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1.
Summary Pit connections (PCs) develop between the parasitic red algaHolmsella and its hostGracilaria. Only parasite cells initiate the formation of host-parasite pit connections. The parasite produces a small connecting cell (termed the conjunctor cell) which moves through the cell wall to fuse with either an adjacent host or parasite cell. The parasite secondary PC, which forms between the conjunctor cell and the parasite cell, is structurally different from a parasite primary PC, and has the distinct structure of a host-parasite PC. Only if the conjunctor cell fuses with another parasite cell will the former parasite-conjunctor cell PC be altered to a typical parasite-parasite PC. If the conjunctor cell fuses with an adjacent host cell the PC continues to develop as host-parasite. Occasionally a conjunctor cell fails to fuse with an adjacent cell (whether host or parasite), and the conjunctor cell and PC eventually breakdown in the cell wall. The parasite overcomes several barriers in order to infect the host, including the formation of host-parasite PCs which appear to be a necessary component of the parasiticHolmsella-Gracilaria association. 相似文献
2.
Summary
Harveyella mirabilis is a colourless red algal alloparasite which grows on and within its photosynthetic hostOdonthalia floccosa. Cells ofHarveyella establish secondary pit connections (PCs) with other parasite cells and with cells of the host. Small, uninucleate conjunctor cells are produced by parasite cells and remain connected to them by PCs. Conjunctor cells may fuse with either an adjacent host or parasite cell, with the parasite-conjunctor cell PC becoming either a host-parasite or parasite-parasite secondary PC. Occasionally the conjunctor cell does not fuse with an adjacent cell (either host or parasite) and degenerates. The secondary pit plug which forms between a parasite cell and its conjunctor cell always develops with two structurally distinct surfaces characteristic of a host-parasite pit plug. Only if the conjunctor cell fuses with another parasite cell will the structure of the pit plug be altered to that of a parasite-parasite pit plug. Fungal hyphae also invade the region of infection, andHarveyella cells respond by producing nonfunctional conjunctor cells that grow towards adjacent hyphae. Evidence suggests that secondary PCs may be induced to form mechanically, by the physical presence of another cell, rather than in direct response to a message received from an adjacent cell. The mechanism of secondary PC formation described here is similar to that reported for the closely related alloparasiteHolmsella and may be common to a number of red algal parasitic associations.
Helen Margaret Quirk, B. Sc. (Hons), M. Sc. (1953–1982), student, research assistant and friend, died after a long illness on October 24, 1982. 相似文献
3.
Summary The thick and anatomically complex stalks of a Western Australian species ofCryptonemia (Cryptonemiales, Rhodophyta) are characterized by growth rings in cross-section. Cells of the medulla may die as the diameter of the stalks increases to maximum widths of over 2 centimeters, the remaining cell walls appearing to function as purely supportive tissue (a phenomenon hitherto unreported in the red algae). All cells of the stalk are enclosed by thick, compact cell walls and are interconnected by pit connections which become progressively more convoluted and fluted with increasing distance of the cells from the stalk surface. This is the first report of such a pit-connection morphology. It is suggested that the modification may serve to aid transport of solutes towards the more deeply-buried layers of living cells. 相似文献
4.
Summary Calcification inRhodogorgon carriebowensis J. Norris et Bucher was associated with a particular cell type in the cortex. Calciferous cells were 4–6 times the length of cortical assimilatory cells. The distal two-thirds of the calcifying cell was invested with a thick wall that stained with periodic acid Schiff. Thick fibrils formed a reticulum and surrounded grains of calcium carbonate that ranged in shape from rhombohedral to subspherical and were up to 200 nm in greatest dimension. The proximal third of the cell was a tapering uncalcified stalk. The narrow base of the cell was attached to the subtending cell of the fascicle by a normal septum with a pit plug. The cell within the calcified wall matrix was usually flattened and had a very small volume. Cellular contents were dense; even when organelles could be discerned, they could not be identified. X-ray microanalysis revealed that other elements commonly found mixed with calcium carbonate are virtually absent from mineral deposits inR. carriebowensis, but electron diffraction study showed d-spacings that varied from those of pure calcite. Current models of red algal calcification are discussed in light of the findings on this alga.Abbreviations CaCO3
calcium carbonate
- DIG
differential interference contrast
- PAS
periodic acid Schiff
- SEM
scanning electron microscopy
- TEM
transmission electron microscopy 相似文献
5.
