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1.
Experiments were conducted during the 1974–75 and 1975–76winter season with the barley (Hordeum vulgare L.) cultivarJyoti. From amongst the various plant parts, the flag leaf bladehad higher in vivo nitrate reductase (NR) activity than thelower two leaf blades, glumes, and grains. However, the potentialof a plant part to reduce NO3 is a function of its freshweight and the NR per unit fresh weight. On this basis, thesecond and third leaf blades could reduce more NO3 thanthe flag leaf blade. N fertilizer application resulted in enhancementof the activity of the leaf blades alone. N fertilizer appliedduring the reproductive phase was taken up and assimilated bythe various plant parts. The studies suggest that, even whenthe fertilizer is applied at optimum levels for obtaining maximumyields, the upper leaf blades have sub-optimal NR activity andthat there is a likelihood of either a preferential flow ofNO3 to the leaf blades or transnational barriers to NO3movement to the ear.  相似文献   

2.
The effects of different applied NO3 concentrations onextension growth and final length and area of leaves 1–4of five cereals and six pasture grasses of temperate originwere examined. Increased applied NO3 in the range 0.1–0.5.0mol m–3 caused decreased duration of growth but increasedgrowth rate and final length of leaves 2–4 of the cerealsAvena saliva, Hordeum vulgare, Secale cereale, x Triticosecaleand Triticum aestivum. For all cereals, increased NO3resulted in increased area of leaves 1–4. Pasture grasseswere supplied either 0.5 or 50 mol m–3 NO3. Increasedapplied NO3 (0.5–5.0 mol m–3) resulted indecreased duration of growth and increased growth rate and finalarea of leaves 1–4 of Bromus wiltdenowii, leaves 2–4ofFestuca arundinaceae and leaves 3 and 4 of Lolium muitiflorum.In addition, length of leaves 3 and 4 of B. witidenowii increasedwith increased NO3. Increased NO3 resulted inincreased area of leaves 2–4 of Dactylis gtomerata andLolium perenne and leaves 3 and 4 of Phalaris aquaiica but hadno effect on extension growth of all three species. Avena sativa L, oat, Hordeum vulgare L, barley, Secale cereale L, rye, x Triticosecale Wittm, triticale, Triticum aestivum L, wheat, Bromus willdenowii Kunth, prairie grass, Dactylis gtomerata L, cocksfoot, Festuca arundinaceae Shreb, tall fescue, Lolium multijlorum Lam, Italian ryegrass, Lolium perenne L, perennial ryegrass, Phalaris aquatica L, nitrate, leaf extension, leaf expansion  相似文献   

3.
The effects of different applied NO3 concentrations onextension growth and final length and area of leaves 1–4of five cereals and six pasture grasses of temperate originwere examined. Increased applied NO3 in the range 0.1–50mol m–3; caused decreased duration of growth but increasedgrowth rate and final length of leaves 2–4 of the cerealsAvena saliva, Hordeum vulgare, Secale cereale x Triticosecaleand Triticum aestivum. For all cereals, increased NO3resulted in increased area of leaves 1-4. Pasture grasses weresupplied either 0.5 or 50 mol m–3; NO3. Increasedapplied NO3 (0.5–50 mol m–3) resulted indecreased duration of growth and increased growth rate and finalarea of leaves 1–4 of Bromus willdenowii leaves 2–4of Festuca arundinaceae and leaves 3 and 4 of Lolium multiflorum.In addition, length of leaves 3 and 4 of B. willdenowii increasedwith increased NO3. Increased NO3 resulted in increased areaof leaves 2–4 of Daciylis glomerata and Lolium perenneand leaves 3 and 4 of Phalaris aquatica but had no effect onextension growth of all three species. Avena saliva L., oat, Hordeum vulgare L., barley, Secale cereaie L., rye, x Triticosecale Wittm, triticale, Triticum aestivum L., wheat, Bromus willdenowii Kunth, prairie grass, Dactylis glomerata L., cocksfoot, Festuca arundinaceae Shreb, tall fescue, Lolium multiflorum Lam, Italian ryegrass, Lolium perenne L, perennial ryegrass, Phalaris aquatica L, nitrate,, leaf extension, leaf expansion  相似文献   

4.
Net photosynthesis rate (Pn), stomatal conductance to CO2 andresidual conductance to CO2 were measured in the last six leaves(the sixth or flag leaf and the preceding five leaves) of Triticumaestivum L. cv. Kolibri plants grown in Mediterranean conditions.Recently fully expanded leaves of well-watered plants were alwaysused. Measurements were made at saturating photosynthetic photonflux density, and at ambient CO2 and O2 levels. The specificleaf area, total organic nitrogen content, some anatomical characteristics,and other parameters, were measured on the same leaves usedfor gas exchange experiments. A progressive xeromorphic adaptation in the leaf structure wasobserved with increasing leaf insertion levels. Furthermore,mesophyll cell volume per unit leaf area (Vmes/A) decreasedby 52·6% from the first leaf to the flag leaf. Mesophyllcell area per unit leaf area also decreased, but only by 24·5%.However, nitrogen content per unit mesophyll cell volume increasedby 50·6% from the first leaf to the flag leaf. This increasecould be associated to an observed higher number of chloroplastcross-sections per mm2 of mesophyll cell cross-sectional areain the flag leaf: values of 23000 in the first leaf and 48000in the flag leaf were obtained. Pn per unit leaf area remainedfairly constant at the different insertion levels: values of33·83±0·93 mg dm–2 h–1 and32·32±1·61 mg dm–2 h–1 wereobtained for the first leaf and the flag leaf, respectively.Residual conductance, however, decreased by 18·2% fromthe first leaf to the flag leaf. Stomatal conductance increasedby 41·7%. The steadiness in Pn per unit leaf area across the leaf insertionlevels could be mainly accounted for by an opposing effect betweena decrease in Vmes/A and a more closely packed arrangement ofphotosynthetic apparatus. Adaptative significance of structuralchanges with increasing leaf insertion levels and the steadinessin Pn per unit leaf area was studied. Key words: Photosynthesis, structure, wheat  相似文献   

5.
Agrostis capillaris L.5, Festuca vivipara L. and Poaalpina L.were grown in outdoor open-top chambers at either ambient (340 3µmol mol–1) or elevated (6804µmol mol–1)concentrations of atmospheric carbon dioxide (CO2) for periodsfrom 79–189 d. Photosynthetic capacity of source leaves of plants grown atboth ambient and elevated CO2 concentrations was measured atsaturating light and 5% CO2. Dark respiration of leaves wasmeasured using a liquid phase oxygen electrode with the buffersolution in equilibrium with air (21% O2, 0.034% CO2). Photo-syntheticcapacity of P. alpina was reduced by growth at 680 µmolmol–1 CO2 by 105 d, and that of F. vivipara was reducedat 65 d and 189 d after CO2 enrichment began, suggesting down-regulationor acclimation. Dark respiration of successive leaf blades ofall three species was unaltered by growth at 680 relative to340 µmol mol–1 CO2. In F. vivipara, leaf respirationrate was markedly lower at 189 d than at either 0 d or 65 d,irrespective of growth CO2 concentration. There was a significantlylower total non-structural carbohydrate (TNC) concentrationin the leaf blades and leaf sheaths of A. capillaris grown at680µmol mol–1 CO2. TNC of roots of A. capillariswas unaltered by CO2 treatment. TNC concentration was increasedin both leaves and sheaths of P. alpina and F. vivipara after105 d and 65 d growth, respectively. A 4-fold increase in thewater-soluble fraction (fructan) in P. alpina and in all carbohydratefractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosyn-theticcapacity and leaf carbohydrate concentration was such that therewas a strong positive correlation between photosynthetic capacityand total leaf N concentration (expressed on a per unit structuraldry weight basis), and total nitrogen concentration of successivemature leaves reduced with time. Multiple regression of leafphotosynthetic capacity upon leaf nitrogen and carbohydrateconcentrations further confirmed that leaf photosynthetic capacitywas mainly determined by leaf N concentration. In P. alpina,leaf photosynthetic capacity was mainly determined by leaf CHOconcentration. Thus there is evidence for down-regulation ofphotosynthetic capacity in P. alpina resulting from increasedcarbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positivelycorrelated in P. alpina and F. vivipara. Leaf dark respirationand soluble carbohydrate concentration of source leaves werepositively correlated in A. capillaris. Changes in source leafphotosynthetic capacity and carbohydrate concentration of plantsgrown at ambient or elevated CO2 are discussed in relation toplant growth, nutrient relations and availability of sinks forcarbon. Key words: Elevated CO2, Climate change, grasses, carbohydrate partitioning, photosynthesis, respiration  相似文献   

6.
Rates of net photosynthesis of the flag leaves of 15 genotypesof wheat and related species were measured throughout theirlife, using intact leaves on plants grown in the field. At thestage when rates were maximal, they were in general highestfor the diploid species, intermediate for the tetraploidspeciesand lowest for Triticum aestivum (means of 38, 32 and 28 mgCO2 dm–2 h–1 respectively). Rates were stronglynegatively correlated with leaf area, leaf width and the meanplan area per mesophyll cell and positvely correlated with stomatalfrequency and number of veins per mm of leaf width. The differencesamong species in these attributes were mainly related to ploidylevel. It was not possible to determine the relative importanceof each anatomical feature, though the changes in stomatal frequencyhad only slight effects on stomatal conductance and the observeddifferences in rates of photosynthesis were much greater thanwould be expected from those in stomatal conductance alone. There was genetic variation in rates of light dependent oxygenevolution of isolated protoplasts and intact chloroplasts butno difference attributable to ploidy. The mean rate, 91 µmolO2 mg–1 chlorophyll h–1, equivalent to 3.9 mg CO2mg-1chlorophyll h-1 was considerably less than the rate of photosynthesisin comparable intact leaves, which was 7.2 mg CO2 mg–1chlorophyll h–1. The total above-ground dry matter yields were least for thewild diploids T. urartu and T. thauodar and the wild tetraploidT. dicoccoides, but the other wild diploids produced as muchdry matter as the hexaploids. The prospects of exploiting differences in photosynthetic ratein the breeding of higher yielding varieties are discussed. Triticum aestivum L., wheat, Aegilops spp, photosynthesis, stomatal conductance, stomatal frequency, polyploidy  相似文献   

7.
Differences in premature leaf abscission and in visible steminjury in genetic lines of poplar followed continuous fumigationswith air pollutant levels of SO2 (90–100 nl l–1)and O3 (70–80 nl l–1) either separately or together.The clones used were: Populus deltoides var. missiouriensisMarsh., P. nigra cv. ‘italicd’ L., and the hybridsP. nigra cv. ‘italica’ xP. deltoides (He-X/3) andP. nigra cv.‘italica’ x P. nigra cv. ‘Serres’(He-K/7). While most leaf abscission occurred within 20 d fromthe start of fumigation, stem lesions (intumescences), appearedonly after 72 d. Their anatomical characteristics include theformation of lysigenous aerenchyma in the lower parts of theintumescence, the sloughing of superficial cells from the injuredarea, and the development of crystalline formations on the surfaceof the lesions. P. deltoides exhibited the least morphologicalresponse to the gases. Ethylene released from fumigated leaves was determined at thesame gas concentration of SO2 (100 nl l–1), O3 (75 nll–1) and their mixture. Leaves of P. deltoides consistentlyshowed the lowest ethylene production after the gas treatments.P. ‘italica’ production was higher but was littlealtered by the treatments. The two hybrids He-X/3 and He-K/7showed the greatest increases in ethylene evolution with time.With He-K/7 exposed to the gas mixture the production of ethylenedecreased after the initial sharp rise during days 1–2,and reflected the considerable leaf damage observed after day3. The results suggest that sensitivity to air pollution, (as shownby leaf abscission and the formation of stem intumescences)can be correlated with the level of pollutant-induced ethyleneevolution from leaves. Initially high levels could induce abscission,whilst prolonged production could be responsible for intumescenceinitiation. The discussion proposes a series of events fromSO2 and/or O3 entry into the leaf and the physiological reasonsfor the clonal differences. Key words: Sulphur dioxide, ozone, ethylene, poplar, leaf abscission, stem lesions  相似文献   

