycobilisomes nor the Chl light-harvesting antenna of PSI changed under the two different CO2tensions during cell growth. Our results are compatible with the hypothesis that, at low CO2concentrations, the greater relative amounts of PSI present may facilitate greater rates of ATP synthesis via cyclic electron flow. The additional ATP may be required for the active uptake of CO2under such condition

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

A split-root growth system was employed to evaluate the effect of NaCl on nodule formation by soybean (Glycine maxL. Merr. cv Davis). By applying the salinity stress and rhizobial inoculum to only one-half the root system, the effects of salinity on shoot growth were eliminated in the nodulation process.Rhizobiumcolonization of inoculated root surfaces was not affected by the salt treatments (0.0, 26.6, 53.2, and 79.9 millimolar NaCl). While shoot dry weight remained unaffected by the treatments, total shoot N declined from 1.26 grams N per pot at 0.0 millimolar NaCl to 0.44 grams N per pot at 79.9 millimolar NaCl. The concentration of N in the shoot decreased from 3.75% N (0.0 millimolar NaCl) to 1.26% N at 79.9 millimolar NaCl. The decrease in shoot N was attributed to a sharp reduction in nodule number and dry weight. Nodule number and weight were reduced by approximately 50% at 26.6 millimolar NaCl, and by more than 90% at 53.2 and 79.9 millimolar NaCl. Nodule development, as evidenced by the average weight of a nodule, was not as greatly affected by salt as was nodule number. Total nitrogenase activity (C2H2reduction) decreased proportionally in relation to nodule number and dry weight. Specific nitrogenase activity, however, was less affected by salinity and was not depressed significantly until 79.9 millimolar NaCl. In a second experiment, isolates ofRhizobium japonicumfrom nodules formed at 79.9 millimolar NaCl did not increase nodulation of roots under salt stress compared to nodule isolates from normal media (0.0 millimolar NaCl). Salt was applied (53.2 millimolar NaCl) to half root systems at 0, 4, 12, and 96 hours from inoculation in a third experiment. By delaying the application of salt for 12 hours, an increase in nodule number, nodule weight, and shoot N was observed. Nodule formation in the 12- and 96-hour treatments was, however, lower than the control. The early steps in nodule initiation are, therefore, extremely sensitive to even low concentrations of NaCl. The sensitivity is not related to rhizobial survival and is probably due to the salt sensitivity of root infection sites.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Water conductance throughAbies amabilisseedlings was measured while the roots were exposed to temperatures from 15 to 0.25°C. Before conductance was measured, the seedlings were preconditioned for 3 months at either a high temperature (23°C) or a low temperature (3°C). For both groups of seedlings, conductance decreased as root temperature decreased. Conductance was lowest at 0.25°C. In addition, preconditioning at 3°C for 3 months significantly lowered conductance to water at all root temperatures. Under the same environmental conditions, seedlings preconditioned at 3°C had less than 25% of the transpirational water loss of seedlings preconditioned at high temperature. A decrease in leaf osmotic potential also resulted from low temperature preconditioning. In trees growing in the subalpine forest, which is the natural habitat ofAbies amabilis, both decreased leaf conductance to water vapor and lower osmotic potentials were evident in winter. Since in winter the temperature of the soil in the subalpine zone remains less than 1°C for many months, lowered leaf conductance and decreased osmotic potentials appear to be mechanisms which aid in preventing desiccation

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Pretreatment of soybean (Glycine maxL. var Ransom) root systems with abscisic acid (ABA) ameliorates the deleterious effect of low temperatures on root hydraulic conductance. ABA treatment of root systems subsequently chilled to 10°C with shoots at 25°C resulted in higher leaf water potentials and lower stomatal resistances. If the root systems are left at 25°C, ABA causes stomatal closure. Membrane alterations are suggested as a mechanism for the ABA action in plant response to chilling stre

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

The mechanism of host-symbiont recognition in the soybean-Rhizobiumsymbiosis was investigated utilizing mutants ofR. japonicumdefective in nodulation. Soybeans were grown in clear plastic growth pouches allowing the identification of the area on the root most susceptible toRhizobiumnodulation; the area between the root tip (RT) and smallest emergent root hair (SERH). The location of nodules in relation to this developing zone is an indication of the rate of nodule initiation. Nodules were scored as to the distance from the RT mark made at the time of inoculation. Seventy-eight per cent of the plants nodulate above the RT mark when inoculated with the wild typeR. japonicumstrain 3I1b110 with the average distance of the uppermost nodule being approximately 2 millimeters above the RT mark. These data indicate that the wild type strain initiates nodulation rapidly within the RT-SERH zone following inoculation. However, inoculation with the slow-to-nodulate mutant strain HS111 resulted in 100% of the plants nodulating only below the RT mark with the average distance of the uppermost nodule being approximately 56 millimeters below the RT mark. Thus, mutant strain HS111 is defective in the ability to rapidly initiate infection leading to nodulation within the RT-SERH zone. The location of the nodules suggest that stain HS111 must `adapt' to the root environment before nodulation can occur. To test this, strain HS111 was incubated in soybean root exudate prior to inoculation. In this case, 68% of the plants nodulated above the RT mark with the average distance of the uppermost nodule being approximately 1 millimeter below the RT mark. Experiments indicated that the change in nodule initiation by strain HS111 brought about by incubation in soybean root exudate was due to a phenotypic, rather than a genotypic change. The half-time of root exudate incubation for strain HS111 necessary for optimal nodulation enhancement was less than 6 hours. Heat sensitivity and trypsin sensitivity of the nodulation enhancement factor(s) in soybean root exudate indicate a protein was involved in the reversal of the delay in nodulation by mutant strain HS111.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Cultures of the cyanobacteriumAnacystis nidulanswere grown under iron-deficient conditions and then restored by the addition of iron. Membrane proteins from iron-deficient and iron-restored cells were analyzed by lithium dodecyl sulfate-polyacrylamide gradient gel electrophoresis. The incorporation of [35S]sulfate into membrane proteins and lactoperoxidase-catalyzed125I iodination were used to monitor the rates of polypeptide biosynthesis and surface exposure of membrane proteins, respectively. These polypeptide profiles revealed major differences in the membrane composition of iron-deficient and normal cells. Iron deficiency caused a decrease in the amount of certain important membrane proteins, reflecting a decreased rate of biosynthesis of these peptides. Several photosystem II peptides also showed an increase in surface exposure after iron stress. In addition, iron deficiency led to the synthesis of proteins at 34 and 52 kilodaltons which were not present in normal cells. When iron was restored to a deficient culture, a metabolic sequence was initiated within the first 12 h after the addition of iron which led to phenotypically normal cells. Pulse labeling with [35S]sulfate during this period demonstrated that iron addition initiates a coordinated pattern of synthesis that leads to the assembly of normal membranes.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

In situmeasurement of sudden leaf water potential changes has not been performed under field conditions. A laboratory investigation involving the measurement of leaf water potential prior to and 2 to 200 minutes after excision of citrus leaves (Citrus jambhiri) showed good linear correlation (r= 0.99) betweenin situleaf psychrometer and Scholander pressure chamber measurements. Following this, a field investigation was conducted which involved psychrometric measurement prior to petiole excision and 1 minute after excision. Simultaneous pressure chamber measurements were performed on neighboring leaves prior to the time of excision and then on the psychrometer leaf about 2 minutes after excision. These data indicate that within the first 2 minutes after excision, psychrometer and pressure chamber measurements were linearly correlated (r= 0.97). Under high evaporative demand conditions, the rate of water potential decrease was between 250 and 700 kilopascals in the first minute after excision. These results show that the thermocouple psychrometer can be used as a dynamic and nondestructive field technique for monitoring leaf water potential.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB

摘要:

Cellulysin-induced ethylene production in tobacco (Nicotiana tabacumL.) leaf discs was enhanced several-fold by prior exposure of the leaf tissue to ethylene. This enhancement in the response of the tissue to Cellulysin increased rapidly during 4 and 8 hours of pretreatment with ethylene and resulted from greater conversion of methionine to ethylene. On treatment with Cellulysin, the content of 1-aminocyclopropane-1-carboxylic acid (ACC) in leaf discs not pretreated with ethylene markedly increased while that of the ethylene-pretreated tissue was only slightly higher than in the tissue incubated in the absence of Cellulysin. Ethylene-treated tissue, however, converted ACC to ethylene at a faster rate than air controls. These data indicate that ethylene stimulates Cellulysin-induced ethylene production by stimulating the conversion of ACC to ethylene. Data are also presented on a possible relation of this phenomenon to ethylene produced by the tobacco leaf upon interaction with its pathogen,Alternaria alternata.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1984

数据来源: ASPB