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1.
Evidence for Symplasmic Ion Transport in Maize Roots 总被引:1,自引:0,他引:1
Excised maize roots, placed in saturated water vapour to limitthe external ionic supply, continued to produce exudates attheir basal ends for at least 24 h. The mean rate of fluid exudationfrom roots in water vapour was about 28 per cent of the correspondingrate in control roote placed in a solution containing0.1 mil CaCl2 and 1 mM KC1. Moreover, the net fluxes (mean ±S.E.)of potassium and calcium ions into the exudate were reducedfrom (35.8±3.2) x 10 and (4.37±0.39) xlO9 mole cm2 h for roots in solution to(10.9±0.6) x 109 and (l.00±0.06)x 109molecm2 h1 respectively for roots in vapour. It isconsidered that the observation of a prolonged exudation ofwater and ions from the roots placed in water vapour demonstratesthe existence of an alternative ionic supply within the roottissue itself and that this parallel route of ion transportto the exudate constitutes the cortical symplasmic pathway. Pre-treatment of the excised roots with 0.8 M mannitol beforeexudation studies in water vapour and solution led to a significantreduction in the rates of fluid and ion exudation which hadbeen observed in untreated roots under similar conditions. Itis concluded that the plas-molysis, induced by mannitol, disruptedthe symplasmic connections between root cells and that thisperturbation significantly reduced the operation of the symplasmicmode of ion transport into the exudate. 相似文献
2.
The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, LEE = 5 ? 104 mho cm1,LpE = 9 ? 106 cm3 s1 cm2 volt1 cm,and LPP = 0.16 cm3 s1 cm2 (J cm3)1cm. In uncut phloem strands LEE is about 1 ? 103 mhocm1. In xylem in 2 x 103 N KCI, Lpp = 50 to 225,LPE = 2 ? 104, and LEE = 4 ? 103. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga long distance current pathway can be the majormotive force for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm1endogenous in the phloem. 相似文献
3.
Pattern of Respiration of a Perennial Ryegrass Crop in the Field 总被引:3,自引:0,他引:3
Dark respiratory losses of CO2 were measured ona one year old sward of S24 perennial ryegrass (Lolium perenneL.) at intervals during a 74 day reproductive growth period,between April and June, and a 21 day vegetative growth period,in July and August. Part of the sward was shaded for one weekbefore measure ments commenced. Measurements of darkrespiration continued for 46 hand it was possible to distinguishtwo components which are designated maintenanceand synthetic Maintenance respiration was taken to be the meanrate of CO2 efflux after 4046 h darkness. When calculatedon a plant d. wt basis at 15°C it ranged between 6 to 32mgCO2 g-1 day-1 during reproductive growth and 1014 mgCO2 g-1 day-1 during vegetative growth. During reproductivegrowth, sward protein content ranged between 723 percent and when maintenance respiration was recalculated on thebasis of protein content it changed relatively little throughoutthe growth period (90140 mg CO2 g pro tein-1 day-1);the value for vegetative growth ranged between 70100mgCO2 g protein-day-1. Total synthetic CO2 flux was determined duringreproductive growth and a rate of synthetic CO2flux was determined during both reproductive and vegetativegrowth. Between 15 and 35 per cent of the CO2 fixed in the previousphotoperiod was lost in synthetic respirationof above-ground material in reproductive swards. Previous shadingincreased the proportion of synthetic CO2 lossfrom above ground. The rate of synthetic CO2 outputduring the first hours of darkness increased with amount ofCO2 fixed in the previous photoperiod, although it was not proportionalto it. There is some evidence that assimilate is carried-overfrom one photoperiod to the next. 相似文献
4.
《Journal of experimental botany》1977,28(6):1247
Effects of coupled solute and water flow in plant roots withspecial reference to Brouwer's experiment. Edwin L. Fiscus. p. 71 Abstract: Line 3 delete interval insertinternal. p. 73 Materials and Methods: line 6: delete diversion insert division line 9 equation should read Jv=Lp PRT(C0C1). 74 Last line of figure legend: 101 should read 1011. 75 Line 11: delete seems insert seem. le 1 column heading106 should read 1011. 77 delete ...membrane in series of... insert membranein series or... Delete final paragraph. 相似文献
5.
6.
The effect of the leafless mutation (in whichtendrils replace leaflets and the stipules are reduced to avestigial form) upon foliage area, photosynthetic net CO2 uptakepotential, dry matter production and seed yield in Pisum sativumwas studied by comparing two near-isogenic lines of genotypeafafstst and ++++. The mutation is of potential agronomic valuein that it offers improved lodging resistance, crop drying andharvester throughput. In the conventional phenotype the total foliage area of themain axis attained a plateau (456 cm2) at day 56 from seedlingemergence, whereas corresponding values for the leaflessmutant showed a total area of 208 cm2 at day 68 with no indicationof a plateau. The agronomic consequence of this is discussed.During the vegetative phase of the plant the maximum CO2 uptakepotential in the fully expanded conventional leaf was 8·5mg CO2 leaf1 h1 and in the leaflessmutant this value was 7·0 mg CO2 leaf1 h1.For most leaves of the latter phenotype this valuewas between 30 and 60 per cent less than for their conventionalcounterpart. There was a consistently higher photosyntheticpotential per unit area in tendrils of the leaflessmutant than in leaflets of the conventional phenotype. The respectivemean specific values for the two phenotypes were 53 and 37 mgCO2 dm2 h1. The problem of obtaining a meaningfulsurface area value for tendrils is discussed and the cylindricalnature of tendrils is taken into account. The leafless mutant consistently accumulated 50per cent less dry matter than did conventional plants in theperiod from seedling emergence to anthesis and yield of maturedry seed per plant showed a reduction of 50 per cent both inseed number and total seed weight. The implications for future breeding and selection programmesaimed at haulm reduction are discussed in relation to evaluatingthe ability of the background genotype to produce adequate tendrilsin the presence of afafstst. Triticum aestivum, wheat, callus culture, organogenesis 相似文献
7.
Translocation in Pteridium 总被引:2,自引:0,他引:2
The distributions of radioactivity with distance have been mappedin the rachis of Pteridium aquilinum at different times afterapplication of 14CO2 to a pinna. Profiles change in shape withtime, from wave to transition and then to diffusion. The apparentdiffusion constant of sucrose may be obtained from transitionand diffusion profiles. Values varied from 2.2 x 103to 3.6 x 102 cm2 sec1. These results are comparedwith those for various angiosperm species. 相似文献
8.
Photosynthetic 14C fixation by Characean cells in solutionsof high pH containing NaH14CO3 gave a measure of the abilityof these cells to take up bicarbonate (H14CO3). Whereascells of Nitella translucens from plants collected and thenstored in the laboratory absorbed bicarbonate at 11.5µµmoles cm2 sec1, rates of 38µµmoles cm2 sec1 were obtained withN. translucens cells from plants grown in the laboratory. Influxesof 56 µµmoles cm2 sec1 wereobtained with Chara australis, 38 µµmolescm2 sec1 with Nitellopsis obtusa, and 15µµmoles cm2 sec1 with Tolypella intricata.It is considered that these influxes represent the activityof a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H14CO3 uptake would be maskedby rapid diffusion of 14CO2 into the cells: the four Characeanspecies fixed 14CO2 at maximum rates of 3040 µµmolescm2 sec1 (at 21° C). 相似文献
9.
The Exudation from Excised Maize Roots Bathed in Sulphate Media 总被引:2,自引:0,他引:2
The fluid exudation fluxes of excised maize roots bathed ina variety of K2SO4 solutions have been measured, along withthe ionic concentrations and osmolalities of the exudates. Anapparent imbalance of inorganic ionic charge in the exudate,and a discrepancy in the total salt concentrations comparedwith the measured osmolalities, suggest the presence of significantamounts of organic anions in the exuded fluid. Thin-layer chromatographicmethods indicate these to be mainly amino-acids and organicacids of the Kreb's cycle. Linear regression analysis showsthat the exudation flux is satisfactorily described by a simpleosmotic process together with a constant non-osmotic water fluxof 0.43 µ1 cm-2 h-1. The osmotic permeability for theroot is found to be 0.18 x 10-6 cm sec-1 atm-1. The exudationfrom sulphate media is contrasted with that from chloride media. 相似文献
10.