Summary High concentrations of proteinaceous crystalloids accumulate in vegetative cells of the red algaWrangelia plumosa
Harvey but disappear prior to sporogenesis. The distinctly structured crystalloids lack a bounding membrane and appear to autopolymerize within the cytoplasm. Chemical analysis of isolated crystalloids showed the presence of all amino acids except cysteine and cysteic acid. Carbohydrate accounted for 7.5% of the preparation. The crystalloids appear to have a storage function during growth and development. 相似文献
6.
Summary The fine structure of the recently described red algaRhodogorgon carriebowensis J. Norris et Bucher was studied by light microscopy and scanning and transmission electron microscopy to aid in the ordinal placement of this unusual alga. Most significant in this context were findings that pit plugs had two-layered plug caps, the outer layer of which formed a large dome and was composed of glycoprotein. Cap membranes appeared to be absent. Medullary cells were remarkable in having extremely thick, layered cell walls, whose inward deposition left little room for cytoplasm. Medullary filaments branched little except near the base of the cortex. The assimilatory filaments that made up most of the cortex contained almost all the pigmentation and starch reserves of the thallus. These filaments terminated in either slender apical cells with smooth cell walls or bulbous apical cells bearing spinulose projections. Two types of elongated cells were found in the cortex, those with calcified cell walls and those surrounded by multiple, spreading layers of wall material. Neither cell type was pigmented. The latter type sometimes supported normal assimilatory cells.The hypothesis is proposed thatRhodogorgon is a descendant of the marine progenitors of the Batrachospermales and thus is a member of this order.Abbreviations DIC
differential interference contrast
- PAS
periodic acid Schiff
- PTA-CA
phosphotungstic acid-chromic acid 相似文献
7.
Ulva cf. lactuca has been a disturbing competitor of experimental Gracilaria conferta outdoor cultures in Israel. The effect of environmental conditions on the competitive ability of Ulva versus Gracilaria, and the main limiting factors for which these seaweeds compete, were studied here. Single and biculture experiments of both seaweeds showed that Ulva outgrew and damaged Gracilaria under all irradiance and temperature combinations. The higher competitive ability of Ulva cf. lactuca in bicultures was not a result of responses to shading or nitrogen shortage, but rather to a shortage of available inorganic carbon, an increase in pH and apparent excretions of Ulva which inhibited the growth of Gracilaria. 相似文献
8.
Summary Phycobilisomes ofPorphyridium cruentum were investigated in ultrathin sectionsin situ and after isolation and positive or negative staining. The phycobilisomes have the approximate shape of one half of a compressed rotation ellipsoid with the following dimensions: length 2 a=40±4 nm, width 2 b=19±2 nm, height c=28±3 nm. The phycobilisomes form rows and pillars on the thylakoid membranes. A plug-like structure (foot) which apparently fixes the phycobilisomes to the thylakoid membrane is described. 相似文献
9.
Polyclonal antibodies specific for the excitatory amino acid, kainic acid (KA), were raised in rabbits. The antibody recognized
KA but did not cross-react with other structurally related amino acids, including glutamate. We used this anti-KA antibody
to localize KA immunohistochemically in the KA-producing red alga Digenea simplex. KA immunoreactivity was most dense in the fine cylindrical thallus, which covers the middle to upper part of the alga. The
cortical cells, but not the inner layers of the main axis, and cells of the rhizoid were also stained with this antibody.
The presence of KA in cells that cover the surface of the alga might reflect its role in chemical defense. At the subcellular
level, KA immunoreactivity was most intense in the nucleus, pit plugs, and the electron-dense areas denoted as “granule bodies”,
which were found only in the pericentral cells of the thallus.
This research was supported by Ministry of Education, Culture, Sports, Science and Technology to R.S. (13660206). 相似文献
10.
Okumura A Sano M Suzuki T Tanaka H Nagao R Nakazato K Iwai M Adachi H Shen JR Enami I 《FEBS letters》2007,581(27):5255-5258
PsbU is one of the extrinsic proteins in red algal Photosystem II (PSII) and functions to optimize the availability of Ca(2+) and Cl(-) cofactors for water oxidation. To determine the functional residue of PsbU, we constructed various PsbU mutants from a red alga Cyanidium caldarium and reconstituted these mutants with the red algal PSII. The results revealed that Tyr-92 of PsbU, especially its aromatic ring, was essential for maintaining its function. From the crystal structure of PSII, Tyr-92 is located close to Pro-340 of D1, suggesting that the aromatic ring of Tyr-92 interacts with the CH group of Pro-340 of D1, and this CH/pi interaction is important for the optimal function of the Mn(4)Ca-cluster. 相似文献
11.
In a previous study (Svirski et al., 1993), it was found that growth inhibition ofGracilaria spp., when cultured in the presence ofUlva cf.lactuca, was not due to shading or nutrient depletion, but seemed to be caused by competition for inorganic carbon or some type of allelopathy. In the present study, we attempted to differentiate between these two possible influences by (1) growing the two algae in biculture under various conditions, but keeping inorganic carbon levels constant and measuring net photosynthesis, respiration and growth rates, and by (2) measuring growth rates ofGracilaria spp. in the presence of extracts derived from media previously used to growUlva cf.lactuca.Both net photosynthesis and growth rates ofGracilaria spp. in biculture were inhibited, despite CO2 (and also HCO3
–) levels being kept constantly high in the culture media. It is likely that these responses were due to markedly enhanced rates of dark respiration inGracilaria spp. when grown together withUlva cf.lactuca. Growth ofGracilaria spp. was also inhibited by extracts derived from seawater in whichUlva cf.lactuca had previously been grown. The strong inhibition by ethyl acetate and chloroform extracts indicate an allelopathic effect onGracilaria spp. 相似文献
12.
P. V. Devi Prasad 《Hydrobiologia》1986,140(2):167-171
Three species of Gracilaria viz G. cervicornis, G. domingensis, G. verrucosa and Solieria tenera (Gigartinales, Rhodophyta) have been studied for their monthly variation in dry wt yields, ash, soluble carbohydrate, protein,
lipid and insoluble carbohydrate contents for one year. The dry wt yields were higher in G. domingensis. Soluble carbohydrate and ash contents showed an inverse relationship in all the species. Protein content was lower, below
5% of the dry wt for all the species. A comparison of protein:carbohydrate ratios showed a similarity between morphologically
similar G. domingensis and G. cervicornis in that there was less variation in the ratio. From this, it is assumed that flattened morphology probably is more efficient
in maintaining nutrient balance to keep up the growth rates. 相似文献
13.
Niche theory predicts that species which share resources should evolve strategies to minimise competition for those resources,
or the less competitive species would be extirpated. Some plant species are constrained to co-occur, for example parasitic
plants and their hosts, and may overlap in their pollination niche if they flower at the same time and attract the same pollinators.
Using field observations and experiments between 1996 and 2006, we tested a series of hypotheses regarding pollination niche
overlap between a specialist parasitic plant Orobanche elatior (Orobanchaceae) and its host Centaurea scabiosa (Asteraceae). These species flower more or less at the same time, with some year-to-year variation. The host is pollinated
by a diverse range of insects, which vary in their effectiveness, whilst the parasite is pollinated by a single species of
bumblebee, Bombus pascuorum, which is also an effective pollinator of the host plant. The two species therefore have partially overlapping pollination
niches. These niches are not finely subdivided by differential pollen placement, or by diurnal segregation of the niches.
We therefore found no evidence of character displacement within the pollination niches of these species, possibly because
pollinators are not a limiting resource for these plants. Direct observation of pollinator movements, coupled with experimental
manipulations of host plant inflorescence density, showed that Bombus pascuorum only rarely moves between inflorescences of the host and the parasite and therefore the presence of one plant is unlikely
to be facilitating pollination in the other. This is the first detailed examination of pollination niche overlap in a plant
parasite system and we suggest avenues for future research in relation to pollination and other shared interactions between
parasitic plants and their hosts. 相似文献
14.
Carmelo Rigano Vittoria Di Martino Rigano Vincenza Vona Amodio Fuggi 《Archives of microbiology》1979,121(2):117-120
Addition ofl-methionine-dl-sulphoximine to cells ofCyanidium caldarium brings about a loss of glutamine synthetase activity. Concomitantly ammonia assimilation is prevented.Under physiological conditions nitrate reductase [NAD(P)H: nitrate oxidoreductase EC 1.6.6.2] is reversibly converted into an inactive enzyme upon addition of ammonia. In the presence of methionine sulphoximine, when glutamine synthetase activity is lost, nitrate reductase is no longer inactivated by ammonia. It is suggested that ammonia itself is not the actual effector of nitrate reductase inactivation.Concomitantly with the failure of nitrate reductase to undergo ammonia-inactivation, in the presence of methionine sulphoximine nitrate reduction is an uncontrolled process, thus, in media with nitrate ammonia continues to be produced and excreted into the external medium at a constant rate.Abbreviations NR
Nitrate reductase
- GS
Glutamine synthetase
- GOGAT
Glutamate syntase
- MSX
l-methionine-dl-sulphoximine 相似文献
15.
The suitability of differentGracilaria spp. and twoSargassum species for bioconversion to methane was determined through bioassays of methane yield.Gracilaria species and strains were excellent feedstocks for high methane yields, ranging from 0.28 to 0.40 m3 kg–1 volatile solids added. These yields ranged from 58 to 95% of theoretical stoichiometric yields. Methane yields were highly correlated with acid soluble carbohydrate components of theGracilaria spp. BothSargassum fluitans andS. pteropleuron were poor feedstocks, with methane yields ranging from 0.12 to 0.19 m3 kg–1 volatile solids added, 27 to 46% of theoretical stoichiometric yields, respectively. The various tissue types of theseSargassum species were also poor feedstocks for anaerobic digestion to methane. While there is no clear explanation for the low methane yields, the twoSargassum spp. appear to contain a high proportion of an insoluble, non-extractable component which may not be available as a substrate for bioconversion to methane. 相似文献
16.
Ester Cecere Orestina D. Saracino Margherita Fanelli Antonella Petrocelli 《Journal of applied phycology》1992,4(4):323-327
A survey is reported of the drifting algal community in Mar Piccolo, a polluted basin subject to sewage outlets. The key role was played by a few key species, mainly floridean red algae. 相似文献
17.
Independent and interactive effects of nutrients and grazers on benthic algal community structure 总被引:1,自引:1,他引:0
Algal responses to nutrients, grazing by Helicopsyche borealis, and concurrent grazing by Helicopsyche and Baetis tricaudatus were examined in recirculating stream chambers. Alagl communities, dominated by Achnanthes minutissima, Cocconeis placentula, and Synedra ulna, were primarily phosphorus-limited. Algal populations responded after only 6 days of nutrient enrichment. Initially, both
the adnate diatom Cocconeis and erect diatom Synedra showed positive response to nutrient enrichment. Accumulation of algal biomass between day 3 and 6 in the P enriched treatment
was resulted primarily from the growth of Synedra, an overstory rosette-like diatom colony. Such a shift in dominant growth from adnate to erect diatoms is a general phenomenon
in periphyton succession in the absence of disturbance. Algal species showed differential responses to an increase of Helicopsyche densities. The accrual rate of Achnanthes continuously decreased with increasing grazer densities. The accrual rates of both Cocconeis and Synedra declined but reached plateaus between medium and high grazing densities. Baetis effectively and exclusively depressed Synedra and had no significant impact on Cocconeis. After concurrent grazing, algal communities were mainly dominated by Cocconeis (approximately 80% of total algal biovolume). The grazer' s mouth structures, grazing efficiencies, and mobility may account
for the differential effects of concurrent grazing on algal communities.
Significant interactive effects of P and grazing by Helicopsyche indicated that both nutrient addition and grazing may exert significant impact on algal communities. However, grazing may
have a much stronger effect on algae than nutrients. Our results indicate that enhancement of algal biomass by P was dampened
by grazing activities and that P had no effect on algal biomass in the presence of grazers. 相似文献
18.
