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1.
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
2.
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
3.
Suboptimal temperature (T) affects germination rates (reciprocalof time to radicle emergence) on a thermal time basis; thatis, the T in excess of a base or minimum temperature multipliedby the time to a given per cent germination [tg) is a constant.Respiration rates are also sensitive to T, and proportionalrelationships are often found between respiration rates andgermination rates. Reduced water potential () delays seed germinationon a hydrotime basis (i.e. the in excess of a base water potentialmultiplied by tg is a constant). It was tested whether respirationrates prior to radicle emergence vary in proportion to T and as expected from the thermal and hydrotime models. Respirationrates (C02 evolution) of cold-tolerant, rapidly germinating(PI 341988) and cold-sensitive, more slowly germinating (T5)tomato [Lycopersicon esculentum Mill.) seeds were evaluatedover a range of T and conditions. For both genotypes, respirationrates until the beginning of radicle emergence were relatedto T on a thermal time basis and increased approximately linearlywith above -2.0 MPa, consistent with the hydrotime model. Respirationrates were uniquely related to germination rates, regardlessof whether germination timing was affected by T, , or genotype.However, germination timing was unaffected when respirationrates were manipulated by varying 02 partial pressure. Thus,while both germination and respiration rates vary with T and consistent with thermal and hydrotime models of biologicaltime, respiration rates per se were not the limiting factorin germination timing of tomato seeds. Key words: Lycopersicon esculentum Mill., tomato, germination, respiration, temperature, water potential 相似文献
4.
The kinetics of primary dormancy loss were investigated in seeds of horse
chestnut (Aesculus hippocastanum L.) harvested in four
different years. Freshly collected seeds from 1991 held for up to 1 year at
temperatures between 2C and 42C exhibited two peaks in germination (radicle
growth), representing a low temperature (2-8°C) and a high
temperature response (31-36°C). Germination at 36°C
generally occurred within 1 month of sowing, but was never fully expressed
in the seedlots investigated. At low temperatures (2-8°C),
germination started after around 4 months. Generally, very low levels of
termination were observed at intermediate temperatures (11-26°C).
Stratification at 6°C prior to germination at warmer temperatures
increased the proportion of seeds that germinated, and the rate of
germination for all seedlots. Within a harvest, germination percentage (on
a probit scale) increased linearly with stratification time and this
relationship was independent of germination temperature (16-26°C).
However, inter-seasonal differences in the increases in germination
capacity following chilling were observed, varying from 0.044 to 0.07
probits d-1 of chilling at 6°C. Increased
sensitivity to chilling was associated with warmer temperatures during the
period of seed filling. The estimated base temperature for germination, Tb,
for newly harvested seeds varied slightly between collection years but was
close to 25°C. For all seedlots, Tb decreased by 1°C every
6 d of chilling at 6°C. This systematic reduction in Tb with
chilling ultimately facilitated germination at 6°C after dormancy
release. 相似文献
5.
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
6.
Seed priming (imbibition in water or osmotic solutions followedby redrying) generally accelerates germination rates upon subsequentre-imbibition, but the response to priming treatments can varyboth within and among seed lots. Seed maturity could influenceresponsiveness to priming, perhaps explaining variable primingeffects among developmentally heterogeneous seed lots. In thecurrent study, muskmelon (Cucumis melo L.) seeds at two stagesof development, maturing (40 d after anthesis (DAA)) and fullymature (60 DAA), were primed in 0?3 M KNO3 for 48 h at 30 ?C,dried, and imbibed in polyethylene glycol 8000 solutions of0 to 1?2 MPa at 15, 20, 25, and 30 ?C. Germination sensitivitiesto temperature and water potential () were quantified as indicatorsof the influence of seed maturity and priming on seed vigour.Germination percentages of 40 and 60 DAA control seeds weresimilar in water at 30 ?C, but the mean germination rate (inverseof time to germination) of 40 DAA seeds was 50% less than thatof 60 DAA seeds. Germination percentages and rates of both 40and 60 DAA seeds decreased at temperatures below 25 ?C. Reductionsin also delayed and inhibited germination, with the 40 DAAseeds being more sensitive to low than the 60 DAA seeds. Primingsignificantly improved the performance of 40 DAA seeds at lowtemperatures and reduced , but had less effect on 60 DAA seeds.Priming lowered both the minimum temperature (Tb) and the minimum (b) at which germination occurred. Overall, priming of 40 DAAseeds improved their germination performance under stress conditionsto equal or exceed that of control 60 DAA seeds, while 60 DAAseeds exhibited only modest improvements due to priming. Asthe osmotic environment inside mature fruits approximates thatof a priming solution, muskmelon seeds may be primedin situ during the late stage of development after maximum dryweight accumulation. Key words: Cucumis melo L., seed priming, germination, vigour, development, temperature 相似文献
7.