During the 1983 el Niño, filter fractionationshowed that over 80% of the chlorophyll-based phytoplanktonbiomass in the Santa Barbara Channel was <5 µm. Largernanoplankton (530 µm) accounted for the chlorophyllin the remaining fraction but, unlike other years, no significantquantities of net plankton <30 µm were detected. Thepopulation as a whole was dominated by chroococcalean cyanobacteriawhich were two times were abundant (123±24x103 cellsml1 than previously reported for the California CurrentSystem (Krempin and Sullivan, 1981). Numbers of other typesof bacteria were uniformly low (277±44x103 cells ml1Cyanobacteria and larger nanoplankton exhibited similar diurnalpatterns of photosynthesis, i.e., maximal rates of light-saturatedphotosynthesis (Pmax) occurred mid-day and day-night amplitudeswere >2.0. In both size fractions the onset of the rise andfall in Pmax preceded sunrise and sunset, respectively, andthe photosynthetic periodicity was independent of both chlorophyllcontent and dark fixation of inorganic carbon. Unlike previousstudies on diel periodicity in phytoplankton, no significantoscillations in light-limited rates of photosynthesis ( 相似文献
11.
Defoliation in White Clover: Nodule Metabolism, Nodule Growth and Maintenance, and Nitrogenase Functioning During Growth and Regrowth 总被引:1,自引:0,他引:1
In two experiments, the functioning and metabolism of nodulesof white clover, following a defoliation which removed abouthalf the shoot tissue, were compared with those of undefoliatedplants. In one experiment, the specific respiration rates of nodulesfrom undefoliated plants varied between 1160 and 1830 µmolCO2 g1h1, of which nodule growth and maintenanceaccounted for 22 ± 2 per cent, or 27 ± 3.6 percent, according to method of calculation. Defoliation reducedspecific nodule respiration and nodule growth and maintenancerespiration by 6070 per cent, and rate of N2 fixationby a similar proportion. The original rate of nodule metabolismwas re-established after about 5 d of regrowth; during regrowthnodule respiration was quantitatively related to rate of N2,fixation: 9.1 µmol CO2 µmol1N2. With the possible exception of nodules examined 24 h after defoliation,the efficiency of energy utilization in nitrogenase functioningin both experiments was the same in defoliated and undefoliatedplants: 2.0±0.1 µmol CO2 µmol1 C2H4;similarly, there was no change in the efficiency of nitrogenasefunctioning as rate of N2 fixation increased with plant growthfrom 1 to 22 µmol N2 per plant h1. Exposure of nodulated white clover root systems to a 10 percent acetylene gas mixture resulted in a sharp peak in rateof ethylene production after 1.52.5 min; subsequently,rate of ethylene production declined rapidly before stabilisingafter 0.51 h at a rate about 50 per cent of that initiallyobserved. Regression of peak rate of ethyleneproduction on rate of N2 fixation indicated a value of 2.9 µmolC2H4 µmol1 N2, for rates of N2 fixation between1 and 22 µmol N2 per plant h1. The relationshipsbetween nitrogenase respiration, acetylene reduction rates andN2 fixation rates are discussed. Trifolium repens, white clover, defoliation, nodule respiration, N2, fixation, nitrogenase 相似文献
12.
A Cytochrome P450 Mediated Naringenin 3'-Hydroxylase from Sweet Orange Cell Cultures 总被引:1,自引:0,他引:1
Doostdar Hamed; Shapiro Jeffrey P.; Niedz Randall; Burke M.D.; McCollum T. Gregory; McDonald Roy E.; Mayer Richard T. 《Plant & cell physiology》1995,36(1):69-77
A microsomal flavonoid 3'-hydroxylase (F3'H) catalyzing themetabolism of naringenin to eriodictyol in Citrus sinensis (L.)Osbeck cv. Hamlin cell suspension cultures wasshown to be a cytochrome P450 enzyme. This reaction requiredO2 and NADPH and was inhibited by CO, with partial reversalof CO-inhibition by light at 450 nm. Cytochrome P450 contentranged from 1020 pmol (mg microsomal protein)1.The F3'H reaction was shown to be linear in regard to proteinconcentration between 2.5 and 25 µg of microsomal protein.The optimum pH for the reaction was 7.47.6 and the temperatureoptimum was between 30 and 37°C. The apparent Km and Vmaxfor naringenin were 24 µM±3.2 and 81.4±7.9pmol eriodictyol min1 (mg protein)1, respectively.The microsomal F3'H was also capable of forming dihydroquercetinfrom dihydrokaempferol (40 pmol min1 (mg protein)1)and of quercetin from kaempferol (3.25 pmol min1 (mgprotein1). Cytochrome c and ketoconazole were the bestinhibitors of WH activity followed by piperonyl butoxide anda-naphthoflavone. Light was shown to be an inducer of the F3'Halmost doubling the specific activity and increasing the microsomalcytochrome P450 content by 30% over that of dark grown cells.F3'H activity was also confirmed in microsomal preparationsof young (new flush) leaves from Hamlin treesand flavedo of Hamlin oranges, Marshgrapefruit, and Lisbon lemon. No activity wasobserved in older, hardened leaves and albedo of all the fruittested. Initiation of embryogenesis in the Hamlincell suspension cultures by switching from a sucrose mediumto a glycerol-based medium resulted in the down-regulation ofF3'H.
1Mention of a trademark, warranty, proprietary product, or vendordoes not constitute a guarantee by the U.S. Department of Agricultureand does not imply its approval to the exclusion of other productsor vendors that may also be suitable. 相似文献
13.
The Sensitivity of Net Photosynthesis in Several Plant Species to Short-term Fumigation with Sulphur Dioxide 总被引:4,自引:0,他引:4
The effects of exposure of up to 2 h with sulphur dioxide ona range of plant species was observed by measuring changes inthe rate of net photosynthesis under closely controlled environmentalconditions. Ryegrass, Lolium perenne S23 was thespecies most sensitive to SO2; significant inhibition was detectedat 200 nl l1. Fumigations at 300 nl l1 also inhibitedphotosynthesis in field bean (Vicia faba cv. Three FoldWhite and Blaze) and in barley (Hordeumvulgare cv. Sonja). No effect was detected inwheat (Triticum aestivum cv. Virtue) at concentrationsup to 600 nl l1 SO2, or in oil-seed rape (Brassica napuscv. Rafal) except at 800 nl l1 SO2). Recoverycommenced immediately after the fumigation was terminated andwas complete within 2 h when inhibition had not exceeded 20%during the SO2 treatment. Key words: Sulphur dioxide, short-term fumigation, photosynthesis 相似文献
14.
The Use of Agar Nutrient Solution to Simulate Lack of Convection in Waterlogged Soils 总被引:12,自引:2,他引:12
Agar at 0.1% in nutrient solution (stagnant solution)was used to prevent turbulence (convection), thus simulatingthe slow gas movements which occur in waterlogged soils. Wheat,aged between 6 and 16 d at the start of the treatment, was usedto test plant growth and development in this stagnant solutionfor 815 d. K-MES buffer at 5 mol m-3was used to retainthe pH of the rhizosphere in the stagnant solution at pH 6.5. The prevention of convection reduced dissolved oxygen concentrationsin the bulk solution from 0.275 to below 0.05 mol m-3after 1d, while ethylene accumulated over 10 d to 6.5x10-6m3m-3(ppm). Aerenchyma of nodal roots grown in stagnant solution comprised22% of the cross sectional area of the root 50 mm behind theroot tip; this was similar to values recorded earlier for nodalroots of wheat in waterlogged soil and contrasts with 7.6% forroots in non-flushed solution without agar (referred to in thispaper as semi-stagnant solution) and 2.4% in N2-flushedsolution. Increases in dry weight and numbers of nodal roots with timewere larger for stagnant and N2-flushed, than for semi-stagnantor aerated solution. In contrast, seminal roots did not growin stagnant solution, while seminal roots in N2-flushed solutiongrew much less than in semi-stagnant or aerated solution. In the stagnant solution, relatively high concentrations ofN, K and P were required to avoid limitations in mineral uptakeinto the roots, due to the long diffusion pathway from the bulksolution imposed by the lack of convection. Nevertheless, ourdata show that the slow growth imposed by the lack of convectionwas due to factors other than low mineral nutrition. The mostlikely cause was the change in the dissolved gas compositionof the root media, particularly of the rhizosphere. In conclusion, in terms of anatomy and morphology the rootsgrown in the stagnant solution more closely resembled thosefrom waterlogged soil than did those grown in either semi-stagnantor N2-flushed solution. Triticum aestivum; wheat; waterlogging; lack of convection; aerenchyma; root development; nutrient uptake 相似文献
15.
