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1.
The Relationship Between Transpiration Rate, Water Potential, and Resistances to Water Movement in Sunflower (Helianthus annuus L.) 总被引:3,自引:0,他引:3
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 m1)when transpiration rates approached zero, but increased sharplyto 5.4 and 2.3 x 105 Pa m1 as transpiration increased.However, the gradients were independent of transpiration ratesabove 0.4 g dm2 h1 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 (0.42.4 g dm2 h1) 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 2.02.5 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
2.
Leaf diffusion resistance interpreted as stomatal resistance,leaf water potential (w), solute potential (s) and leaf turgorpotential (p) of the chilling sensitive species Phaseolus vulgariswere determined during chilling at 4 °C in the light. Bothchill-hardened and non-hardened plants were used. For comparison,the chilling resistant species Pisum sativum was also used. The results for chilled P. sativum were similar to those obtainedfor chill-hardened P. vulgaris plants receiving a chilling treatment.In both cases a reduction in stomatal aperture and the maintenanceof a positive leaf turgor were the responses to chilling. Leavesof chilled but non-hardened P. vulgaris plants were found tomaintain open stomata throughout the chilling treatment despitea severe wilt developing after 7 h at 4 °C. This was incontrast to the chill-resistant P. sativum. which showed a rapidclosing and subsequent re-opening of the stomata to a new reducedaperture. During the first 12 h of chilling wof P. vulgaris leaves changedfrom 0.47 MPa to 1.24 MPa. On more prolonged chillingw tended to return to pre-chilling values. In addition. p decreasedfrom 0.42 MPa to zero after only 9 h of chilling, and remainedat this value for the remainder of the chilling period, s, changedrapidly from 0.89 MPa to 1.35 MPa in the first7.5 h, and after 9 h. w and s, were equal, i.e. zero p. In contrast,the chilling resistant plant P. sativum maintained a positivep throughout the chilling period, and there was little differencebetween values of w, and s in control and chilled leaves. Key words: Chilling, Stomata, ater relations, Phaseolus vulgaris, Pisum sativum 相似文献
3.
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
4.
Diurnal Changes in Endogenous Abscisic Acid in Leaves of Pearl Millet (Pennisetum americanum (L. ) Leeke) under Field Conditions 总被引:2,自引:0,他引:2
HENSON I. E.; ALAGARSWAMY G.; MAHALAKSHMI V.; BIDINGER F. R. 《Journal of experimental botany》1982,33(3):416-425
Diurnal variation in leaf abscisic acid (ABA) content was investigatedin pearl millet (Pennisetum americanum (L. ) Leeke) growingin the field in the semi-arid tropics and subjected to varyingdegrees of water stress. There was a two- to three-fold change in ABA content duringthe photoperiod in three groups of severely stressedplants of the genotype BJ 104. Maximum ABA occurred mid-morning(1030 h). ABA levels then declined to a minimum at 1500 h. Changesin ABA content of moderately stressed and fullyirrigated plants were smaller, but still significant. Though,when averaged over the day, levels of ABA of the five groupswere positively related to the degree of water stress, relationshipsbetween ABA concentration and total water () or turgor (p) potentialsvaried considerably with time of sampling. Within groups, changesin ABA contents during the day were not always accounted forby changes in or p. Temporal changes in leaf ABA content similar to those foundin BJ 104, and largely unrelated to , were observed in the genotypesSerere 39 and B282 in a subsequent year. Leaf ABA content of droughted plants (BJ 104) did not declineappreciably overnight despite a marked increase in . However,a large reduction in ABA content with increase in did occurfollowing heavy rainfall. Diurnal changes in stomatal conductance (g1) of BJ 104 couldnot be simply accounted for by temporal changes in total leafABA content, even when allowance was made for effects of irradianceand other environmental variables on g1. It is suggested thatthe sensitivity of stomata to ABA, or accessibility of the hormoneto the stomatal complex, changes during the day. 相似文献
5.
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
6.
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
7.
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 Bunchand Florunner leaves decreased to zero at l of1.2 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 of1.6 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
8.