A quantitative model for loss of primary dormancy and induction of secondary dormancy in imbibed seeds of Orobanche spp 总被引:1,自引:0,他引:1
Seeds of three species of Orobanche were conditioned
(e.e. stored fully imbibed in darkness) for periods up to 210 d in order to
model relief of primary dormancy and induction of secondary dormancy. The
data were consistent with the hypothesis that periods for loss and
induction of formancy and loss of viability are normally distributed in
populations of imbibed sees and that these three processes are independent.
There was a positive, linear relationship between the rate of loss of
primary dormancy and temperature from 10-30C
in O. aegyptiaca and O. cernua
and 10-25C in O.
crenata. In all three species, the rate of induction of
secondary dormancy was highest at 10°C and decreased with increase
of temperature up to about 20°C, above which there was little
further change in the rate with temperature. The resulting model explained
over 90% of the variation in germination after conditioning in both
O. aegyptiaca and O. cernua. In
O. crenata, however, this model was only satisfactory
at 10 and 15°C. At higher temperatures, dormancy was relatively
stable for periods of conditioning from 70 to about 154 d. Possible
explanations for this are discussed. Applications of these models for
estimating the time required to reduce Orobanche
infestations in the field are also briefly discussed.Key words:
Orobanche spp., broomrape, seed dormancy, temperature, dormancy
model
相似文献
8.
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
9.
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
10.
An improved strain-gauge device for continuous field measurement of stem and fruit diameter 总被引:7,自引:2,他引:5
An improved strain-gauge dendrometer was tested on apple (Pyrus
malus L.) tree trunks and fruit to measure thickness dynamics.
The sensor is similar to previous devices, but is more flexible allowing
for a greater range of thickness change before it has to be physically
reset. The practical resolution of the measurement system is given as one
standard deviation about the mean of 51 observations taken on an Invar
metal alloy in the field when temperatures ranged between 16C and 17C. The mean
of these observations was 3.68356 mm with one standard deviation of 0.00947
mm. There is a positive correlation between temperature and sensor output
having a slope of 2.96 m°C-1. For a typical
daily temperature change of 21°C, this causes an apparent change of
62 m. Stem thickness varied 0.7 mm diurnally
with maximum values at night and minimum values during the day. Apple fruit
diameter increased 3.3 mm over the 15 d period.Keywords:
Strain gauge dendrometer, plant stem and fruit thickness sensor,
plant water status, growth.
相似文献
11.
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
12.
