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1.
Callus cells of two wheat cultivars in liquid medium rapidlyabsorbed (4-chloro-2-methylphenoxy)acetic acid (MCPA) and convertedit to ethanol-soluble products. The herbicide was transformedby methyl-hydroxylation, the major terminal residue being analcoholic glycoside of (4-chloro-2-hydroxymethylphenoxy)aceticacid. Minor metabolites were an ether-soluble conjugate of MCPA,an MCPA-glycoside and five additional aglycones. No metaboliteswere released into the medium. The rate of metabolism was lowerthan that of uptake such that a substantial amount of the radioactivityinitially accumulating in the cells was unmodified MCPA. Metabolismwas qualitatively and quantitatively similar to that in shootsexcised from seedlings. Cells also absorbed an ether-solubleconjugate of MCPA which had been isolated from carrot (Daucuscarota L. ), though less readily than MCPA itself. MCPA andthe above metabolites were produced, with the alcoholic glycosideagain as the major residue. Some MCPA was present in the medium,due probably to the action of extracellular hydrolases. Key words: MCPA, Triticum aestivum, Cell culture, Hydroxylation  相似文献   

2.
The auxin herbicide (4-chloro-2-methylphenoxy)-acetic acid (MCPA) was absorbed by liquid cultured callus cells of Phaseolus vulgaris L. and subsequently became hydroxylated at the methyl group. The alcohol remained largely unconjugated and was partly released to the culture medium. Several glycosides and an ether-soluble conjugate of MCPA appeared as minor metabolites. Unsubstituted phenoxyacetic acid (POA) was metabolised primarily by 4-hydroxylation and subsequent phenolic glucoside formation. Metabolites of POA were retained by the cells. In the case of both substrates, metabolism in cells correlated well with that observed in apical buds excised from etiolated seedlings.Abbreviations MCPA (4-chloro-2-methylphenoxy)-acetic acid - OH-MCPA (4-chloro-2-hydroxymethylphenoxy)acetic acid - POA phenoxyacetic acid - 4-OH-POA 4-hydroxyphenoxyacetic acid  相似文献   

3.
Light-enhanced active pyruvate uptake into mesophyll chloroplastsof C4 plants was reported to be mimicked by either of the twotypes of cation jump: H+-jump in maize and phylogenically relatedspecies (H+-type) and Na+-jump in all the other C4 species tested(Na+-type) [Aoki, N., Ohnishi, J. and Kanai, R. (1992) PlantCell Physiol. 33: 805]. In this study, medium and stromal pH was monitored in the suspensionof C4 mesophyll chloroplasts. Medium alkalization lasting for5 to 10 seconds after pyruvate addition was detected by a pHelectrode and observed only in the light and only in mesophyllchloroplasts from H+-type species, Zea mays L. and Coix lacryma-jobiL., but not in those from Na+-type species Panicum miliaceumL., Setaria italica (L.) Beauv. and Panicum maximum Jacq. Theinitial rate of H+ consumption showed good correlation with[14C]pyruvate uptake measured by silicone oil filtering centrifugation,both being inhibited by N-ethylmaleimide and 7-chloro-4-nitrobenzo-2-oxa-l,3-diazole to the same degree. The ratio of the rate of H+ uptaketo that of pyruvate uptake was always about 1. Pyruvate-inducedacidification of the stroma was observed in maize mesophyllchloroplasts. These results show one to one cotransport of H+and pyruvate anion into mesophyll chloroplasts of H+-type C4species in the light. (Received January 5, 1994; Accepted May 6, 1994)  相似文献   

4.
Negative linear relations were detected (P < 0·005)between the rate of progress from sowing to panicle initiationand CO2 concentration (210-720 µmol CO2 mol-1 air) fortwo genotypes of sorghum [Sorghum bicolor (L.) Moench]. Relationsbetween CO2 concentration and the rate of progress from sowingto first flowering were also negative in soyabean [Glycine max(L.) Merrill] (P < 0·025), but positive in cowpea[Vigna unguiculata (L.) Walp.] (P < 0·025), albeitthat in both grain legumes sensitivity was much less than insorghum. Thus CO2 elevation does not delay flowering in allshort-day species. The considerable effect of CO2 concentrationon times to panicle initiation resulted in large differencesamong the sorghum plants at this developmental stage; with increasein CO2 concentration, plants were taller with slightly moreleaves and more pronounced apical extension. At the same timeafter sowing however, sorghum plants were heavier (P < 0·05)at 210 than at 360 µmol CO2 mol-1 air. In contrast, relationsbetween the dry masses of the soyabean and cowpea plants andCO2 concentration were positive and curvilinear (P < 0·05).It is suggested that the impact of global environmental changecould be severe for sorghum production in the semi-arid tropics.Copyright1995, 1999 Academic Press Sorghum bicolor (L.) Moench., sorghum, Glycine max (L.) Merrill, soyabean, Vigna unguiculata (L.) Walp., cowpea, development, flowering, CO2, dry matter accumulation, environmental change  相似文献   

5.
To investigate the duration of the CO2 response and its interactionwith mineral nutrition, CO2-enrichment experiments were performedon four British grasses of differing ecology and functionaltype: Arrhenatherum elatius (L.) Beauv., Festuca ovina L., Festucarubra L. and Poa annua L. Naturally-lit, glasshouse cabinetswere used, with a non-limiting water supply and a daytime meantemperature of 18 °C. Two CO2 treatments were maintainedat nominal concentrations of 350 and 700 vpm and were combinedfactorially with two levels of balanced mineral nutrition atconductivities of 0·1 and 1 mS cm-1. Harvests took placeat planting-out, and at 16, 37 and 58 d thereafter. Fitted curves were used to derive instantaneous values of totaldry weight, relative growth rate (RGR), shoot weight fraction(SWF) and unit shoot rate (USR) for all combinations of species,CO2 level, nutrient level and time of harvesting. At the higher nutrient level there was a reasonably close agreementwith previous estimates of the CO2 response in the four species.The response, if any, most often arose from an increase in USRbeing accompanied by a less than proportionate decline in SWF.Responses were sustained throughout the period studied. At thelower nutrient level, all species showed a CO2 response initially,but this declined at a rate which was inversely related to theCO2-responsiveness of the species at the higher nutrient level. The underlying ontogenetic drift appeared to be markedly towardsadjustment in SWF and away from that of USR. However, this driftwas retarded, suspended or even reversed by low-nutrient conditionsand/or by high CO2 responsiveness in the species itself.Copyright1995, 1999 Academic Press Climate change, CO2 enrichment, plant strategies, mineral nutrition, growth analysis, relative growth rate, shoot weight fraction, unit shoot rate, functional equilibria  相似文献   

6.
Activities of Carboxylation Enzymes in Freshwater Macrophytes   总被引:2,自引:0,他引:2  
Fifteen species of freshwater macrophytes, mainly from cool,temperate waters, were assayed for ribulose bisphosphate carboxylase-oxygenase(RuBPCase) and phosphoenolpyruvate carboxylase (PEPCase) activities.In extracts from all the species RuBPCase was the most activecarboxylation enzyme, and the RuBPCase/PEPCase ratio was atleast 2·0, even for the submersed species Isoetes lacustrisL. and Littorella unifiora (L.) Aschers. which have been reportedto show Crassulacean Acid Metabolism (CAM) activity. The PEPCaseactivity in I.lacustris was lower than that found in some non-CAM-likespecies. In this respect, I.lacustris and L unifiora differfrom most terrestrial CAM plants. However, these two species,along with Potamogeton praelongus Wulf. and Juncus bulbosusvar.fluitans L., had the lowest RuBPCASE/PEPCase ratios, lowerthan found in terrestrial C3 species; suggesting that the potentialfor substantial photosynthetic metabolism of C4 acids existsin some temperate, submersed plants. In the three amphibiousspecies (Potamogeton polygonifolius Pourr., Mentha aquaticaL., and Hippuris vulgaris L.) examined, the aerial leaves exhibitedhigher RuBPCase activities than the submersed leaves. Key words: Ribulose bisphosphate carboxylase-oxygenase, phosphoenolpruvate carboxylase, freshwater macrophytes  相似文献   

7.
Fatty acids of chain length from C4 to C12 inhibited ethyleneproduction in wounded albedo tissue of Hassaku (Citrus hassakuHort. ex Tanaka) fruit. Of the fatty acids tested, caprylicacid (C8) and capric acid (C10) were the most effective. Lauricacid (C12) was less effective, and caproic acid (C6) and butyricacid (C4) were the least effective. Caprylic acid at 5 mM markedlyinhibited ethylene production in not only wounded albedo tissueof citrus fruit but also apple (Malus sylvestris Mill.) cortex,tomato (Lycopersicon esculentum Mill.) pericarp, cucumber (Cucumissativus L.) cortex, banana (Musa AAA group Cavendish subgroup)pulp, broccoli (Brassica oleracea L.) floret, spinach (Spinaciaoleracea L.) leaf, lettuce (Lactuca sativa L.) leaf and mungbean (Vigna radiata [L.] Wilczek) hypocotyl. Caprylic acid inhibitedethylene production at the step of conversion of l-aminocyclopropane-l-carboxylicacid to ethylene. The inhibition could be partially relievedby transferring the tissue to caprylic acid-free medium. (Received June 15, 1982; Accepted August 13, 1982)  相似文献   

8.
The effect of six phenoxy-acid herbicides, 4-chloro-2-methylphenoxyaceticacid (MCPA), 4-(4-chloro-2-thylphenoxy)butyric acid (MCPB),2, 4-dichlorophenoxyacetic acid (2, 4-D), 4-(2, 4-dichlorophenoxy)butyricacid (2, 4-DB), 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T),and 4-(2, 4, 5-trichlorophenoxy)butyric acid (2, 4, 5-TB) onoxidative phosphorylation of mitochondria isolated from younghypocotyls of Vicia faba L. has been investigated. When NADHwas used as substrate all the test herbicides were found tostimulate state 4 respiration with the loss of phosphorylationand respiratory control in varying degrees. When malate andsuccinate were used separately as substrates, treatment with2, 4-DB, 2, 4, 5-T, and 2, 4, 5-TB at low concentration resultedin a marked stimulation of state 4 respiration; this effectwas not obtained with MCPA, MCPB, or 2, 4-D. At higher concentrationsall herbicides strongly inhibited respiration. These compoundsreleased oligomycin inhibition during NADH oxidation in varyingdegrees, stimulated mitochondrial adenosine-triphosphatase activity,and induced swelling of isolated mitochondria. In many respectsand in differing degrees they resemble 2, 4-dinitrophenol (DNP)in their action as uncouplers. Phenoxy-butyric acids were foundto be more toxic in vitro as uncouplers than their correspondingphenoxyacetic acids. Phenoxyacetic acids were very active as uncouplers in vivo whilephenoxybutyric acids had negligible effect. It is concludedthat in vivo, non-activity of phenoxybutyric acids is due totheir restricted entry into plants and that if available atthe site of action they would be inherently toxic.  相似文献   

9.
Chloroplast envelopes were isolated from chloroplasts purifiedfrom Spinacea oleracea L. (C3), Panicum miliaceum L. (NAD-malicenzyme-type C1), Digitaria sanguinalis (L.) Scop. (NADP-malicenzyme-type C4), Kalanchoe daigremontiana Hamet et Perrier (constitutiveCAM), and from Mesembryanthemum crystallinum L. (inducible CAM)performing either C3 photosynthesis or Crassulacean acid metabolism(CAM). For each species, methods were developed to isolate chloroplastenvelopes free of thylakoid contamination. The polypeptidesof ribulose bisphosphate (RuBP) carboxylase which has been consistentlyreported in envelope preparations of spinach were not foundin envelope preparations of C4 mesophyll chloroplasts. Silverstaining of envelope polypeptides resolved electrophoreticallyon sodium dodecylsulfate polyacrylamide gradient slab gels produceda more complex profile than did Coomassie staining which haspreviously been used with C3 envelope preparations, even thoughsilver reacted poorly with polypeptides corresponding to thesubunits of RuBP carboxylase. All of the plants examined possesseda major polypeptide of 27 to 29 kilodaltons (kD) which was previouslysuggested to be the phosphate translocator in spinach. WithC3 M. crystallinum, the 29 kD polypeptide stained most intensely.After induction of CAM, a 32 kD polypeptide also stained intensely,giving a profile similar to that obtained with the constitutiveCAM species. A 32 kD polypeptide was also prominent in C4 envelopepreparations, suggesting that a 32 kD polypeptide may be a translocatorprotein which is required in Crassulacean acid metabolism andC4 photosynthesis, but not in C3 photosynthesis. (Received April 25, 1983; Accepted July 9, 1983)  相似文献   

10.
The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) ‘Valencia’ sweet orange (Citrus sinensis (L.)Osb.) and ‘Femminello’ lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 5–15% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO2assimilation rate (ACO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerACO2than their diploids. There were no significant differencesin ACO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower ACO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO2diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; ‘Valencia’ sweet orange; ‘Femminello’ lemon  相似文献   

11.
The activity of photosynthesis and mitochondrial respiration,nocturnal organic acid accumulation and water relations wereinvestigated in Prenia sladeniana L. Bol. [malic enzyme (ME)-type]andCrassula lycopodioides Lam. [phosphoenolpyruvate carboxykinase(PEPCK)-type] to compare the physiological responses to waterdeficit in crassulacean acid metabolism (CAM) plants differingin their decarboxylating enzyme systems. Withholding water inhibiteddaytime gas exchange within 2 d while night time CO2gain andmalic acid accumulation remained relatively unchanged in bothspecies. In P. sladeniana, maximum photochemical efficiency(Fv/Fm) and photosynthetic electron transport declined to nearlythe same degree as CO2supply was restricted during drought.Despite limited CO2availability, photosynthetic activity waslargely unaffected in C. lycopodioides, as were mitochondrialproperties. There is no indication of a drought-induced increasein the capability to totally oxidize malate, yielding 4 CO2, in either species. Nevertheless, the enhanced ratio of malateto glycine oxidation may have increased the in vivo capabilityfor malate oxidation in P. sladeniana. Although pressure potentialwas maintained throughout the experiment in both species, activeosmotic adaptation occurred only inP. sladeniana. The observeddecrease in photosynthetic and mitochondrial activity may haveresulted from the large increase in osmotic concentration inthis species. Copyright 2000 Annals of Botany Company Chlorophyll fluorescence analysis, Crassula lycopodioides Lam., crassulacean acid metabolism, citric acid, gas exchange, malic acid, mitochondria, photosynthetic electron transport, Prenia sladeniana L. Bol., water relations  相似文献   

12.
By means of paper partition chromatography and a suitable biologicaltest, the number and variety of the Orobanche and Striga germinationstimulants produced by maize roots have been assessed. It isshown that extracts of maize roots and aqueous solutions inwhich roots have been suspended (diffusate solutions) containa complex of stimulating substances consisting of, at least,one water-soluble and a number of ether-soluble stimulants.Germination of O. minor is promoted by the water-soluble stimulantand one of the ether-soluble stimulants (Mo). Germination ofS. hermonthica is promoted by another ether-soluble stimulant(Ms). Aqueous extracts are rich in Ms and the water-solublematerial, whereas the diffusate contains a higher proportionof Mo and only a trace of the water-soluble stimulant. The complex of ether-soluble stimulants, but not the water-solublestimulant, accumulates in a solution of glucose when it is exposedto fragments of maize roots. These solutions contain a highproportion of Mo which is synthesized by the fragments and passesout into the sugar solution. It is suggested that the water-solublestimulant is a precursor of Mo. The effects of the water-soluble stimulant and of Ms and Moare greatly enhanced if a trace of the diffusate solution fromlinseed roots is mixed with them. The significance of the enhancementis discussed.  相似文献   

13.
The expolinear equation for crop growth (Goudriaan and MonteithAnnalsof Botany66: 695–701, 1990) was fitted to measurementsof above ground dry weight made on two cultivars of each ofthree species, faba bean (Vicia fabaL.), peas (Pisum sativumL.)and lentils (Lens culinarsMedic.), each grown at three densitiesat the University of Reading, UK in 1992 and 1993. The expolinearequation fitted the data well but required frequent samplingto obtain good estimates of the parameters. The equation hasthree parameters,Rmthe maximum relative growth rate,Cma maximumcrop growth rate, andtbthe time at which the crop effectivelyreaches a linear phase of growth.Rmdid not differ between densities,cultivars or species but differed between years.Cmincreasedwith increased density and was lower for lentils than for fababeans or peas.tbdecreased with increased density for faba beanbut not for the other species. Incorporating an extinction coefficientfor solar radiation and the maximum fraction of radiation interceptedenabled reasonably accurate time courses of leaf area indexto be derived, as suggested by Goudriaan (1994. In: MontiethJL, Scott RK, Unsworth MH, eds.Resource capture by crops. Nottingham:Nottingham University Press, 99–110).Copyright 1998 Annalsof Botany Company Expolinear equation, grain legumes, crop growth rate, crop density, relative growth rate, growth modelling, faba bean,Vicia fabaL., peas,Pisum sativumL., lentils,Lens culinarsMedic.  相似文献   

