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1.
The role of solute accumulation, osmotic adjustment and changes in cell wall elasticity in drought tolerance in Ziziphus mauritiana (Lamk.) 总被引:3,自引:0,他引:3
Clifford S; Arndt S; Corlett J; Joshi S; Sankhla N; Popp M; Jones H 《Journal of experimental botany》1998,49(323):967-977
Ber (Ziziphus mauritiana Lamk.) is a major fruit tree
crop of the north-west Indian arid zone. In a study of the physiological
basis of drought tolerance in this species, two glasshouse experiments were
conducted in which trees were droughted during single stress-cycles. In the
first experiment, during a 13 d drying cycle, pre-dawn leaf water
(leaf) and osmotic () potentials in droughted
trees declined from -0.5 and -1.4 MPa to -1.7 and -2.2 MPa, respectively,
for a decrease in relative water content () of 14%. During
drought stress, changes in sugar metabolism were associated with
significant increases in concentrations of hexose sugars (3.8-fold),
cyclitol (scyllo-inositol; 1.5-fold), and proline (35-fold; expressed per
unit dry weight), suggesting that altered solute partitioning may be an
important factor in drought tolerance of Ziziphus. On
rewatering pre-dawn leaf and recovered fully, but
remained depressed by 0.4 MPa relative to control
values, indicating that solute concentration per unit water content had
changed during the drought cycle.Evidence for osmotic adjustment was
provided from a second study during which a gradual drought was imposed.
Pressure-volume analysis revealed a 0.7 MPa reduction in osmotic potential
at full turgor, with leaf at turgor loss depressed by 1 MPa in
drought-stressed leaves. Coupled with osmotic adjustment, during gradual
drought, was a 65% increase in bulk tissue elastic modulus (wall rigidity)
which resulted in turgor loss at the same in both stressed and
unstressed leaves. The possible ecological significance of maintenance of
turgor potential and cell volume at low water potentials for drought
tolerance in Ziziphus is discussed.Keywords:
Ziziphus mauritiana, drought, solute
accumulation, osmotic adjustment, proline.
相似文献
2.
Foliar dehydration tolerance of twelve deciduous tree species 总被引:1,自引:0,他引:1
The potential for foliar dehydration tolerance and maximum capacity for
osmotic adjustment were compared among 12 temperate, deciduous tree
species, under standardized soil and atmospheric conditions. Dehydration
tolerance was operationally defined as lethal leaf water potential
(); the of the last remaining leaves surviving a
continuous, lethal soil drying episode. Nyssa
sylvatica Marsh., and Liriodendron
tulipifera L. were most sensitive to dehydration, having lethal
leaf of -2.04 and -2.38 MPa, respectively. Chionanthus
virginicus L., Quercus prinus L.,
Acer saccharum Marsh., and Quercus
acutissima Carruthers withstood the most dehydration, with
leaves not drying until leaf dropped to -5.63 MPa or below.
Lethal leaf (in MPa) of other, intermediate species were:
Quercus rubra L. (-3.34), Oxydendrum
arboreum (L.) D.C. (-3.98), Halesia
carolina L. (-4.11), Acer rubrum L.
(-4.43), Quercus alba L. (-4.60), and Cornus
florida L. (-4.88). Decreasing lethal leaf was
significantly correlated with increasing capacity for osmotic adjustment.
C. virginicus and Q. acutissima
showed the most osmotic adjustment during the lethal soil drying episode,
with osmotic potential at full turgor declining by 1.73 and 1.44 MPa,
respectively. Other species having reductions in osmotic potential at full
turgor exceeding 0.50 MPa were (in MPa) Q. prinus
(0.89), A. saccharum (0.71), Q.
alba (0.68), H. carolina (0.67),
Q. rubra (0.60), and C. florida
(0.52). 相似文献
3.
