ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00200.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe distribution of tubulin and centrin in vegetative cells and during gametogenesis ofEctocarpus siliculosuswas studied by immunofluorescence. In interphase cells bundles of microtubules are focused on the centriolar region near the nuclear surface. Some of the bundles ensheath the nucleus while others traverse the cytoplasm in various directions, sometimes reaching the cell cortex. Evaluation of serial optical sections by confocal laser scanning microscopy (CLSM) revealed that the perinuclear and “cytoplasmic” microtubule bundles presumably constitute a single complex. In interphase cells centrin is localized as a single bright spot in the centriolar region. In dividing cells duplication and separation of the microtubular complex and the centrin spot takes place. In post‐mitotic cells with two nuclei, the centrioles are located at opposite cell poles, short microtubule bundles emanate from them and partially encompass the nucleus. During gametogenesis a gradual transformation of the vegetative cytoskeleton to the gametic flagellar apparatus o

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00201.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractAn unusual cell organelle of some basidiomycetes, the symplechosome, is described and illustrated in detail usingSaccoblastia farinaceaas an example. Symplechosomes are structurally similar, but not identical to “classical” dictyosomes of green plants and animals. As is typical for dictyosomes, each symplechosome consists of a stack of platelike cisternae. The central portions of the symplechosome‐cisternae are flattened, and adjacent cisternae are separated in the mid‐region by an intercisternal space of constant width. In contrast to dictyosomes, the intracisternal spaces are completely obliterated in the central area, and hexagonally arranged bars extend between adjacent cisternae. Identical bars often connect the symplechosomes with mitochondria. Symplechosomes are highly complex‐structured organelles which differ significantly from the simple individual Golgi cisternae or “Golgi bodies” observed in asco‐ and

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00202.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPlasmodesmata are occluded whenFunariachloronemata are fragmented by the development of tmema cells (TCs). The TC deposits a new wall layer along the cross wall toward the neighbouring non‐sister cell (NC). This wall layer cuts off the plasmodesmata and its connection with the cross wall is soon lost. The plasmodesmata become isolated when the NC forms a new wall layer along the former cross wall. At the end of TC development, before its disintegration, the sister cell (SC) also deposits a new wall layer along the cross wall toward the TC, cutting off the plasmodesmata. For some time the plasmalemma of the plasmodesmata remains connected to the NC or the TC, whereas the desmotubule soon disappears. Relicts of the plasmalemma remain even after the isolation of the plasmodesmata and the disintegration of the TC. During the decay of the plasmodesmata, a cylinder of electron‐dense material is frequently formed along the border of the plasmodesmatal channel. This may extend over the surface of the cell wall. Eventually, the plasmodesmatal channel is filled with wall material. Callose is only observed around functional plasmodesmata and does not seem to play a role in their occlus

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00203.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractHorizontally positionedChararhizoids continue growth without gravitropic bending when the statoliths are removed from the apex by basipetal centrifugation. The transport of statoliths in centrifuged rhizoids is bidirectional: 50–60 % of the statoliths are re‐transported on a straight course to the apex at velocities from 1 to 14 μm . min−1increasing towards the rhizoid tip. The centrifuged statoliths which are located closest to the nucleus are basipetally transported and caught up in the cytoplasmic streaming of the cell. Those statoliths which are located near the apical side of the nucleus are transported either apically or basally. A de‐novo‐formation of statoliths was not observed. After retransport to the apex some statoliths transiently sediment, a process which can induce a local inhibition of cell wall growth. The rhizoid bends again gravitropically only if a few statoliths finally sediment in the apex; the more statoliths that sediment in the apex the shorter the radius of bending becomes. The transport of statoliths is mediated by actin filaments which form a network of thin filaments in the apical and subapical zone of the rhizoid, and thicker parallel bundles in the basal zone where cytoplasmic streaming occurs. Both subpopulations of actin filaments overlap in the nu

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00204.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractHigh humidity (95 % RH) and temperature (38/45 °C) stress for 4h applied to pollen grains ofNicotiana tabacumdid not affect pollen viability, assessed on the basis of the fluorochromatic reaction test, but affectedin vitrogermination; pollen grains treated at 38 °C showed marked delay in germination, while those treated at 45 °C failed to germinatein vitro.The major ultrastructural effect of the stress was on RER. Stacks of RER, characteristically present in fresh pollen, were largely dissociated in the stressed pollen. The extent of dissociation of RER was greater in pollen samples stressed at 45 °C than at 38 °C. The generative cell did not show any obvious change in the stressed pollen. RER was restored in pollen grains which showed germination following culture; but not in those which failed to germinate. Apart from affecting other RER‐related functions the dissociation of RER is likely to result in the destruction of long‐lived mRNA and thus affect the ability of pollen grains to initiate protein synthesis needed for ger

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00205.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractEukaryotic vacuolar H+‐ATPases (V‐ATPases) are related to the F0F1‐ATPases of chloroplasts and mitochondria and are believed to be organized into peripheral and integral membrane complexes. Vacuolar membranes isolated from purified carrot (Daucus carota) root vacuoles were observed to be coated with F1‐like particles after negative staining with phosphotungstic acid. The F1‐like particles formed typical “ball and stalk” structures, about 9.4 nm in diameter and 13.6 nm in height. The head portion frequently had a characteristic bifurcation or cleft at the apex and appeared to be composed of subunits. Such “V1” complexes were frequently associated with smaller stalked particles emerging near the base. In contrast, negatively‐stained carrot mitochondrial F1complexes averaged 8.7 nm in diameter and 11.7 nm in height. The head groups of the mitochondrial F1s were nearly always spherical, and had no other smaller structures associated with them. The V1complexes of carrot are thus similar in form to the V1complexes ofNeurospora(Bowman et al. J. Biol. Chem. 264

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00206.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe structure of the vacuolar ATPase from mesophyll tonoplasts ofMesembryanthemum crystallinumhas been studied by electron microscopy using negatively stained specimens of membrane‐bound and detergent‐solubilized ATPase molecules. We observed a high density of particles on the surface of tonoplast vesicles and “head and stalk” structures on the edge of the membrane, similar to the F0F1‐ATPases of mitochondrial and chloroplast membranes. The staining conditions, which are often critical for such small objects, were improved by using methylamine tungstate as negative stain for the membrane‐bound ATPase. Compared to other staining solutions generally applied, dissociation of the F1‐like enzyme complex from the membrane was best prevented and structural damage of the vesicles was least observed with methylamine tungstate.In freeze‐fracture electron microscopy of tonoplast vesicles, where dissociation never occurs since no detergent is used, we also observed “head and stalk” structures on the edge of the membranes, beside many particles on the fracture faces.The detergent‐solubilized ATPase forms string‐like structures, caused by the aggregation of the hydrophobic membrane‐embedded F0‐like part of the enzyme. After negative staining the F1‐like enzyme complex is arranged alternately along both sides of the string an

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00207.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractDiazotrophic cultures of three species ofAzolla (Az. caroliniana, Az. microphylla, Az. pinnata)symbiotic withAnabaena azollaeaccumulated some 0.10–0.24 mol organic anion per mol N assimilated (0.010–0.018 mol organic anion per mol C assimilated), with a corresponding efflux of 0.05–0.11 mol H+per mol N assimilated (0.006–0.009 mol H+per mol C assimilated). These values are lower than those found for terrestrial diazotrophic vascular plants; this may be related to the decreased possibility of increasing Fe and P availability by rhizosphere acidification in a free‐floating plant. Modification of the organic anion content, and of the quantity (and direction) of H+exchange with the medium, with 5 mol m−3NH+4or NO−3added to diazotrophic cultures, are consistent with substantial N acquisition from combined N as well as N2assimilation. This conclusion is consistent with previously published

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00208.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe mode of adaptation of the photosynthetic apparatus of three unicellular green algae,Ankistrodesmus braunii, Chlorella fuscaandChlorella saccharophilato red and blue light are documented by the fluence‐rate curves of photosynthetic oxygen evolution. For all three algae tested photosynthetic capacity, respiration and light compensation point were higher for cells grown under red light, while the chlorophyll content increased in blue light‐grown cells. Blue light‐adapted cells have a lower chlorophyll a to chlorophyll b ratio and more chlorophyll in the light‐harvesting system than red light‐adapted cells, as shown in the electrophoretic profile of the pigment‐protein complexes. It is concluded that the action of red light resembles that of high levels of white light, while blue light causes the same effects as low levels of white light. In agreement with previous publications these findings indicate that the mode of adaptation to different light qualities is ubiquitous in unicellular

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00209.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY