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1.
Excised 20-d-old sunflower roots (Helianthus annuus L.
cv. Sun-Gro 380) with different Ca2+ status were
used to study the effects of root Ca2+ status and
abscisic acid (ABA) on the exudation rate (Jv), the
hydraulic conductivity of the root (Lpr), the flux of
exuded Ca2+ (JCa, and the
gradient of osmotic pressure between the xylem and the external medium.
Jv and Lpr increased in direct
proportion to the Ca2+ status of the root. Addition
of ABA (4 M) at the onset of exudation in the
external medium made Jv and Lpr
rise, and this effect also increased with the Ca2+
status. The effects of HgCl2 and its interaction with ABA on water
transport in the root were also studied. Addition of HgCl2 (1 M) 2 h after the onset of exudation in the external
medium quickly inhibited Jv, independently of the
presence of ABA in the root medium. The results recorded here point to the
involvement of ABA and Ca2+ in the regulation of
root water flow, as well as the existence of aquaporins in the cell
membranes of sunflower roots. 相似文献
2.
Mechanisms of Inhibition of Water Movement in Anaerobically Treated Roots of Zea mays L. 总被引:2,自引:0,他引:2
Changes in water flux (Jv) across detopped, 7-d-old, maize rootswere characterized during the initial 24 h of being made anoxicby exposure to an anaerobic nutrient solution. Suction (50 kPa)was applied to the xylem and samples of the xylem sap were collectedat intervals and the osmolality and ionic content were measured. Values of Jv through anoxic roots fell below those of aerobiccontrols 1 h after the equilibrium oxygen partial pressure inthe bathing medium dropped below 20 kPa (air = 20.6 kPa). Thereduction in Jv was due primarily to a nullification of thediurnal rhythm in hydraulic conductivity (Lp) that was measuredin aerobic roots. However, about one-quarter of the reductionin Jv could be accounted for by a smaller osmotic componentof the driving force () on water movement. The significance of changes in Jv in anoxic roots is discussedin terms of the reliability of estimates of Lp, the reflectioncoefficient () and . Key words: Anaerobiosis, hydraulic conductivity, osmotic potential, water 相似文献
3.
Mechanisms Controlling Changes in Water Movement Through the Roots of Helianthus annuus L. During Continuous Exposure to Oxygen Deficiency 总被引:2,自引:0,他引:2
The effects of oxygen deficiency on suction-induced water flux(Jv) through detached roots of hydroponically-grown sunflowerwere investigated over a period of up to 6 d. Jv was reducedby the time the oxygen partial pressure in the solution, spargedwith oxygen-free N2, had fallen below 2 kPa (air 20.6kPa). This reduction resulted from a decline in the hydraulicconductivity of the radial pathway for water movement (Lp),although up to 46% of the decline was attributable to changesin the osmotic component of the driving force (). Lp (mm s1MPa1), for aerobic roots was 2.23 ? 105 and foranaerobic roots during the initial 16 h, 1.21 ? 105. At 22 h after the onset of anaerobic treatments, Jv and Lp increased,with Lp values becoming 3 times greater than those measuredbetween 4 h and 16 h of treatment and 1.4 times greater thanin aerated roots. However, Lp increased a further 15-fold whenroots were killed by immersion in boiling water for 2 min. Duringand up to 6 d of anaerobic treatment, some roots retained Lpvalues similar to those at 22 h, while others displayed characteristicstypical of dead roots. At no time was there any indication ofreduced axial conductivity due to xylem vessel blockage. The results are discussed in terms of possible energy sourcesfor the maintenance of root integrity and their importance toplant survival during long periods of severe oxygen shortage. Key words: Anaerobiosis, oxygen deficiency, hydraulic conductivity, osmotic potential, water 相似文献
4.
Previous research suggested that the hydraulic properties of root systems
of intact plants could be described by two parameters: the hydraulic
conductivity (Lpr) or the slope of the
flow-density/water potential gradient relationship, and the offset or
minimum water potential gradient required to induce flow. In this study
Lpr and offset were correlated with anatomical
features of the root radial path in plants with contrasting root anatomy.
Two woody and three herbaceous species were examined which exhibit a range
of root anatomical features: Asparagus densiflorus
(Kunth) Jessop (asparagus), Dendrobium superbum Rchb.
f. (dendrobium), Glycine max (L.) Merr. (soybean),
Prunus persica (L.) Batsch. (peach), Citrus
aurantium L. (sour orange). Lpr varied
about 8-fold, and the offset varied about 6-fold among the five species.
Lpr was inversely related to root diameter
(r20.39) and cortex width
(r20.55), suggesting that species with thinner
roots or roots with a thin cortex had the highest Lpr.
Further observations suggested that the cortex width was a stronger
determinant of Lpr than root diameter. However, the
offset was not correlated with root diameter, stele diameter or cortex
width, but was >2-fold higher in species having an exodermis in the
root radial path (sour orange, asparagus, and dendrobium) compared to those
lacking an exodermis (peach and soybean). The data on root
Lr obtained were similar to those given in the
literature for both intact plants and excised roots which have been
measured with different techniques. It is concluded that
Lpr and offset, which describe the flow-water
potential relationship for intact root systems, are related to differences
in the root cortex; specifically, its thickness and the presence/absence of
a suberized exodermis. Hence, these anatomical differences may, in part,
cause the variability in root hydralic properties that exists among plant
species. 相似文献
5.
The effect of rhizosphere dissolved inorganic carbon on gas exchange characteristics and growth rates of tomato seedlings 总被引:2,自引:0,他引:2
The possibility that an enhanced supply of dissolved inorganic carbon
(DIC=CO2+HCO3-) to the root solution could increase
the growth of Lycopersicon esculentum (L.) Mill. cv.
F144 was investigated under both saline and non-saline root medium
conditions. Tomato seedlings were grown in hydroponic culture with and
without NaCl and the root solution was aerated with CO2 concentrations in
the range between 0 and 5000 mol
mol-1. The biomass of both control and
salinity-stressed plants grown at high temperatures (daily maximum of
37C) and an irradiance of 1500 mol m-2
s-1 was increased by up to 200% by enriched
rhizosphere DIC. The growth rates of plants grown with irradiances of less
than 100 mol m-2 s-1
were increased by elevated rhizosphere DIC concentrations only when grown
at high shoot temperatures (35C) or with
salinity 28°C). At high light intensities, the photosynthetic rate,
the CO2 and light-saturated photosynthetic rate (jmax)
and the stomatal conductance of plants grown at high light intensity were
lower in plants supplied with enriched compared to ambient DIC. This was
interpreted as 'down-regulation' of the photosynthetic system in plants
supplied with elevated DIC. Labelled organic carbon in the xylem sap
derived from root DI14C incorporation was found to
be sufficient to deliver carbon to the shoot at rates equivalent to 1% and
10% of the photosynthetic rate of the plants supplied with ambient- and
enriched-DIC, respectively. It was concluded that organic carbon derived
from DIC incorporation and translocated in the xylem from the root to the
shoot may provide a source of carbon for the shoots, especially under
conditions where low stomatal conductance may be advantageous, such as
salinity stress, high shoot temperatures and high light
intensities. 相似文献
6.
The temperature dependence of the stimulation of photosynthesis by elevated carbon dioxide in wheat and barley 总被引:9,自引:3,他引:6
The temperature dependencies of the solubility of carbon dioxide and oxygen
in water and the temperature dependency of the kinetic characteristics of
the ribulose-1,5 bisphosphate carboxylase/oxygenase (Rubisco) enzyme result
in the short-term stimulation of photosynthesis with a doubling of carbon
dioxide from 350 to 700 mol
mol-1 usually decreasing from about 90% at 30C to about 25% at 10C
at high photon flux. In field-grown wheat and barley, the expected values
at 30°C were observed, but also values as high as 60% at
10°C. The much larger than expected stimulation at cool
temperatures in these species also occurred in plants grown at
15°C, but not at 23°C in controlled environment chambers.
Gas exchange analysis indicated that an unusually high diffusive limitation
was not an explanation for the large response. Assessment of the apparent
in vivo specificity of Rubisco by determining the
carbon dioxide concentration at which carboxylation equalled carbon dioxide
release from oxygenation, indicated that growth at low temperatures altered
the apparent enzyme specificity in these species compared to these species
grown at the warmer temperature. Inserting the observed specificities into
a biochemical model of photosynthesis indicated that altered Rubisco
specificity was consistent with the observed rates of assimilation. Whether
altered apparent Rubisco specificity is caused by altered stoichiometry of
photorespiration or an actual change in enzyme specificity, the results
indicate that the temperature dependence of the stimulation of
photosynthesis by elevated carbon dioxide may vary greatly with species and
with prior exposure to low temperature.Keywords:
Barley, carbon dioxide, photosynthesis, temperature, wheat.
相似文献
7.
Tolerance to low temperature and paraquat-mediated oxidative stress in two maize genotypes 总被引:9,自引:0,他引:9
Iannelli M; van Breusegem F; van Montagu M; Inze D; Massacci A 《Journal of experimental botany》1999,50(333):523-532
Tolerance to low temperature and paraquat-mediated oxidative stress was
investigated in two Zea mays genotypes, VA36 and A619,
grown at 25/22 C and 16/14 C for 50 d after germination. VA36, the tolerant
genotype, showed an enhanced resistance to paraquat as compared to A619,
the sensitive genotype, when grown at low temperature. In VA36, superoxide
dismutase and ascorbate peroxidase activities increased during growth at
both 25/22 °C or 16/14 °C. In A619, superoxide dismutase
activity was similar in plants grown at both 16/14 °C or 25/22
°C. Ascorbate peroxidase activity was always significantly lower in
plants grown at low temperature than in plants grown at 25/22 °C.
The total ascorbate peroxidase activity was correlated with the cytosolic
ascorbate peroxidase protein content in all but A619 plants grown at low
temperature for 25 d. The isozyme pattern of SOD showed a higher abundance
of MnSOD in VA36 than in A619 and of FeSOD in A619 compared to VA36. Growth
at low temperature enhanced resistance to paraquat infiltration more in
VA36 than in A619. SOD and APX activities were generally higher and more
stable with the increase of paraquat concentration in VA36 than in A619.
Damage indicated by Fv/Fm and ion
leakage after paraquat infiltration were generally higher in plants grown
at 25/22 °C than at 16/14 °C and higher in A619 than in
VA36. However, no causal link is proved between the extent of damage and
the increase of SOD and APX activities alone. It is suggested that
tolerance to oxidative stress requires an integrated enhancement of the
antioxidant system. 相似文献
8.
Hydraulic and osmotic properties of oak roots 总被引:3,自引:1,他引:2
Hydraulic and osmotic properties of root systems of 2.58-months-oldoak seedlings (Quercus robur and Q. petraea) were measured usingthe root pressure probe. Root pressures of excised roots rangedbetween 0.05 and 0.15 MPa which was similar to values obtainedfor herbaceous species. Root hydraulic conductivity (Lpr; perunit of root surface area) was much larger in the presence ofhydrostatic than in the presence of osmotic pressure differencesdriving water flow across the roots. Differences were as largeas a factor of 20 to 470. Roots of the young seedlings of Q.robur grew more rapidly than those of Q. petraea and had a hydraulicconductivity which was substantially higher. Nitrogen nutritionaffected root growth of Q. robur more than that of Q. petraea,but did not affect root Lpr of either species. For Q. robur,Lpr decreased with root age (size) which is interpreted by aneffect of suberization during the development of fine roots.Root hydraulic conductance remained constant for both species.For Q. robur, this was due to the fact that the overall decreasein Lpr was compensated for by an increase in root surface area.Root reflection coefficients (sr) were low and ranged betweensr=0.1 and 0.5 for solutes for which cell membranes exhibitreflection coefficients of virtually unity (salts, sugars etc.).Solute permeability was small and was usually not measurablewith the technique. When root systems were attached to the rootpressure probe for longer periods of time (up to 10d), solutepermeability increased due to ageing effects which, however,did not cause a general leakiness of the roots as Lpr decreased.Hence, values were only used from measurements taken duringthe first day. Transport properties of oak roots are comparedwith those recently obtained for spruce (Rdinger et al., 1994).They are discussed in terms of a composite transport model ofthe root which explains low root sr at low solute permeabilityand reasonable rootLpr The model predicts differences betweenosmotic and hydraulic water flow and differences in the transportproperties of roots of herbs and trees as found. Key words: Composite transport, hydraulic conductivity, nitrogen nutrition, Quercus, reflection coefficient, root transport, water relations 相似文献
9.