In a companion paper several methods of calculating the marginal unit water
cost of plant carbon gain (E/A) were tested to determine
whether stomata were behaving optimally in relation to regulating leaf gas
exchange. In this paper one method is applied to several tropical tree
species when leaf-to-air vapour pressure difference (D), photosynthetic
photon flux density, leaf temperature, and atmospheric soil water
availability were manipulated. The response of leaves that had expanded
during the dry season were also compared to that of leaves that had
expanded in the wet season. Few differences in absolute value of
E/A, or the form of the relationship, were observed
between species or between seasons. In the majority of species,
E/A increased significantly as either leaf-to-air vapour
pressure difference increased, at a leaf temperature of either 33C or 38C, or as in
photosynthetic photon flux density increased. In contrast, as leaf
temperature increased at constant D, E/A was generally
constant. As pre-dawn water potential declined, E/A
declined. The relationship between E/A and D did not
differ whether internal or ambient carbon dioxide concentration were kept
constant. It is concluded that stomata are only behaving optimally over a
very small range of D. If a larger range of D is used, to incorporate
values that more closely reflect those experienced by tropical trees in a
savanna environment optimization is incomplete.Key
words: Stomatal optimization theory, marginal unit water cost.
相似文献
4.
The changes in leaf extension, plant dryweight, leaf area, netassimilation rate (E), relative growth-rate (RW), and relativeleaf growth-rate (RL), have been studied for four species grownfor 2 weeks in solutions of polyethylene glycol 4000 of controlledosmotic potentials. All aspects of growth were decreased bydecreasing the osmotic potential (sol) of the root medium andthe leaf water potential (), and ceased when / was greater than 10 bars in bean, cotton, maize. These plants were moresusceptible than ryegrass to water stress. Growth of bean stoppedat equal to about 6 bars, but even at 10 barsryegrass was capable of some growth. Slight decrease in fromthe values in the control plants decreased growth during thefirst week but partial recovery was apparent during the secondweek's growth in solution culture, when leaf extension, E, RLand RW increased in plants subjected to stress. Examinationof the water balance, water potential, osmotic potential andturgor of the leaf in relation to relative water content suggeststhat recovery was related to increased turgor and that the abilityof the plants to grow at reduced values of the osmotic potentialof the root medium and of the leaf water potential depend onthe maintenance of turgor. 相似文献
5.
In recent years alternative ways have been proposed to transformmeasurements of leaf water potential, , and relative water content,R*, in order to derive values of osmotic pressure at full turgidityin leaves and shoots, o(when 0). Two types of transformationsare usually considered: 1/ versus R* and versus 1/R*, and linearregression is used to fit the data in the region where turgoris thought to be zero. It appears that when o is estimated bylinear extrapolation of 1/Psi; versus R* then apoplastic watermight not influence the accuracy of o but when the versus \/R*transformation is used apoplastic water causes an underestimateof o. We examine the accuracy of the estimate of o obtainedfrom the two transformations when there are random errors in, systematic errors in , and when the osmotic solutions arenon-ideal. The 1/ versus R* transformation generally producesthe best estimate of 0 by linear extrapolation. 相似文献
6.
Mechanisms of Inhibition of Water Movement in Anaerobically Treated Roots of Zea mays L. 总被引:2,自引:0,他引:2
Changes in water flux (Jv) across detopped, 7-d-old, maize rootswere characterized during the initial 24 h of being made anoxicby exposure to an anaerobic nutrient solution. Suction (50 kPa)was applied to the xylem and samples of the xylem sap were collectedat intervals and the osmolality and ionic content were measured. Values of Jv through anoxic roots fell below those of aerobiccontrols 1 h after the equilibrium oxygen partial pressure inthe bathing medium dropped below 20 kPa (air = 20.6 kPa). Thereduction in Jv was due primarily to a nullification of thediurnal rhythm in hydraulic conductivity (Lp) that was measuredin aerobic roots. However, about one-quarter of the reductionin Jv could be accounted for by a smaller osmotic componentof the driving force () on water movement. The significance of changes in Jv in anoxic roots is discussedin terms of the reliability of estimates of Lp, the reflectioncoefficient () and . Key words: Anaerobiosis, hydraulic conductivity, osmotic potential, water 相似文献
7.
