摘要:

ABSTRACTThe mechanisms of gravity perception are still hypothetical, but there are sufficient data from experiments with plants to enable mathematical modelling to imitate the behaviour of gravitropic response systems. We have a much less complete picture of gravitropic kinetics in agaric mushrooms. However, some existing mathematical models which imitate plant responses are in principle universal because their conceptual components are not limited to any specific cellular entities. In this work we have used such models to compare plant and fungal gravitropism, using recently acquired kinetic data from the agaricsCoprinus cinereiusandFlammulina velutipes. The results show striking similarities between plants and fungi. First, it is evident that the basic assumptions of the plant models are logically applicable to fungi. Secondly, the mechanism of bending is the same (differential growth of opposite flanks of the growing organ). Thirdly, the distribution of growth seems very similar: in both plants and fungi growth of the organ is most intensive just behind the apex and is almost absent at the apex and at the base. Fourthly, in both fungi and plants the gravitropic response exhibits a substantial time delay suggesting that many time‐consuming processes are involved in reception, transduction and realization of gravitropic stimuli. Important differences in plant and fungal gravitropism kinetics were: (i) the agaric stem apex always returned to the vertical, whereas some plant organs show stable plagiogravitropic growth; (ii) inflections were usually seen inC. cinereusstem gravitropism time courses suggesting that a curvature compensation process delayed bending for a time; (iii)C. cinercusstems very rarely overshot or oscillated around the vertical although many plant subjects oscillate and the (limited) data forF. velutipesshowed a single, exaggerated overshoot and oscillation. In this latter case, experimental modelling with parameters characteristic of a low level of perception improved the fit to theF. velutipesdata, indicating that the two fungi may differ in this factor. Application of the plant models focused future research attention on the urgent need for data bearing on angle‐response and acceleration–response relationships in fungi, and their detection–level thresholds for gravitational acceleration. Since the modelling also highlighted some fundamental kinetic differences between the only two fungi for which sufficient data are available at the moment, it is also clear that detailed observations need to be made of gravitropism kinetics in a larger number and wider range o

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00416.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe NADPH‐dependent conversion of amino acids to their aldoximes is an initial step in glucosinolate biosynthesis. A number of microsomal aldoxime‐forming monooxygenase activities were detected in leaves from a variety of glucosi‐nolate‐containing species, whereas barley, bean and tobacco leaves did not contain any such activities. The substrates for these monooxygenases in each species largely correlated with the spectrum of glucosinolates found in that species. No activity was detected that metabolized homomethionine (supposed precursor of 2‐propenylglucosinolate [sinigrin]), even in species where sinigrin was the major glucosinolate. InSinapisspecies containing hydroxybenzylglucosinolate (sinalbin), activity with L‐Tyr was detected, whereasBrassicaspecies containing sinalbin had no such activity. However, these Brassicas did contain an L‐Phe monooxygenase activity. Partial characterization of the monooxygenases indicated that inBrassicaspecies,Nasturtium officinalisandRaphanus sativusthese resembled the flavin‐linked monooxygenases previously found in oilseed rape (Brassica napus) and Chinese cabbage (Brassica campestris). The L‐Tyr‐dependent activity inSinapisspecies, and the L‐Phe‐dependent activity inTropacolum majus, had characteristics of cytochrome P450‐type enzymes. No similarity was found with any other known amino acid metabolizing enzymes (including decarboxylases, amino acid oxidases and di

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00417.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIon contents in needles from Norway spruce trees [Picea abies(L.) Karst.] growing in Würzburg and in the SO2‐polluted Erzgebirge mountains were analysed to quantify cations which accumulate together with sulphate. In Würzburg there was a positive correlation of potassium (0.680 ± 0.300 Eq Eq−1SO4−2), magnesium (0.415 ± 0.111 Eq Eq−1SO4−2) and zinc (0.059 ± 0.006 Eq Eq−1SO42−). In the Erzgebirge, potassium was also the stoichiometrically most important cation (0–887 ± 0–180 Eq K+Eq−1SO42−). All other correlations examined were weak or statistically non‐significant. At both sites the calcium content of spruce needles did not depend on the sulphate content. The lack of a role for Ca2+in neutralizing sulphate is a consequence of the presence of free oxalic acid in needles. Soluble oxalic acid precipitates Ca2+, which thereby becomes unavailable as a counterion for SO42−. The activity coefficients of Ca2+and oxalate2−, and the solubility product of Ca‐oxalate, were determined fromin vivodata. It is concluded that the chronic accumulation of atmospheric sulphate in spruce needle vacuoles depletes available potassium and thereby strongly interferes with spruce growth and canopy turnover. This leads to impaired spruce vitality, even at sites where a

