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1.
A thermocouple psychrometer method, previously described foruse in determining tissue and sap water potentials, has beenadapted for determining matric potentials. Matric values ranging from approximately zero to 10 x105 Pa were observed with wilting wheat leaves. Mean valuesof total tissue water potential and of its solute (osmotic),matric, and cell wall pressure components were 16.6,18.3, 30 and +4.7 Pa x 105, respectively. Matric potentials are often ignored in investigations of plantwater relations. This practice is shown to result in underestimationof wall pressures (in this case by a mean of 64 per cent) andsometimes in spuriously negative values. 相似文献
2.
Poor crop stand is a common problem in saline areas. Germination and seedling emergence may be depressed as a result of impeded
aeration, saline or dry conditions. In this study, we examined the effects of salinity and moisture stress and their interactions
on seed germination and seedling growth of carrots. Variable soil matric and osmotic potentials were either obtained by equilibrating
soil salinized to different degrees on a 0.5 MPa ceramic plate soil moisture extractor or by adding different amounts of salt
solutions to the same mass of air-dried soil, based on a previously determined soil moisture release curve, and allowing to
equilibrate for 1 week.
Germination decreased significantly in the investigated silty soil (Aquic Ustifluvent) at soil moisture potentials higher
than −0.01 MPa, whereas osmotic potentials as low as −0.5 MPa did not influence germination. Matric potentials of −0.3 and
−0.4 MPa, respectively, resulted in a strong decrease (35–95%) of germination and delayed germination by 2 to 5 days in the
silty soil to which different amounts (18 and 36%, respectively) and sizes (0.8–1.2 mm and 1.5–2.2 mm, respectively) of sand
particles had been added. No effect of sand and grain diameter was detected. Germination was not affected by comparable osmotic
potentials.
Seedling growth showed a much higher sensitivity than germination to decreasing matric potentials, but was not affected by
osmotic potentials ranging from −0.05 to −0.5 MPa. Optimum shoot growth occurred at matric potentials between −0.025 and −0.1
MPa. Shoot and root growth decreased markedly at matric potentials higher than −0.01 MPa. Fresh weight of shoots decreased
gradually at matric potentials lower than −0.2 MPa. Root growth was significantly increased at matric potentials of −0.1 to
−0.3 MPa, whereas comparable osmotic potentials did not have equivalent effects.
It is concluded that germination and seedling growth are differently affected by comparable matric and osmotic stresses and
that water stress exerts a more negative effect than salt stress. 相似文献
3.
Root Confinement and its Effects on the Water Relations, Growth and Assimilate Partitioning of Tomato (Lycopersicon esculentum Mill) 总被引:2,自引:0,他引:2
Although it is well established that the root growth in manyspecies is very sensitive to mechanical impedance or to confinementin small volumes, little is known about the consequent effectson growth of the whole plant and the mechanisms involved. Thiswork investigated the effects of root confinement on the waterrelations, growth and assimilate partitioning of tomato (Lycopersiconesculentum Mill) grown in solution culture. Six-week old plants were transferred to either 4500 ml or 75ml containers filled with nutrient solution, and allowed togrow for 14 d. Transpiration, leaf-air temperature differences,and leaf diffusive resistances were measured frequently. Leaf,stem and shoot dry masses, leaf area and root length, were estimatedwhen the treatments were imposed and at the end of the experiment.After 14 d growth the root and shoot hydraulic resistances wereestimated from measurements of leaf water potential and transpirationrate, using a steady-state technique. Confining root growth to the small containers substantiallyreduced shoot and root growth and increased the proportion oftotal dry matter present in the stems. These effects were dueto drought stress. The hydraulic resistance of the root systemwas greatest in the confined plants. This led to more negativeleaf water potentials, increased leaf diffusive resistance,and reduced the net assimilation rate by a factor of 2.5. Transpirationper unit leaf area was less affected. However, cumulative transpirationwas also reduced by a factor of 2.5. mostly because of the smallerleaf area on the confined plants. Root hydraulic resistivitywas measured at 3.1 x 1012s m1 in the control treatment,but increased to 3.9 x 1012 s m1 for roots in the smallcontainer. The mechanisms by which root confinement caused drought stressand disrupted the pattern of assimilate partitioning are discussedin detail. Assimilate partitioning, Lycopersicon esculentum, root confinement, plant growth, root growth, root resistance, shoot resistance, tomato, transpiration, water-use efficiency 相似文献
4.
