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1.
The pressure-volume technique was employed to compare waterrelations and moisture stress-induced osmotic adjustment ofPeriwinkle (Catharanthus roseus) cv. Pink (PC), Oscillatus (REC)and White (WC). Leaf water potential (w), osmotic potential(s), turgor potential (p), bulk modulus of elasticity (), boundwater (RWCw) and leaf hydration (H), were estimated by exposingthe plants to a drying cycle during which well watered plantswere dehydrated to zero turgor, and then irrigated. Osmoticadjustment (w 100) was calculated by comparing a at full hydration(a 100) in stressed plants after recovery, with a 100 in controlplants. Values of 2100 were 0.76, 0.33 and 0.11 MPa in cv. PC,REC and WC, respectively. Maintenance of p at lower 3 and relativeleaf water content (RWC) in prestressed PC was attributableto a higher alkaloid content and greater leaf cell wall elasticity.RWCW was plotted against p to determine its contribution tohydration maintenance at lower p. Genotype PC showed greaterRWCw at lower p compared with REC and WC. The present studyhas demonstrated that there are cultivar differences in alkaloidaccumulation and water relations in acclimated plants and thatthe relative ranking for drought resistance within periwinkleappeared to correspond with the changes in osmotic properties. Medicinal plant, drought resistance, alkaloids, periwinkle [Catharanthus roseus (L.) G. Don] 相似文献
2.
Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Sequential Responses to Water Stress in the Leaf 总被引:1,自引:0,他引:1
Water stress was imposed by withholding water at an early vegetativestage from plants of two rice cultivars (IR20 and 6383)grown in pots. As stress intensified the following sequenceof responses of the leaves was observed: (i) rise in abscisicacid (ABA) content, (ii) closure of stomata, (iii) initiationof leaf rolling. In both cultivars, turgor (p) declined linearly with total waterpotential () of the leaf. Bulk leaf ABA content increased linearlyas p declined, and attained twice the control (unstressed) levelfollowing a reduction in p of about 0.12 MPa. Stomatal conductance exhibited a sigmoidal relationship to p,declining abruptly when a particular criticalp was reached (threshold response). The critical potentialsvaried considerably between experiments, but were closely correlatedwith control potentials and with the potentials at which ABAconcentration doubled relative to controls. Leaf rolling was initiated at s near to zero p. Increases inthe ratio of adaxial to abaxial conductance were associatedwith rolling. Variations in the above responses could be accounted for byvariations in the rate of stress development, which in termsof reduction ranged from 0.38 to 0.86 MPa day1. Fastdrying rates resulted in: (a) reduced osmotic adjustment, (b)increased amounts of ABA in the leaf at a given level of orp, (c) an increase in the ABA concentration present at 50 percent stomatal closure, and (d) initiation of leaf rolling ata higher . Oryza sativa L., rice, water stress, stomata, leaf rolling, abscisic acid 相似文献
3.
Various kinds of measurement of tissue water status were madeseveral times during water stress and recovery in Brassica juncea(cv Canadian Black) and B napus (cv Drakkar) Unstressed plantsof the two species had similar leaf water potentials (w), solute(s) and turgor potentials (p) Values of relative water content(RWC) and the slope of the linear relationship between p andRWC (p/RWC) were greater in B napus than in B juncea Statistical correlations of pooled data for the watered andstressed treatments differentiated the relationships among RWC,w and its components in the two species The major statisticaldifference was that p/RWC was related to RWC in B napus andto w and s in B juncea A decline in p/RWC with decreasing sin B juncea may be a mechanism for maintaining p at low soilwater potentials through maintenance of more elastic cell walls. Brassica juncea, Brassica napus, osmotic adjustment, tissue elasticity, water relations 相似文献
4.
Wilting of leaves of Vicia faba L., which occurs when the pressurepotential (p) is zero, and the leaf-water potential () at wiltingboth depend entirely upon the solute potential at incipientplasmolysis (so) and not on soil-water status. Wilting in V.faba is acropetal; this is consistent with the hypothesis thatthere is a gradient of decreasing so up the plant and that wateris transferred from the lower to the upper leaves, hasteningthe overall water loss from the lower leaves to the point whenp is zero. The gradient in so up the plant is of the order of38 bar. It is proposed that wilting when p>0 (i.e. > so) shouldbe apparent wilting and that when p0 (i.e. so),true wilting. 相似文献
5.
Sitka spruce[Picea sitchensis(Bong.) Carr] seedlings were subjectedto varying degrees of root damage in a growth room, rangingfrom careful transplanting to exposure of the root system toair for up to 3 h. After replanting, transpiration (E), leafwater potential (1) and growth of the shoot and root were measuredand observations made on plant survival. Some plants in the root exposure treatments died 2085days after planting. In plants which eventually died, E wasdepressed directly after treatment, but 1 showed a variableresponse. In some plants 1 decreased from 8·0x 105 to 30 x 105 Pa after only 10 days but in othersthere was little change in 1 for 50 days. In spite of the maintenanceof a high water potential in some of the latter plants for longperiods, no root or shoot growth occurred. In plants which lived, the root damage reduced root and shootgrowth relative to untreated controls, and most treatments stronglydepressed E but had little or no effect on 1. The changes of E and 1 in treated plants suggest that the suppressionof E was often independent of 1 although water stress eventuallydeveloped in some of the severely treated plants. Sitka spruce, Picea sitchensis (Bong.)Carr, water relations, root damage, transpiration, leaf water potential 相似文献
6.
Water-relations parameters were measured on sections of secondaryphloem from red oak (Quercus borealis michx. f.) and white ash(Fraxinus americana var. biltmoreana [Beadle] J. Wright) usinga linear displacement transducer. Changes in tissue thicknessin response to changes in the osmotic pressure of the bathingsolution were used to calculate the volumetric elastic modulusplus osmotic pressure (v + ) of the tissue, and an applied forcemethod was used to estimate the time constant for water equilibration(T). The hydraulic conductivity of the cell membranes (Lp) wascalculated utilizing v + and r values. The time-dependent behaviour of the tissue was much more complexthan originally expected. A correction for a time-dependentprocess that we call drift was required to obtainnumbers for v + . Furthermore, v + was calculated on two assumptionsin order to relate changes in tissue dimensions to sieve elementparameters. In the first case, a lower limit for v + of thesieve elements was determined by attributing all changes intissue dimensions to these cells. For red oak the average v+ on this assumption is 72 bars. Assuming that all cell typeswere equally responsible for the changes in tissue dimensionsresulted in an v + value of 192 bars for oak. If v + and rare the same for all cells in the tissue, Lp for the sieve elementsof oak is 9.6 x 108 cm s1 bar1. Exudationfrom the sieve elements of white ash during excision of thephloem led to artificially high values of v + for that species. Quercus borealis michx. f., Fraxinus americana var, biltmoreana (Beadle) J. Wright, red oak, white ash, water relations, phloem, volumetric elastic modulus, membrane hydraulic conductivity 相似文献
7.
Osmotic Adjustment in Lolium perenne; Its Heritability and the Nature of Solute Accumulation 总被引:1,自引:0,他引:1
Plants derived from Lolium perenne L. cv. Mellewere selected on the basis of extreme high or low lamina solutepotential (s) and pair-crossed to produce divergent G2 lines.The high and low lines had mean lamina s values significantlydifferent from each other and from Melle, andshowed an enhanced range of phenotypic expression of s duringdrought. Both mature lamina s and meristem s values of droughtedplants were highly heritable. Extreme G2 genotypes were selectedand clonally replicated for further study. During drought mean 2 values fell from 1·21 to1·80 MPa. Fructans of large molecular weight,and total free amino acids, especially proline, all accumulatedwhen estimated on a dry-matter (DM) or plant-water (PW) basis.Oligosaccharide content was largely unchanged. Minerals declinedwhen estimated on a DM basis but accumulated on a PW basis becausehydration (g water in turgid tissue per g DM) declined morerapidly. In comparison with genotypes having high constitutive s, low-sgenotypes (a) were larger, had faster leaf extension rate, hadfewer tillers, and were proportionally more affected by drought,(b) showed greater osmotic adjustment, (c) contained and accumulatedmuch more fructan (but not oligosaccharides), and amino acids,especially proline, and (d) accumulated more mineral ions ona PW basis, but less on a DM basis. The relatively high repeatabilitiesfor organic solutes in particular show that further divergentselection for individual solutes would not be difficult. Solutes accumulated, probably because they were not consumedin growth. There was no evidence of competitionbetween growth and osmotic adjustment for metabolites, or thatplants which accumulated more solutes were better able to recoverwhen water deficits were relieved. Perennial ryegrass, drought, genetic variation, carbohydrate, amino acids, proline, mineral uptake, Lolium perenne L. cv. Melle 相似文献
8.
9.
The water content and osmotic potential (2) of the differentparts of the pea fruit have been measured during developmentof the seed in two lines near-isogenic except for the r locus.During the early development of both genotypes, the testa possesseda more negative 2 than either embryo, endosperm or pod while,at stages when liquid endosperm was present, the embryo alwaysmaintained 2, more negative than the endosperm. A clear effectof the r locus on water content and 2 was only observed in embryotissue wrinkled (rr) embryos possessing more water andmaintaining a more negative 2 than round (RR) for most of thedevelopmental period studied. The more negative 2 of wrinkledembryos correlated with their greater uptake of water in vivo. When cultured in vitro, the embryos of both genotypes showedmaximum growth (fresh or dry weight) if 10 per cent sucrosewas added to the medium (equivalent to about 1.2 MPa).Round embryos, however, increased in weight more than wrinkledat all sucrose concentrations examined. Cultured embryos maintaineda similar or more negative 2 than their surrounding medium;wrinkled more negative than round. Embryo culture, osmotic potential, Pisum sativum, pea, r locus, seed development, tissue culture, water content 相似文献
10.
Water Relations of Potato Leaves. II. Pressure--Volume Analysis and Inferences About the Constancy of the Apoplastic Fraction 总被引:1,自引:0,他引:1
Water relations characteristics of potato (Solanum tuberosumL. cv. Bintje) leaves were determined from pressurevolumeanalysis using a pressure chamber. Turgor was 077 MPa and thebulk volumetric modulus of elasticity 81 MPa at full turgidity;turgor loss occurred when water potential () had declined to087 MPa at a relative water content (RWC) of 0912;the apoplastic water fraction (A) was 0235. As is usually found,there was a linear relation between 1/ and RWC beyond turgorloss. This finding supports the assumptions of the constancyof A during leaf dehydration. Beyond turgor loss the difference between and [measured afterfreezing and thawing (d)] was about 01 MPa. This differencedid not increase as the leaf water content decreased. This resultcontradicts the constancy of A. It was concluded from calculations with a simple model of leafdehydration that analysis of the relation between and d providesmore insight in the changes in the apoplastic fraction thanthe relation between 1/ and RWC. Research on the size of theapoplastic fraction and its changes with water potential wouldcomplement current understanding of leaf water relations. Solanum tuberosum, L., water potential, pressure chamber, osmotic potential, pressure potential, relative water content, apoplast, symplast 相似文献
11.
Responses of Soybean Leaf Angle, Photosynthesis and Stomatal Conductance to Leaf and Soil Water Potential 总被引:2,自引:0,他引:2
The hypothesis that soil water potential (s) is better correlatedto heliotropic leaf orientation, photosaturated photosyntheticCO2 assimilation and stomatal conductance during periods oflimited water availability than is bulk leaf water potential(1) was examined in greenhouse-grown soybean (Glycine max) plants,submitted to a progressive drought. Paired plants were exposedto either 1000 or 100 µmol m2 s1 photonflux densities (PFD) for 4560 mins. The higher irradianceinduced short-term decreases in 1, due to increased transpiration,while l in the plant exposed to low PFD did not decrease. Thesechanges in 1 occurred independently of changes in soil waterstatus. Concurrent to the light treatments, a single attachedleaf from each of the two plants was isolated from the restof the plant by shading, and the pulvinus of its terminal leafletwas exposed to a perpendicular PFD of 500 µmol m2S1. Leaf movement of this leaflet was recorded in responseto this light, until a stable leaflet angle was achieved. Valuesof s and l (before and after light treatment), and photosaturatedrates of photosynthesis and stomatal conductance, were thenmeasured on these leaves. Leaflet angle and gas exchange werebetter correlated with s (r2 = 0.50, 0.50 and 0.57 for angle,photosynthesis and conductance, respectively) than with l especiallywhen l was the result of short-term, high-light induced changesin leaf water status (r2 = 0.36, 0.32 and 0.49, for the sameparameters). Leaflet angle was also correlated with stomatalconductance (r2 = 0.61) and photosynthetic rate (r2 = 0.60),suggesting a close association between leaf orientation, leafmetabolism and soil water availability. Glycine max (L.) Merr. cv. Essex, soybean, heliotropism, water potential, photosynthesis, stomatal conductance, solar tracking 相似文献
12.
A morphologically explicit numerical model for analysing wateruptake by individual roots was developed based on a conductornetwork, with specific conductors representing axial or radialconductivities for discrete root segments. Hydraulic conductivity(Lp; m s1 MPa1) was measured for roots of Agavedeserti Engelm. and Opuntia ficus-indica (L.) Miller by applyinga partial vacuum to the proximal ends of excised roots in solution.Lp was also measured for 40- to 80-mm segments along a root,followed by measurements of axial conductivity and calculationof radial conductivity. Predicted values of Lp for entire rootsbased on two to ten segments per root averaged 1.04±0.07(mean±s.e. mean for n = 3) of the measured Lp for A.deserti and 1.06±0.10 for O. ficus-indica. The modelalso closely predicted the drop in water potential along theroot xylem (xylem); when a tension of 50 kPa was applied tothe proximal ends of 0.2 m-long roots of A. deserti and O. ficus-indica,the measured xylem to midroot averaged 30 kPa compared witha predicted decrease of 36 kPa. Such steep gradients in xylemsuggest that the driving force for water movement from the soilto young distal roots may be relatively small. The model, whichagreed with an analytical solution for a simple hypotheticalsituation, can quantify situations without analytical solutions,such as when root and soil properties vary arbitrarily alonga root. Agave deserti, electrical circuit analog, hydraulic conductivity, Opuntia ficus-indica, water potential 相似文献
13.
Winter wheat and winter barley were tested for their photochemicaland osmotic potentials during the course of one growth cyclein the field. Prolonged winter conditions induced an absolutehigh in potential net photosynthesis (PN) of winter wheat. Barleyexhibited relatively low PN rates, which may explain the inferiorfrost hardiness of this species. Osmotic potentials () in bothspecies were quite similar, followed rather uniform trends andwere never extreme. There are doubts, however, whether the assessments truly reflected the osmotic stress on cell membranesin frost-hardened leaves. Increased deposition of cryoprotective assimilates in wheatas the cause of continued frost hardiness is discussed. Triticum aestivum, Hordeum sativum, wheat, barley, potential photosynthesis, winter hardiness 相似文献
14.
Attached 2-month-old roots of the succulent plant, Opuntia ficus-indica,shrank 0.4% radially during periods of maximal transpirationunder wet conditions. In contrast, reversible decreases in diameterof nearly 20% occurred for these roots as their ambient waterpotential () in the vapour phase decreased from 0.01to 10 MPa over 8 d, the changes being slightly more rapidat 40 °C than at 10 °C. Such substantial diameter changesbecame progressively less with root age, from a 43% decreasein diameter at 3 weeks to a 6% decrease at 12 months Root shrinkagewas slight when was decreased from 0.01 to 0.3MPa, the latter being similar to the root water potential.As was further decreased from 0.3 to 10 MPa,water movement out of cortical cells caused considerable rootshrinkage. The root hydraulic conductivity (Lp) decreased only30 to 60% for a change in from 0.01 to 10 MPacompared with a decrease of over 106-fold for the soil hydraulicconductivity over this range. The overall conductivity of thesoil, the root-soil air gap, and the root was predicted to bedominated by Lp for soil above 0.3 MPa. As simulatedsoil decreased below 0.3 MPa, the root-soil air gap initiallybecame the primary limiter of water loss from the roots. Below5 MPa for 1-month-old roots and below 2 MPa for12-month-old roots, the soil became the main limiter of waterloss. Thus, water uptake from wet soils apparently was mainlycontrolled by root properties Water loss to drying soils wascontrolled by the development of a root-soil air gap aroundshrinking roots during the initial phase of soil drying andby the reduction of the soil hydraulic conductivity at evenlower soil. Root diameter, root hydraulic conductivity, root-soil air gap, soil hydraulic conductivity 相似文献
15.
Thomas, H. 1987. Physiological responses to drought of Loliumperenne L.: Measurement of, and genetic variation in, waterpotential, solute potential, elasticity and cell hydration.J.exp. Bot. 38: 115125. Clonally-replicated genotypes of Loiium perenne L. were grownin a controlled environment. Leaf water potential (w) osmoticpotential (s), turgor potential (p = w s), elasticity(E), leaf hydration (g water per g dry matter, H) and numberof green leaves per tiller (NGL) were measured before and duringa 42 d drought treatment. A simplified method of estimating E (at w < 1?0 MPa) usingonly six measurements was developed to permit a measurementrate of 8 leaves per hour. Measurement errors in all characterswere 3% or less. During drought, w and s (at w = 0?5 MPa) decreased significantly,p and E increased significantly, and H decreased slightly. Plantsize during drought was negatively correlated with s, and Hand positively correlated with p, osmotic adjustment, E andNGL. Measurements made on the genotypes before draughting didnot give a reliable indication of their physiological conditionafter adaptation to drought. Genetically controlled variation (broad sense heritability)of drought-adapted plants for E was 15%, w 23%, s, 34%, p, 35%,H 34% and NGL 64%. The possibilities for, and effectivenessof, divergent selection of genotypes with high and low expressionof the characters are discussed. Key words: Water relations, Lolium, genetic variation 相似文献
16.
Water Relations of Chromium VI Treated Bush Bean Plants (Phaseolus vulgaris L. cv. Contender) under both Normal and Water Stress Conditions 总被引:1,自引:0,他引:1
BARCEL? JUAN; POSCHENRIEDER CHARLOTTE; GUNS? BENET 《Journal of experimental botany》1986,37(2):178-187
The effect of Chromium VI on leaf water potential (w), solutepotential (a), turgor potential (p) and relative water content(RWC) of primary and first trifoliatc leaves of Phaseolus vulgarisL. was studied under normal growth conditions and during anartificially induced water stress period in order to establishthe possible influence of this heavy metal on the water stressresistance of plants. Plants were grown on perlite with nutrientsolution containing 0, 10, 25, 50 or 100µg cm3 Cr as Na2Cr2O7.2H2O. The effect of Cr onwater relations was highly concentration dependent, and primaryand first trifoliate leaves were affected differently. The growthreducing concentrations of Cr (25, 50 and 100µg cm3) generally decreased s and w and increasedp in primary leaves. The 10 µg cm3 Cr treatmentdid not affect growth, but altered water relations substantially:in primary leaves w and p were increased and s decreased, whilein trifoliate leaves the effect was the opposite. All Cr treatedplants resisted water stress for longer than control plants.The higher water stress resistance may be due to the lower sand to the increased cell wall elasticity observed in Cr VItreated plants. Key words: Phaseolus vulgaris, Chromium VI, water stress, Richter plot 相似文献
17.
By analysing the relationship between inverse water potential(1), and relative water content (RWC) measured on leavesof roses (Rosa hybrida cv. Sonia), grown soilless, it was foundthat a non-linear (NL) model was better suited than a linearmodel to reproduce values observed in the non-turgid region.To explain this apparent curvature, it is assumed that a reductionof the non-osmotic water fraction (Ap) takes place when decreases.Osmotic potentials () measured on fresh and frozen leaf discstend to support this hypothesis. A method for exploiting PVcurves, which takes into account the variation of Ap, is described.It delivers values for the turgor pressure (p), the relativeosmotic water content, and the mean bulk volumetric elasticitycoefficient, lower than those given by the linear model. Onthe other hand, it gives higher estimates for Ap and for . Whenapplying the traditional model to obtain estimates for waterrelations characteristics of rose leaves, and comparing resultsfrom two distinct salinity treatments (electrical conductivitiesof 1·8 mS cm1 and 3·8 mS cm1, respectively),one deduces a significant reduction of at turgor-loss in thehigh salinity treatment. The NL method is, in addition, ablesimultaneously to reveal a reduction of and a significant increasein p at RWC=100% this proves that soillessgrown roseplants are able to osmoregulate when subjected to a constantand relatively high degree of salinity. Key words: Apoplastic water, non-linear regression, pressure-volume curves, tissue-water relations 相似文献
18.
LARQUE-SAAVEDRA A.; RODRIGUEZ M. T.; TREJO C.; NAVA T. 《Journal of experimental botany》1985,36(11):1787-1792
Larqué-Saavedra, A., Rodriguez, M. T., Trejo, C. andNava, T. 1985. Abscisic acid accumulation and water relationsof four cultivars of Phaseolus vulgaris L. under drought.J.exp. Bot 36: 17871792. Plants of four cultivars of Phaseolus vulgaris L. differingin drought resistance were grown in pots under greenhouse conditionsand prior to flowering water was withheld from the pots untilthe mid-day transpiration rate reached values below 1.0 µgH2O cm2 s1 (designated the droughtstage). At this point leaves were harvested on 3 or 4 occasionsover 24 h to determine the abscisic acid (ABA) concentration,total water potential (), solute potential (1) and turgor potential(p). Results showed that values of , 1, and p differed between cultivarswhen they reached the drought stage. The stomatalsensitivity to changes in and p, was as follows: Michoacán12A3 > Negro 150 Cacahuate 72 > Flor de Mayo. These datacorrelated well with the pattern of drought resistance reportedfor the cultivars. ABA accumulation at the drought stage differedbetween cultivars at each sampling time, but overall differencesin ABA level between cultivars were not significant. ABA levelsdid not, therefore, correlate with the drought resistance propertiesreported for the cultivars. Results are discussed in relationto and hour of the day when bean samples were taken for ABAanalysis. Key words: Phaseolus vulgaris L., drought resistance, abscisic acid 相似文献
19.
Sugar-responsive gene expression, invertase activity, and senescence in aborting maize ovaries at low water potentials 总被引:11,自引:1,他引:10
Background and Aims Ovary abortion can occur in maize(Zea mays) if water deficits lower the water potential (w) sufficientlyto inhibit photosynthesis around the time of pollination. Theabortion decreases kernel number. The present work exploredthe activity of ovary acid invertases and their genes, togetherwith other genes for sucrose-processing enzymes, when this kindof abortion occurred. Cytological evidence suggested that senescencemay have been initiated after 2 or 3 d of low w, and the expressionof some likely senescence genes was also determined. Methods Ovary abortion was assessed at kernel maturity.Acid invertase activities were localized in vivo and in situ.Time courses for mRNA abundance were measured with real timePCR. Sucrose was fed to the stems to vary the sugar flux. Key Results Many kernels developed in controls but mostaborted when w became low. Ovary invertase was active in controlsbut severely inhibited at low w for cell wall-bound forms invivo and soluble forms in situ. All ovary genes for sucroseprocessing enzymes were rapidly down-regulated at low w exceptfor a gene for invertase inhibitor peptide that appeared tobe constitutively expressed. Some ovary genes for senescencewere subsequently up-regulated (RIP2 and PLD1). In some genes,these regulatory changes were reversed by feeding sucrose tothe stems. Abortion was partially prevented by feeding sucrose. Conclusions A general response to low w in maize ovarieswas an early down-regulation of genes for sucrose processingenzymes followed by up-regulation of some genes involved insenescence. Because some of these genes were sucrose responsive,the partial prevention of abortion with sucrose feeding mayhave been caused in part by the differential sugar-responsivenessof these genes. The late up-regulation of senescence genes mayhave caused the irreversibility of abortion. 相似文献
20.
Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: II. GERMINATION AT REDUCED WATER POTENTIAL 总被引:3,自引:0,他引:3
Seed germination rates (GR =inverse of time to germination)are sensitive to genetic, environmental, and physiological factors.We have compared the GR of tomato (Lycopersicon esculentum Mill.)seeds of cultivar T5 to those of rapidly germinating L. esculentumgenotypes PI 341988 and PI 120256 over a range of water potential(). The influence of seed priming treatments and removal ofthe endosperm/testa cap enclosing the radicle tip on germinationat reduced were also assessed. Germination time-courses atdifferent 's were analysed according to a model that identifieda base, or minimum, allowing germination of a specific percentage(g) of the seed population (b(g)), and a hydrotime constant(H) indicating the rate of progress toward germination per MPa.h.The distribution of b(g) determined by probit analysis was characterizedby a mean base (b) and the standard deviation in b among seeds(b). The three derived parameters, b, b) and H, were sufficientto predict the time-courses of germination of intact seeds atany . A normalized time-scale for comparing germination responsesto reduced is introduced. The time to germination at any (tg())can be normalized to be equivalent to that observed in water(tg(0)) according to the equation tg(0)=[l(/b(g))]tg().PI 341988 seeds were more tolerant of reduced and had a morerapid GR than T5 seeds due to both a lower b and a smaller H.The rapid germination of PI 120256, on the other hand, couldbe attributed entirely to a smaller H. Seed priming (6 d in1.2 MPa polyethylene glycol 8000 solution at 20 ?C followedby drying) increased GR at all >b(g), but did not lower theminimum allowing germination; i.e. priming reduced H withoutlowering b. Removing the endosperm/testa cap (cut seeds) markedlyincreased GR and lowered the mean required to inhibit germinationby 0.7 to 0.9 MPa. However, this resulted primarily from downwardadjustment in b during the incubation of cut seeds at low inthe test solutions. The difference in b between intact and cutseeds incubated at high was much less (0.l MPa), indicatingthat at the time of radicle protrusion, the endosperm had weakenedto the point where it constituted only a small mechanical barrier.In the intact seed, endosperm weakening and the downward adjustmentin embryo b ceased at < 0.6 MPa, while the reductionin H associated with priming proceeded down to at least 1.2MPa. Based on these data and on the pressure required to pushthe embryos from the seeds at various times after imbibition,it appears that the primary effect of priming was to shortenthe time required for final endosperm weakening to occur. However,as priming increased GR even in cut seeds, priming effects onthe embryo may control the rate of endosperm weakening. Key words: tomato, Lycopersicon esculentum Mill., water potential, germination rate, seed priming, genetic variation 相似文献