14.
Carbon exchange was measured on whole plants of field bean,lucerne, chick pea, kidney bean, pea and tobacco. The maintenance respiration rate was measured in three ways:(i) by allowing the CO2 efflux to decay in prolonged darknessto an asymptotic value which was then taken to be the maintenancevalue (the dark decay method); (ii) by plotting the dark CO2efflux as a function of the net CO2 uptake over a range of irradiancesand taking maintenance as the dark CO2 efflux when the net CO2uptake was zero (the dynamic method); and (iii) by plottingthe total CO2 uptake as a function of the growth rate and takingmaintenance respiration as the CO2 efflux when the growth ratewas zero (the zero growth rate method). The range of valuesfor the maintenance coefficient over all species was from 1.6to 2.1 per cent of the dry weight per day, 1.8 to 2.1 per centand 2.7 to 2.9 per cent as determined by these three methodsrespectively. There was a linear relationship, common to allspecies, between the maintenance respiration rate (dark decaymethod) and dry weight, total nitrogen and the organic nitrogencontent. The growth coefficient (0.69±0.01) was the samefor field bean, chick pea and lucerne and was unaffected bythe method of estimation. It was concluded that the dark decay method provided the bestestimate of the minimal maintenance requirements in the plantsstudied. Vicia faba L., Medicago sativa L., Cicer arientinum L., Phaseolus vulgaris L., Pisum sativum L., Nicotiana tobacum L., field bean, lucerne, chick pea, kidney bean, pea, tobacco, respiration, maintenance, growth, nitrogen content  相似文献   

15.
Methionine sulfoximine caused ammonia accumulation and photosyntheticrate inhibition in leaf discs from two C4 species, Zea maysL. cv. F. M. Cross (Hybrid) and Sorghum bicolor L. Moench cv.NC-70X, as well as one C3 plant species, Datura stramonium L.cv. stramonium. Similar results were obtained earlier with theC3 species Spinacia oleracea L. The effect occurred in the absenceof inorganic nitrogen reduction and was light dependent. Ammoniaaccumulation rates were similar in all four species examined.The results support a role for glutamine synthetase in leafammonia recycling in both C4 and C3 leaves. 1 Current address: Cetus Madison Corporation, 2208 Parview Road,Middleton, WI 53562, U.S.A. (Received November 2, 1981; Accepted April 28, 1982)  相似文献   

16.
Two models for canopy photosynthesis (modified versions of thoseof Acock et al. , 1978 and of Thornley, 1976) were examinedby comparison with experimental photosynthesis data of cucumber(Cucumis sativus L.), sweet pepper (Capsicum annuum L.) andtomato (Lycopersicon esculentum Mill.). The data were obtainedin six large-scale, long-term, semi-commercial cultivationsin greenhouses (Nederhoff and Vegter, 1994). Measured environmentalconditions and measured LAI were input to the model. The emphasiswas on the models' sensitivity to the prevailing CO2 concentration. The (modified) Acock model with 'standard' (originally published)parameters underestimated the photosynthesis rate. This modeltuned to one of our experimental data sets did not fit verywell to the other data sets. As expected, if the model was tunedto each particular data set, it was fairly in agreement withthe measurements, but the fitted parameter values were sometimesquestionable. With the (modified) Thornley model it was obligatoryto estimate or tune the light extinction. The model performedreasonably if all parameters were tuned and also if only thelight extinction was tuned. The modified models were considered usable for practical applications,after parameter tuning. As the sensitivity to CO2 was not alwaysequal among the models and the measurements, care should betaken when applying the models for CO2 supply control.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, cucumber, CO2, Cucumis sativus L., glasshouse, greenhouse, Lycopersicon esculentum Mill., measurements, model, sweet pepper, tomato  相似文献   

17.
Bunce  James A. 《Annals of botany》2001,87(4):463-468
Predicting responses of plant and global carbon balance to theincreasing concentration of carbon dioxide in the atmosphererequires an understanding of the response of plant respirationto carbon dioxide concentration ([CO2]). Direct effects of thecarbon dioxide concentration at which rates of respiration ofplant tissue are measured are quite variable and their effectsremain controversial. One possible source of variation in responsivenessis the energy status of the tissue, which could influence thecontrol coefficients of enzymes, such as cytochrome-c oxidase,whose activity is sensitive to [CO2]. In this study we comparedresponses of respiration rate to [CO2] over the range of 60to 1000 µmol mol-1in fully expanded leaves of four C3andfour C4herbaceous species. Responses were measured near themiddle of the normal 10 h dark period, and also after another24 h of darkness. On average, rates of respiration were reducedabout 70% by the prolonged dark period, and leaf dry mass perunit area decreased about 30%. In all species studied, the relativedecrease in respiration rate with increasing [CO2] was largerafter prolonged darkness. In the C3species, rates measured at1000 µmol mol-1CO2averaged 0.89 of those measured at 60µmol mol-1in the middle of the normal dark period, and0.70-times when measured after prolonged darkness. In the C4species,rates measured at 1000 µmol mol-1CO2averaged 0.79 of thoseat 60 µmol mol-1CO2in the middle of the normal dark period,and 0.51-times when measured after prolonged darkness. In threeof the C3species and one of the C4species, the decrease in theabsolute respiration rate between 60 and 1000 µmol mol-1CO2wasessentially the same in the middle of the normal night periodand after prolonged darkness. In the other species, the decreasein the absolute rate of respiration with increase in [CO2] wassubstantially less after prolonged darkness than in the middleof the normal night period. These results indicated that increasingthe [CO2] at the time of measurement decreased respiration inall species examined, and that this effect was relatively largerin tissues in which the respiration rate was substrate-limited.The larger relative effect of [CO2] on respiration in tissuesafter prolonged darkness is evidence against a controlling roleof cytochrome-c oxidase in the direct effects of [CO2] on respiration.Copyright 2001 Annals of Botany Company Carbon dioxide, respiration, Abutilon theophrasti(L.), Amaranthus retroflexus(L.),Amaranthus hypochondriacus (L.), Datura stramonium(L.), Helianthus annuus(L.), Solanum melongena(L.), Sorghum bicolor(L. Moench), Zea mays  相似文献   

18.
The effects of the foliar application of phytocidal concentrationsof 2-methyl-4-chlorophenoxyacetic acid (MCPA) on change in totaldry weight, and in ‘available carbohydrate’ (starch,‘total’ and ‘reducing’ sugars), totalnitrogen, phosphorus, potassium, calcium, and magnesium of ‘tops’and roots of tomato plants have been followed over a periodof 14 days following spraying. There were two main treatments—‘nutrient’(nutrient supply to roots continued after spraying) and ‘water’(distilled water only supplied to roots after spraying) and‘water’ (distilled water only supplied to rootsafter spraying)—the sub-treatments consisting of ‘MCPA’versus ‘no-MCPA’ for each of the main treatments.Twelve different times of sampling were used. In analysing the present data, the quantity ‘residualdry weight’ (total dry weight less ‘available carbohydrate’),which was originally introduced by Mason and Maskell as a basisof reference for analyses of plant organs in short-period experimentsnot involving appreciable growth, has been used as an estimateof the permanent structure of plant growth. This new use ofthe ‘residual dry weight’ basis has brought outimportant features which were obscured when the data were leftin their primary form (as percentages of total dry weight oramounts per plant). Growth, as measured by increase in ‘residual dry weight’,was greatly inhibited by 2-methyl-4-chlorophenoxyacetic acidshortly after spraying, in both the presence and the absenceof nutrient. In the presence of 2-methyl-4-chlorophenoxyacetic acid, netassimilation rate (estimated as rate of increase in total dryweight per gram ‘residual dry weight’ of the ‘tops’)was greatly diminished while uptake of total nitrogen and ofP2O5 (estimated as increase in total nitrogen or of P2O5 ofthe whole plant per day per 1 g. ‘residual dry weight’of the roots) appeared to undergo a similar but much smallerdiminution. It seemed probable, however, that in the presenceof MCPA a larger proportion of the carbohydrate actually formedwas utilized for synthesis of aminoacids and protein. In the plant as a whole there was no evidence of actual depletionof ‘available carbohydrate’ as a result of MCPAtreatment, this fraction showing a steady increase in all treatmentsthroughout the experiment. The rate of increase was, however,much reduced by MCPA treatment. The ‘tops’ presentedmuch the same picture as the whole plant, but for the rootsthe situation was quite different. While the roots of the ‘no-MCPA’plants and also of the ‘MCPA-water’ plants showeda steady increase in available carbohydrate, those of the ‘MCPA-nutrient’plants rose only very slightly (from the initial value of 8mg. per plant to about 10 mg.) during the first 2 days, andthen in the next 2 days declined to a value (about 6 mg.) belowthe initial and remained at this low level for the rest of theexperiment. It is suggested that the phytocidal effect of 2-methyl-4-chlorophenoxyaceticacid in the presence of nutrient may be due to depletion ofthe ‘available carbohydrate’ supplies in the roots,which is shown to be brought about, in part, by reduced transportfrom the tops, and partly by the relatively greater utilizationof the carbohydrate present. These results offer an explanationfor the facts that plants showing vigorous growth are more easilykilled by MCPA and that perennial plants, particularly thosewith storage tissues in their roots, are more resistant. Further,they suggest the useful practical application that MCPA treatmentshould be given when the carbohydrate reserves of the rootsare at a minimum. For perennial plants, conditions might beexpected to be optimal for the application of MCPA in late spring,at a time when the first ‘flush’ of growth is slowingdown and before any appreciable new reserves of carbohydratehave been accumulated. It was also shown that 2-methyl-4-chlorophenoxyacetic acid preventedthe net synthesis of starch, but still permitted an appreciablenet formation of sucrose. 2-methyl-4-chlorophenoxyacetic acid appeared to have no effecton the uptake of potassium, calcium, or of magnesium. The lackof effect on potassium is contrasted with the previous observationby Rhodes, Templeman, and Thruston (1950) that sub-lethal concentrationsof MCPA, applied over a relatively long period to the rootsof tomato plants, specifically depressed the uptake of potassium.  相似文献   

