ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00823.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractDetergent‐isolated flagellar apparatuses of the flagellate green algaDunaliella bioculataretain remnants of the nucleus (the karyoskeleton) which are linked to the basal bodies by the centrin‐containing nucleus basal body connectors (NBBC). Such complexes were subjected to different calcium concentrations (1 × 10−9M − 5 × 10−4M Ca2+) and the distance between the basal bodies and the karyoskeleton was measured by light microscopy. The threshold concentration of Ca2+for NBBC contraction was determined to be around 5 × 10−8M Ca2+. At>10−7M Ca2+NBBC were maximally contracted and the distance between the basal bodies and the karyoskeleton was only about 50% of the initial distance. Using a polyclonal antibody generated against centrin (Salisbury et al., 1984), the NBBC were visualized by indirect immunofluorescence in both the extended and contracted state. Our results demonstrate thatin vitrocontraction of centrin‐containing filaments in green algae is initiated at about the same free Ca2+concentration in three different centrin‐containing basal apparatus components (i.e. the distal connecting fibre, the flagellar transitional

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractEpidermal plus hypodermal peels from tulip peduncles produced bands of acidity on agar containing bromocresol purple. Peels from horizontally oriented peduncles gave rise to an acidity band which corresponded to the lower side of the peduncle. The band began 3–6 cm beneath the flower and extended basipetally within the region of gravitropic bending. No corresponding band appeared in an agar layer laid on the cortical surface exposed by peeling. Peduncles growing in the normal vertical position showed circumnutations with a period in the range of 4 h. The peels from these stalks produced one or two bands more acid than the remaining part of the peel. Since the acidity band in horizontally positioned stalks corresponds to the zone of faster growth causing gravitropic bending, we infer that the band(s) produced by vertical stalks also correspond to zones of differential growth involved in circumnutation. On the basis of a previous finding that tulip leaves give rise to an oscillating acidity pattern, we infer that vertical stalks also show such a pattern. This inference fits the model proposing the involvement of an internal oscillator in circumnutation. However, the ratio of the circumnutation period to the gravitropic lag phase in tulip peduncles is such as predicted by the gravitropic‐feedback model of circumnutat

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractTonoplast membranes were prepared from tissue homogenates and from vacuoles isolated from beetroot storage tissue (Beta vulgarisL., ssp.conditiva) for transmission electron microscopic analysis of the structure of the beetroot vacuolar ATPase using the negative staining technique. By comparison of the specific inhibitor sensitivities of the ATPase activity, i.e. ATP hydrolysis and H+‐pumping, the purity of the tonoplast preparations with respect to contamination with mitochondrial inner membranes was assessed to avoid confusion with mitochondrial F1F0‐ATPase. Membranes prepared in Hepes/Tris or BTP/Mes‐containing media rarely showed typical head‐and‐stalk structures although characteristic nitrate‐ and bafilomycin A1‐sensitive ATP‐hydrolysis and H+‐pumping could be measured. However, typical head‐and‐stalk structures were observed regularly when these buffers were replaced by K‐phosphate buffer. Under these conditions, the beetroot vacuolar ATPase is characterized by a large head group with a central cleft, a thin stalk, connecting it to the membrane and by basal components projecting from the base of the stalks near the vacuolar membrane and forming a distinct layer of electron‐light particles between the vacuolar membrane and the layer o

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00826.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFollowing assimilation of14CO2by leaves ofStachys sieboldii,14C‐stachyose is translocated into the tubers. Stachyose is accumulated and stored in the vacuoles of the pith parenchyma. Protoplasts and vacuoles were isolated and the uptake of sugars was examined. Uptake of sucrose and sucrosyl oligosaccharides of the raffinose family by protoplasts was very low compared to glucose. Transport parameters for glucose indicated a carrier mediated transport in the lower concentration range which was superimposed by diffusion at higher concentrations (>10 mM). The very low sugar uptake by protoplasts and the sparse enzyme activities of stachyose synthase in the storage parenchyma as well as acid invertase and α‐galactosidase in the cell walls indicated symplastic unloading of stachyose in the tubers. Experiments on14C‐stachyose uptake by isolated vacuoles confirmed previous observations by Keller (1992).Isolated vacuoles exhibited ATP and PP hydrolysis and were capable of generating a proton gradient across the tonoplast by a V‐type H+‐ATPase and H+‐PPase. This was demonstrated by fluorescence quenching of quinacrine. Fluorescence could be restored by the addition of gramicidin and partly recovered by the addition of stachyose; mannitol, sorbitol and glucose had no effect. Fluorescence recovery depended on the concentration of stachyose and revealed saturation kinetics (Km= 28 mM). Comparable results have been obtained with tonoplast vesicles by Greutert and Keller (1993).Experimental data presented here provide circumstantial evidence for symplastic unloading of stachyose in the tubers ofStachys sieboldiiand demonstrate that the stachyose concentration in the cytoplasm of storage parenchyma cells is kept low by active stachyose transport into the vacuoles. The results suggest a stachyose/H+‐a