A Study of the Exudation of Excised Maize Roots after Removal of the Epidermis and Outer Cortex 总被引:1,自引:1,他引:0
The fluid exudation rates and the ionic composition of the exudatesof isolated maize roots were compared with those of similarroots from which the epidermal and outer cortical cells hadbeen removed. The results indicate that in low ionic strengthmedia the salt fluxes into the exudation stream are severaltimes larger in the control than in the treated roots. As theionic strength of the bathing medium increases to 10 mM KClor greater, the salt fluxes become equal. A mechanism to accountfor this behaviour is discussed. The values of Lp, the hydraulic conductivity of the roots toradial water flow, are 0.26 x 106 cm sec1 atm1for treated and 0.14 x 106 cm sec1 atm1for control roots, but a statistical technicality precludeda significance test on this apparent difference. The kinetics of tritiated water exchange from external mediumto the exudation fluid in both control and treated roots werenot significantly different. The entry of labelled water seemsto be achieved by the fluid exudation rate in both cases; thusthe barrier to water movement to the exudate compartment remainsintact after removal of the epidermis. 相似文献
16.
Zoea I larvae of the brown shrimp Crangon crangon (Decapoda)were exposed to varying levels of UV radiation in a sunshinesimulator. Short-term exposures (08 h)were used to determine the highest UV dose with no significanteffect (NOEC; defined by limit of detection) and the lethaldose of 10 and 50% mortality (LD10 and LD50). Crangon crangonshowed a relatively high sensitivity to UVB radiation (NOEC= 10 kJ m2, LD10 = 15 kJ m2, LD50 = 24 kJ m2)compared to other crust-acean species. LD values (19971998)showed no adaptation to seasonal light regimes. Long-termexposures (010 days) were carried out to assessthe range where the law of reciprocity is valid.The larvae were exposed to UV levels of 0.2, 0.4 and 0.7 J m2for appropriate time intervals, always cumulating in a sublethaldose of 5 kJ m2 day1. Results reflect a possiblethreshold (0.20.4 J m2 UVB) in the effect of thedifferent UVB doses used; thus, a proportional relationshipof intensity and exposure time can only be shown at UVB levelsabove this threshold intensity. 相似文献
17.
Fully light-intercepting simulated swards of S24 perennial ryegrasswere exposed to contrasting environmental conditions in a growthroom for 4 days. Half experienced 20 h days of 120 Wm2(400700. nm) and 5 °C, and came to have a WSC (watersoluble carbohydrate) content of 235 mg g1 and half 4h days of 20 Wm2 and 25 °C leading to a WSC of 25mg g1. Their rates of CO2 efflux were monitored at anumber of temperatures during an 8 h dark period; half experiencedincreasing (530 °C) and half decreasing (305°C) temperatures. The high WSC swards hadrespiration rates of 3.7 mg CO2 g1 (d. wt) h1at 15 °C, and the low swards 0.8 mg CO2 g1h1. The order in which the temperatures were experiencedwas immaterial. Even the low WSC swards showedno evidence of a respiratory decline during the dark periodthat could be attributed to substrate shortage. The relationshipbetween temperature and CO2 efflux was best represented by logisticcurves. Even so, a Q10 of 2 fitted the data reasonably well,at least up to 20 °C, and has practical advantages wheninterpolating estimated between measured values of respirationin the construction of a carbon balance sheet. Lohum perenne L., ryegrass, respiration, temperature, Q10, soluble carbohydrate content, simulated sward 相似文献
18.