8.
The Uptake of Gaseous Ammonia by the Leaves of Italian Ryegrass   总被引:5,自引:0,他引:5  
Lockyer, D. R. and Whitehead, D. C. 1986. The uptake of gaseousammonia by the leaves of Italian ryegrass.—J. exp. Bot.37: 919–927. Plants of Italian ryegrass (Lolium multiflorum Lam.) grown insoil with two rates of added 15N-labelled nitrate were exposed,in chambers, for 40 d to NH3 in the air at concentrations of16, 118 and 520 µg m–3. At the highest concentrationof NH3, this source provided 47?3% of the total nitrogen inplants grown with the lower rate of nitrate addition (100mgN kg–1 dry soil) and 35?2% with the higher rate (200mgN kg–1 dry soil) At the intermediate concentration ofNH3, the contributions to total plant N were 19?6% and 10?8%,respectively, at low and high nitrate while, at the lowest concentrationof NH3, they were 5?1% and 32%. Most of the N derived from theNH3 remained in the leaves, but some was transported to theroots. The amount of N derived from the NH3 that was presentin the leaves was not reduced by washing the leaves in waterat pH 5?0 before harvesting, indicating that the N was assimilatedby the plant and not adsorbed superficially. Rates of uptakeof NH3 per unit leaf area ranged from 1?7 µg dm–2h–1 at a concentration of 16 µg m–3 to 29?0µg dm–2 h–1 at a concentration of 520 µgm–3 and with the lower rate of nitrate addition. Increasingthe supply of nitrate to the roots slightly reduced the rateof uptake of NH3 per unit leaf area. Uptake of N from the higherrate of nitrate was reduced at the highest concentration ofNH3 in the air. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum  相似文献   

9.
This research examined the hypothesis that as cacti evolve tothe leafless condition, the stem epidermis and cortex becomemore leaflike and more compatible with a photosynthetic role.All cacti in the relict genus Pereskia have non-succulent stemsand broad, thin leaves. All members of the derived subfamilyCactoideae are ‘leafless’, having an expanded cortexthat is the plant's only photosynthetic tissue. In Pereskia,leaves have a high stomatal density (mean: 50.7 stomata mm–2in the lower epidermis, 38.1 mm–2 in the upper epidermis),but stems have low stomatal densities (mean: 11.3 mm 2, threeof the species have none). Stems of Cactoideae have a high stomataldensity (mean: 31.1 mm–2, all species have stomata). Theouter cortex cells of stems of Cactoideae occur in columns,forming a palisade cortex similar to a leaf palisade parenchyma.In this palisade cortex, the fraction of tissue volume availablefor gas diffusion has a mean volume of 12.9%, which is identicalto that of Pereskia leaf palisade parenchyma. Pereskia stemcortex is much less aerenchymatous (mean: 5.3% of cortex volume).Cactoideae palisade cortex has a high internal surface density(0.0207 cm2 cm–2 which is higher than in Pereskia stemcortex (0.0150 cm2 cm–3) but not as high as Pereskia leafpalisade parenchyma (0.0396 cm2 cm–3). Pereskia stem cortexhas no cortical bundles, but Cactoideae cortexes have extensivenetworks of collateral vascular bundles that resemble leaf veins. Cactaceae, cactus, intercellular space, stomatal density, internal surface/volume, evolution  相似文献   

10.
The relation of the in vivo nitrate reductase (NR) activityto growth period was studied in the nodules and the leaves ofthe summer moong (Vigna radiata). The maximum NR activity wasobserved 31 days after sowing (DAS) in the leaves and 28 DASin the case of the nodules. In a pot experiment, the effectof the various nitrogen concentrations, namely 0, 3, 6, 9 and12 mg kg–1 was studied on NR activity at three growthstages. The maximum NR activity was observed at 6 mg kg–1N during the pre-flowering stage (26 DAS). Though the noduleshave higher NR activity, its expression was limited by substrateavailability. The NR activity in the leaf could be used as anindex of NR activity in the nodules. Nitrate reductase, nitrogen, nitrate, moong, Vigna radiata  相似文献   

11.
Ribulose bisphosphate carboxylase (EC 4.1.1.39 [EC] ) activity wasvery low in tomato leaf extracts unless prepared in the presenceof Mg2+, and polyclar AT. With young leaves, but not with fully-expanded leaves, the RuBP carboxylase activityextracted was increased by prolonged illumination of the leaves(2 h). The main effect of the light treatment was to increasethe specific activity of the enzyme but there was also a smallincrease in RuBP carboxylase protein. Tomato leaf RuBP carboxylasein extracts had specific activities in the range 0.2–0–6µmol CO2 min–1 mg–-1 total protein extracted,or 0.5–1.2 µmol CO2 min–1 mg–1 RuBPcarboxylase, and an apparent Km (CO2) at 20 ?C of 9.3 ? 1.2µM (using a of 6.407). Key words: Tomato leaf, RuBP carboxylase, Properties  相似文献   