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00827.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractExperimentsin vitrohave shown that γ‐EC synthesis, the first step in GSH formation, is subject to feedback inhibition by physiological GSH concentrations. In order to evaluate the role of this feedback inhibition on γ‐EC synthetasein vivoGSH synthesis was modulated in suspension cultures ofP. crispumandN. tabacumby administration of cadmium. The alterations in the thiol contents were measured and in addition the effect of Cd exposure on γ‐EC synthetase (E.C. 6.3.2.2) and GSH synthetase (E.C. 6.3.2.3) was studied. Decreasing cellular GSH concentrations by cadmium induced PC synthesis caused 7–10 fold increase in the rate of glutathione synthesis as measured by the accumulation of (γ‐EC)nG. This increase was not linked to an increase in extractable activities of γ‐EC‐ or GSH synthetase in parsley. In tobacco the activities of γ‐EC‐ and GSH synthetase increased by a factor of 1.6 and 1.8, respectively, after 3 d of Cd exposure. In both species the exposure to Cd resulted in an increased cellular γ‐EC content that reached a plateau within 24 h, and in a doubling of the cysteine content.In vitroexperiments showed that GSH synthetase activity is inhibited by cadmium concentrations that have no effect on γ‐EC synthetase activity. This may explain the accumulation of γ‐EC in Cd exposed cells. Incubation with 0.25 mM cysteine did not effect the γ‐EC‐ and GSH content in tobacco cells. In parsley the cellular GSH content increased threefold and the y‐EC content twofold and stayed constant thereafter at the elevated levels. Taken together the results show that GSH synthesisin vivois controlled by feedback inhibition as well as by the supply with cysteine. In the latter case the feedback inhibition may act as a kind of safety valve and prevent the accumulation of unphysiological GSH concentrations

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00828.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractSpinach plants (Spinacea oleraceaL. cv. Estivato) were grown on nutrient solutions under deficient, normal and excess sulfate supply. In both young and mature plants net uptake of sulfate and its transport to the shoot increased with increasing sulfate supply, but both processes proceeded at a higher rate in young as compared to mature plants. The relative sulfate transport, i.e. the relative amount of the sulfate taken up that is transported to the shoot, decreased with increasing sulfate supply. Apparently, net uptake of sulfate is not strictly controlled by the sulfur demand of the shoot, but xylem loading appears to counteract excess transport of sulfate to the shoot.Fumigation with H2S or SO2reduced net uptake of sulfate by the roots in sulfur‐deficient plants and absolute as well as relative sulfate transport to the shoot independent of the three sulfate levels supplied to the plant. At the same time thiol contents of the shoot and the root were enhanced by fumigation with H2S and SO2. These findings are consistent with the idea that thiols produced in the leaves can mediate demand‐driven control of sulfate uptake by the roots and its transport to the sh

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00829.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractElectron microscopical investigations of primary haustoria ofOrobanche crenataparasitizing the roots of the highly compatible host,Vicia narbonensis, reveal an uninterrupted phloem system connecting both partners. Individual sieve elements belonging to the host and parasite could be identified by the cell markers: plastids, mitochondria and P‐protein, which in the present system turned out to have species‐specific fine structure.Sieve pores of normal structure interconnect the sieve elements of host and parasite. They originate from interspecific plasmodesm

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00830.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to answer the question whether functioning phloem connections exist between graft partners, phloem transport has been studied in cultured explant‐grafts after application of14C‐sucrose and carboxyfluorescein (CF) to the scion. Autografts ofLycopersicon esculentumandHelianthus annuuswere investigated at various regeneration periods. Ungrafted internodes served as controls.A segmental analysis was used to determine the tissue distribution of14C‐sucrose in a graft. The14C‐profiles obtained show that sucrose translocation across the graft interface started 4 days after grafting and increased later. The observed translocation appears to occur via wound phloem, since at this time the first complete wound‐phloem bridges (shown as files of aniline‐blue‐positive sieve plates) traverse the graft interface. In 7‐d‐old autografts, sucrose transport across the graft interface returned to normal again, as indicated by the distribution of the label. In addition,14C‐profiles reveal accumulation of label in sink tissues. Here the basal callus of the stock, and temporarily the graft union itself, represent the main sinks for labelled sucrose.Translocation of CF was analyzed in hand sections of the grafts. The beginning of translocation into the stock was confirmed with the dye. Moreover, effective phloem translocation across the graft interface, visualized with CF, could undoubtedly be assigned to wound‐phloem bridges reconnecting the cut vascular bundles of scion and stock. Thus, the function of phloem connections in regeneratedin vitro‐g

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1995.tb00831.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY