scholarly journals Temporal relationships of host cell and algal mitosis in the green hydra symbiosis

1982 ◽  
Vol 58 (1) ◽  
pp. 423-431
Author(s):  
P.J. McAuley
Keyword(s):  
Cell Division ◽  
Host Cell ◽  
Digestive Cell ◽  
Digestive Cells ◽  
Symbiotic Algae ◽  
Green Hydra ◽  
Temporal Relationships ◽  
Dividing Cells ◽  
Cell Mitosis ◽  
Mitotic Cells

In fed hydra or excised regenerating peduncles there are increases in the mitotic indices of both digestive cells and the symbiotic algae that reside within them. Conversely, algal and digestive cell mitotic indices decrease in starved hydra. The temporal relationships of algal and host cell division differ in fed hydra and regenerating peduncles. After feeding, algal and digestive cell mitotic indices both reach a peak at about the same time; during regeneration, first the algae and then the digestive cells divide. Thus, mitotic digestive cells in regenerating peduncles contain more algae than those in gastric regions of fed hydra. However, in both cases mitotic digestive cells contain more algae than non-mitotic cells. The algae appear to be partitioned at random between daughter digestive cells at teleophase. It is suggested that the division of the symbiotic algae is closely related to that of the digestive cells in which they maintained. Mitosis of algae is stimulated by host cell mitosis, but in non-dividing cells algal mitosis is restricted. Possible mechanisms by which the host digestive cells could restrict algal division are discussed.

The cell cycle of symbiotic Chlorella. I. The relationship between host feeding and algal cell growth and division

1985 ◽  
Vol 77 (1) ◽  
pp. 225-239
Author(s):  
P.J. McAuley
Keyword(s):  
Cell Division ◽  
Cell Growth ◽  
Host Cell ◽  
Algal Cell ◽  
Host Cells ◽  
Digestive Cell ◽  
Host Feeding ◽  
Digestive Cells ◽  
Division Factor ◽  
Cell Mitosis

When green hydra were starved, cell division of the symbiotic algae within their digestive cells was inhibited, but algal cell growth, measured as increase in either mean volume or protein content per cell, was not. Therefore, control of algal division by the host digestive cells must be effected by direct inhibition of algal mitosis rather than by controlling algal cell growth. The number of algae per digestive cell increased slightly during starvation, eventually reaching a new stable level. A number of experiments demonstrated that although there was a relationship between host cell and algal mitosis, this was not causal: the apparent entrainment of algal mitosis to that of the host cells could be disrupted. Thus, there was a delay in algal but not host cell mitosis when hydra were fed after prolonged starvation, and algae repopulated starved hydra with lower than normal numbers of algae (reinfected aposymbionts or hydra transferred to light after growth in continuous darkness). Two experiments demonstrated a direct stimulation of algal cell division by host feeding. Relationships of algal and host cell mitosis to numbers of Artemia digested per hydra were different, and in hydra fed extracted Artemia algal, but not host cell, mitosis was reduced in comparison to that in control hydra fed live shrimp. It is proposed that algal division may be dependent on a division factor, derived from host digestion of prey, whose supply is controlled by the host cells. Numbers of algae per cell would be regulated by competition for division factor, except at host cell mitosis, when the algae may have temporarily uncontrolled access to host pools of division factor. The identity of the division factor is not known, but presumably is a metabolite needed by both host cells and algae.

The cell cycle of symbiotic Chlorella. III. Numbers of algae in green hydra digestive cells are regulated at digestive cell division

1986 ◽  
Vol 85 (1) ◽  
pp. 63-71
Author(s):  
P.J. McAuley
Keyword(s):  
Cell Division ◽  
Host Cell ◽  
Algal Cell ◽  
Host Cells ◽  
Digestive Cell ◽  
Digestive Cells ◽  
Daughter Cells ◽  
Green Hydra ◽  
Mother And Daughter ◽  
Chlorella Algae

Regression analysis of the relationship between the size of interphase and mitotic digestive cells of green hydra, and the numbers and total volume of the symbiotic Chlorella algae they contain showed a partial correlation only, suggesting that numbers of algae per cell are not regulated by limiting them to a specific proportion of the host cell, and that the variation observed in numbers of algae per cell is not due to variation in host cell size. After hydra were fed, which stimulates algae and digestive cells to divide at the same time, numbers of algae per cell were higher in prophase than in interphase cells, and numbers increased as mitosis proceeded. In excised regenerating peduncles algae divide before digestive cells, and at the onset of digestive cell division mitotic cells were found to contain almost twice the number of algae as before excision. Thus, almost all of the algal cell division necessary to maintain a constant population size was associated with digestive cell division. Analysis of variance in numbers of algae in telophase mother and daughter cells suggested that the proportion of algae dividing as a result of host cell mitosis was greater in digestive cells with few algae than in those with many algae. The fact that the mechanism controlling the proportion of algae dividing in host cells is expressed at host cell division and is manifested in the daughter cells may contribute to wide variation in numbers of algae per cell.