Summer nutrient dynamics of the Middle Atlantic Bight: nitrogen uptake and regeneration 总被引:4,自引:0,他引:4
Harrison W.G.; Douglas D.; Falkowski P.; Rowe G.; Vidal J. 《Journal of plankton research》1983,5(4):539-556
Nitrate and ammonium uptake and ammonium regeneration rates(by zooplankton, microplankton and benthos) were measured onthe Atlantic continental shelf (Middle Atlantic Bight) duringsummer, 1980. Euphotic zone profiles of NO3 and NH4+uptake rates were similar in magnitude and vertical structureover a large geographical area. Microplankton NH4+ regenerationrates, although measured less frequently, also showed a relativelyconsistent vertical structure; rates were positively correlatedwith uptake rates. Nitrate assimilation (new production)was used to estimate vertical eddy diffusivity and paniculatesinking rates. Eddy diffusion estimates ranged from <0.1to >2.0 cm2 s1 and were positively related to arealprimary production. Estimated particulate sinking rates averaged5 mg at Nm2d1 and compared favorably with sedimentationrates measured from free-floating and moored sediment traps.Benthic nitrogen regeneration rates represented <10% of thispaniculate nitrogen flux. Within the mixed layer, NH4+ assimilation(regenerated production) represented 5080%of the total (NO3 + NH4+ ) nitrogen productivity and33% for the euphotic zone. Of this, 30% was attributed to zooplankton,63% to microplankton (<100 µm) and 7% to benthos. Onthe average, 74% of the microplankton NH4+ regeneration wasassociated with organisms passing 1 µm filters. 相似文献
19.
The effect of morphactin (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate)on basipetal transport of auxin (Indol-3-ylacetic acid-2-14C)was studied in bean (Phaseolus vulgaris) hypocotyl with thedonor-receiver block method. Morphactin (5 x 106m) reduced IAA (5 x 106m) transportintensity by an average of 83 per cent and auxin transport capacityby 90 per cent, but transport velocity was not affected. Morphactin did not inhibit uptake of IAA into hypocotyl tissue,but it did prevent transfer of IAA from the tissue into receiverblocks. Chromatographic analysis of the tissue after 4 h IAA-2-14Ctransport showed that 54 per cent of the total activity wasin the form of IAA in the control and 42 per cent in the morphactintreated tissue. No difference was found in the rate of decarboxylationof IAA-1-14C between control and morphactin treated tissue sections.Nor could any difference between control and morphactin be shownin the radioactivity associated with a TCA ppt fraction. Ina study of the transportable auxin pool, morphactin decreasedthe size of the pool and increased the half-life of decay ofauxin transport from 122 h to 385 h. In a kineticanalysis of the reversal of morphactin (5 x 106m) inhibitionby increasing concentration of IAA-2-14C (5 x 106m to2 x 105m), it was shown that IAA transport resemblesMichaelis-Menten enzyme reaction kinetics, and that inhibitionby morphactin fitted a mixed type model. IAA hada dissociation constant of 85 x 106m and morphactinthat of 43 x 107m with a Km for the transport processof 85 x 106m. 相似文献
20.
Pith callus tissues were grown under continuous blue (450 mµ),green (545 mµ), red (650 mµ), and white(full-spectrum) light, and in the dark for 22 days at 27±2°C at energy levels of 15,000 ergs cm2 sec1. Mean increases in fresh weight of tissues grown under whiteand blue light were significantly greater than those of tissuesgrown in green and red light and in the dark. Tissues grownin the dark yielded mean fresh weight increases significantlylower than tissues grown under blue, red, and whitelight. No significant differences were shown between blue andwhite, red and green, and green and dark treatmentsrespectively. Cell differentiation occurred in all treatmentsonly to the extent of vessel element formation. There were nodifferences in degree of differentiation between treatments. It was proposed that the high-energy reaction of photomorphogenesiswas in operation in the Pelargonium callus tissue. The resultsindicated the presence in the tissue of high-energy photoreceptor(s).The use of high-intensity, incandescent illumination for experimentalprocedures approximating natural conditions of irradiation wasindicated as desirable for pith callus tissues of Pelargoniumzonale var. Enchantress Fiat. 相似文献