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991.
992.
The activation by abscisic acid (ABA) of current through outward-rectifying K+ channels and its dependence on cytoplasmic pH (pHi) was examined in stomatal guard cells of Vicia faba L. Intact guard cells were impaled with multibarrelled and H+-selective microelectrodes to record membrane potentials and pHi during exposures to ABA and the weak acid butyrate. Potassium channel currents were monitored under voltage clamp and, in some experiments, guard cells were loaded with pH buffers by iontophoresis to suppress changes in pHi. Following impalements, stable pHi values ranged between 7.53 and 7.81 (7.67±0.04, n = 17). On adding 20 M ABA, pHi rose over periods of 5–8 min to values 0.27±0.03 pH units above the pHi before ABA addition, and declined slowly thereafter. Concurrent voltage-clamp measurements showed a parallel rise in the outward-rectifying K+ channel current (IK, out) and, once evoked, both pHi and IK, out responses were unaffected by ABA washout. Acid loads, imposed with external butyrate, abolished the ABA-evoked rise in IK, out. Butyrate concentrations of 10 and 30 mM (pH0 6.1) caused pHi to fall to values near 7.0 and below, both before and after adding ABA, consistent with a cytoplasmic buffer capacity of 128±12 mM per pH unit (n = 10) near neutrality. Butyrate washout was characterised by an appreciable alkaline overshoot in pHi and concomitant swell in the steady-state conductance of IK, out. The rise in pHi and iK, out in ABA were also virtually eliminated when guard cells were first loaded with pH buffers to raise the cytoplasmic buffer capacity four- to sixfold; however, buffer loading was without appreciable effect on the ABA-evoked inactivation of a second, inward-rectifying class of K+ channels (IK, in). The pHi dependence of IK, out was consistent with a cooperative binding of at least 2H+ (apparent pKa = 8.3) to achieve a voltage-independent block of the channel. These results establish a causal link previously implicated between cytoplasmic alkalinisation and the activation of IK, out in ABA and, thus, affirm a role for H+ in signalling and transport control in plants distinct from its function as a substrate in H+-coupled transport. Additional evidence implicates a coordinate control of IK, in by cytoplasmic-free [Ca2+] and pHi.Abbreviations ABA
abscisic acid
- [Ca2+]i
cytoplasmic free [Ca2+]i
- EK
K+ equilibrium potential
- IK, out, IK, in
outward-, inward-rectifying K+ channel (current)
- I-V
current-voltage (relation)
- Mes
2-(N-morpholino)ethanesulfonic acid
- pHi
cytoplasmic pH
- Tes
2-{[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-amino}ethanesulfonic acid
- Vm
membrane potential
We are grateful to G. Thiel (Pflanzenphysiologisches Institut, Universität Göttingen, Germany) for helpful discussions. This work was possible with equipment grants-in-aid from the Gatsby Charitable Foundation, the Royal Society and the University of London Central Research Fund. F.A. holds a Sainsbury Studentship. 相似文献
993.
The presence of the glycolytic enzymes from hexokinase to pyruvate kinase in plastids of seedling pea (Pisum sativum L.) roots was investigated. The recoveries, latencies and specific activities of each enzyme in different fractions was compared with those of organelle marker enzymes. Tryptic-digestion experiments were performed on each enzyme to determine whether activities were bound within membranes. The results indicate that hexokinase (EC 2.7.1.2) and phosphoglyceromutase (EC 5.4.2.1) are absent from pea root plastids. The possible function of the remaining enzymes is considered.Abbreviations GADPH
glyceraldehyde 3-phosphate dehydrogenase
- PFK
phosphofructokinase
- PFP
pyrophosphate: fructose 6-phosphate 1-phosphotransferase
Bronwen A. Trimming gratefully acknowledges the award of a studentship from the Science and Engineering Research Council 相似文献
994.
Synthesis of indole-3-acetic acid (IAA), using stable-isotope incorporation, was investigated in Zea mays L. Incorporation of 2H from 2H2O into IAA molecules was shown to occur in intact plantlets and excised primary roots cultured in vitro. This demonstrates the de-novo formation of IAA, a process which is quantitatively well defined and is initiated early in germination.Abbreviations IAA
indole-3-acetic acid 相似文献
995.
996.
The purpose of this work was to test whether induction of massive -carotene synthesis in the alga Dunaliella bardawil is triggered by oxygen radicals. The following results were obtained: (i) The induction of -carotene synthesis is preceded by a lag period of about 4 h during which the cells swell and photosynthesis is partially inhibited, (ii) Addition of promoters of oxygen radicals or of azide (an inhibitor of catalase and superoxide dismutase) during the induction period, under conditions which are suboptimal for massive -carotene accumulation, greatly enhances -carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis, (iii) High irradiance, which induces massive -carotene accumulation, also induces a high catalase activity. It is suggested that photosynthetically produced oxygen radicals are involved in triggering massive -carotene accumulation in D. bardawil. 相似文献
997.
Ross M. Welch Wendell A. Norvell Stephen C. Schaefer Jon E. Shaff Leon V. Kochian 《Planta》1993,190(4):555-561
We investigated the effects of Fe and Cu status of pea (Pisum sativum L.) seedlings on the regulation of the putative root plasma-membrane Fe(III)-chelate reductase that is involved in Fe(III)-chelate reduction and Fe2+ absorption in dicotyledons and nongraminaceous monocotyledons. Additionally, we investigated the ability of this reductase system to reduce Cu(II)-chelates as well as Fe(III)-chelates. Pea seedlings were grown in full nutrient solutions under control, -Fe, and -Cu conditions for up to 18 d. Iron(III) and Cu(II) reductase activity was visualized by placing roots in an agarose gel containing either Fe(III)-EDTA and the Fe(II) chelate, Na2bathophenanthrolinedisulfonic acid (BPDS), for Fe(III) reduction, or CuSO4, Na3citrate, and Na2-2,9-dimethyl-4,7-diphenyl-1, 10-phenanthrolinedisulfonic acid (BCDS) for Cu(II) reduction. Rates of root Fe(III) and Cu(II) reduction were determined via spectrophotometric assay of the Fe(II)-BPDS or the Cu(I)-BCDS chromophore. Reductase activity was induced or stimulated by either Fe deficiency or Cu depletion of the seedlings. Roots from both Fe-deficient and Cu-depleted plants were able to reduce exogenous Cu(II)-chelate as well as Fe(III)-chelate. When this reductase was induced by Fe deficiency, the accumulation of a number of mineral cations (i.e., Cu, Mn, Fe, Mg, and K) in leaves of pea seedlings was significantly increased. We suggest that, in addition to playing a critical role in Fe absorption, this plasma-membrane reductase system also plays a more general role in the regulation of cation absorption by root cells, possibly via the reduction of critical sulfhydryl groups in transport proteins involved in divalent-cation transport (divalent-cation channels?) across the root-cell plasmalemma. 相似文献
998.
Transfer of a marine DNA virus fromEctocarpus toFeldmannia (Ectocarpales,Phaeophyceae): aberrant symptoms and restitution of the host 总被引:1,自引:0,他引:1
Summary The marine brown algaEctocarpus siliculosus is invaded by a polyhedric virus, whose genome consists of circular, double-stranded DNA. In laboratory experiments this virus can infect a different host species,Feldmannia simplex. InfectedFeldmannia plants show severe somatic malformations. However, no functional virus particles are formed. SuchFeldmannia plants recover to resume a normal, symptom-free appearance. This result raises the possibility of intergeneric gene transfer in the natural habitat. 相似文献
999.
Larval cuticle ofHelicoverpa (Heliothis)zea and yeast extract added to a minimal medium (MM) induced germination of conidia ofNomuraea rileyi whereas sterile distilled water or MM alone did not. Yeast extract increased mycelial yield, but when cuticle was added, mycelial yield significantly decreased. Proteases and chitinases ofN. rileyi were only expressed when cuticle was added to the MM.This article reports the results of research only. Mention of a proprietary product in this paper does not constitute a recommendation for use by US Department of Agriculture. 相似文献
1000.
The extra-thecal epithelia of cryofixed undecalcified, freeze-substituted polyps of the scleractinian corals Galaxea fascicularis and Tubastrea faulkneri and axial and basal polyps of Acropora formosa have been examined, in anhydrously prepared thick slices, by confocal laser scanning light microscopy. The avoidance of chemical fixation and decalcification makes it possible to determine whether previously seen structures are real or artefactual products of swelling, shrinkage and distortion. All of the epithelia of all the corals examined are characterised by well defined intercellular spaces. Mucocytes are present in all cell layers in Galaxea and Tubastrea but are not present in any cell layers in the axial polyp of Acropora although they are abundant in the oral ectoderm of the basal polyps in this coral. Zooxanthellae are absent in Tubastrea, the epithelia of the exert septa of Galaxea and the axial polyp of Acropora. The calicoblastic ectoderm is generally composed of thin squamous cells with large intercellular spaces. At rapidly calcifying regions such as the tips of the exert septa of Galaxea, the calicoblastic cells are elongated with extensive arborisation of the basal regions of the cells. They are separated by large intercellular spaces and contain numerous fluorescent granules. The apical regions of these cells appear to be closely applied to the surface of the skeleton. There is no evidence of a space between the apical region of the calicoblastic cells and the skeleton. 相似文献