Moisture stress and method of inoculation greatly affected thenumber and distribution of infected root hairs and nodules ofyoung seedlings of Trifolium subterraneum. A reduction of soilmoisture from 5·5 to 3·5% (0·36to 3·6 x 105 Pa) significantly decreased the numberof infection threads and completely inhibited nodulation, althoughthe number of rhizobia in the rhizosphere was unaffected. Atlow soil moisture levels the root hairs were abnormally shortand swollen. Infection and nodulation were little affected between5·5 and 9·5% moisture (0·36 to 0·089x 105 Pa). Distribution of infected root hairs depended on the initialplacement of the inoculum; with the inoculum mixed evenly throughthe soil, infection threads occurred at discrete foci alongthe root. With seedlings inoculated at planting, infection threadswere restricted to the top 12 cm of root, even at thehighest soil moisture tested. Watering increased the number of infections in plants grownat 3·5% moisture; nodules were formed at a rate equivalentto non-stressed plants. Watering also enabled movement of theseedling-borne inocula; new infections were formed along theroot surface bearing mature root hairs. 相似文献
5.
Measurements of the growth of sainfoin and lucerne were madein the field after cutting on 31 May 1977. Sainfoin reacheda total above-ground dry weight of 408 g m2 over thegrowing period of 48 days compared with 598 g m2 in lucerne.Final leaf area indices (LAIs) were 2.8 in sainfoin and 6.1in lucerne. The specific leaf areas (SLAs) for sainfoin wereapproximately half those of lucerne throughout the regrowthperiod. The maximum rates of leaf appearance were 0.12 leavesper day in sainfoin and 0.85 leaves per day in lucerne. Themaximum mean rate of plant extension growth for lucerne of 2.12mm h1 occurred during the night, whereas, in sainfointhe maximum rate of 1.72 mm h1 occurred during the day. Measurements of extinction coefficients for PAR ranged from0.45 to 0.89 in sainfoin and from 0 42 to 0.57 in lucerne. Asthe lucerne crop increased in size leaf water potentials andsolute potentials became more negative. In sainfoin leaf waterpotentials remained remarkably high throughout the growth period,solute potentials decreased and turgor potentials increased.The stomatal conductances of the two species were similar. The photosynthetic capacities and rates of dark respirationper unit leaf area in both species were similar. The rate ofcanopy gross photosynthesis at 295 W m2was always greater in lucerne than in sainfoin. This was largelya matter of differences between the species in LAI, althoughat higher LAIs the more erect structure of lucerne leads toa better utilization of photosynthetically active radiation. Onobrychis vicifolia Scop, sainfoin, Medicago sativa L., lucerne, photosynthesis, water relations, temperature, canopy structure 相似文献
6.
The Arrhenius equation describes the response of biologicalprocesses to temperature. This study was conducted to examinethe applicability of the Arrhenius equation to whole plant processesand to explore the application of the Arrhenius equation asa basis for characterizing plant responses to water stress.Rates of growth of leaf area and shoot dry mass of spring wheatseedlings were measured at combinations of five soil water potentials(0.03, 0.06, 0.10, 0.17 and 0.25MPa) and seven root temperatures (12, 14, 17, 22, 27, 29 and32 C). A non-linear least square procedure was used to fitthe modified Arrhenius equation to experimental observations.Adequate distribution of experimental observations with respectto temperature reduces the uncertainties in parameter evaluations.The standard error of the estimate of optimum temperature forleaf area growth increased from 1.4 C to 6.3 C when one ofthe data points was omitted. The optimum temperature and theenthalpy of denaturalization of enzyme systems were independentof soil water potential. A linear relation was found betweenthe rate constant and the activation energy:
The Arrhenius equation was modified using this linear relation,leaving the activation energy as the only parameter affectedby water stress. The activation energy increased linearly assoil water potential decreased, with slopes of 27.18 103 and 28.09 102 K MPa1 for the rates ofgrowth of leaf area and shoot dry mass, respectively. Theseslopes could be used as indicators of the sensitivity of plantprocesses to water stress. Temperature, water, plants, Arrhenius equation 相似文献
7.
The Occurrence of Nitrate Reduction in the Leaves of Woody Plants 总被引:13,自引:1,他引:12
Nitrate reductase activities greater than 02 µmol h1g1 f. wt, measured by an in vivo assay, occurred in 41per cent of a large sample (555 species) of woody plants. Ifseveral taxonomic groups (Gymnosperms, Ericaceae and Proteaceae)with consistently low activities were discounted activitiesgreater than 02 µmol h1 g1 f. wt occurredin 73 per cent of the species. This compares with 93 per centin herbaceous species, suggesting that leaf nitrate reductionis of common occurrence in woody plants. In a small sample ofspecies leaf nitrate reductase activity correlated with nitrateconcentration in the xylem sap. Low activities occurred consistentlyin the Gymnosperms, Ericaceae and Proteaceae. Feeding cut shootsof representatives of these groups with nitrate caused inductionof leaf nitrate reductase activity in the Gymnosperms and Proteaceae,but only limited induction in the Ericaceae. The Ericaceae,with the exception of two species, had low activities and lownitrate reductase inducibility. Root assimilation may predominatein the Gymnosperms and Proteaceae. It is suggested that nitratereduction generally occurs in the leaves of trees from a varietyof plant communities and that this may be related to the lowerenergy cost of leaf, as opposed to root, nitrate assimilation. Nitrate reductase, trees and shrubs, leaves, nitrate assimilation, nitrate translocation, nitrate reductase induction, energy cost, plant ecology 相似文献
8.
2-iodo-4-chlorophenoxyaCetic acid (ICPA) labelled with I131was applied in the form of a 0·25 per cent. olive oilsolution (using 2·5 per cent, ethyl alcohol as accessorysolvent) to the upper leaf surface of young broad bean and oatplants at the rate of 0·01 ml. solution per plant. Theinitial activity of the solution was 3·75 mc. per ml.Epinastic effects were induced in the bean but not in the oat.The movement of the I131 within the plattt was followed by meansof autoradiographs. Results indicate rapid absorption and translocationof a high proportion of the applied material in the broad bean,radioactivity appearing in quantity in every part of the plantwithin 27 hours of treatment, with a marked cáncentrationat the upper end of the stem and another at the lower end ofthe stem and top of the tap root. In the oat, on the other hand,absorption and translocation were much slower; only under themost favourable conditions did a small amount of of I131 reachthe root in 27 hours, and the amount absorbed was much lessthan in the bean. There was no upward movement of the I131 intountreated leaves of the oat. 相似文献
9.
Effects of soil mechanical impedance on the development of Golgiapparatus in the root cap cells of maize were studied undercontrolled soil-water conditions Heavily compacted soil (bulkdensity = 1.50 g cm2) had 3.3 to 3.4 times greater mechanicalimpedance than control soil (bulk density = 1.33 g cm3),but their oxygen diffusion rates were not significantly differentThe number of dictyosomes and the number and area of secretoryvesicles per unit area of tangentially sub-peripheral root capcells in the heavily compacted soil increased compared to thosein the control These results suggest that secretory activityof the root cap cells is promoted by soil mechanical impedance Dictyosome, Golgi apparatus, maize, mucilage, root cap, secretory activity, secretory vesicles, soil mechanical impedance, Zea mays L 相似文献
10.
CLIFFORD S. C.; STRONACH I. M.; MOHAMED A. D.; AZAM-ALI S. N.; CROUT N. M. J. 《Journal of experimental botany》1993,44(12):1763-1770
Stands of groundnut (Arachis hypogaea L.), a C3 legume, weregrown in controlled-environment glasshouses at 28 °C (±5°C)under two levels of atmospheric CO2 (350 ppmv or 700 ppmv) andtwo levels of soil moisture (irrigated weekly or no water from35 d after sowing). Elevated CO2 increased the maximum rate of net photosynthesisby up to 40%, with an increase in conversion coefficient forintercepted radiation of 30% (from 166 to 216g MJ1) in well-irrigated conditions, and 94% (from 064to 1·24 g MJ1) on a drying soil profile. In plantswell supplied with water, elevated CO2 increased dry matteraccumulation by 16% (from 13·79 to 16·03 t 1) and pod yield by 25% (from 2·7 to 3·4t ha1).However, the harvest index (total poddry weight/above-grounddry weight) was unaffected by CO2 treatment. The beneficial effects of elevated CO2 were enhanced under severewater stress, dry matter production increased by 112% (from4·13 to 8·87 t ha1) and a pod yield of1·34t ha1 was obtained in elevated CO2, whereascomparable plotsat 350 ppmv CO2 only yielded 0·22 t ha-1.There was a corresponding decrease in harvest index from 0·15to 0·05. Following the withholding of irrigation, plants growing on astored soil water profile in elevated CO2 could maintain significantlyless negative leaf water potentials (P<0·01) for theremainder of the season than comparable plants grown in ambientCO2, allowing prolonged plant activity during drought. In plants which were well supplied with water, allocation ofdry matter between leaves, stems, roots, and pods was similarin both CO2 treatments. On a drying soil profile, allocationin plants grown in 350 ppmv CO2 changed in favour of root developmentfar earlier in the season than plants grown at 700 ppmv CO2,indicating that severe waterstress was reached earlier at 350ppmv CO2. The primary effects of elevated CO2 on growth and yield of groundnutstands weremediated by an increase in the conversion coefficientfor intercepted radiation and the prolonged maintenance of higherleaf water potentials during increasing drought stress. Key words: Arachis hypogaea, elevated CO2, water stress, dry matter production 相似文献
11.
Low temperature (6 C) growth was examined in two cultivarsof Vicia faba L. supplied with 4 and 20 mol m3 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 m3 urea-N gavesubstantially greater growth (all parameters measured) than20 mol m3 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
12.
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: 919927. 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 m3. At the highest concentrationof NH3, this source provided 47?3% of the total nitrogen inplants grown with the lower rate of nitrate addition (100mgN kg1 dry soil) and 35?2% with the higher rate (200mgN kg1 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 dm2h1 at a concentration of 16 µg m3 to 29?0µg dm2 h1 at a concentration of 520 µgm3 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
13.
- Phyllosinol is a phytotoxic metabolite of Phyllosticta sp. Thissubstance at 100 µg/ml produced dark grey necrotic lesionson the leaf of red clover. Sensitivities of various plant speciesto phyllosinol differed both quantitatively and qualitatively.
- Phyllosinol reduced root growth in rice seedlings by 60% at104 M, whereas stimulation of root elongation occurredat a concentration range from 109 to 105 M.
- Phyllosinolat 2.5x104M promoted adventitious root formationin epicotylsof Azukia cuttings by about 100%. Promotion waspartly reducedby simultaneous application of cysteine.
- IAA-induced elongationof isolated Avena coleoptile sectionswas inhibited by phyllosinolat a concentration range from 105to 103M.
- Sulfhydrylcompounds, i.e. cysteine and glutathione relievedinhibitioncaused by phyllosinol in IAA-induced elongation ofAvena coleoptilesections.
- GA3-induced elongation of wheat leaf sections wasslightly inhibitedby phyllosinol at 104M.
- Phyllosinolalso has antibiotic activity. Among the organismstested, Phycomycetesand Gram-negative bacteria appeared mostsusceptible to phyllosinol.
14.
Experiments were conducted during the 197475 and 197576winter 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
15.
Effects of foliar applications of CCC and CEPA on dry matterdistribution in two cowpea cultivars which exhibit differentdegrees of premature abscission of fruits were investigated.At the concentration of 0-1 mg11, CCC increased stemweight in the cultivar Adzuki, but had no effect on the cv.Mala (which exhibits a relatively high degree of premature abscission).While CCC did not significantly influence root weight in Adzuki,the concentrations of 1 and 10 mg 11 increased root weightin Mala. In both cultivars, the 1000 mg11 treatment decreasedseed weight, with a greater decrease in Adzuki. All concentrations of CEPA, up to 1000 mg 11, decreasedstem and root weights in Mala, and leaf weight in Adzuki. The10 mg11 concentration increased seed weight in Mala by100 percent, and leaf weight by 28 percent, without any significanteffect on pod weight, or on the weight of the whole plant. Therewas also no increase in pod number. Overall, Mala was more responsive than Adzuki to the growthregulators, particularly CEPA. In the low concentration responses,CEPA increased seed weight not by increasing gross plant weight,but mainly by causing a change in distribution of dry matter. 相似文献
16.
Nitrogen fertilizer applied to sugar-beet increased plant androot dry weight and leaf area, and decreased the sugar contentof the roots per cent of both fresh and dry weight. Change inleaf area accounted wholly for the increase in plant dry weightproduced by nitrogen, because net assimilation rate was unaffected.Nitrogen did not alter the partition of the total assimilatebetween roots and shoots, but increased the fraction of totalassimilate entering the roots that was used in growth, at theexpense of that stored as sugar. Thus, plants with more nitrogenhad a smaller proportion of their root dry weight as sugar becausemore was metabolized in growth of the roots, and not becauseless entered the roots. The heavier roots of plants given more nitrogen were largerin cross-sectional area because the areas of both parenchymaand vascular zones of each peripheral ring within the root werelarger; the number of rings was not increased. Nitrogen increasedthe areas of the tissues in these zones by enlarging cell volumes,not by increasing the number of cells within the tissues. Increasein cell volume was accompanied by proportional increases inthe weights of non-sugar dry matter per cell and water per cell,but the amount of sugar per cell was proportional to cell volumeonly during the initial stage of cell expansion up to cell volumesof about 15x108 cm2; thereafter it was less than proportional,so that sugar per cent of both fresh and dry weight decreasedas cell size increased beyond 15x108 cm2. The relationof sugar per cell to cell volume was the same with both amountsof nitrogen given. This implies that increase in nitrogen supplymade the sugar concentration of the root less by increasingthe size of the root cells and not by a specific effect on sugarstorage. 相似文献
17.
Cramer M.D.; Schierholt A.; Wang Y.Z.; Lips S.H. 《Journal of experimental botany》1995,46(10):1569-1577
In hydroponically grown Lycopersicon esculentum (L.) Mill. cv.F144 the site of NO3 reduction and assimilation withinthe plant was shifted from the shoot to the root by salinity.Uptake of NO3 from the root solution was strongly inhibitedby salinization. Consequently, NO3 concentrations inthe leaf, stem and root tissues as well as the nitrate reductaseactivities of the leaves were lower in salinized than in controlplants. Lower NO3, but higher reduced-N, concentrationswere observed in the xylem sap as a result of the enhanced participationof the root in NO3 reduction in salinized plants. Lowerstem K+ concentrations and leaf malate concentrations were foundin salinized compared to control plants which indicates reducedfunctioning of the K+shuttle in the salinized plants. Incorporation of inorganic carbon by the root was determinedby supplying a pulse of NaH14CO3 followed by extraction andseparation of the labelled products on ion exchange resins.The rate of H14CO3 incorporation was c. 2-fold higherin control than in salinized plants. In salinized plants theproducts of H14CO3 incorporation within the roots werediverted into amino acids, while the control plants divertedrelatively more 14C into organic acids. Products of inorganiccarbon incorporation in the roots of salinized plants providean anaplerotic source of carbon for assimilation of reducedNO3 into amino acids, while in control plants the productswere predominantly organic acids as part of mechanisms to maintainionic balance in the cells and in the xylem sap. Key words: Tomato, nitrate, PEPc, respiration, salinity 相似文献
18.
Plants of Helianthus annuus were pot-grown in soil, with approximately30% of the root system protruding through the base. After 7d, the upper part of the root system of half of the plants wasexposed to drought (internal roots) while the lower part waskept in aerated nutrient solution (protruding root). The treatmentrapidly reduced the internal roots' water content from 26.1to 21.9 g g1 dry weight (DW), while in protruding rootsof stressed plants it slowly and continuously decreased from31.9 to 25.2 g g1 DW. Leaf water content rapidly decreasedin treated plants from 7.4 to 6.4 g g1 DW in the first2d and then reached a plateau. In stressed plants leaf stomatalresistance was significantly higher in the first 3 d while leafwater potential was lower only on the last day. Abscisic acid (ABA) concentration in treated plants increasedsignificantly compared to the controls. In treated internalroots, ABA rose from the first day, reaching a maximum of 1.48±0.49nmol g1 DW after 3 d. In treated protruding roots a maximumof 0.99±0.09 nmol g1 DW was reached after 1 d.ABA concentration in the xylem sap increased 2 d and 3 d afterthe start of soil drying, with a maximum of 113±12nmoll1 during the third day. The ABA rise in the leaves oftreated plants was less significant. Indol-3yl-acetic acid (IAA) concentration in internal rootsof treated plants reached a maximum of 22.54±3.34 nmolg1 DW on the third day, then decreased dramatically.The protruding root system of control plants showed a maximumvalue of 16.05±1.77 nmol g1 DW on the sixth day. Little difference in cytokinin content of xylem sap was notedbetween control and treated plants. Hormonal variations in different parts of the plant are discussedin relation to drought stress. Key words: Soil drying, roots, ABA, IAA, cytokinins 相似文献
19.
Guttation was used as a non-destructive way to study the flowof water and mineral ions from the roots and compared with parallelmeasurements of root exudation. Guttation of the leaves of barley seedlings depends on age andon the culture solution. Best rates of guttation were obtainedwith the primary leaves of 6- to 7-day-old seedlings grown onfull mineral nutrient solution. The growing leaf tissue becomessaturated with K+ below 1.5 mM K+ in the medium, whereas K+concentration in the guttated fluid still increases furtheras K+ concentration in the medium is raised. At 3 mM K+ averagevalues of guttation were 1.42.4 mm3 h1 per plantwith a K+ concentration of 1020 mM; for exuding plantsthe flow was 4.27.6 mm3 h1 per plant and K+ concentration3555 mM. Abscisic acid (ABA) at 106 to 104 M 02h after addition to the root medium increased volume flow ofguttation and exudation and the amount of K+ exported. Threeh after addition of ABA both volume and amount of K+ were reduced.There was an ABA-dependent increase in water permeability (Lp)of exuding roots shortly after ABA addition. Later Lp was decreasedby 35 per cent and salt export by 60 per cent suggesting aneffect of ABA on salt transport to the xylem apart from itseffect on Lp. Benzyladenine (5 x 108 to 105 M)and kinetin (5 x 106 M) progressively reduced volumeflow and K+ export in guttation and exudation and reduced Lp. Guttation showed a qualitatively similar response to phytohormonesas found here and elsewhere using exuding roots. Hordeum vulgare L., barley, guttation, abscisic acid, cytokinins, benzyl adenine, kinetin 相似文献
20.
U. SCHMIDHALTER 《Plant, cell & environment》1997,20(7):953-960
Uptake of soil water by plants may result in significant gradients between bulk soil and soil in the vicinity of roots. Few experimental studies of water potential gradients in close proximity to roots, and no studies on the relationship of water potential gradients to the root and leaf water potentials, have been conducted. The occurrence and importance of pre-dawn gradients in the soil and their relation to the pre-dawn root and leaf water potentials were investigated with seedlings of four species. Pre-germinated seeds were grown without watering for 7 and lid in a silt loam soil with initial soil matric potentials of -0.02, -0.1 and -0.22 MPa. Significant gradients, independent of the species, were observed only at pre-dawn soil matric potentials lower than -0.25 MPa; the initial soil matric potentials were -0.1 MPa. At an initial bulk soil matric potential of -0.22 MPa, a steep gradient between bulk and rhizoplane soil was observed after 7 d for maize (Zea mays L. cv. Issa) and sunflower (Helianthus annuus L. cv. Nanus), in contrast to barley (Hordeum vulgare L. cv. Athos) and wheat (Triticum aestivum L. cv. Kolibri). Pre-dawn root water potentials were usually about the same as the bulk soil matric potential and were higher than the rhizoplane soil matric potential. Pre-dawn root and leaf water potentials tended to be much higher than rhizoplane soil matric potentials when the latter were lower than -0.5 MPa. It is concluded that plants tend to become equilibrated overnight with the wetter bulk soil or with wetter zones in the bulk soil. Plants can thus circumvent negative effects of localized steep pre-dawn soil matric potential gradients. This may be of considerable importance for water uptake and growth in drying soil. 相似文献