12.
Ion chromatographic methods determined organic acids and mainnutrient minerals in the apoplastic solution from leaves ofseveral Fagaceae (Quercus ilex L., Quercus cerris L., Quercusvirgiliana (Ten.) Ten, and Fagus sylvatica L.). The anions oforganic acids found in high amounts (250 to 650 µM) werequinate, malate, and oxalate. Lactate, pyruvate, formate andacetate were detected in relatively low amounts with concentrationsbetween 20 and 200 µM. The total concentration of organicacids in the apoplastic sap ranged between 1.5 and 2 mM. Thetotal concentration of inorganic cations (K+, Mg2+, NH4+, Ca2+,Na+) and anions (C1, NO3, SO2–4 and PO3–4)in the apoplastic sap varied between 5 and 10 mM, and 0.35 and1.8 mM, respectively. We conclude that the concentration oforganic acid ions in the leaf apoplast depends mainly on theexchange with the leaf cells and is influenced by the electrochemicalgradient between the symplast and the apoplast in relation tothe water potential of the leaf. The determination of formateand acetate in the apoplastic compartment of leaves lend weightto the argument that the production of these acids by treesis a important emission source to the atmosphere. (Received June 9, 1998; Accepted April 8, 1999)  相似文献   

13.
KAMALUDDIN  M.; GRACE  J. 《Annals of botany》1992,69(6):557-562
Acclimation of fully developed leaves of Bischofia javanicaBlume to shadelight was examined. Seedlings were grown undersimulated daylight (1000 µmol m–2 s–1), thentransferred to a simulated shadelight (40 µmol m–2s–1). When a high-light leaf was transferred to low light, large negativenet photosynthetic rates (Pm) were recorded. This decrease wasrapid, but within 7 d the rate increased and became equal tothe low-light control leaf. These changes in photosynthesisdid not follow the pattern of changes in stomatal conductance(gs). Transfer to the low light resulted in a dramatic decreasein leaf weight per unit area (Lw), and most of the decreasesin Lw occurred within 3 d of transfer when the Pm of the transferredleaf was well below that of the low-light control leaf. There was a significant decrease in chlorophyll a in the transferredleaf without an appreciable change in chlorophyll b resultingin a large decrease in the chlorophyll a to chlorophyll b ratio.Leaf chlorophylls per unit area were higher in the transferredleaf than the low-light control leaf. Maximum photosyntheticrate in the transferred leaf was decreased by 40% compared tothat for the high-control leaf, but was almost at the same extenthigher than the low-light control leaf The results are discussedin the context of carbon gain capacity of its seedlings underlight-limiting forest understorey habitats. Bischofia, chlorophylls, light, photosynthesis, shade acclimation, tree seedlings, tropical tree  相似文献   

14.
Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO2 concentration of either 340 or680µI 1–1 CO2. Following complete acclimation tothe environmental regimes, leaf and whole plant CO2 effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO2 increased rates of photosynthesis of young, fullyexpanded leaves by 35–46% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI–1 CO2 reduced rates of photosynthesis in bothCO2 regimes, compared with plants acclimated to 340µll–1. There was no significant effect of CO2 regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO2 exhibited generally lower ratesthan those developed in 340µI I–1 CO2. Initially the seedling plants in elevated CO2 grew faster thantheir counterparts in 340µI I–1 CO2, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO2 regime, specific leaf area was persistently13–40% lower in elevated CO2 while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO2reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO2 on plant growthwas primarily due to the fact that CO2 concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO2, photosynthesis, respiration, growth, development  相似文献   

15.
Ward, D. A. and Drake, B. G. 1987. Photoinhibition under atmosphericO2, the activation state of RuBP carboxylase and the contentof photosynthetic intermediates in soybean and wheat.—J.exp. Bot. 38: 1937–1948. Associations between photosynthesis, the activation state ofRuBP carboxylase and the contents of photosynthetic intermediateswere compared in soybean and wheat leaves before and after exposureto photoinhibitory treatments in the presence of atmosphericO2. Exposing attached leaves to a supra-saturating irradiance(3 800 µmol quanta m– 2 s–1) for 2 h in CO2-freeair decreased carboxylation efficiency and the light-saturatedphotosynthetic rate in air by approximately 50%. Exposure tothe photoinhibitory treatment for periods in excess of 2 h didnot cause a further decrease of photosynthesis in soybean. Althoughphotosynthesis was reduced, the initial and total (fully-activated)activities of ribulose 1,5-bisphosphate carboxylase (RuBPCase)in leaf extracts were unaltered in each species by the photoinhibitorytreatment. This was true for leaves sampled under both air andat a rate-limiting intercellular CO2 partial pressure (Ci) of75 µPa Pa–1. The contents of ribulose l,5-bisphosphate(RuBP) and 3-phosphoglyceric acid (3-PGA) were reduced by thephotoinhibitory treatment in soybean leaves sampled in air andat a rate-limiting Ci, although the RuBP/3-PGA ratio was unaffected.The relative reduction of RuBP content in soybean leaves atrate-limiting C1 was similar to the corresponding reductionof carboxylation efficiency. For wheat,the relative reductionof RuBP content at rate-limiting Ci (–19%) caused by thephotoinhibitory treatment was considerably less than the correspondingdecrease of carboxylation efficiency (–49%).The RuBP/3-PGAratio of wheat was also increased significantly by the photoinhibitorytreatment The significance of these observations to the regulationof CO2-limited photosynthesis in leaves experiencing photoinhibitionunder atmospheric oxygen is discussed. Consideration is alsogiven to the previous contention that contemporary measurementsof initial activity in crude extracts may provide a spuriousindication of the amount of the enzyme-CO2-Mg2 + form of RuBPcarboxylase present in the leaf. Key words: Carboxylation efficiency, RuBP carboxylase, photoinhibition, RuBP, 3-PGA  相似文献   

16.
HO  L. C. 《Annals of botany》1976,40(6):1153-1162
The rate of carbon transport from an old tomato leaf (54 days),grown at 80 W m–2, was measured under light flux densitiesbetween 7 and 90 W m–2. Under low light, the rate of carbontransport over a 6 h period was about 1 mg C dm–2 h–1,well in excess of the concurrent photosynthetic rate. The lossfrom these leaves of 14C-leaf assimilate which was fixed beforethe experimental period amounted to 62 per cent of the totalinitial uptake and was higher than that from leaves with higherconcurrent photosynthetic rates. The higher loss of 14C fromleaves with low photosynthetic rates was due to a greater contributionof 14C from the starch and residue fractions. The rate of transportappeared to be determined by the concentration of the labilesucrose, not the total sucrose concentration. In comparisonwith young fully-expanded tomato leaves (Ho, 1976) the sizeof the labile sucrose pool appeared to decrease with age. Thephotosynthesistranslocation coefficient was low (k1k2=0•21)for an old tomato leaf. Based on these results a scheme of carbonpartitioning in relation to translocation is proposed. Criteriafor assessing the efficiency of translocation in leaves arediscussed.  相似文献   

17.
Woodrow, L. and Grodzinski, B. 1987. Ethylene evolution trombracts and leaves ol Poinsettia, Euphorbia pulcherrima Willd.—J.exp. Bot. 38: 2024–2032. Ethylene release from fully expanded, red and white bracts andleaves of poinsettia, Euphorbia pulcherrima Willd., was compared.On a laminar (area) basis leaves contained about 50 times morechlorophyll and demonstrated 10 times the photosynthetic rateof the bracts. Both tissues contained starch, however, solublecarbohydrate in the bracts consisted primarily of reducing hexoseswhile the leaves contained mainly sucrose for translocation.The total free alpha-amino nitrogen content of the bract tissuewas twice that of the leaf tissue. The leaves contained moreACC (1-aminocyclopropane-1-carboxylic acid) and produced proportionallymore endogenous C2H4 than either the red or white bracts. ACC-stimulated2H4 release was also greatest from the green tissue indicatingthat the EFE (ethylene forming enzyme) was most active in theleaves. The specific activity of the 14C2H4/12C2H4 releasedfrom [2,3-14C]ACC confirmed ACC as the primary precursor ofC2H4 in this tissue. Ethylene release from the non-photosynthetic,bract tissue was not markedly affected by alterations in CO2or light conditions. In green leaf tissue endogeneous ethylenerelease increased from 1·5 to 6·0 pmol C2H4 cm–2h–1 while ACC-stimulated ethylene release increased from10 to 35 pmol C2H4 cm2– h1– as the CO2 partial pressureincreased from 100 to 1 200 µbar. Key words: Poinsettia, ethylene, bracts  相似文献   

18.
The possible role in drought resistance played by sclerophyllywas studied in the Mediterranean oaks Quercus ilex, Q. suberand Q. pubescens. Studies were conducted on leaves at 30, 50and 80% of their final surface area, as well as on mature leavesof the current year's growth in June and September and on 1-year-oldleaves. Leaves of different ages of the three species showed quite differentdegrees of sclerophylly (DS). Q. ilex leaves reached the definitiveDS of 1.75 g dm–2 during leaf expansion; Q. pubescensleaves hardened at the end of their expansion, with a finalDS of 0.93 g dm–2; Q. suber showed the lowest DS of 0.76g dm–2. Leaf conductance to water vapour (g1) of 1-year-old leaves ofQ. ilex, measured in the field, showed a duration of the g1peak values about twice that of the other two species. The minimumleaf relative water content (RWC), however, was near the samein the three species, indicating that water loss was recoveredpartly by Q. ilex leaves. This was apparently due to the higherbulk modulus of elasticity (  相似文献   

19.
The relationships between CO2 concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO2 supply around the roots. Free CO2 in sediment-interstitial-waterranged from 1–01 mol m–3 (Esthwaite), 0.79 mol m–3(peat), 0.32 mol m–3 (silt) and 0–17 mol m–3(sand), with plants maintained under PAR of 40 µmol m–2s–1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO2 had larger leaf fresh weight (0–69 g) andtotal surface area (223 cm2 g–1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm2g–1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO2 concentration[CO2], was highest in the sand-grown plants (2–69 molm–3, corresponding to 6.5% CO2 in air) and lowest inthe Esthwaite plants (1–08 mol m–3). Expressionof CAM in transplants was also greatest in the low CO2 regime,with H+ (measured as dawn-dusk titratable acidity) of 50µmolg fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO2]1 and would makea major contribution to daytime CO2 fixation in vivo. A range of leaf sections (0–2, 1–0, 5–0 and17–0 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO2 evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO2 and 1–0mol m–3 exogenous CO2 was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O2 g–1 fr. wt. h–1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO2 g–1 fr. wt. h–1) with a K0.5 of 80 mmol m–3.In terms of light response, saturation of photosynthesis intissue slices occurred at 850–1000 µmol m–2s–1 although light compensation points (6–11 µmolm–2s–1) and chlorophyll a: b ratios (1.3) were low.While CO2 and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO2 supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO2 concentrating mechanisms interact inintact plants to maintain saturating CO2 levels within leaflacunae, although the responses of the various components ofCO2 supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO2 concentration, crassulacean acid metabolism, root inorganic carbon supply, CO2 concentrating mechanism  相似文献   

20.
To examine 14CO2 fixation, potential translocation, and carbonflow among leaf chemical fractions of young developing leaves,the shoot tip of 24-leaf cottonwood (Populus deltoides Bartr.ex. Marsh) plants were cut off under water, placed in artificialxylem sap, and treated with 14CO2 in continuous and pulse-chaseexperiments. Additional leaves on whole plants were spot treatedon the lamina tip to follow export from the tip only. The analysedleaves ranged in age from leaf plastochron index(LPI) –5to 3, the spot treated leaves from LPI 2 to 5. After 30 minfixation, the specific activity in the lamina tip increasedlinearly with leaf age from LPI –5 to 1 (0.5 to 4.5 kBqmg–1). Specific activity in the lower lamina increasedslowly with leaf age and did not reach 500 kBq mg–1 untilLPI –1. Total 14CO2 fixed in the lower lamina exceededthat fixed in the tip by LPI –2 because of the large amountof tissue present in the lower lamina. Although the lamina tipfixed high levels of 14CO2, pulse-chase studies coupled withautoradiography indicated no vein loading or translocation fromthe tip until about LPI 4 or 5. The 14C fixed in both tip andlower lamina was incorporated at the site of fixation and wasnot distributed to younger tissue or translocated from the lamina.Although the percentage distribution (14C in each chemical fractioncompared with the total in all fractions) of 14C among certainchemical fractions, e.g. sugars, amino acids and proteins, indicatedthat the mesophyll of the tip was more mature than the lowerlamina, physiologically both leaf sectors were immature basedon the expected 14C distribution in mature tissue. Informationfrom this and other studies indicates that the extreme tip ofa developing cottonwood leaf first begins to export photosynthateabout LPI 4 or 5 on a 24-leaf plant. The first photosynthatetranslocated may be incorporated into the vascular tissues andmesophyll directly below the tip. However, as the tip continuesto mature photosynthate is translocated past the immature lowerlamina into the petiole and out of the leaf. Populus deltoides Bartr. ex. Marsh, eastern cottonwood, translocation, leaf development, 14C fixation, carbon metabolism  相似文献   

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