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00418.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTPhotoinhibition of macroalgae in the epilithic algal community (KAC) of coral reefs was studied using chlorophyll fluorescence techniques at One Tree Island, Great Barrier Reef, Australia.Fv/Fm(variable to maximum fluorescence, darkened samples) of shallow macroalgae declined by 50% on fine summer and winter days, recovering in late afternoon. Within a species, thalli from low‐light habitats were more photoinhibited (2h at 1400μimol m−2s−1) than those from high‐light habitats. The sensitivity ofLobophora variegata(Phacophyta) andChlorodesmis fastigiata(Chlorophyta) increased with depth (1 versus 20 m). However, shallowHalimeda tuna(Chlorophyta) plants growing between corals were more photoinhibited than those from deep, open areas.Photoinhibition and recovery were depth‐ and species‐specific. ShallowLobophoraandChlorodesmismaintained a greater degree ofQAoxidation during photoinhibition. In deep thalli, reduced effective quantum yield of open photosystem II centres reflected lower proportions and excitation capture efficiencies of open centres. InLobophora, zeaxanthin formation accompanied non‐photochemical fluorescence quenching (NPQ), but inChlorodesmisNPQ was limited and no zeaxanthin or antherxanthin formed. Higher photosynthetic efficiency in the lower storey of the EAC may compensate for photoinhibition in the upper storey, thereby reconciling photoinhibition of individual thalli with previous observations of no net inhibition of communit

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00419.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTCurrent‐voltage (I/V) analysis and pharmacological dissection were applied to membranes ofLamprothamniumat the time of hypotonic stress. At least three types of process were found to be involved in the response to this stress.1The first 10min of exposure to hypotonic medium resulted in a depolarization of about 50mV accompanied by a decrease or no change in conductance. This depolarization occurred with either K+or Ca2+(and consequently C−channels inactivated.2The CI−channels opened mainly in the first 15min of the hypotonic stress, increasing the membrane conductance by about an order of magnitude.3The K+conductance rose as the Cl−conductance started to diminish and reached a maximum after about 40 min.Both types of channel were strongly potential‐dependent with a conductance peak between ‐150 and 0mV. An inactivation of K+or CI−channels resulted in moving the membrane potential away from the conductance maximum toward eitherEKor ECI, diminishing the ion efflux (and turgor regulation). The time courses of the conductance increases remained the same, suggesting that the conductance changes are not driven by feedback to some preset turgor level. The electrophysiology of theLamprothamniumtransporters is compared to that of salt‐sensit

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00420.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTGlutamine synthetase (GS) exists as two main isoforms in plants, a cytosolic form (GSI) and a chloroplast or plastidie form (GS2). Fifty‐five species of legume, representing a phylogenetically diverse group of tropical and temperate species, were screened by western blotting for the presence of GS2 in their roots. A remarkably strong correlation was found between the climatic origin of the species and the presence or absence of a GS2‐like polypeptide in the root. Root GS2 was found in all 31 temperate species examined (30 papilionoids, one caesalpinoid), but was not detected in any of the 17 tropical papilionoid species. It was also absent in the roots of four out of seven tropical non‐papil‐ionoid species. The ‘in vivo’ NR activities of roots, stems and leaves of 46 of the legume species were analysed to establish their major site of nitrate reduction, and the ratio of nitrate: reduced N in the xylem sap was determined for some species, but no clear correlation between possession of a root GS2 and a preference for root nitrate assimilation was found. We discuss the possibility that expression of GS2 in the root was part of a more extensive physiological adaptation to root nitrate assimilation that evolved in temperate species to suit the alkaline, nitrate rich soils found in the centres of origin in temperat

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00421.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe compared influxes and internal transport in soybean plants (Glycine maxcv. Kingsoy) of labelled N from external solutions where either ammonium or nitrate was labelled with the stable isotope15N and the radioactive isotope13N. The objective was to see whether mass spectrometric determinations of tissue15N content were sufficiently sensitive to measure influxes accurately over short time periods. Our findings were as follows. (1) There was a close quantitative correspondence between estimates of N influx of individual plants using15N or13N measurements with either NO3/−or NH4+at 4 or 2 mol−3, respectively in the external solution. (2) Transport to the shoot of N from NO3absorbed over a 5–15 min period could be monitored when the external NO3−concentration ranged from 0–05 to 4 mol m−3. NH4+as the N source labelled shoot tissue more slowly, and estimates of the transport between root and shoot could be made only with13N. (3) Influx of NO3−into root tissue could be measured by15N enrichment after 5–10 min at concentrations approaching the probableKMof the high‐affinity transport system. (4) There was some indication of isotope discrimination, especially with respect to the movement of labelled N to the shoot, when NO3−is the N source.For many purposes,15N tracing can be used satisfactorily to estimate influxes of both NO3−and NH4+in soybean roots. Use of the short‐lived radio nuclide13N remains the method of choice for more refined measurements of internal distri

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00422.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWe present the first experimental results on salinity tolerance and regulation mechanisms in the genusTolypella. The two species investigated,T. nidificaandT. glomerata, regulate turgor pressure with almost complete effectiveness by adjustment of K+ and CT concentrations. Sucrose is also involved. The mechanism is basically identical to the mechanism of turgor pressure regulation previously identified in representatives of the generaCharaandLamprothamnium. SinceCharaandLamprothamniumon the one hand andTolypellaon the other belong to different phylogenetic branches that separated early in the geological history of the Characeae, the K+ regulation mechanism can be assumed to represent an ancient pattern derived from a salt‐tolerant common ancestor. Furthermore, our experiments provide evidence that salinity is a limiting factor for fertility in bothT. nidificaandT. glomerata. Although the onset of gametangia covers the whole range of salinities tested here (0–29 psu), 12psu was the inhibitory level for the formation of mature oospores. Fertilization is probably disturbed by an increase in salinity. An inability to reproduce sexually under euryhaline conditions could explain why the distribution of the two species is restricted to oligo‐ and mesohaline environments, despite the wide range of salinity tolerance of their vegetative appa

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00423.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIn previous studies of the calcicolesCentaurea scabiosaandLeontodon hispidus, the stomata on isolated epidermis closed partially when the concentration of calcium in the medium was above 1 mol m−3. This is a much smaller concentration than that believed to be delivered into the leaves in xylem sap when the plants are growing in a calcium‐rich medium, and hence the mechanism for ‘protecting’ stomata from excessive exposure to free calcium is thought to be of great physiological significance. It is shown here that, in the leaves of both species, a substantial amount of the calcium they contain is located within meso‐phyll cells, and virtually all of that which does enter the epidermis is contained within trichomes, probably as calcium oxalate. The amounts of calcium in the vicinity of the stomata thus remain small despite high concentrations elsewhere, ensuring that the essential role of Ca2+in intra‐cellular signalling in guard cells can continue to be performed without

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00424.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe relationship among water use efficiency (WUE), productivity and carbon isotopic composition (δ13C) in white spruce (Picea glauca(Moench) Voss) seedlings was investigated. Sixteen hundred seedlings representing 10 controlled crosses were planted in the field in individual buried sand‐filled cylinders. The soil water content in the cylinders was measured using time domain reflectometry over two growing seasons and seedling water use determined by water balance. Two watering treatments were imposed: irrigation and dry land. There was significant (1.6–2.0%c) genetic variation in needle δ13C. Ranking of crosses in terms of δ13C was generally maintained over watering treatments and there was not a significant genetic versus environmental interaction. There was a positive correlation between δ13C and both intrinsic and long‐term WUE (more positive δ13C with increased WUE) and between δ13C and productivity, suggesting a correlation due to variation in photosynthetic capacity. Root to shoot ratios did not increase in water‐stressed plants, indicating that responses to drought were primarily at the level of gas exchange, rather than through morphological changes. Our results indicate that it should be possible to use δ13C as a surrogate for WUE and to select white spruce genotypes for high WUE without comp

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00425.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY