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1.
Smith, J. R. 1987. Potassium transport across the membranesof Chara. II. 42K fluxes and the electrical current as a functionof membrane voltage.—J. exp. Bot. 38: 752–777. The current required to clamp the trans-membrane voltage ofinternodal cells of Chara australis at different levels wasmeasured simultaneously with either the 42K influx or efflux.Examination of the voltage-dependence of the ratio of the electricalcurrent to the unidirectional tracer fluxes yielded no evidenceof any amplification of the electrical driving force on theK+ ions. There was thus no evidence for the interaction of K+ions with themselves or any other species during their passageacross the membrane. These measurements allow the determinationof , the fraction of the electrical current carried by K+ ions.When the external [K+] = 10 mol m–3, the average valueof was 0?85 for Vm > –125 mV and 07?5 for Vm <–150 mV. When the external [K+] = 0?1 mol m–3, was 0?6 for Vm < –80 mV and 0?1 for Vm > –250mV. It was also found that the conductance associated with K+transport was inhibited by hyperpolarization. Key words: Potassium, conductance, flux-ratio  相似文献   

2.
Measurements of Cl influx in cells of Chara corallinashow that control of this flux contributes to the ability ofthis cell to regulate its osmotic pressure. Transcellular osmosiswas used to generate cell fragments with abnormally high 1,(H-cells), and with abnormally low 1, (L-cells). Plasmalemmainflux (oc) was very high in L-cells, and markedly reduced inH-cells. Influx was not affected by the presence of sucrosein the pond water and the consequent reduction in turgor. InH-cells the chloride flux from cytoplasm to vacuole (cv) wasalso strongly inhibited. It is suggested that control of Clfluxes at both plasmalemma and tonoplast is involved in osmoregulationin these cells. Key words: Chara corallina, osmoregulation, Cl flux  相似文献   

3.
The dynamic and steady state aspects of the pH and electricpotential () profiles, that develop in the experimental mediumin association with the photosynthetic assimilation of exogenousHCO3 by internodal cells of Chara corallina, were investigated.A theoretical treatment is presented which explains the originof the phenomenon. This theory was tested by comparing thepH and values generated by a numerical analysis model (whichsimulated the experimental system) against experimental data.Verification of our model indicates that the steady state ionicfluxes, associated with HCO3 assimilation (HCO3,OH, and CO23, are not significantly influencedby the electric potential gradients. The main driving forcecausing the observed fluxes is the diffusion gradient associatedwith the respective ion. By simultaneous measurement of and pH, at the centre of analkaline band, a direct correlation was established betweenlight-activation and dark-deactivation of the OH transportsystem and the light-mediated changes in at the cell surface.In addition, under steady state conditions, an almost perfectcorrelation was observed between alkaline band pH centres andthe negative electric potential maxima. These data offer strongsupport for the hypothesis that OHefflux, in this system,is an electrogenic process. Based on our present analysis, the profile along the cell indicatesthat, in terms of the spatial aspect of HCO3 transport,the rate of HCO3 influx varies quite dramatically alongthe length of an internodal cell. This aspect is discussed interms of the cellular integration of OH and HCO3transport in this species.  相似文献   

4.
The effects of transpiration rate on the vertical gradientsof leaf and stem xylem water potential ( and ) were examinedusing hydroponic sunflower plants. Transpiration was variedby stepwise alterations of environmental conditions. The gradientsof and were relatively small (2.3 and 0.8 x 105 Pa m–1)when transpiration rates approached zero, but increased sharplyto 5.4 and 2.3 x 105 Pa m–1 as transpiration increased.However, the gradients were independent of transpiration ratesabove 0.4 g dm–2 h–1 owing to variability of theplant resistance. The gradients of I were usually less thanhalf those of I. 1 in individual leaves remained constant over a wide range oftranspiration rates (0.4—2.4 g dm–2 h–1) andeach leaf possessed a characteristic plateau value related toits elevation. I responded similarly but was approximately 2.0x 105 Pa higher than I at the same elevation. Identical resultswere obtained regardless of the procedure employed to vary transpiration. The drop in water potential between stem and leaf implies thatthe leaf resistance is appreciable. This was confirmed usingrapidly transpiring excised leaves freely supplied with water.I increased by 2.0–2.5 x 105 Pa following removal of theroot resistance but remained 2 x 105 Pa lower than similar excisedleaves in darkness. Furthermore, I in excised leaves remainedconstant over a wide range of transporting rates, demonstratingthat the leaf resistance is also variable. The results are discussed in relation to previous reports.  相似文献   

5.
This work aimed to study the impacts of acquisition and assimilationof various nitrogen sources, i.e. NO3, NH4+ or NH4NO3,in combination with gaseous NH3 on plant growth and acid-basebalance in higher plants. Plants of C3 Triticum aestivum L.and C4 Zea mays L. grown with shoots in ambient air in hydroponicculture solutions with 2 mol m–3 of nitrogen source asNO3, NH4+ or NH4NO3 for 21 d and 18 d, respectively,had their shoots exposed either to 320 µg m–3 NH3or to ambient air for 7 d. Variations in plant growth (leaves,stubble and roots), and OH and H+ extrusions as wellas the relative increases in nitrogen, carbon and carboxylatewere determined. These data were computed as H+/N, H+/C, (C-A)/N,and (C-A)/C to analyse influences of different nitrogen sourceson acid-base balance in C3 Triticum aestivum and C4 Zea maysplants. Root growth in dry weight gain was significantly reduced bytreatment with 320 µg m–3 NH3 in Triticum aestivumand Zea mays growing with different N-forms, whereas leaf growthwas not significantly affected by NH3. In comparison with C3Triticum aestivum, non-fumigated C4 Zea mays had low ratiosof OH/N in NO3–3-grown plants and of H+/N in NH4+- and NH 4NO3-grown plants. Utilization of NH3 from the atmospherereduced both the OHN ratios in NO3 -grown plantsand the H+/N ratio in NH4+ - and NH4NO3 -grown plants of bothspecies. Furthermore, Zea mays had higher ratios of (C-A)/Nin NH4+ - and NH4NO3-grown plants than Triticum aestivum. Thismeans that C4 Zea mays had synthesized more organic anion perunit increase in organic N than C3 Triticum aestivum plants.Within both species, different nitrogen sources altered theratios of (C-A)/N in the order: NH4NO3>NH4+>NO3.Fumigation with NH3 increased organic acid synthesis in NO3- and NH4+ - grown plants of Triticum aestivum, whereas it decreasedorganic acid synthesis in Zea mays plants under the same conditions.Furthermore, these differences in acid-base regulation betweenC3 Triticum aestivum and C4 Zea mays plants growing with differentnitrogen sources are discussed. Key words: Acid-base balance, ammonia, ammonium, nitrate, ammonium nitrate, C3 Triticum aestivum L., C4 Zea mays L.  相似文献   

6.
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: 1787–1792. 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 cm–2 s–1 (designated the ‘drought’stage). 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   

7.
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, 1•0, 2•5, 5•0 or 10•0µg cm–3 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 (2•5, 5•0 and 10•0µg cm–3) generally decreased s and w and increasedp in primary leaves. The 1•0 µg cm–3 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   

8.
Changes in the concentrations of K+ and Cl occur in parallelduring turgor regulation, and account for the changes in osmoticpressure. Thus it is impossible to single out one ion whoseconcentration is directly controlled by a turgor regulatorymechanism. After an increase in external osmolality (o) of 400mosmol kg–1, turgor is restored to its normal value in4–5 d. The response to a decrease in o is much more rapid,with most of the change in 1 occurring in the first 2 h. Apparentcytoplasmic concentrations of sucrose are similar to vacuolarconcentrations, and increase slightly with increasing 1.  相似文献   

9.
The effects of -hydroxy-2-pyridinemethanesulphonic acid (-HPMS)upon net photosynthesis (Pn, the CO2 compensation point (),post-lower illumination burst of CO2 (PLIB) and post-lower temperatureburst of CO2 (PLTB) in detached rye (Secale cereale L.) leaveswere investigated. At low concentrations ( 0.5 mol m–3),-HPMS initially stimulated Pn and decreased the magnitude ofboth PLIB and PLTB. The decreased at all concentrations of-HPMS (0.05–5.0 mol m–3. The effects of -HPMS onPn and were time-dependent and, after a few minutes, the Pnwas inhibited while values increased considerably. At a higherconcentration (5.0 mol m –3), the transient effects of-HPMS were shorter () or not observed at all (Pn. Both PLIBand PLTB, when expressed in relation to Pn, increased at higherlevels of this compound. Similar data with respect to the effectsof -HPMS on PLIB and PLTB were found for leaves of dandelion(Taraxacum officinale L.). The results suggest that -HPMS may stimulate Pn by inhibitingphotorespiration, as originally suggested by Zelitch (1966),but only at low concentrations and over a short time span. Thedecrease of PLIB and PLTB values at low -HPMS levels is consistentwith these processes being a residual activity of the glycolatepathway. Key words: CO2 compensation point, -hydroxy-2-pyridinemethanesulphonic acid, photorespiration, photosynthesis  相似文献   

10.
During transpiration, water vapour diffusing through the stomatamoves through air that has no mean motion: its diffusive inwardflux is balanced by a general outward mass flow. The effectis to accelerate outward diffusive flows (water vapour, CO2in respiration) and retard inward diffusive flows (air, CO2for assimilation) and alter the apparent ratio of diffusioncoefficients. The magnitude of the effect is calculated theoretically,and estimated practically for an experiment in sugar-beet leaves.For this particular case the error in estimating mesophyll diffusiveresistance is near 2 per cent, but for other conditions couldbe much larger. Estimated values of the apparent ratio of thediffusion coefficient of water vapour and carbon dioxide (truevalue = 1.59) ranged from –0.027 to 2.79, but could lieanywhere between – and +.  相似文献   

11.
The euryhaline charophyte Lamprothamnium papulosum (Wallr.)J. Gr. was adapted to media with decreasing salinities rangingfrom 550 to 0 mosmol kg–1. Vegetative plants grown inmedia with osmotic pressures (0) in the range of 550 to 130mosmol kg–1 maintained a constant turgor pressure () at309 + 7 mosmol kg–1. 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 kg–1. 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 m–3. 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   

12.
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 cm–1 and 3·8 mS cm–1, 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 soilless–grown 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   

13.
Ion contents and concentrations (K+, Na+, Cl, Ca2+, Mg2+,SO2–4, NO3, HPOJ2–4, amino and organic acids)of P. purpurea have been studied in relation to salinity variation.Cells were shown to accumulate large amounts of K+ and Clagainst their respective gradients of electrochemical potentialin all dilute and concentrated seawater media. Active influxof SOJ2–4, NO3, and HPOJ2–4 is also suggested,while Na+ is actively excluded from cells under hyposaline andhypersaline conditions. The relative proportions of individualcomponents of the internal osmotic potential were found to changeaccording to the external salt concentration. KCL forms themajor fraction of j} in concentrated seawater media while K+-aminoacids form the major fraction in dilute seawaters. Other intracellularsolutes comprise less than 15% oftj, in all media. Unidirectional fluxes of K+ and Cl were studied by radioisotopicmeans. Fluxes of K+ and Cl are reduced in hyposalinemedia, as is absolute KCL content per cell. Intracelhilar KCLcontent was also found to be markedly dependent upon externalK+ concentration, rather than water potential. Changes in KC1levels induced by salinity variation occur over a 6 h period.  相似文献   

14.
Corrigendum     
Light response curves for (•) gross 16O2 evolution, and() CO2 uptake in 210 mmol mol–1 O2 with 900–1000µbar CO2 or () in air by leaves of Hirschfeldia incana.The difference between (•) and () or () was quantitativelyequivalent to the measured 18O2 uptake. The areas under thecurves are labelled to identify regions of assimilatory andnon-assimilatory electron flow redrawn from data of Canvin etal. (1980). It should be noted that the data and the labelling of the figureaxes are correct as printed.  相似文献   

15.
The vacuolar pH (pHv) and the cytoplasmic pH (pHc) of the marinegiant-celled green alga Chaetomorpha darwinii were measuredby pH microelectrode techniques on extracted vacuolar sap, andby the [I4C]DMO distribution method respectively. Equilibrationof DMO occurred with a half-time of about 2 h, with an apparentPDMO of 3.6 x 10–5 cm s–1, but the vacuolar concentrationof free, undissociated DMO was always less than the externalconcentration. The explanation offered for freshwater giant-celledalgae of net DMO leakage across the plasmalemma cannotapply to Chaetomorpha darwinii, since electrically-driven DMOexit from the cytoplasm should be similar across the plasmalemmaand the tonoplast in these cells with large, vacuole-positivepotential differences across the tonoplast. pHc was accordinglycomputed assuming either tonoplast or plasmalemma equilibrationof DMO, with correction for DMO metabolism within the cell.pHc was 8.0–8.3 in the light in artificial seawater (pHoabout 8.0), was some 0.5 units lower in the dark, and was slightlylower with an external pH of 7. Vacuolar pH was 6.5–6.9,without consistent effects of illumination or of external pHof 7 rather than 8. While µH+ at the tonoplast was similarto that in giant-celled freshwater algae (although with a greatercontribution from relative to pH), µH+ at the plasmalemmawas less than 8 kJ mol–1, i.e. less than one-third ofthe value in freshwater green algae. µNa+ was some 13kJ mol–1 at the plasmalemma. The possibility that theprimary active transport process at the plasmalemma of Chaetomorphadarwinii (and certain other marine algae) is Na+ efflux ratherthan H+ efflux is discussed.  相似文献   

16.
The effects of Cl and pretreatment on 36Clinflux and influx into Characorallina cells were examined. Both treatments reduced 36Clinflux into C. corallina cells in the acid pH range (4.5–7.0). pretreatment stimulated influx into C. corallina cells, but Cl pretreatment hadno effect. There was a direct inhibitory effect of CI on influx into C. corallina cells, but no apparenteffect on net NO uptake. The time course of 36Cl accumulation into cytoplasmic and vacuolarcompartments during incubation of the cells with showed that significant radioactivity appeared in the vacuolarsap after 30 min. There was a linear increase in the percentageof total 36CI which crossed the tonoplast (c-v). There was noeffect of Cl or pretreatment on accumulation of radioactivity in the vacuole. Thin layer chromatography ofthe vacuolar sap showed that after 2 h only one component waspresent which had an RF which was similar to 36CI. Therate of accumulation of 36C1 in the vacuole could beused to estimate rates of reduction. Key words: Chloride, Chlorate, Chara, Nitrate  相似文献   

17.
The electrical potential differences (Eex) and the electrochemicalpotential differences for potassium and chloride in the xylemexudate of excised maize roots were determined and the valuesobtained indicated active transport of both ions to the xylemexudate. The potential differences were depolarized by increasesin the external KCl concentration ([KCl]o), and Eex was a linearfuction of log[KCl]o. The corresponding data for the cell vacuolesof the same roots were also determined and trends similar tothose found for the exudate were obtained. The electrochemicalpotential differences between the cell vacuoles and the externalsolution for potassium (µrac.k) and chloride (µvac.Cl)indicated that both ions were actively transported to the vacuoles.Both µvac.k and µvac.cl decreased in a linear manneras [KCl]o was increased. However, in spite of the similar trendsin both sets of data, the values of the electrical potentialand chloride electrochemical potential differences were alwaysmarkedly larger for the vacuoles than for the exudate. For potassium,there were no significant differences. It is concluded thatthe discrepancy between the data for the vacuoles and the wholeroots does not support the idea that the exuding root systembehaves like a single cell, as has been suggested by some workers.  相似文献   

18.
Changes in components of leaf water potential during soil waterdeficits influence many physiological processes. Research resultsfocusing on these changes during desiccation of peanut (Arachishypogeae L.) leaves are apparently not available. The presentstudy was conducted to examine the relationships of leaf waterl, solute s and turgor p potentials, and percent relative watercontent (RWC) of peanut leaves during desiccation of detachedleaves and also during naturally occurring soil moisture deficitsin the field. The relationship of p to l and RWC was evaluated by calculatingp from differences in l and s determined by thermocouple psychrometryand by constructing pressure-volume (P-V) curves from the land RWC measurements. Turgor potentials of ‘Early Bunch’and ‘Florunner’ leaves decreased to zero at l of–1.2 to –1.3 MPa and RWC of 87%. There were no cultivardifferences in the l at which p became zero. P-V curves indicatedthat the error of measuring s after freezing due to dilutionof the cellular constituents was small but resulted in artefactualnegative p values. Random measurements on two dates of l, s, and calculation ofp from well-watered and water-stressed field plots consistingof several genotypes indicated that zero p occurred at l of–1.6 MPa. It was concluded that the relationships of p,l, s, and RWC of peanut leaves were similar to leaves of othercrops and that these relationships conferred no unique droughtresistance mechanism to peanut.  相似文献   

19.
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: 115–125. Clonally-replicated genotypes of Loiium perenne L. were grownin a controlled environment. Leaf water potential (w) osmoticpotential (s), turgor potential (p = ws), 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   

20.
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 in–1.2 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   

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