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1.
The development of taurine uptake into the unicellular greenalga Chlorella fusca 211-8b was characterized as a specificresponse to either nitrate or sulphate limitation. Taurine transportunder nitrogen starvation was stimulated by low pH and showeda biphasic kinetics with Km-values of 1.1 x 10–3 mol dm–3and 1.0 x 10–2 mol dm–3. Uptake was substantiallyinhibited by all - and ß-amino acids tested, whereassulphonate analogues failed to diminish taurine accumulation.Thus, uptake seemed to be mediated by a ‘general aminoacid permease’, unable to discriminate between carboxyland sulphonyl groups. However, Chlorella fusca could not catabolizethis unusual ß-amino acid and mobilize the amino-boundnitrogen for growth. Only a small group of -amino acids supportedthe growth of Chlorella fusca as an efficient nitrogen source. Key words: Taurine uptake, nitrogen starvation, amino acid uptake, Chlorella fusca.  相似文献   

2.
Inhibition of Nodule Development in Soybean by Nitrate or Reduced Nitrogen   总被引:5,自引:1,他引:4  
Imsande, J. 1986. Inhibition of nodule development in soybeanby nitrate or reduced nitrogen.—J. exp. Bot. 37: 348–355. Nodulation of hydroponically grown soybean plants [Glycine max(L.) Merr.] is inhibited by continuous growth in the presenceof 4· mol m–3 KNO3 The presence of 4·0 molm–3 ‘starter nitrate’ for 3-6 d during noduledevelopment, however, subsequently stimulates nodule dry weightaccumulation and nitrogenase activity. These stimulations occureven though 4· mol m–3 nitrate temporarily delaysnodule development, i.e. the late steps of nodule developmentare reversibly inhibited by a short-term exposure to 4·0mol m–3 nitrate. On the other hand, treatment with 4·0mol m–3 nitrate in excess of 14 d significantly reducesnodule dry weight Thus, extended growth in the presence of 4·0mol m–3 KNO3 seems to block both early and late stepsof nodule development. Nodulation of hydroponically grown soybeansis also inhibited by continuous growth in the presence of 2·0mol m–3 (NH4)2SO4 This inhibition is not caused by acidityof the growth medium. On the other hand, nodule development6 d after inoculation with Rhizoblum japonicum is not delayedby a 7-d exposure to 2·0 mol m–3 (NH4)2SO4 butis partially inhibited by a prolonged exposure to (NH4)2SO4Because repression of nodulation by 4·0 mol m–3KNO3 is more severe than that by 2·0 mol m–3 (NH4)2SO4and because ammonium taken up by the soybean plant is not activelyoxidized to nitrate, it is suggested that there are at leasttwo mechanisms by which nitrate utilization represses noduleformation in soybean. Key words: Glycine max, nitrogen, nitrogen fixation, nodulation  相似文献   

3.
Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m–3 CaCl2 r, P, Y and were20.7±4.6 µm min–1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min–1MPa–1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m–3 KC1 these parametersbecame 12.3±3.5 µm min–1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min–1MPa–1. After 24 h osmotic adjustment in 150 mol m–3mannitol/0.5 mol m–3 CaCl2 r= 19.6±4.2 µmmin–1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min–1 MPa–01, respectively.After 24 h growth in 350 mol m–3 mannitol/0.5 mol m–3CaCl2 r= 13.3±4.1 µm min–1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min–1MPa–1. During osmotic adjustment in 200 mol m–3mannitol/0.5 mol m–3 CaCl2, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min–1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min–1MPa–1. Therefore, Y and are influenced by 10 mol m–3 K+ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur  相似文献   

4.
Imsande, J. 1986. Nitrate-ammonium ratio required for pH homeostasisin hydroponically grown soybean.—J. exp. Bot. 37: 341–347. Plant acid-base homeostasis is achieved when the mmoles of hydroxylions produced in the plant equal the mmoles of protons. Reductionof nitrate to ammonia is the major source of hydroxyl ions whereasammonium uptake-assimilation and the metabolism of neutral sugarsto organic acids are the primary sources of protons. Soybean[Glycine max (L.) Merr plants were grown hydroponically on mediumsupplemented with 3·0 mol m–3 nitrogen providedas various combinations of KNO3 and NH4NO3 Plant growth consumedessentially all available nitrogen in each case; however, onlyin flasks supplemented with approximately 1·8 minolesof KNO3 plus 0·6 mmole of NH4NO3 was the pH of the mediumunchanged. Thus, for every mmole of nitrogen assimilated, approximately0·6 mmole of dissociable protons must have been producedby the conversion of neutral sugars to carboxylic acids. Also,it was shown that a plant obtaining all of its nitrogen fromnitrate must neutralize or excrete approximately 0·5mmole of hydroxyl ion d–1. Conversely, the plant derivingall of its nitrogen from dinitrogen must excrete or neutralizeat least 0·8 mmole of hydrogen ion d–1 whereasthe plant deriving all of its nitrogen from aminonium must excreteor neutralize approximately 2·1 mmoles of hydrogen iond–1. Nevertheless, plants grown on medium supplementedwith 2·4 mol m–1 nitrate plus 0·6 mol m–3ammonium did not achieve a higher growth rate than plants grownon 3·0 mol m–3 nitrate. Key words: Glycine max, nitrogen fixation, nitrate utilization  相似文献   

5.
Salt Tolerance in the Succulent, Coastal Halophyte, Sarcocornia natalensis   总被引:2,自引:0,他引:2  
The effects of 0, 50, 100, 200, 300, 400 and 500 mol m–3NaCl on growth and ion accumulation in the succulent, coastalhalophyte Sarcocornia natalensis (Bunge ex Ung.-Sternb.) A.J. Scott were investigated. Increase in salinity from 0 to 300 mol m–3 NaCl stimulatedproduction of fresh, dry, and organic dry mass, increased succulenceand shifted resource allocation from roots to shoots. Growthwas optimal at 300 mol m–3 and decreased with furtherincrease in salinity. Water contributed to a large proportion of the increase in freshmass. Inorganic ions, especially Na+ and Cl– contributedsubstantially to the dry mass. At 300 mol m–3 NaCl inorganicions contributed to 37% of total dry mass and NaCl concentrationin the shoots was 482 mol m–3. Expressed sap osmotic potentialsdecreased from –2.10 to –3.95 MPa as salinity increasedfrom 0 to 300 mol m–3 NaCl. Massive accumulation of inorganicions, especially Na+ and Cl, accounted for 86% of theosmotic adjustment at 300 mol m–3 NaCl. Salinity treatments decreased the concentrations of K+ in shoots.Plant Na+ :K+ ratios increased steadily with salinity and reacheda maximum of 16.6 at 400 mol m3 NaCl. It is suggested that the exceptional salt tolerance of S. natalensisis achieved by massive inorganic ion accumulation which providessufficient solutes for osmoregulation, increased water fluxand turgor-induced growth. Key words: Sarcocornia natalensis, salt tolerance, halophyte  相似文献   

6.
The effects of a range of applied nitrate (NO3) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO3 concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO3 concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO3 concentration of 0 to 1·0 mol m–3then decreased only slightly with further increases in appliedNO3 of about 5·0 mol m–3. Root and shoot growth, NO3 accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m–3 NO3 at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO3 butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m–3 NO3 than with zero NO3.Root dry wt. was unaffected by NO3. Nitrate concentrationand NRA in root and shoot were always low without NO3.At 1·0 and 10 mol m3 NO3, NO3 accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO3 concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO3. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO3was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence  相似文献   

7.
Nitrate reduction in leaves of tomato occurred at the same ratein plants grown in 8.0 mol m–3 nitrate as in plants grownin 2.0 mol m–3 nitrate, but at a much slower rate in plantsgrown in 0.1 mol m–3 nitrate. However, the plants grownin 8.0 mol m–3 nitrate had a larger leaf system than theplants grown in 2.0 mol m–3 nitrate, and so the totalcapacity to assimilate nitrate was greater in the plants grownin the higher concentration. It was shown that plants grownin 8.0 mol m–3 nitrate were better buffered against nitratewithdrawal than plants grown in 2.0 mol m–3 nitrate asthe rate of nitrate reduction declined more slowly when plantswere transferred to 0.1 mol m–3 nitrate from the higherconcentration than from the lower concentration. Furthermore,leaf expansion continued in the plants transferred from thehigher concentration, whereas it ceased abruptly in the plantstransferred from the lower concentration. It was concluded thatboth continuing expansion and continuing nitrate reduction wereaccompanied, and possibly caused by, a release of nitrate fromstorage pools in the lower part of the stem or the roots. Duringwithdrawal of nitrate the leaves were shown to maintain potentialactivity of the enzyme nitrate reductase although there wasno nitrate to be reduced. When nitrate was resupplied it couldbe reduced very quickly and reduction in the leaves was seento increase within 5 h of resupply. By 3 d after resupply furtherenzyme activity had been induced. Key words: Lycopersicon esculentum Mill, nitrate assimilation, nitrate reductase activity, nitrate withdrawal  相似文献   

8.
Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO-3) content of root and shoot and NO-3 and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO-3 concentrations (0·1–20mol m–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m–3 NO-3 For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO-3 concentration on the partitioning of NO-3 assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m–3 NO-3 and that for all cereals, shoot assimilationincreased in importance as applied NO-3 concentration increasedfrom 1.0 to 20 mol m–3 At 5.0–20 mol m–3 NO3,the data indicated that the shoot played an important if notmajor role in NO-3 assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO-3 assimilation at 0.5 mol m–3NO-3 but shoot assimilation was predominant at 5.0 mol m–3NO-3 Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m–3 NO-3 Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap  相似文献   

9.
Salt Tolerance in the Triticeae: Leymus sabulosus   总被引:1,自引:0,他引:1  
Elymus dahuhcus, Leymus giganteus, L. angustus, L. sabulosusand, to a lesser extent, L. triticoides, were found to tolerate200 mol m–3 NaCl in solution culture. Elymus dahuricusdiffered from the Leymus species in its ion-uptake characteristics,showing a greater uptake of Cl and Na and a greater loss ofK from the shoots. In a more detailed experiment on Leymus sabulosusit was found that transpiration rates altered rapidly in responseto changes in external salinity whereas the accumulation ofNa and Cl in the leaves exhibited a lag of several days. Insalt stressed L. sabulosus Cl partially replaced the high levelsof nitrate found in the leaves of control plants. Glycinebetainelevels increased in the leaves from 8.0 mol m–3 plantsap in the controls to 28 mol m–3 plant sap at 250 molm–3 NaCl. Key words: Salt stress, Transpiration, Solute accumulation, Leymus  相似文献   

10.
Growth and ion accumulation were measured in callus culturesof Cicer arietinum L. cv. BG-203, grown on media supplementedwith 0–200 mol m–3 NaCl. Fresh and dry weights decreasedat concentrations ranging from 100–200 mol m–3,the reduction being greater during the third and fourth weeksof culture. Slight stimulation of growth was observed at 25and 50 mol m–3 NaCl. There was also a decrease in tissuewater content (fresh weight: dry weight) at 100–200 molm–3 NaCl. The concentration of Na+ and Cl in thetissue increased with increasing salinity of the medium. Mostof the accumulation of these ions occurred by the first weekwhile significant growth inhibition became apparent by onlythe third week of culture. Tissue K+ and Mg2+ decreased withincreasing salinization, the decrease being greater in K+ levels.Levels of Ca2+, however, were maintained throughout the experimentalrange. Key words: Cicer arietinum, NaCl stress, Callus cultures, Ion accumulation  相似文献   

11.
Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO3 by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO3 at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d–1, or constant external concentrations ([NO3)of 3, 10, 20, and 100 mmol m–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d-1, although growth was notlimited by N supply at RAR =0.18 d-1. Growth rates showed littlechange with [NO3–] between 10–100 mmol m–3(RGR=0·15 –0·16 d-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO3, accumulation of NO3 in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO3 from 1 mol m–3 solutions were assessed relativeto the growth-related requirement for NO3, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d–1 , but decreased thereafter to a theoretical minimumvalue at RGR  相似文献   

12.
Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m–1 (34.2 mol m–3 NaCl)and nodulation was completely inhibited at 7 dS m–1 (61.6mol m–3 NaCl); the plants died at 8 dS m–1 (71.8mol m–3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 1–4 dS m–1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N2 fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N2 fixation, Rhizobium, salinity  相似文献   

13.
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   

14.
In studies of Trifolium repens nitrogen nutrition, the controlof nutrient solution pH using dipolar buffers, was evaluatedin tube culture under sterile conditions. Five buffers; MES,ADA, ACES, BES and MOPS with pK2s (20 °C) of 6.15, 6.60,6.90, 7.15 and 7.20 respectively, at a concentration of 2.0mol m–3, were provided to inoculated Trifolium repensgrowing in nutrient solution containing 7.13 mol m–3 nitrogenas (NH4)2SO4. Initial pH of each solution was adjusted to theappropriate buffer pK2 Two buffers, ADA and ACES completelyinhibited plant growth. The remaining buffers had little effectin limiting pH change, although plant dry matter was higherand nodule numbers lower in the presence of these buffers. MESand MOPS were supplied to nutrient solutions with and without7.13 mol m–3 (NH4)2SO4, at concentrations ranging from0–12 mol m–3. MES at 9 mol m–3 and 12 molm–3 reduced growth of plants reliant on the symbiosisfor providing nitrogen. The provision of MES to plants providedwith NH4+ significantly increased plant yield and reduced nodulenumber at all concentrations. MOPS did not affect plant yieldor nodule number. The use of dipolar buffers in legume nitrogennutrition studies is considered in terms of buffering capacity,and the side effects on plant growth and symbiotic development. Key words: Ammonium, Dipolar buffer, Nitrogen nutrition, pH control, Symbiosis, Trifolium repens  相似文献   

15.
Cultures of nine potato genotypes (seven Solanum tuberosum oneS. sparsipilum and one S. oplocense genotypes) were examinedfor their response to growing on medium containing either 60mol m–3, 40 mol m–3 or 20 mol m–3 nitrogen.Genotypes differed in their response to nitrogen. Reducing thenitrogen regime tended to produce taller plants with longerinternodes, shoots had larger leaves but contained less chlorophyll.No change in fresh weight or number of nodes was observed. Genotypex nitrogen interactions were significant for chlorophyll content,shoot length and internode length. Results suggest that thechanges observed were as a result of changes in the total nitrogenlevel rather than changes in the ammonium : nitrate ratio. Thisstudy suggests that for certain potato genotypes, nitrogen levelsin MS medium are too high for producing desirable microplantsin terms of leaf area and shoot length Key words: Solanum tuberosum, S. sparsipilum, S. oplocense, micropropagation, morphogenesis  相似文献   

16.
Low temperature (6 C) growth was examined in two cultivarsof Vicia faba L. supplied with 4 and 20 mol m–3 N as nitrateor urea. Both cultivars showed similar growth responses to increasedapplied-N concentration regardless of N-form. Total leaf areaincreased, as did root, stem and leaf dry weight, total carboncontent and total nitrogen content. In contrast to findingsat higher growth temperatures, 20 mol m–3 urea-N gavesubstantially greater growth (all parameters measured) than20 mol m–3 nitrate-N. The increased carbon content per plant associated with increasedapplied nitrate or urea concentration, or with urea in comparisonto nitrate, was due to a greater leaf area per plant for CO2uptake and not an increased CO2, uptake per unit area, carbon,chlorophyll or dry weight, all of which either remained constantor decreased. Nitrate reductase activity was substantial inplants given nitrate but negligible in plants given urea. Neitherfree nitrate nor free urea contributed greatly to nitrogen levelsin plant tissues. It is concluded that there is no evidence for a restrictionin nitrate reduction at 6 C, and it is likely that urea givesgreater growth than nitrate because of greater rates of uptake. Vicia faba, broad bean, low temperature growth, carbon assimilation, nitrogen assimilation  相似文献   

17.
Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) weregrown in modified Hoagland nutrient solution with various combinationsof NaCl and CaCl2. Marking experiments and numerical analysiswere conducted to characterize the spatial and temporal patternsof cotton root growth at varied Na/Ca ratios. At 1 mol m–3Ca, 150 mol m–3 NaCl reduced overall root elongation rateto 60% of the control, while increasing Ca to 10 mol m–3at the same NaCl concentration restored the elongation rateto 80% of the control. Analysis of the spatial distributionof elongation revealed that the presence of 150 mol m–3NaCl in the medium shortened the growth zone by about 2 mm fromthe approximate 10 mm in the control and also reduced the relativeelemental elongation rate (i.e. the longitudinal strain rate,defined as the derivatives of displacement velocity of a cellularparticle with respect to position on root axis). Supply of 10mol m–3 Ca at the high salt condition restored partiallythe relative elemental elongation rate, but not the length ofthe growth zone. Compared to the control, the growth trajectoriesshowed that at 1 mol m–3 CaCl2 it took more time for acellular particle to move through the growth zone at 150 molm–3 NaCl, while at 10 mol m–3 CaCl it took lesstime and there was no difference between the NaCl treatments Key words: Gossypium hirsutum, salinity stress, root growth kinematics  相似文献   

18.
Rapid, Reversible Inhibition of Nitrate Influx in Barley by Ammonium   总被引:18,自引:2,他引:16  
The rate of influx of nitrate into the roots of intact barleyplants was measured over a period of 3–5 min from externalnitrate concentrations of 1–150 mmol m–3, using13N-labelled nitrate as tracer. Ammonium at external concentrationsof 0.005–50 mol m–3 inhibited nitrate influx ina manner which did not conform to a simple kinetic model butincreased approximately as the logarithm of the ammonium concentration.At any particular ammonium concentration, inhibition of nitrateinflux reached its full extent within 3 min of the ammoniumbeing supplied and was not made more severe by up to 17 minpre-treatment with ammonium. On removing the external ammonium,nitrate influx returned to its original rate within about 3min. Potassium at 0.005–50 mol m–3 did not reproducethe rapid effect of ammonium on nitrate influx. Net uptake of nitrate also decreased when ammonium was supplied,over a similar timescale and to a similar extent as nitrateinflux. The decrease in nitrate influx caused by ammonium wassufficient to account for the observed reduction in net uptake,without necessitating any acceleration of nitrate efflux. Key words: Hordeum vulgare, roots, ion transport, short-lived isotopes, 13N  相似文献   

19.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.—J.exp. Bot. 38: 1055–1068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm–3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m–3. Mg2+ was also very effectiveat less than 50 mol m–3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m–3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m–3, Vmax(HCO3) 0·26µmol O2 mg–1 chl min–1), but use of citratesalts above 500 mol m–2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m–3, Vmax(HCO3)0·68 µmol O2 mg–1 chl min–1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity  相似文献   

20.
The Relationship Between Growth and Oxygen Uptake in Hypoxic Rice Seedlings   总被引:1,自引:0,他引:1  
Atwell, B. J. and Green way, H. 1987. The relationship betweengrowth and oxygen uptake in hypoxic rice seedlings.—J.exp. Bot. 38: 454–465. Rice seedlings (Oryza saliva L.) were grown in the dark forup to 4 d in solutions containing various concentrations ofO2. Compared with seedlings grown at 0·250 mol O2 m–3,the dry weight of the growing seedling was 14% lower at 0·110mol O2 m–3 and 60% lower at 0 mol O2 m–3. Decreasesin fresh weight were similar but not identical to decreasesin dry weight, possibly because leaf growth was suppressed evenabove 0·110 mol O2 m–3. Oxygen deficiency inhibitedroot growth more severely than coleoptile growth. Coleoptiles from seedlings grown in aerated solution were exposedto an atmosphere of pure N2 for 30 min. Anoxia caused a declinein ATP content and energy charge, suggestive of decreased oxidativephosphorylation. It is not clear whether the decline in oxidativephosphorylation was solely responsible for impaired growth inhypoxia. In seedlings growing at O2 concentrations less than 0·110mol O2 m–3, significant amounts of ethanol were synthesized.The rate of O2 uptake decreased markedly below 0·06 molO2 m–3; this was presumably near the external O2 concentrationat which oxidative phosphorylation became limited by the supplyof O2. The stage of development of the seedlings appeared toinfluence O2 uptake, possibly through changes in conductanceof the tissue to O2. Uncouplers were used to confirm that thecritical O2 concentration was dependent on O2 diffusion ratherthan enzyme kinetics. Impaired growth above 0·110 molO2 m–3 may have been due to a decreased activity of oxygenasesof relatively low affinity for O2, which in turn altered cellmetabolism. Key words: Growth, oxygen uptake, rice seedlings, hypoxia  相似文献   

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