The fine structure of the perineural endothelium 总被引:1,自引:0,他引:1
Prof. K. Akert C. Sandri E. R. Weibel K. Peper H. Moor 《Cell and tissue research》1976,165(3):281-295
Summary Fine strands of motor nerves were examined with the electron microscope using thin section as well as freeze-etching techniques. The specimens were taken from frog cutaneous pectoris nerve, rat sciatic nerve, mouse and shrew phrenic nerves and from human skin nerves. The perineural sheath (Henle, Ranvier, Key and Retzius) consists of one to several concentric laminae of endothelial cells; it encases nerve fascicles and eventually individual nerve fibers and terminals. The endothelial cells are extremely thin and fitted together smoothly by overlap and dove-tailing of their border zones. The cell contacts are formed by continuous zonulae occludentes, often reinforced by maculae adhaerentes, and in depth they comprise 3–15 strands with an average of 5–6 strands per junction. The membranes of endothelial cells are studded with attachment sites and stomata of plasmalemmal vesicles suggesting a high level of pinocytotic activity. This phenomenon is by no means restricted to the external laminae of the endothelial sheath. Each endothelial lamina is vested with basement membranes on both (epineural and endoneural) sides, and the spaces between laminae contain a few collagen fibers and fibroblasts. Occasionally, punctate tight junctions are seen between laminae. Cytological evidence supports the hypothesis that the perineural endothelium provides a relatively tight and highly selective barrier separating the peripheral nerves from surrounding tissue and its extracellular fluid spaces. This effect is achieved on the one hand by the sealing of pericellular spaces and on the other hand by a membrane controlled transcellular transport mechanism (pinocytosis), both of which are enhanced by their serial arrangement.Dedicated to Professor Wolfgang Bargmann, Kiel, on the occasion of his 70th birthday.The technical assistance of Dr. F. Dreyer, Mr. D. Savini, Miss H. Claassen and Miss R. Emch is gratefully acknowledged.Financial support was received by the following institutions: Swiss National Foundation for Scientific Research, grants Nrs. 3.368.0.74, 3.774.72, 3.259.74, 3.045.73. Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 38, Projekt N). The Dr. Eric Slack-Gyr Stiftung in Zürich and the Hartmann-Müller Stiftung for Medical Research in Zürich. 相似文献
19.
The DNA sequence and structural organization of the GC2 plasmid from the red alga Gracilaria chilensis 总被引:1,自引:0,他引:1
Richard Villemur 《Plant molecular biology》1990,15(2):237-243
20.
Summary Mitosis in the marine red algaLomentaria baileyana (Rhodymeniales, Rhodophyta) was studied with the electron microscope. Nucleus associated organelles known as polar rings (PRs) migrate to establish the division poles at prophase. At prometaphase, shallow invaginations in the nuclear envelope (NE) form on two sides of each PR and soon rupture. The gaps that are consequently formed contain several small fragments of NE. A larger region of NE remains intact between the two gaps. By metaphase several cisternae of perinuclear endoplasmic reticulum (PER) have enclosed most of the nucleus but remain absent from the polar regions. The nucleolus disperses partially and a typical metaphase plate of chromosomes is formed. Each PR has disjoined into separate proximal and distal portions. MTs converge widely on all regions of the polar area, but do not extend into the cytoplasm. Some MTs end near or at the chromosomes while others extend slightly farther past the chromosomes or diagonally to the NE. As chromosomes move to opposite poles at anaphase, they are accompanied by nucleolar material. An interzonal midpiece (IZM) is created as the pole to pole distance increases and the NE remains intact except for the polar gaps. Following detachment from the IZM, the daughter nuclei are separated by a large central vacuole as a cleavage furrow develops and eventually constricts to form two cells following pit connection formation. It is suggested that mitosis inLomentaria represents an evolutionary intermediate between that seen in the higher and lower groups of red algae. This conclusion is in agreement with conventional morphological and light microscopic criteria used to placeLomentaria in theRhodymeniales, which is considered to be the next to most advanced order in theRhodophyta. 相似文献