19.
An understanding of volatilization of nitrogen (N) from leavesof crop and weed species may be important to the improvementof crop production. Foliar N loss (both reduced and oxidizedforms), net CO2 uptake, and transpiration rates were measuredconcomitantly at 30°C on soyabean (Glycine max (L.) Merr.)and sorghum (Sorghum bicolor (L.) Moench) leaves at low (1 percent), ambient (20 per cent), and high (40 per cent) levelsof oxygen. In soyabeans, maximum reduced and total N losseswere found at the highest O2 concentration, and the lowest Nlosses were measured at the lowest O2 level. Net CO2 assimilationwas significantly reduced with increasing O2 during two of threesamplings. Quantities of oxidized N lost were not altered. Sorghumshowed no significant effects from O2 on N loss or net CO2 assimilation.The increased ammonia released from soyabean foliage in thepresence of higher concentration of O2 probably affects metabolicpathways that contribute to the total reduced N volatilization. Glycine max, Sorghum bicolor, CO2 assimilation, nitrogen loss  相似文献   

20.
Plants of all eight isolines of three maturity genes (all combinationsof two alleles at the three lociE1/e1,E2/e2,E3/e3) of soyabean[Glycine max(L.) Merrill] were grown in four different photoperiods(12, 13, 14 or 15 h d-1) at 30/24 °C from first flower openingto harvest maturity. Photoperiod, isoline, and their interaction,affected significantly (P<0.01) the duration between firstand last flowering, and reproductive duration. The interactionsbetween genotype and photoperiod were sufficiently strong thatconsiderable differences in these durations were detected amongisolines in the least-inductive environment (15 h d-1) whereasdifferences were negligible in the most-inductive regime (12h d-1). There was a negative linear relation between photoperiodand both rate of progress from the appearance of the first tothe last flower, and rate of progress from first flowering toharvest maturity; sensitivity to photoperiod varied (P<0.05)six- and five-fold, respectively, among the extreme isolines(e1e2e3andE1E2E3). The three dominant allelesE1,E2andE3, singly,had comparatively little effect on post-flowering traits, butconsiderable epistasis (particularly betweenE1andE2) was detectedfor sensitivity to photoperiod in respect of rates of progressfrom the appearance of the first to the last flower, and fromfirst flower to harvest maturity. Thus the large variationsdetected for these traits are the consequence of genexgene (xgene)xenvironmentinteractions.Copyright 1998 Annals of Botany Company. Glycine max(L.) Merrill, soyabean, maturity genes, flowering, photoperiod.  相似文献   

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