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991.
It is commonly known that calcium promotes NO3
- uptake in many crop species. However, calcium enhancement of NH4
+ uptake by plants has received little attention. This study aimed to evaluate the effect of Ca supplements on NH4
+ uptake and plant growth in solution cultured rice. Supplemental Ca applied at vegetative and reproductive phases of plant
ontogeny tended to stimulate NH4
+ absorption, and accordingly resulted in a better straw and grain yield. However, excessively supplied Ca (400 ppm) was detrimental
to plant growth. Increases in straw and grain yield observed at Ca levels up to 300 ppm were linked to the Ca-enhanced activities
of glutamine synthetase (GS), glutamate synthase (GOGAT), and ribulose 1, 5-bisphosphate carboxylase/oxygenase (Rubisco). 相似文献
992.
Effect of zeatin on the growth and indolyl-3-acetic acid and abscisic acid levels in maize roots 总被引:1,自引:0,他引:1
Elongation, indolyl-3-acetic acid (IAA) and abscisic acid (ABA) levels, – gas chromatography-mass spectrometry quantification –, in the elongating zone were analysed for maize ( Zea mays L., Cv. LG11) roots immersed in buffer solution with or without zeatin (Z). The effect of Z depends on the initial extension rate of roots. The slower growing roots are more strongly inhibited by Z (10−7 −10−5 M ) and they show a greater increase in IAA and ABA content. When compared to the rapidly growing roots, the larger reactivity of the 'slow'ones cannot be attributed to a higher Z uptake as shown when using [14 C]-Z. It is suggested that Z could regulate root elongation by acting on the IAA and/or ABA level. The comparative action of these two hormones is discussed. 相似文献
993.
The characteristics of Cl– transport in isolated tonoplast vesicles from red-beet (Beta vulgaris L.) storage tissue have been investigated using the Cl–-sensitive fluorescent probe, 6-methoxy-1-(3-sulfonatopropyl)-quinolinium (SPQ). The imposition of (inside) positive diffusion potentials, generated with K+ and valinomycin, increased the initial rate of Cl– transport, demonstrating that Cl– could be electrically driven into the vesicles. Chloride influx was unaffected by SO
4
2-
, but was competitively blocked by NO
3
–
, indicating that both Cl– and NO
3
–
may be transported by the same porter. In some preparations, increases in free-Ca2+ concentration from 10–8 to 10–5 mol·dm–3 caused a significant decrease in Cl– influx, which may indicate that cytosolic Ca2+ concentration has a role in controlling Cl– fluxes at the tonoplast. However, this effect was only seen in about 50% of membrane preparations and some doubt remains over its physiological significance. A range of compounds known to block anion transport in other systems was tested, and some partially blocked Cl– transport. However, many of these inhibitors interfered with SPQ fluorescence and so only irreversible effects could be tested. The results are discussed in the context of recent advances made using the patch-clamp technique on isolated vacuoles.Abbreviations and Symbols BTP
1,3-bis[tris(hydroxymethyl)-methylamino]propane
- DTT
dithiothreitol
- EDTA
ethylenediaminetetraacetic acid
-
membrane potential
- pH
pH gradient
- SPQ
6-methoxy-1-(3-sulfonatopropyl)quinolinium
- Tricine
N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl] glycine 相似文献
994.
Nodules of cowpea plants (Vigna unguiculata (L.) Walp. cv. Vita 3 :Bradyrhizobium CB756) cultured for periods of 23 d with their root systems maintained in atmospheres containing a range of partial pressures
of O2 (pO2; 1–80%, v/v, in N2) formed and exported ureides (allantoin and allantoic acid) as the major products of fixation at all pO2 tested. In sub-ambient pO2 (1 and 2.5%) nodules contained specific activities of uricase (urate: O2 oxidoreductase; EC 1.7.3.3) and allantoinase (allantoin hydrolyase; EC 3.5.2.5) as much as sevenfold higher than in those
from air. On a cell basis, uninfected cells in nodules from 1% O2 contained around five times the level of uricase. Except for NAD: glutamate synthase (EC 1.4.1.14), which was reduced in
sub-ambient O2, the activities of other enzymes of ureide synthesis were relatively unaffected by pO2. Short-term effects of pO2 on assimilation of fixed nitrogen were measured in nodules of air-grown plants exposed to subambient pO2 (1, 2.5 or 5%, v/v in N2) and15N2. Despite a fall in total15N2 fixation, ureide synthesis and export was maintained at a high level except in 1% O2 where formation was halved. The data indicate that in addition to the structural and diffusional adaptations of cowpea nodules
which allow the balance between O2 supply and demand to be maintained over a wide range of pO2, nodules also show evidence of biochemical adaptations which maintain and enhance normal pathways for the assimilation of
fixed nitrogen.
This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian Development Assistance
Bureau postgraduate fellowship (to F.D.D.). 相似文献
995.
Cortical microtubules (MTs) in protoplasts prepared from tobacco (Nicotiana tabacum L.) BY-2 cells were found to be sensitive to cold. However, as the protoplasts regenerated cell walls they became resistant
to cold, indicating that the cell wall stabilizes cortical MTs against the effects of cold. Since poly-l-lysine was found to stabilize MTs in protoplasts, we examined extensin, an important polycationic component of the cell wall,
and found it also to be effective in stabilizing the MTs of protoplasts. Both extensin isolated from culture filtrates of
tobacco BY-2 cells and extensin isolated in a similar way from cultures of tobacco XD-6S cells rendered the cortical MTs in
protoplasts resistant to cold. Extensin at 0.1 mg·ml−1 was as effective as the cell wall in this respect. It is probable that extensin in the cell wall plays an important role
in stabilizing cortical MTs in tobacco BY-2 cells. 相似文献
996.
997.
Estimation of the effect of photoinhibition on the carbon gain in leaves of a willow canopy 总被引:21,自引:0,他引:21
The occurrence of photoinhibition of photosynthesis in leaves of a willow canopy was examined by measuring the chlorophyll-a fluorescence ratio of F
V/F
M (FM is the maximum fluorescence level of the induction curve, and FV is the variable fluorescence, F
V=F
M–F
0, where F0 is the minimal fluorescence). The majority of the leaves situated on the upper parts of peripheral shoots showed an afternoon inhibition of this ratio on clear days. This was the consequence of both a decrease in F
M and a rise in F
O. In the same leaves the diurnal variation in intercepted photosynthetic photon flux density (PPFD) was monitored using leaf-mounted sensors. Using the multivariate method, partial least squares in latent variables, it is shown that the dose of PPFD, integrated and linearly weighted over the last 6-h period, best predicts photoinhibition. Photoinhibition occurred even among leaves that did not intercept PPFDs above 1000 mol·m–2·s–1. Exposure of leaves to a standard photoinhibitory treatment demonstrated that the depression in the F
V/F
M ratio was paralleled by an equal depression in the maximal quantum yield of CO2 uptake and a nearly equal depression in the rate of bending (convexity) of the light-response curve of CO2 uptake. As a result, the rate of net photosynthesis is depressed over the whole natural range of PPFD. By simulating the daily course in the rate of net photosynthesis, it is estimated that in the order of one-tenth of the potential carbon gain of peripheral willow shoots is lost on clear days as a result of photoinhibition. This applies to conditions of optimal temperatures. Photoinhibition is even more pronounced at air temperatures below 23° C, as judged from measurements of the FV/FM ratio on clear days: the afternoon inhibition of this ratio increased in a curvilinear manner from 15% to 25% with a temperature decrease from 23° to 14° C.Abbreviations and Symbols FO
minimum fluorescence
- FV
variable fluorescence
- FM
maximum fluorescence
- PLS
partial least squares in latent variables
- PPFD
photosynthetic photon flux density
- VPD
water vapour-pressure deficit
This study was supported by the Swedish Natural Science Research Council. We are indebted to Dr. Jerry Leverenz (Department of Plant Physiology, University of Umeå, Sweden) for guidance with the modelling of the photosynthesis data. 相似文献
998.
-Oxidation enzymes were detected both in the mitochondria and microbodies of Arum maculatum L. spadices and Brassica napus L. seeds. It is apparent that the mitochondrial membrane barrier, which remains intact after sucrose-density-gradient centrifugation, prevents rapid access of acyl-GoA substrates to matrix oxidation tes. Thus intact mitochondria showed little -oxidation enzyme activity. Rupturing of the mitochondrial membrane allowed rapid access of acyl CoAs to matrix sites. Consequently, in ruptured mitochondria, high -oxidation enzyme activities were measured.C. Masterson thanks the Science and Engineering Research Council for the award of a postgraduate student maintenance grant. D.R. Thomas and C. Wood thank their relatives for continuing financial support. The authors also thank West Cumberland Farmers Ltd., Hexham, UK for their gift of oilseed rape seeds. 相似文献
999.
Gravitropic stimulation of maize (Zea mays L.) seedlings resulted in a continuous curvature of the coleoptiles in a direction opposing the vector of gravity when the seedlings were rotated on a horizontal clinostat. The orientation of this response, however, was reversed when the gravitropic stimulation was preceeded by symmetric preirradiation with blue light (12.7 mol photons·m–2). The fluence-response curve of this blue light exhibited a lower threshold at 0.5 mol·m–2, and could be separated into two parts: fluences exceeding 5 mol·m–2 reversed the direction of the gravitropic response, whereas for a range between the threshold and 4 mol·m–2 a split population was obtained. In all cases a very strong curvature resulted either in the direction of gravity or in the opposite orientation. A minor fraction of seedlings, however, curved towards the caryopsis. Furthermore, the capacity of blue light to reverse the direction of the gravitropic response disappeared with the duration of gravitropic stimulation and it depended on the delay time between both stimulations. Thistonic blue-light influence appears to be transient, which is in contrast to the stability observed fortropistic blue-light effects.This work was supported by the Deutsche Forschungsgemeinschaft. 相似文献
1000.
Determination of the pressure in the water-conducting vessels of intactNicotiana rustica L. plants showed that the pressure probe technique gave less-negative values than the Scholander-bomb method. Even though
absolute values of the order of −0.1 MPa could be directly recorded in the xylem by means of the pressure probe, pressures
between zero and atmospheric were also frequently found. The data obtained by the pressure probe for excised leaves showed
that the Scholander bomb apparently did not read the actual tension in the xylem vessles ofNicotiana plants. The possibility that the pressure probe gave false readings was excluded by several experimental controls. In addition,
cavitation and leaks either during the insertion of the microcapillary of the pressure probe, or else during the measurements
were easily recognized when they occurred because of the sudden increase of the absolute xylem tension to that of water vapour
or to atmospheric, respectively. Tension values of the same order could also be measured by means of the pressure probe in
the xylem vessels of pieces of stem cut from leaves and roots under water and clamped at both ends. The magnitude of the absolute
tension depended on the osmolarity of the bathing solution which was adjusted by addition of appropriate concentrations of
polyethylene glycol. Partial and uniform pressurisation of plant tissues or organs, or of entire plants (by means of the Scholander
bomb or of a hyperbaric chamber, respectively) and simultaneous recording of the xylem tension using the pressure probe showed
that a 1∶1 response in xylem pressure only occurred under a few circumstances. A 1∶1 response required that the xylem vessels
were in direct contact with an external water reservoir and/or that the tissue was (pre-)infiltrated with water. Corresponding
pressure-probe measurements in isolated vascular bundles ofPlantago major L. orP. lanceolata L. plants attached to a Hepp-type osmometer indicated that the magnitude of the tension in the xylem vessels was determined
by the external osmotic pressure of the reservoir. These and other experiments, as well as analysis of the data using classical
thermodynamics, indicated that the turgor and the internal osmotic pressure of the accessory cells along the xylem vessels
play an important role in the maintenance of a constant xylem tension. This conclusion is consistent with the cohesion theory.
In agreement with the literature (P.E. Weatherley, 1976, Philos. Trans. R. Soc. London Ser. B23, 435–444; 1982, Encyclopedia of plant physiology, vol. 12B, 79-109), it was found that the tension in the xylem of intact
plants under normal and elevated ambient pressure (as measured with the pressure probe) under quasi-stationary conditions
was independent of the transpiration rate over a large range, indicating that the conductance of the flow path must be flow-dependent. 相似文献