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991.
Ruth G. Shaw Gerrit A. J. Platenkamp 《Evolution; international journal of organic evolution》1993,47(3):801-812
To determine the potential for adaptation to a local biotic environment, we examined the magnitude and nature of genetic variation in response to neighboring plants within a natural population of the native California annual, Nemophila menziesii. A total of 22 plants from a natural population were crossed in three reciprocal factorials. The progeny were grown in a greenhouse in nine treatments that varied in conspecific density and in the density of a naturally co-occurring grass species, Bromus diandrus. Increasing the density of each species significantly reduced individual survival, fruit number, and dry weight. Among survivors, we found small to moderate heritability of dry weight within treatments. Additive genetic correlations (rA) of dry weight between competitive regimes were generally large and positive. In no case were they significantly different from 1, as expected under the null hypothesis that the relative performance of the genotypes under consideration is the same in all environments. On the basis of these results, we cannot conclude that the structure of genetic covariation within this population would promote genetic differentiation in response to locally varying conditions of density of these two species. Aspects of the experiment that may have compromised our ability to detect rA differing from 1 are discussed. 相似文献
992.
993.
Gibberellin (GA) biosynthesis in cell-free systems from Cucurbita maxima L. endosperm was reinvestigated using incubation conditions different from those employed in previous work. The metabolism of GA12 yielded GA13, GA43 and 12α-hydroxyGA43 as major products, GA4, GA37, GA39, GA46 and four unidentified compounds as minor products. The intermediates GA15, GA24 and GA25 accumulated at low protein concentrations. The structure of the previously uncharacterised 12α-hydroxyGA43 was inferred from its mass spectrum and by its formation from both GA39 and GA43. Gibberellin A39 and 12α-hydroxyGA43 were formed by a soluble 12α-hydroxylase that had not been detected before. Gibberellin A12-aldehyde was metabolised to essentially the same products as GA12 but with less efficiency. A new 13-hydroxylation pathway was found. Gibberellin A53, formed from GA12 by a microsomal oxidase, was converted by soluble 2-oxoglutarate-dependent oxidases to GA1 GA23, GA28, GA44, and putative 2β-hydroxyGA28. Minor products were GA19, GA20, GA38 and three unidentified GAs. Microsomal 13-hydroxylation (the formation of GA53) was suppressed by the cofactors for 2-oxoglutarate-dependent enzymes. Reinvestigation of the endogenous GAs confirmed the significance of the new metabolic products. In addition to the endogenous GAs reported by Blechschmidt et al. (1984, Phytochemistry 23, 553–558), GA1, GA8, GA25, GA28, GA36, GA48 and 12α-hydroxyGA43 were identified by full-scan capillary gas chromatography-mass spectrometry and Kovats retention indices. Thus both the 12α-hydroxylation and the 13-hydroxylation pathways found in the cell-free system operate also in vivo, giving rise to 12α-hydroxyGA43 and GA1 (or GA8), respectively, as their end products. Evidence for endogenous GA20 and GA24 was also obtained but it was less conclusive due to interference. 相似文献
994.
A. Gollotte V. Gianinazzi-Pearson M. Giovannetti C. Sbrana L. Avio S. Gianinazzi 《Planta》1993,191(1):112-122
Pisum sativum L. myc– mutants which fail to form arbuscular mycorrhiza have recently been identified amongst nod– mutants (Duc et al., 1989, Plant Sci. 60, 215–222). The reason for this resistance to symbiotic fungi has been investigated in the case of a locus a mutant (P2) inoculated with Glomus mosseae (Nicol. and Gerd.) Gerd, and Trappe. The fungal symbiont formed viable appressoria in contact with the root surface but its development was stopped at the root epidermis. Abundant material was deposited on the inner face of root cell walls adjacent to the appressoria in the P2 mutant, but not in the wild-genotype parent cultivar (Frisson) forming a symbiotic mycorrhizal infection. Fluorescence, histochemical, cytochemical and immunocytological approaches were used to characterize the paramural deposits in epidermal and hypodermal cells of the mutant. Strong fluorescence under blue light indicated the accumulation of phenolic compounds although polymers like lignin or suberin were not localized. Proteins and glycoproteins were homogeneously distributed within the paramural deposits. In the latter, the periodic acid-thiocarbohydrazide-silver proteinate (PATAg) reaction for 1,4-polysaccharide detection showed a heterogeneous composition with electron-dense points surrounded by non-reactive material, but cytological tests for cellulose and pectin gave weak responses as compared to epidermal and hypodermal walls of the wild genotype. -1,3-Glucans indicative of callose were detected by in-situ immunolocalization in the paramural deposits below appressoria on mutant roots, but not in walls of the wild genotype. Thus, appressorium formation by G. mosseae on roots of the locus a P. sativum mutant elicits wall modifications usually associated with activation of defence responses to pathogens. It is proposed that this locus must be involved in a key event in symbiotic infection processes in P. sativum, and the possible role of complex regulatory interactions between symbiosis and defence genes in endomycorrhiza development is discussed.Abbreviations DAPI
4,6-diamino-2-phenylindole
- FDA
fluo-rescein diacetate
- PATAg
periodic acid-thiocarbohydrazide-silver proteinate
The authors are grateful to C. Arnould for technical assistance, K. Niehaus for the purified Sirofluor, K. Roberts for the AFRC JIM5 antibody and J. Lherminier (INRA, Dijon, France), for useful discussion. This collaborative research programme was financially supported by MRT, INRA, EPR-Bourgogne (grant to A.G., Contrat de Plan project 3060A), EEC COST ACTION 8.10 (Endomycorrhizas) and the National Research Council of Italy, Special Project RAISA, Sub-project N.2, Paper N. 801 相似文献
995.
When fenugreek (Trigonella foenum-graecum L.) endosperms plus testa (endosperms), which had been isolated from 5-h-imbibed seeds, were incubated for at least 2 h under germination conditions, they leaked substances which, like exogenous abscisic acid (ABA), inhibited the production of fenugreek endosperm -galactosidase. However, unlike ABA, 8 h treatment with these inhibitors had no effect on fenugreek endosperms which had been isolated from 15-h-imbibed seeds and leached for 2 h. This indicated that either their inhibitory action was on processes which were related to the production of -galactosidase and had been completed by this time, or that there might be factors present which inactivate these inhibitors. It was also concluded that the action of the endosperm leachate could not be attributed to the presence of ABA. The activity of the leachate decreased when it originated from endosperms imbibed for periods longer than 25 h and thin-layer chromatography (TLC) of extracts from these endosperms showed decreased contents of the leachable inhibitors as imbibition proceeded. From the seed leachate, which had a TLC pattern and inhibitory action similar to that of the endosperm, were isolated three substances which, when applied to endosperms, inhibited the production of -galactosidase activity. According to their chromatographic behaviour and their reaction with specific reagents, there are strong indications that these substances are saponins. These diffusible saponin-like substances were located in both endosperm and perisperm and their physiological role is discussed.Abbreviations ABA
abscisic acid
- PEG
polyethylenglycol
- TLC
thin-layer chromatography
We wish to thank the Alexander S. Onasis Public Benefit Foundation for a grant to K.Z. and Dr. J.S.G. Reid (University of Stirling, Scotland) for a kind gift of fenugreek seeds. 相似文献
996.
The characteristics of sulphate uptake into right-side-out plasma-membrane vesicles isolated from roots of Brassica napus L., Metzger, cv. Drakkar, and purified by aqueous polymer two-phase partitioning, were investigated. Sulphate uptake into the vesicles was driven by an artificially imposed pH gradient (acid outside), and could be observed for 5–10 min before a plateau was reached and no further net uptake occurred. The uptake was partially inhibited in the presence of depolarizing agents and little uptake was observed in the absence of an imposed pH gradient. Uptake was strongly pH-dependent, being greatest at more acidic pH. After imposition of a pH gradient, the capacity for uptake decreased slowly (t1/2>10 min). The uptake had a high-affinity component which was strongly dependent on the external proton concentration (K m=10μM at pH 5.0, 64 μM at pH 6.5). The K m for protons varied from 0.4–1.9 μM as the sulphate concentration was reduced from 33 to 1 μM. A low-affinity component was observed which could be resolved at low temperatures (0 °C). Microsomal membranes that partitioned into the lower phase of the two-phase system gave no indication of high-affinity sulphate transport. Sulphate uptake into plasma-membrane vesicles isolated from sulphur-starved plant material was approximately twofold greater than that observed in those isolated from sulphate-fed plant material. Isolated vesicles therefore mirror the well-known in-vivo response of roots, indicating an increase in the number of transporters to be, at least in part, the underlying cause of derepression. 相似文献
997.
998.
The effect of nitrogen starvation on the NO3-dependent induction of nitrate reductase (NR) and nitrite reductases (NIR) has been investigated in the halophilic alga Dunaliella salina. When D. salina cells previously grown in a medium with NH 4 + as the only nitrogen source (NH 4 + -cells) were transferred into NO 3 ? medium, NR was induced in the light. In contrast, when cells previously grown in N-free medium were transferred into a medium containing NO 3 ? , NR was induced in light or in darkness. Nitrate-dependent NR induction, in darkness, in D. salina cells previously grown at a photon flux density of 500 umol · m?2 s?1 was observed after 4 h preculture in N-free medium, whilst in cells grown at 100 umol · m?2 s?1 NR induction was observed after 7–8 h. An inhibitor of mRNA synthesis (6-methylpurine) did not inhibit NO 3 ? -induced NR synthesis when the cells, previously grown in NH 4 + medium, were transferred into NO 3 ? medium (at time 0 h) after 4-h-N starvation. However, when 6-methylpurine was added simultaneously with the transfer of the cells from NH 4 + to NO 3 ? medium (at time 0 h), NO 3 ? induced NR synthesis was completely inhibited. The activity of NIR decreased in N-starved cells and the addition of NO 3 ? to those cells greatly stimulated NIR activity in the light. The ability to induce NR in darkness was observed when glutamine synthetase activity reached its maximal level during N starvation. Although cells grown in NO 3 ? medium exhibited high NR activity, only 0.33% of the total NR was found in intact chloroplasts. We suggest that the ability, to induce NR in darkness is dependent on the level of N starvation, and that NR in D. salina is located in the cytosol. Light seems to play an indirect regulatory role on NO 3 ? uptake and NR induction due to the expression of NR and NO 3 ? -transporter mRNAs. 相似文献
999.
1000.
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