Osmotic Adjustment to Water Stress in Pearl Millet (Pennisetum americanum (L. ) Leeke) in a Controlled Environment 总被引:2,自引:0,他引:2
A pressure-volume (P-V) and an expressed sap (cryoscopic) techniquewere compared for assessing osmotic adjustment to water stressby pearl millet (Pennisetum americanum (L. ) Leeke) plants grownin a controlled environment cabinet. For leaf water potentials( ) above the point of zero turgor, there was good agreementbetween estimates of solute potential ( s)and turgor ( p) obtainedby the two methods. Reductions in pre-dawn leaf to 1.8 MPa over 56d resulted in net solute accumulation as indicated by a fallin s at full hydration of about 0.3 MPa. The degree of osmoticadjustment increased linearly with the decrease in pre-dawn. Adjustment in cv. BJ 104 was significantly (P < 0.05) lessduring a second drought than during a first, and cv. Serere39 was significantly (P < 0.05) less able to adjust osmoticallythan BJ 104. Adjustment was greater in leaves which were undergoing extensiongrowth during the drought than in leaves already fully extendedbefore drought started. Much of the adjustment was lost within24 h following rewatering, the loss being most complete in theolder, fully extended leaves. 相似文献
9.
Aspects of the water relations of spring wheat (Triticum aestivumL.) are described for cultivars Highbury (low ABA) and TW269/9(high ABA), and low and high ABA accumulating F6selections derivedfrom a cross between them. In a pot experiment, pressure-volume (P-V) curves were constructedfor main stem leaf four (MSL4) of well-watered plants of Highburyand TW269/9. Estimates of solute potential (2) from these curveswere similar for the two cultivars, but varied with the timeof sampling and the time allowed for hydration in dim light. In a field experiment with four low and four high ABA F6lines,P-V curves for flag leaves from both droughted and irrigatedplants gave at both zero turgor (p) and zero water potential(1) which differed with degree of stress, sampling time andgenotype. 1was strongly dependent on the initialL of the leafand was reduced on average by c. 0.4 MPa per MPa decline ininitial L.5, was lower (more negative) by c. 0.1-MPa in theafternoon than in the morning. Overall, was also 0.1 MPa lowerin low ABA lines than in high ABA lines. In another field experiment, flag leaves of five low and fivehigh ABA F6lines were sampled over a 4 week period from droughtedplots and L and 5, measured (the latter by osmometry with expressedsap). For these leaves 5, at zero p or zero L was consistentlylower by 0.30.5 MPa than estimates of 5, from the P-Vcurves with flag leaves. However, data for the low ABA lineswere again lower (by c. 0.1 MPa) than those for high ABA lines. The consequences of these differences in 1 are discussed inrelation to the stimulation of ABA accumulation in low and highABA selections. Key words: Water potential, Solute potential, P-V curves, Wheat (Triticum aestivum), Drought stress 相似文献
10.
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
11.
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
12.
Field Studies of Cereal Leaf Growth: IV. WINTER WHEAT LEAF EXTENSION IN RELATION TO TEMPERATURE AND LEAF WATER STATUS 总被引:1,自引:0,他引:1
Throughout winter and early spring, rule and auxanometer measurementsshowed that leaf extension rate (RE) was directly related totemperature and stopped at about 0°C. During this period,both night and day time RE responded similarly to temperature.Bright sunshine in late April and May caused fast transpirationwhich was associated with low leaf water potential () and slowRE. When bright sun was obscured by cloud, RE increased butthis did not compensate for previous slow RE. Leaf turgor potential,calculated as the difference between and leaf osmotic potential,was large (0.61.8 MPa) and bore little relation to RE.Low was associated with slower RE than would have been expectedwithout water stress, but the relation was not unique. On abright day in May, adaptation to low occurred and during theafternoon RE was faster than at similar values of and meristemtemperatures before noon. The response of RE and duration ofleaf extension to temperature suggested that for any particularleaf grown under field conditions, variation in mean growingtemperature would affect final leaf length only slightly. Becausesevere water stress slows RE without affecting the durationof leaf extension markedly, it decreases final leaf size. 相似文献
13.
LOBODA T.; KLECZKOWSKI L. A.; TARLOWSKI J.; NALBORCZYK E. 《Journal of experimental botany》1988,39(12):1765-1770
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 m3),-HPMS initially stimulated Pn and decreased the magnitude ofboth PLIB and PLTB. The decreased at all concentrations of-HPMS (0.055.0 mol m3. 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
14.