Even moderate chilling temperatures may cause important modifications in
assimilate movement in maize seedlings from the shoot to the roots, but
there is no information on long-distance transport of assimilates in plants
subjected to vertical gradients of moderately low temperatures in the root
zone. Seedlings of a chilling-tolerant (KW1074) and a chilling-sensitive
inbred line (CM109) of maize were grown in a system that allowed the
maintenance of temperature gradients between the topsoil (0-10 cm) and the
subsoil (10-50 cm). After pregrowth at 24C
until the third-leaf stage, plants were subjected to chilling-stress
regimes for 6 d (17/17/17C,
17/17/12°C, 12/12/12°C, 12/12/17°C,
air/topsoil/subsoil). The time taken for the assimilates to enter the
phloem from the second leaf increased at low temperatures for both lines,
but to a much greater extent in CM109. Although mainly influenced by air
and topsoil temperature, low temperature in the subsoil also affected this
trait in CM109. The speed of assimilate transport between the second leaf
and the mesocotyl in KW1074 was strongly reduced by cool temperatures in
the shoot and topsoil as well as by 12°C in the subsoil in CM109,
because the latter line had a larger portion of its root system in the
subsoil as compared to KW1074. The portion of assimilates allocated to the
root decreased at low temperatures in both lines, but to a greater extent
in CM109, and was controlled mostly by the subsoil temperature. After
rewarming, values of all measured parameters of assimilate transport
returned to near pregrowth levels within a few days.Keywords:
Assimilate transport, low temperature stress, root growth,
vertical soil temperature gradients, Zea mays L.
相似文献
10.
11.
Stage of development is an important determinant in the effect of nitrate on photoassimilate (13C) partitioning in chicory (Cichorium intybus) 总被引:1,自引:0,他引:1
Amziane R.; Delens E.; Noctor G.; Morot-Gaudry J-F.; Limami M.A. 《Journal of experimental botany》1997,48(1):25-33
The effect of nitrogen supply to chicory plants on carbon partitioningbetween shoot, root and tuberized root was studied at differentstages of vegetative growth, using long-term 13CO2 labelling-chaseexperiments. This approach was complemented by measurement ofstorage carbohydrates and activities of enzymes involved inroot sucrose metabolism (sucrose-sucrose fructosyl transferase(SST), sucrose synthase, invertase). In both young and matureplants, low resulted in a 3035% decrease in 13C assimilation. However, the partitioningof 13C between shoot and root was affected differently at differentstages of development. In young plants, in which carbohydrateswere being used for structural root and shoot growth, neither13C shoot/13C root ratio nor root activities of the above enzymeswere modified by supply. In contrast, in mature plants storing large amounts of carbohydratesas fructan in the tuberized root, low caused the ratio to decrease from 0.6 to 0.2, despiteunchanged net flux of 13C from shoot to root. The extractableactivity of SST was elevated in mature plants, compared to youngplants, at both low and high , consistent with its role in fructan synthesis. However, matureplants grown at low exhibited SST activity double that of plants grown at high . From these results, it is concluded that the observeddecrease in shoot/root dry weight ratio at low supply is caused by increased utilization of carbohydratesfor storage due to elevated root SST activity. Key words: Chicory, nitrate, 13C, shoot/root ratio, fructans, SST 相似文献
12.
A controlled environment chamber for whole plants is described in which
vapour pressure deficit (VPD) and temperature can be controlled
independently. Plant responses to changes in VPD at constant temperature
were measured in terms of leaf extension and plant transpiration rates.
Manipulation of VPD independently of temperature was shown to be capable of
altering the leaf extension rates of the C4 grass Miscanthus x
giganteus grown in hydroponics. The effects of VPD on leaf
extension are attributed to changes in transpiration rate and hence leaf
water status. It was found that, at a temperature of 20C, the influence of a fixed change in VPD was
proportionally less than those observed at temperatures which are close to
the threshold for growth (between 6 and 10C). These responses are discussed in relation to our
current understanding of the mechanisms of cell growth. The fact that the
VPD effects on leaf expansion rates were largely transient suggest that
simple models driven by temperature alone are adequate to predict leaf
expansion within the temperature range 6-20°C, for this genotype of
Miscanthus, in the field.Key
words: Leaf growth, Miscanthus x giganteus,
temperature, vapour pressure deficit, C4 plants.
相似文献
13.
The changes in photosynthetic activity and composition of pigments induced
by changes in temperature were examined in the third leaf of three
chilling-tolerant and three chilling-sensitive genotypes of maize
(Zea mays L.). The plants were grown under a
controlled environment at a photon flux density of 550 mol m-2
s-1, a 12 h photoperiod and at a suboptimal
temperature of 14/12 C (day/night) until the
full expansion of the third leaf. After this treatment, the
chilling-tolerant genotypes, when compared with the sensitive ones,
displayed a higher photosynthetic activity, a higher content of chlorophyll
(Chl) a+b, a higher Chl
a/b ratio, a larger total carotenoid pool size as well
as a different carotenoid composition. When temperature was subsequently
increased to 24/22 C for 3 d the composition
of the pigments changed, but the chilling-sensitive genotypes, while
adjusting their lower Chl a/b ratio and their
different carotenoid composition, were unable to adjust their lower content
of chlorophyll, their smaller total carotenoid pool size or their lower
photosynthetic performance. Moreover, while the chilling-tolerant genotypes
converted the most part of zeaxanthin to violaxanthin in the xanthophyll
cycle, the chilling-sensitive genotypes retained high amounts of
zeaxanthin. The changes in pigment composition that occurred over the 3 d
at 24/22 °C were largely conserved when the plants were returned to
14/12 °C, but photosynthetic activity decreased and zeaxanthin
accumulated again. The results suggest that the capability of the
chilling-tolerant genotypes, when compared with the sensitive ones, to
retain high amounts of pigments and to form a competent photosynthetic
apparatus at low temperature is the basis for their more vigorous growth in
cool climates. 相似文献
14.
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
15.
Chlorophyll fluorescence as a selection tool for cold tolerance of photosynthesis in maize (Zea mays L.) 总被引:10,自引:0,他引:10
Fracheboud Y; Haldimann P; Leipner J; Stamp P 《Journal of experimental botany》1999,50(338):1533-1540
The possibility of using quenching analysis of chlorophyll
a fluorescence as a selection tool for improving the
cold tolerance of maize was investigated in six genotypes differing greatly
in the ability to develop a competent photosynthetic apparatus at low
temperature. Upon gradual cooling measurements of the quantum yield of
electron transport (PSII) indicated that leaves of tolerant
genotypes, that developed at suboptimal temperature (15C), maintained higher rates of electron transport
than leaves of sensitive genotypes. This difference was largely due to the
ability of the tolerant plants to keep higher efficiency of excitation
energy capture by open photosystem II reaction centres (F'v/F'm). The
absence of genotypic differences in leaves that developed at optimal
temperature indicates that the trait is not expressed constitutively, but
relies on adaptation mechanisms. Furthermore, the genotypic difference was
not expressed under increasing illumination at 15C and 25°C suggesting that the trait is also
low-temperature-specific and is not expressed solely in response to
increasing excess light energy. Applying the method to flint and dent
breeding population led to a substantial increase (up to 31%) in the
photosynthetic capacity of hybrids between selected F3 inbreeding families
grown at suboptimal temperature, demonstrating that the method is an
efficient selection tool for improving the cold tolerance of maize through
breeding. 相似文献
16.
MACDUFF J. H.; GORDON A. J.; RYLE G. J. A.; POWELL C. E. 《Journal of experimental botany》1989,40(5):517-526
Established, nodulated white clover plants (Trifolium repensL. cv. Blanca) were transferred to eight plant culture unitsof a system of flowing solution culture. Solution temperatureswere 5, 11, 17, and 25 ?C (two units per temperature), withshoot temperature of 25/15 ?C day/night and light regime commonto all plants. After 7 d, was supplied at 10 mmol m3 to one of each pair of culture units and thenet uptake of was monitored over 14 d. The remaining four culture units served as controls in which plantswere entirely dependent on N2 fixation, as estimated by sequentialharvesting and the change in the amount of N in plants. Totalfresh and dry weights increased exponentially with time andwith increasing root temperature, between 525 ?C in nitrateplants and 517 ?C in control plants, respectively, byfactors of 2.9 and 1.8. Nodule dry weight of nitrate plantsshowed little increase after 6 d compared with control plants.Dry weight shoot: root ratios increased with time in all treatmentsexcept 5 ?C control plants. Total net uptake of over 13 d was 0.41, 4.27, 11.92, and 12.77 mmol plant-1, respectively,at 5, 11, 17, and 25 ?C. At all temperatures except 5 ?C, plantsaccumulated high concentrations of (1040 mol m3) in leaflets and roots, within 2 or 3 days ofsupplying . Daily mean unit absorption rates of increased 12-fold with increasing temperature between 5 and 25 ?C, and showed little change with time at 5,17, and 25 ?C. The total N2 fixed by nitrate plants over 14d increased 5-fold with temperature between 5 and 17 ?C, butwas always less than the amount fixed by control plants. Thepercentage contributed by N2 fixation to total N acquisitionby nitrate plants over 14 d decreased with increasing temperature,from 77% at 5 ?C to 11 % at 25 ?C. Mean daily rates of N2 fixationper unit dry weight of nodule were lower in nitrate plants thanin control plants throughout treatment at 5 ?C and 25 ?C, butat 11 ?C and 17 ?C the rates for nitrate plants increased progressivelywith time and exceeded the rates for control plants after 8d. In both nitrate and control plants the effect of temperatureon N2 fixation per nodule dry weight was proportionately lessthan that on unit absorption rate of . The results are discussed in terms of the overall regulation ofN accumulation by white clover and the adaptive significanceof differences in the sensitivities of uptake and N2 fixation to root temperature. Key words: Trifolium repens, white clover, root temperature, N2 fixation, nitrate uptake 相似文献
17.
Switching off the heater: influence of ambient temperature on thermoregulation by eastern skunk cabbage Symplocarpus foetidus 总被引:1,自引:0,他引:1
The protogynous inflorescences of eastern skunk cabbage,
Symplocarpus foetidus, are thermogenic and regulate
spadix temperature (Ts) well above ambient temperature
(Ta). Continuous records of oxygen consumption, carbon
dioxide production, and temperatures of plants were made at a field site in
Canada. At Ta between 3-24C, Ts ranged between
16-26C, and the warmest inflorescences were
those in the receptive female or early pollen-bearing stages. Respiratory
rates of the 2-g spadices increased with declining Ta,
and reached a maximum of 0.54 mol
O2s-1 (0.73 ml min-1),
equivalent to 0.26 W of heat production. At Ta below
3°C, several inflorescences failed to maintain high
Ts and abruptly switched Ts to
near freezing. Some froze when Ta dropped to about
-10°C. Those that did not freeze could quickly switch to the warm
state if Ta rose above about 3°C. Switching
was related to the balance between heat production and heat loss that
tended to produce stable equilibria at either high or low
Ts. Switching between warm and cool states resulted in
a bimodal distribution of Ts in the field. A
respiratory quotient of 1.0 showed that carbohydrate was the substrate for
thermogenesis, and bomb calorimetry of florets confirmed that energy was
imported from the root. Only 11 invertebrates, including only one flying
insect, were found in 195 inflorescences, suggesting that heat production
and temperature regulation are not closely associated with
cross-pollination. 相似文献
18.
Influence of UV-B radiation and Cd2+ on chlorophyll fluorescence, growth and nutrient content in Brassica napus 总被引:8,自引:0,他引:8
The possible interaction of two stresses, UV-B radiation and cadmium,
applied simultaneously, was investigated in Brassica
napus L. cv. Paroll with respect of chlorophyll fluorescence,
growth and uptake of selected elements. Plants were grown in nutrient
solution containing CdCl2, (0, 0.5, 2 or 5 M)
and irradiated with photosynthetically active radiation
(PAR, 400-700 nm, 800 mol m-2
s-1) with or without supplemental ultraviolet-B
radiation (UV-B, 280-320 nm, 15 kJ m-2
d-1, weighted irradiance). After 14 d of treatment,
the most pronounced effects were found at 2 and 5 M CdCl2 with and
without supplemental UV-B radiation. Exposure to cadmium significantly
increased the amount of Cd in both roots and shoots. In addition, increases
occurred in the concentrations of Fe, Zn, Cu, and P in roots, while K was
reduced. In shoots the S content rose significantly both in the presence
and absence of UV-B radiation, while significant increases in Mg, Ca, P,
Cu, and K occurred only in plants exposed to Cd and UV-B radiation.
Manganese decreased significantly under the combined exposure treatment.
The rise in S content may have been due to stimulated glutathione and
phytochelatin synthesis. Cadmium exposure significantly decreased root dry
weight, leaf area, total chlorophyll content, carotenoid content, and the
photochemical quantum yield of photosynthesis. As an estimation of energy
dissipation processes in photosynthesis, non-photochemical quenching
(qNPQ) was measured using a pulse amplitude modulated
fluorometer. The qNPQ increased with increasing Cd,
while the combination of cadmium and UV-B reduced the
qNPQ compared to that in plants exposed only to
cadmium or UV-B radiation. The chlorophyll a:b ratio
showed a reduction with UV-B at no or low Cd concentrations (0 M,
0.5 M CdCl2), but not at the higher Cd concentrations used (2
M, 5 M CdCl2). Thus in some instances there appeared to
be a UV-B and Cd interaction, while in other plants response could be
attributed to either treatment alone.Keywords:
Brassica napus, cadmium, ultraviolet-B
radiation.
相似文献
19.
Characterization of the elicitor-induced biosynthesis and secretion of genistein from roots of Lupinus luteus L 总被引:2,自引:0,他引:2
Genistein is a multi-functional isoflavonoid naturally secreted from roots
of hydroponically grown legume plants. Roots of hydroponically cultivated
yellow lupin (Lupinus luteus L.) plants, transferred
into water secreted minor amounts of genistein (about 5 g g-1 fr. wt.). Secretion of
genistein from L. luteus roots (rhizosecretion) was
stimulated dramatically to over 100 g
g-1 root fresh weight by soluble chitosan, salicylic
acid (SA) and potassium cyanide (KCN) supplied at 0.12% (w/v), 800
M and 400 M, respectively. Other identified elicitors
caused a smaller induction of genistein rhizosecretion. Increased levels of
genistein in root exudates corresponded to greater amounts of genistein in
root tissue. Elicitor-induced rhizosecretion of genistein was based on
de novo synthesis and was inhibited by glyphosate and
other less specific metabolic inhibitors. Except for NaF:AICI3, all tested
elicitors of genistein rhizosecretion produced a distinct bell-shaped
dose-response curve. Most of the elicitor-induced rhizosecretion of
genistein occurred during the first day, followed by a gradual decline.
Further addition of elicitor treatments had little effect of genistein
rhizosecretion, indicating that the induction of genistein rhizosecretion
by the identified elicitors is a once only event.Keywords:
Genistein, isoflavonoids, Lupinus luteus,
elicitation, exudation.
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