TOLLEY-HENRY LESLIE; RAPER C. DAVID JR.; GRANATO TOM C. 《Journal of experimental botany》1988,39(5):613-622
Net uptake of by non-nodulated soybean plants [Glycine max (L.) Merr.cv. Ransom] growing in flowing hydroponiccultures containing 05, 1.0 and 10-0 mol m3 was measured daily during a 24-d period of vegetativedevelopment to determine if amplitude of maximum and minimumrates of net uptake are responsive to external concentrations of . Removal of from the replenished solutions during each 24-h period was determinedby ion chromatography. Neither dry matter accumulation nor theperiodicity of oscillations in net uptakerate was altered bythe external concentrations. The maxima of the oscillations in net uptake rate, however, increased nearly3-fold in response to external concentrations. The maxima and minima, respectively, changed from 4.0 and 06mmol per gram root dry weight per day at an external solution level of 05 mol m3 to 152and -27 mmol per gram root dry weight per day at an external solution level of 100mol m3 . The negative values for minimum net uptake rate from100 mol m3 solutions show that net efflux was occurring andindicate thatthe magnitude of the efflux component of net uptake was responsiveto external concentration of . Key words: Nitrate uptake rate, carbon-nitrogen partitioning, flowing solution culture 相似文献
8.
BECANA MANUEL; APARICIO-TEJO PEDRO; PE?A JOSE; AGUIRREOLEA JONE; S?NCHEZ-D?AZ MANUEL 《Journal of experimental botany》1986,37(5):597-605
Nitrate and water stress were used to induce senescence in rootnodules of alfalfa (Medicago sativa L. cv. Aragon). Nodule senescencewas assessed by determinations of the nitrogenase (C2H2-reducing)activity, and the leghaemoglobin (LHb) and total soluble proteincontents of the nodules. Nodules responded similarly to and water stress in many respects, but there was a significant difference.All parameters of nodule activity, expressed on the basis ofnodule dry weight (DW), consistently decreased following treatmentwith or during drought; there was a significant interaction (synergism) between the inhibitory effects of and water stress on nitrogenase activity, but sucheffects were merely additive in the case of LHb content or LHb/solubleprotein ratio. However, caused the selective decay of LHb with respect to other nodular soluble proteins,whereas the decrease of LHb during water stress was due to ageneral inhibition of protein synthesis and to an increasedproteolytic activity in the nodule cytosol rather than to aspecific proteolysis of LHb. Key words: Leghaemoglobin, Medicago saliva, nitrogen fixation, root nodule senescence, water stress 相似文献
9.
HENSON I. E.; ALAGARSWAMY G.; MAHALAKSHMI V.; BIDINGER F. R. 《Journal of experimental botany》1983,34(4):442-450
The water potential () at which stomata completed closure (8Lmin)was determined for pearl millet (Pennisetum americanum [L.]Leeke) at two growth stages by monitoring changes in leaf conductance(gL) and following shoot detachment. Leaf water status wasevaluated concurrently using a pressure-volume (P-V) technique. In a pot experiment with young vegetative plants, 8Lmin closelyapproximated to the estimated at zero turgor (u) both for controland for drought-conditioned plants which had osmotically adjusted.However, for penultimate leaves of field-grown flowering plants,8Lmin was found to be 0.61 (irrigated plants) and 0.87 (droughtedplants) MPa below u. In drought-stressed field-grown plants,osmotic adjustment (characterized by a decrease in solute (osmotic)potential (s ) at both full hydration and zero turgor) was insufficientto maintain a positive bulk leaf turgor potential (p) once had declined to below about -1.5 MPa. It is suggested that localizedadjustment by the stomatal complex in response to environmentaldifferences, leaf ageing and/or ontogenetic change, is responsiblefor the uncoupling of stomatal from bulk leaf water status. Key words: Stomata, Water stress, Pennisetum americanum 相似文献
10.
Bromus tectorum L. (cheatgrass) is an invasive winter
annual whose seeds lose dormancy through dry after-ripening. In this paper
a thermal after-ripening time model for simulating seed dormancy loss of
B. tectorum in the field is presented. The model
employs the hydrothermal time parameter mean base water potential
(b(50)) as an index of dormancy status. Other parameters of the
hydrothermal time equation (the hydrothermal time constant HT,
the standard deviation of base water potentials b, and
the base temperature Tb) are held constant, while
b(50) is allowed to vary and accounts for changes in germination
time-course curves due to stage of after-ripening or incubation
temperature. To obtain hydrothermal time parameters for each of four
collections, seeds were stored dry at 20C
for different intervals, then incubated in water (O MPA) or polyethylene
glycol (PEG) solutions (-0.5, -1.0, -1.5 MPa) at 15 and 25C. Germination data for the thermal after-ripening
time model were obtained from seeds stored dry in the laboratory at 10, 15,
20, 30, 40, and 50°C for 0 to 42 weeks, then incubated at two
alternating temperatures in water. Change in b(50) was
characterized for each collection and incubation temperature as a linear
function of thermal time in storage. Measurements of seed zone temperature
at a field site were combined with equations describing changes in
b(50) during after-ripening to make predictions of seed dormancy
loss in the field. Model predictions were compared with values derived from
incubation of seeds retrieved weekly from the field site. Predictions of
changes in b(50) were generally close to observed values,
suggesting the model is useful for simulating seed dormancy loss during
after-ripening in the field. 相似文献
11.
Periods of limited soil water availability are a feature of many temperate
pasture systems and these have the potential to modify pasture plant and
community responses to elevated atmospheric CO2. Using large pasture
turves, previously exposed to elevated CO2 concentrations of 350 or 700
mol mol-1 for 324 d
under well-watered conditions the morphological and physiological responses
of pasture species growing at these CO2 concentrations were compared when
subjected to a soil moisture deficit-and to recovery from the deficit-with
those that continued to be well watered.Net leaf photosynthesis of
Trifolium repens (C3 legume), Plantago
lanceolata (C3) and Paspalum dilatatum (C4)
was increased by exposure to elevated CO2, but there was no consistent
effect of CO2 on stomatal conductance. At low soil moistures, net
photosynthesis declined and stomatal conductance increased in these three
species. There was a strong CO2 x water interaction in respect of net
photosynthesis; in Trifolium repens, for example,
elevated CO2 increased net photosynthesis by approximately 50% under
well-watered conditions and this increased to over 300% when soil moisture
levels reached their minimum values. Similar values were recorded for both
Paspalum dilatatum and Plantago
lanceolata. Potential water use efficiency (net
photosynthesis/stomatal conductance) was increased by both exposure to
elevated CO2 and drought.Leaf water status was measured in three species:
Trifolium repens, Paspalum dilatatum and Holcus
lanatus (C3). Total leaf water potential (t) and osmotic
potential () were decreased by drought, but CO2
concentration had no consistent effect. t and
were highest in the C4 species Paspalum dilatatum and
lowest in the legume Trifolium repens.In the wet
turves, rates of leaf extension of the C3 grasses Holcus
lanatus and Lolium perenne at elevated CO2
were frequently higher than those at ambient CO2, but there was no effect
of CO2 concentration on the rate recorded in the C4 grass
Paspalum dilatatum or the rate of leaf appearance in
the legume Trifolium repens. Drought reduced leaf
extension rate irrespective of CO2 in all species, but in Holcus
lanatus the reduction was less severe at elevated CO2.
Immediately after the dry turves were rewatered the leaf extension rate on
tillers of Holcus lanatus and Lolium
perenne were higher than on tillers in the wet turves, but only
at ambient CO2. Consequently, despite the greater leaf extension rate
during the soil moisture deficit at elevated CO2, because of the
overcompensation after rewatering at ambient CO2, total leaf extension over
both the drying and rewetting period did not differ between CO2
concentrations for these C3 grass species. Further investigation of this
difference in response between CO2 treatments is warranted given the
frequent drying and wetting cycles experienced by many temperate
grasslands. 相似文献
12.
Derivation of Pressure-Volume Curves by a Non-Linear Regression Procedure and Determination of Apoplastic Water 总被引:1,自引:0,他引:1
Data from pressure-volume (PV) analysis may be submitted totransformation I [i.e. leaf water potential (1) versus inverserelative water content (1/R)] or to transformation II (i.e.1/1 versus R). This may cause an essential distortion of theerror structure especially in transformation II due to the relativelylarge range which is to be covered by the 1/1 ratio. Similarly,logarithmic transformation of leaf turgor potential (P) whenderiving the sensitivity factor of elasticity (ß)by linear regression from values of In p and 1/R may distortthe error structure. In order to investigate the magnitude ofthe distortion effect on parameters derived from PV analysisby regression a non-linear regression procedure was comparedwith the common linear procedure when calculating p from ßin the turgid region and leaf osmotic potential (P) in boththe turgid and non-turgid region. As test plants we used fieldgrown species of spring barley (Hordeum distichum L., cvs Gunnarand Alis). The results show that transformations and applicationof linear regression procedures distort the error structureof p more than the error structure of ', which was only slightlyaffected. However, we recommend the use of the non-linear procedurein both cases. Furthermore, from PV analysis, obtained by thermocouple hygrometryon living and killed leaf tissue, respectively, we derived themathematical basis for calculating the apoplastic water fraction(Ra). Ra was 0.15 at R= 1 and decreased with dehydration. The equations describing the relation between and R and betweenp and R were extended to take into account the apoplastic waterfraction. Key words: Apoplastic water, distortion errors, non-linear regression, pressure-volume curves 相似文献
13.
The Meaning of Matric Potential 总被引:6,自引:1,他引:5
The commonly used equation, = P - + , which describes thepartitioning of plant water potential, , into components ofhydrostatic pressure, P, osmotic pressure, , and matric potential,, is misleading. The term , which is supposed to show the influenceof a solid phase on , is zero if a consistent definition ofpressure is used in the standard thermodynamic derivation. However,it can be usefully defined by = + D, where D is the osmoticpressure of the equilibrium dialysate of the system. The practicaland theoretical significance of this definition is discussed. 相似文献
14.
Developmental Responses to Drought and Abscisic Acid in Sunflower Roots: I. ROOT GROWTH, APICAL ANATOMY, OSMOTIC ADJUSTMENT 总被引:1,自引:0,他引:1
ROBERTSON J. MASON; HUBICK KERRY T; YEUNG EDWARD C.; REID DAVID M 《Journal of experimental botany》1990,41(3):325-327
Aeroponically grown sunflower seedlings (Helianthus annuus L.cv. Russian Giant) were droughted or treated with abscisic acid(ABA) for 7 d. Drought stress prompted a three-phase growthresponse in sunflower roots: an initial phase of increased rootelongation was followed by a period of almost complete inhibitionbetween about 6 h and 72 h; this was followed, in turn, by aphase of partial recovery in the rate of root elongation. Droughtdecreased the size of the apical meristem as cells in the proximalregion of the meristem vacuolated and elongated. Root-to-shootbiomass ratios (R:S) increased initially but declined after72 h. Drought stress decreased water potential () and osmoticpotential ( and increased turgor pressure p in the apical 30mm of the roots. These initial changes were transitory, lastingabout 3 h. Thereafter, and began to rise; p fell back to controllevels. In the later stages of treatment, fell as the stressgrew more severe, but fp was maintained by osmotic adjustment.Desiccation for 1 h increased turgor pressures in excised 30mm apical segments. The transitory increase in root elongationwas contemporary with the initial rise in p in the root apices,while the periods of greatest inhibition and partial recoveryin root elongation were contemporary with the periods of declineand partial recovery in the length of the apical meristem respectively.The inhibition of root elongation and the anatomical changesin the root apices were not determined by loss of turgor orlack of photosynthate, but rather appeared to be an active responseby the meristem to a drop in external . Treatment with ABA triggeredmany of the same changes as drought stress: ABA promoted a three-phasegrowth response, increased R:S, triggered the same initial changesin , , and p, increased p in excised 3.0 mm apical segments,and induced the same pattern of anatomical changes in the rootapices as drought stress. It is proposed that ABA mediates drought-inducedchanges in the primary development of sunflower roots. Key words: Abscisic acid, apical meristem, drought, osmotic adjustmen 相似文献
15.
The euryhaline charophyte Lamprothamnium papulosum (Wallr.)J. Gr. was adapted to media with decreasing salinities rangingfrom 550 to 0 mosmol kg1. Vegetative plants grown inmedia with osmotic pressures (0) in the range of 550 to 130mosmol kg1 maintained a constant turgor pressure () at309 + 7 mosmol kg1. The ions K+, Na+ and Cl, werethe predominant solutes in the vacuole. Changes in their concentrationsaccount for the variation in internal osmotic pressure (1) with,0. The divalent ions Mg2+, Ca2+ and were also present in significant amounts, but their concentrationsdid not alter with changes in, 0. In cells subjected to hypo-osmotic shock the regulation of was incomplete. The turgor pressure increased from 302 to 383mosmol kg1. The first rapid response to the sudden decreasein 0 was a loss of K+ and Cl. In contrast to the decreasein ionic concentrations an accumulation of sucrose occurredwhich could account for the increase of . The increase in sucroseconcentration started 24 to 48 h after the downshock and reachedits highest value after 3 to 4 weeks. The sucrose concentrationin the vacuole was up to 320 mol m3. During this timethe ionic content continued to decrease but did not counterbalancethe sucrose concentration sufficiently to regain the original. High sucrose levels accompanied by an enhanced were also observedduring the period of fructification (sexual reproduction: formationof antheridia and oogonia) in Lamprothamnium kept under conditionsof constant salinity. It is concluded that high sucrose content and elevated arecharacteristic of sexual reproduction in this charophyte. Lamprothamniumis able to tolerate different during various developmentalstages (e.g. vegetative and reproductive phases). Key words: Lamprothamnium papulosum, sucrose, turgor pressure 相似文献
16.
An equation is derived expressing average turgor pressure ofa leaf (p) as a function of relative water content (RWC). Basedon this derivation, the relationships of the bulk elastic modulus(v) and both RWC and p, are formulated and discussed. The bulkelastic modulus (v) becomes zero for p = 0, that is at the turgorloss point for the leaf. At full water saturation the valueof ev is proportional to the water saturation turgor potentialp(max). The factor relating P and v (structure coefficient ,Burstrom, Uhrstr?m and Olausson, 1970) changes only very littlefor values of p, which are not too close to zero. An exampleis given for the calculation from experimental data of the turgorpressure function, the structure coefficient function, and thev function. Key words: Cell wall, Turgor pressure, Bulk elastic modulus 相似文献
17.
Hydrothermal time analysis of tomato seed germination responses to priming treatments 总被引:5,自引:1,他引:4
Controlled hydration of seeds followed by drying (seed priming) is used to
break dormancy, speed germination, and improve uniformity of radicle
emergence. To date, empirical trials are used to predict optimal priming
conditions for a given seed lot. Since priming is based upon seed water
relations, it was hypothesized that the sensitivity of germination to
reduced water potential before priming might be mechanistically related to,
and therefore predictive of, priming responsiveness. Analyses of
germination of 13 tomato (Lycopersicon esculentum
Mill.) seed lots at two temperatures (15C
and 20C) and three water potentials (0,
-0.28 and -0.43 MPa) showed that seed lot germination responses could be
quantitatively characterized by parameters derived from thermal time,
hydrotime, and hydrothermal time models
(R20.73-0.99). Six of the seed
lots were primed at two temperatures (15°C and 20°C) and
three water potentials (-1.0, -1.5 and -2.0 MPa) for various durations,
dried, and their subsequent germination rates analysed according to
hydropriming time and hydrothermal priming time models. The responses of
germination rates to priming were characterized by hydropriming time
(HP) and hydrothermal priming time (HTP) constants and
the minimum water potential (min) and temperature
(Tmin) for achieving a priming effect. The values of
min and Tmin varied relatively little among
tomato seed lots, and the generalized values of min=2.39 MPa and
Tmin=9.10°C accounted for 74% (15°C),
57% (20°C), and 62% (across both temperatures) of the increase in
germination rates following priming. Nonetheless, while the hydrothermal
time models described germination patterns both before and after priming,
there was relatively little predictive relationship between
them. 相似文献
18.
A karyopherin (LeKAP1) cDNA was isolated from tomato
plants. The deduced LeKAP1 protein sequence of 527 amino acids
showed similarity to other plant karyopherin proteins. When
LeKAP1 was expressed in a yeast two-hybrid
system together with the gene coding for the capsid protein (CP) of the
tomato yellow curl leaf virus (TYLCV), it interacted directly with CP.
Thus, LeKAP1 may be involved in the nuclear import of TYLCV CP
and, potentially, the TYLCV genomes during viral infection of the host
tomato cells. 相似文献
19.
Short communication. A steep Ca2[IMAGE]-dependence of a K[IMAGE] channel in a unicellular green alga
Bauer C; Plieth C; Hansen U; Simonis W; Schonknecht G 《Journal of experimental botany》1998,49(327):1761-1765
An increase of cytosolic Ca2 in the
unicellular green alga Eremosphaera viridis activities
Ca2-dependent
K channels causing a hyperpolarization of
the plasma membrane. Data from parallel calcium, and potential measurements
were combined with I/V relationships. This yielded a
steep Ca2-dependence of
K channels with a co-operativity of 4 and
an affinity of 300 nM.Key words: Eremosphaera viridis,
plasma membrane, Ca2-dependent
K channel, co-operative binding.
相似文献
20.
Nitrate Uptake and Assimilation following Nitrate Deprivation 总被引:2,自引:0,他引:2
Upon first exposure to , the uptake and reduction capacities of dark-grown corn (Zea maysL.) roots are initially low, but increase markedly within 6h. The development of the accelerated uptake rate appears to be substrate induced as is reductase (NR), the first enzyme in the assimilatory pathway. However, the inductionof uptake is independent of NR induction. The effect of deprivation was studied to determine the role of endogenous on subsequent uptake and reduction. Corn roots were induced for 24 h in 05 mol m3 nutrient solution and then exposed for 0 to 32 h to -free nutrient solution. Uptake and reduction of were determined periodically by exposing sets of roots to a1 h pulse of 0.5 mol m3 . Neither uptake (4.57 µmol root1 h1)nor the percentage of absorbed reduced (27%) was changed significantly (P 0.05) by exogenous deprivation. However, the estimated induced componentof uptake decreased significantly (50% after 32 h). Concurrently, the non-induced basal componentof uptake increased. Previously accumulated decreased from 23 to 4.5 µmol root1 after 32 h of exogenous deprivation. Nearly equivalent quantities of endogenous were used for translocation and reduction during deprivation. During each 1 h pulse, the amounts of translocation and net efflux of to the uptake solution were similar. Net efflux of was strongly correlated (r = 0.991) to the amount of endogenous . The remaining endogenous and its rate of utilization were apparently sufficient to minimize a rapid declineor complete loss in both the induced uptake state and the rate of in vivo assimilation. Key words: reduction, translocation, efflux, root, Zea mays L 相似文献