Legge, N. J. 1985. Water movement from soil to root investigatedthrough simultaneous measurement of soil and stem water potentialin potted trees.J. exp. Bot. 36: 15831589. Osmotic tensiometers implanted in the stems of three mountainash (Eucalyptus regnans F. Muell.) saplings growing in largeplastic bins recorded stem water potential, w, while soil waterpotential, w, was simultaneously recorded by instruments nearthe trees' roots and in the surrounding root-free soil Earlyin a drying cycle, with the soil still wet, the diurnal variationin 1, was often slight, despite diurnal variations in u approaching2.0 M Pa. Late in a drying cycle the diurnal fluctuations in1, and u were very similar although changes in 1, still laggedup to 1.5 h behind changes in u. 1values at this time occasionallyreached 3.0 MPa with no apparent damage to the treesWatering the bins in daytime led to a response in 1, valueswithin about 5 min, whereas u, values did not respond for afurther 20 min. u values then rose rapidly but after only 1h began to decline again, while 1, values remained at or nearsaturation for the rest of the day. Water uptake hypotheseswhich attribute an important role to a soil-root interface resistanceare not supported by these data Key words: Soil water potential, penrhizal gradients 相似文献
15.
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
16.
Plasmalemma Transport of OH- in Chara corallina: II. FURTHER ANALYSIS OF THE DIFFUSION SYSTEM ASSOCIATED WITH- OH EFFLUX 总被引:1,自引:0,他引:1
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
17.
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
18.
Information on the biological activities of gibberellins (GAs)in the barley aleurone, Tangin-bozu dwarf rice, dwarf pea, lettucehypocotyl and cucumber hypocotyl bioassays is reviewed and discussedin the context of GA structure-activity relationships. The barley aleurone bioassay exhibits a limited response toGAs and it is suggested that this may be because the aleuronecells are able to carry out few GA interconversions. Consequentlyactivity is determined by the degree of compatibility betweenthe GAs and a receptor site. In this assay high biological activityis associated with GAs having a 3ß-hydroxy--lactonestructure. This activity is substantially enhanced by the additionalpresence of a 13-hydroxyl group. The substitution of a -lactoneor a -lactol for a -lactone results in reduced activity while3ß,13-dihydroxy GAs with either 20-carboxyl or 20-methylfunctions are completely inactive. The Tanginbozu dwarf ricebioassay responds to many more GAs than the barley aleuronesystem possibly because the rice seedlings can carry out extensiveGA interconversions. Under these circumstances GAs that areinactive per se can be metabolically converted to active forms.There is no interaction between the 3ß- and 13-hydroxyfunctions of GA molecules in the rice assay. Activity appearsto be determined by the degree oxidation of the C-20 group.The order of activity is usually -lactone > -lactol >-lactone > methyl > carboxyl. It is suggested this mayindicate that in rice seedlings C20-GAs are converted to C19-GAsvia a Baeyer-Villiger type oxidation. Activity in the dwarfpea bioassay is dependent upon GAs possessing both 3ß-and 13-hydroxyl groups and is again related to the state ofoxidation at the C-20 locus. In the lettuce bioassay activityis restricted to GAs with a -lactone function. In some instancesa -lactone, but not a -lactol, can substitute effectively. Thismay imply that the applied C20-GAs are not converted to C19-GAsand that the response to the -lactone results from the six-memberedring mimicking the -lactone at the receptor site. Only GAs havinga 19,10 or a 19,20 lactonic bridge show substantial activityin the cucumber bioassay. The additional presence of eithera 12- or a 13-hydroxyl group severely reduces activity. 相似文献
19.
CORNFORD C. A.; BLACK M.; DAUSSANT J.; MURDOCH K. M. 《Journal of experimental botany》1987,38(2):277-285
Embryo/scutellar tissue of pre-mature wheat grains usually containslittle -amylase but readily produces the enzyme upon removalfrom the caryopsis. Enzyme production is accompanied by cytologicalchanges in the scutellar epithelium cells characteristic ofgerminating mature embryos, although -amylase production bypre-mature tissue is not always associated with germinativegrowth of the embryonic axis. Production of -amylase is influencedby embryo age, stimulated by GA3 and overall is inhibited byABA. Examination by isoelectric focussing and rocket-line immuno-electrophoresisreveals the presence of both -AMYl and -AMY2 isoenzymes, thelatter being the major constituent. In the presence of ABA certain-AMY2 isoenzymes not detected previously are observed. Key words: a-Amylase, wheat, embryo 相似文献
20.
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