The effects of storage conditions on the germination of developingmuskmelon (Cucumis melo L.) seeds were tested to determine whetherafter-ripening is required to obtain maximum seed vigour. Seedswere harvested at 5 d intervals from 35 (immature) to 60 (fullymature) days after anthesis (DAA), washed, dried, and storedat water contents of 3·3 to 19% (dry weight basis) at6, 20, or 30°C for up to one year. Germination was testedin water and in polyethylene glycol 8000 solutions ( 0·2to 1·2 MPa osmotic potential) at 15, 20, 25 or30°C. Germination percentages and rates (inverse of meantimes to radicle emergence) were compared to those of newlyharvested, washed and dried seeds. For 40 and 60 DAA seeds,one year of storage at 20°C and water contents <6·5%significantly increased germination percentages and rates at20°C, but had little effect on germination at 25 and 30°C.Storage reduced the estimated base temperature (Tb) and meanbase water potential (b) for germination of both 40 and 60 DAAseeds by approximately 5°C and 0·3 MPa, respectively.Immature 35 DAA seeds showed the greatest benefit from storageat 3 to 5% water content and 30°C, as germination percentagesand rates increased at all water potentials (). Storage underthese same conditions had little effect on the germination ofmature seeds in water, but increased germination percentagesand rates at reduced 's. Accelerated ageing for one month at30°C and water contents from 15 to 19° increased germinationrates and percentages of mature seeds at reduced 's, but longerdurations resulted in sharp declines in both parameters. Immatureseeds lost viability within one month under accelerated ageingconditions. An after-ripening period is required at all stagesof muskmelon seed development to expand the temperature andwater potential ranges allowing germination and to achieve maximumgerminability and vigour. Post-harvest dormancy is deepest atthe point of maximum seed dry weight accumulation and declinesthereafter, both in situ within the ripening fruit and duringdry storage. Key words: Muskmelon, Cucumis melo L., seed, development, dormancy, germination, vigour, after-ripening 相似文献
13.
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
14.
Cyclic AMP and GA3 stimulated both -amylase activity in riceendosperm and the germination of the seed. In combination theyalso induced germination of ABA-treated seeds but cyclic AMPalone failed to neutralize the inhibitory effect of ABA; withadded kinetin, however, it promoted the -amylase activity ofthe dormant seeds. The enzyme activity decreased as the storageperiod of seeds increased. Cyclic AMP and GA 相似文献
15.
Yellow cedar (Chamaecyparis nootkatensis) seeds
exhibit prolonged dormancy following their dispersal from the parent plant.
Embryos excised fully from their enclosing seed tissues exhibit 100%
germination, indicating that the seed tissues enclosing the embryo (the
testa, remnants of the nucellus and the megagametophyte) play an inhibitory
role and prevent radicle emergence. As part of an assessment of the role of
seed tissues in the dormancy mechanism of yellow cedar seeds, light
microscopy was used to examine changes within the major structures of the
seed following a 90 d war (26C)/cold
(4C) moist treatment ('stratification') and
during germination. In the micropylar tip of the seed, the nucellus forms a
hard nucellar cap covering the radicle. The nucellar cap is composed
primarily of degenerated cells; histological staining with ruthenium red
revealed a predominance of pectins. There were no obvious cellular or
morphological differences (detected by light microscopy) between mature
seeds subjected to a 3 d soak and seeds subjected to a 3 d soak and the 90
d dormancy-breaking treatment. However, just prior to germination there was
an outward projection of the nucellar cap through the micropyle, which
appeared to be caused by the extension of highly folded proteinaceous
strands lying immediately in front of the radicle. When the testa was
removed, the embryo enclosed within the intact megagametophyte was
incapable of germination. If, however, the megagametophyte surrounding the
embryo was slit or the embryo surrounded by an intact megagametophyte was
subjected to a 3d rinse in water, some germination occurred, perhaps as a
result of an enhanced release of inhibitors from the megagametophyte. After
stratification, dormancy of yellow cedar seeds is broken; concurrent with
dormancy breakage, there was a mechanical weakening of the megagametophyte.
The embryo also underwent changes that included an increase in turgor and a
reduced sensitivity to highly negative osmotic potential. It is concluded
that coat-imposed dormancy of yellow cedar seeds is enforced by mechanical
restraint of the megagametophyte as well as a leachable chemical inhibitor
(most probably ABA). 相似文献
16.
Stomatal sensitivity of six temperate, deciduous tree species to non-hydraulic root-to-shoot signalling of partial soil drying 总被引:2,自引:1,他引:1
The objective of this study were to (1) characterize stomatal response of
six deciduous tree species to non-hydraulic, root-sourced signals of soil
drying, and (2) test whether species sensitivity to non-hydraulic
signalling is allied with their drought avoidance and tolerance profiles.
Saplings were grown with roots divided between two pots. Three treatments
were compared: one half of the root system watered and half droughted (WD),
one half of the root system watered and half severed (WS), both halves
watered (WW). Drying about half of the root system caused non-hydraulic
declines in stomatal conductance (gs) in all species,
with gs of WD plants reduced to from 40% to 60% of WS
controls. Declines in stomatal conductance were closely related to
declining soil matric potential (m) between -0.01 and -0.10 MPa.
Soil m required to cause declines in gs of
WD plants to 80% of WS controls varied from a high of -0.013 to a low of
-0.044 MPa. Stomatal inhibition varied somewhat with leaf age in half of
the species. Leaf osmotic potentials during soil drying were mostly similar
among treatments. Although stomatal sensitivity to the non-hydraulic,
root-sourced signal (characterized as decline in gs
per unit decline in soil ) was not closely correlated with
previously identified lethal leaf water potentials or capacity for osmotic
adjustment, species having the highest stomatal sensitivity also had the
least hydration tolerance. This suggests that stomatal sensitivity to
non-hydraulic root signals may be mechanistically linked to a limited
extent with other characteristics defining relative species drought
tolerance. 相似文献
17.
Dead seeds that expand to nearly twice their normal volume whenfully hydrated are called osmotically distended (OD). Theseseeds swell osmotically in response to a water potential ()gradient created by solutes trapped in the free space betweenthe embryo and the surrounding endosperm or perisperm tissues.The formation of OD seeds in planta is poorly understood, althoughthey often occur in newly harvested muskmelon (Cucumis meloL. Reticulatus group) seed lots. Muskmelon fruit senescenceand seed germinability were contrasted with Armenian cucumber(Cucumis melo L. Flexuosus group) from 50 d after anthesis (DAA)to when seeds were released from the fruit. Fifty DAA muskmelonseeds were incubated in the laboratory for 30 d at 15, 25, and35 °C in factorial combinations of ethanol, acetic acid,and to simulate conditions in decaying fruits. Seed releasefrom Armenian cucumber occurred 20 d earlier than muskmelon.In both years of the study, less than 25% of the muskmelon seedsreleased from the fruit were viable, and 52% and 24% of thedead seeds were OD in year one and two, respectively. All Armeniancucumber seeds were viable or had germinated precociously atseed release. From 50 to 60 DAA, soluble solids in muskmelonfruit pericarp tissue declined from 11·4 to 7·8° Brix, pH declined from 6·2 to 5·1, increasedfrom 1·76 to 1·36 MPa, acetic acidincreased to 61 mol m3;, and ethanol content rose from0·1% to 0·3%. O2 and CO2 partial pressures inthe seed cavities of 40 to 55 DAA fruits were generally 12 and8 kPa, respectively, at midday. All 50 DAA muskmelon seeds incubatedin acetic acid and ethanol germinated, because these chemicalscould not penetrate the perisperm tissue. Incubating 50 DAAmuskmelon seeds in the laboratory for 30 d at 15 or 25 °Chad little effect on germinability, regardless of . Germinationpercentages of muskmelon seeds incubated at 35 °C and 's<1·28MPa were less than 50%. Muskmelon seeds died and became OD insidedecaying fruits in the field because of the combined effectsof low , high temperature, and low O2 partial pressures. Fruitsof muskmelon cultivars bred to resist decomposition and to havehigh sugar content showed decreased reproductive capacity comparedto Armenian cucumber which decomposed more rapidly. Key words: Muskmelon, seed, fruit, germination, senescence, water potential, temperature, oxygen, carbon dioxide 相似文献
18.
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
19.
Bernal-Lugo I; Rodriguez M; Gavilanes-Ruiz M; Hamabata A 《Journal of experimental botany》1999,50(332):311-317
With the aim of determining the level at which ageing exerts its effect on
the expression of -amylase, GA3 regulation
of -amylase production was studied in
isolated aleurone layers from aged wheat seeds. GA3-induced
-amylase activity was lower in the tissue from aged seeds than in
controls. However, the proportion of 35S-methionine
incorporated into -amylase was higher in the aged than in control
tissue. The pattern of -amylase isoforms was resolved by
isoelectric focusing and showed that two isogroups were present with the
activity of the high-pI isogroup being higher in the control than in the
aged lot. These apparently contradictory results may be explained in terms
of differences in isozyme expression. Studies on the expression of
-amylase genes indicated a reduction in the level of high-pI mRNA
in aged tissue. Dose-response curves showed lower GA3-responsiveness of
aleurone layers from aged seeds as compared to the controls. From these
results, it is proposed that the diminished capacity of -amylase
production in aleurone from aged seeds is apparently due to a decrease in
the expression of the high-pI -amylase genes, and this reduction
is associated with a decrease in the response to GA3.Key
words: Seed ageing, wheat aleurone, gibberellic acid,
-amylase isozymes, gene expression.
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20.
Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: I. GERMINATION AT SUBOPTIMAL TEMPERATURE 总被引:2,自引:0,他引:2
DAHAL PEETAMBAR; BRADFORD KENT J.; JONES RICHARD A. 《Journal of experimental botany》1990,41(11):1431-1439
The bases of differences in germination rates (GRg = inverseof time to germination [tg] of percentage g) among three cold/salt-toleranttomato (Lycopersicon esculentum Mill.) accessions (PI 341988,PI 120256, and PI 174263) and one cold/salt-sensitive tomatocultivar (T5) were investigated. The effects of seed priming(6 d imbibition in aerated 1.2 MPa polyethylene glycolsolution at 20 ?C followed by redrying) and of removing theendosperm/testa cap covering the radicle on the temperaturesensitivity of GRg, and the interaction of these treatmentswith genotypes, were also examined. GRg decreased linearly withdecreasing temperature for all genotypes and seed treatments.The minimum or base temperatures for germination (Tb) variedby 1 ?C among the tomato lines, so genotypic differences inGRg were due to differing thermal time requirements for germination.The mean thermal time requirement for germination of T5 seeds was 22% and 19% greater than that of PI 341988 andPI 120256 seeds, respectively, but only 9% greater than thatof PI 174263 seeds. Seed priming did not lower Tb of any genotype,but significantly reduced by 24, 49, 41, and 49% in T5, PI 341988, PI 120256, and PI 174263, respectively,indicating that priming increased the rate at which the seedsprogressed towards germination when T>Tb, but did not lowerthe minimum temperature at which germination could occur. Primingincreased the GRg of T5 seeds to equal or exceed those of control(non-primed) seeds of the cold/salt-tolerant genotypes at anyT>Tb, but the PI lines exhibited an even greater responseto priming. Times to germination within each seed lot were normallydistributed on a logarithmic scale. Priming increased the variancein tg within a seed lot when compared to control seeds. However,the variation in thermal time for germination between the 10thand 90th percentiles of the seed population (T(1090))was relatively unaffected by priming due to the reduction in in primed seeds. Removing the endosperm cap and testa opposite the radicle tip decreased almost 6-fold and and reduced Tb by 5 ?C in T5 and PI 341988,implicating processes in the endosperm/testa as the limitingfactors in germination at suboptimal temperatures. Key words: Lycopersicon esculentum Mill., tomato, genetic variation, seed priming, thermal time, germination rate 相似文献