Partitioning of symbiotic Chlorella at host cell telophase in the green hydra symbiosis

1990 ◽  
Vol 329 (1252) ◽  
pp. 47-53 ◽  
Keyword(s):  
Cell Division ◽  
Host Cell ◽  
Daughter Cell ◽  
Control Cell ◽  
Culture Conditions ◽  
Digestive Cells ◽  
Density Dependent ◽  
Green Hydra ◽  
The Mean ◽  
Control Cell Division

Although there is much evidence that green hydra digestive cells control cell division of their Chlorella symbionts, so that the symbionts divide only at host cell division, it is not clear how the population size of symbionts (numbers per cell) is regulated. In constant culture conditions the mean number of symbionts per cell also remains constant, but with a very large variance about the mean. The way in which symbionts are partitioned at host cell division appears to account for that variation. By counting numbers of Chlorella in daughter cells at late telophase it was found that partitioning of Chlorella symbionts was not symmetrical, but at random, closely following that predicted by the binomial distribution if it is assumed that each symbiont had an equal probability of entering either host daughter cell. A better fit to the predicted distribution was obtained from observations of partition in digestive cells from excised regenerating peduncles than in those from recently fed gastric regions, possibly because in the former, algae have completed their division before the host cell divides, while in the latter algal and host cell division takes place at the same time. There was only a small effect of differences in daughter cell volume on numbers of symbionts received, but comparison of variance and coefficient of variation of numbers of algae in mother (post-algal division, pre-partition) and daughter telophase digestive cells (pre-division, post-partition) suggested that algal division at host mitosis was density dependent. Random partitioning of algae at host cell telophase would account for the wide variation in numbers of algae per cell, and compensatory density-dependent algal division at the next host cell mitosis would ensure stability of the mean algal population.

The green hydra symbiosis. VII. Conservation of the host cell habitat by the symbiotic algae

1982 ◽  
Vol 216 (1205) ◽  
pp. 415-426 ◽  
Keyword(s):  
Host Cell ◽  
Lysosomal Degradation ◽  
Normal Complement ◽  
Calcofluor White ◽  
Digestive Cells ◽  
Symbiotic Algae ◽  
Green Hydra ◽  
Fluorescent Agent ◽  
Almost All ◽  
Cell Base

Freshly isolated ‘European’ algae phagocytosed by digestive cells of ‘European’ green hydra were distinguished from the pre-existing popu­lation of algae by prestaining with the fluorescent agent Calcofluor White. Only a small number of phagocytosed ‘European’ algae or algae cultured from Paramecium bursaria avoided lysosomal degradation and were transported to the cell base in symbiotic digestive cells, although in aposymbionts up to 50% of phagocytosed algae were transported. Degradation of almost all phagocytosed algae also occurred in digestive cells of hydra containing only half the normal complement of algae, and in those of hydra symbiotic with algae cultured from Paramecium . The presence of algae at the bases of digestive cells appears to negate the mechanism by which potentially symbiotic algae normally avoid lysosomal attack. This protects the host cell and its symbionts from invasion by ‘foreign’ algae and suggests that once established the green hydra symbiosis is conservative in nature.

The green hydra symbiosis. IV. Entry of symbionts into digestive cells

1982 ◽  
Vol 216 (1202) ◽  
pp. 1-6 ◽  
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Plasma Membrane ◽  
Digestive Cell ◽  
Particle Type ◽  
Digestive Cells ◽  
Symbiotic Algae ◽  
Green Hydra ◽  
Different Types ◽  
Scanning Electron

Scanning electron microscopy showed that particles, including symbiotic algae, non-symbiotic algae and latex spheres, entered digestive cells of European green hydra by two different types of phagocytosis: (i) they sank into crater-like formations of the digestive-cell surface; or (ii) they were enveloped by raised, funnel-like extensions of plasma membrane. The morphology selected did not depend on particle type: there was no evidence for specific recognition of symbiotic algae during phagocytosis.

The green hydra symbiosis. V. Stages in the intracellular recognition of algal symbionts by digestive cells

1982 ◽  
Vol 216 (1202) ◽  
pp. 7-23 ◽  
Keyword(s):  
Host Cell ◽  
Transport Mechanism ◽  
Digestive Cell ◽  
Digestive Cells ◽  
Maltose Transport ◽  
Green Hydra ◽  
Algal Symbionts ◽  
Wide Range ◽  
Cell Base

Aposymbiotic (alga-free) green hydra may be reinfected by injecting a suspension of Chlorella symbionts into their coelenterons. Digestive cells could phagocytose a wide range of Chlorella types, but transport to the cell base, where the symbionts normally reside, was limited to algae that release detectable amounts of maltose. Transport of their own symbionts was inhibited when maltose release was curtailed by prolonged pretreatment with a photosynthetic inhibitor. After phagocytosis, only about half of their own symbionts were transported, the rest remaining at the digestive cell apex where they disintegrated. This phenomenon was termed sorting. It was not due to damage of algae during isolation, nor to saturation of the transport mechanism. A further stage of discrimination was observed to take place up to 5 days after injection; some symbionts that had been transported to the cell bases were removed to the apices and disintegrated or were ejected (re-sorting). It is concluded that recognition of suitable algae is unlikely to involve identification of a single algal character by the European digestive cells. The establishment of the symbiosis may depend upon a number of algal properties and interactions within the host cell.

The green hydra symbiosis. VIII. Mechanisms in symbiont regulation

1984 ◽  
Vol 221 (1224) ◽  
pp. 291-319 ◽  
Keyword(s):  
Cell Division ◽  
Algal Cell ◽  
Algal Growth ◽  
Culture Conditions ◽  
Continuous Illumination ◽  
Digestive Cell ◽  
Green Hydra ◽  
European Strain ◽  
Standard Culture ◽  
Feeding Regimes

The relative amount of symbiotic algae and animal tissue in the European strain of green hydra was altered by changes in illumination and feeding regimes. This indicates that the host can regulate the algal population to different sizes depending on external conditions. For animals maintained in continuous illumination, 12 h light: 12 h dark, and continous darkness, each with thrice-weekly feeding, a highly significant regression of algal volume per digestive cell on digestive cell volume was demonstrated, suggesting that the space available for the algae may be one factor that determines the population size of the algal symbionts. Seven strains of Chlorella originally symbiotic with other invertebrates formed stable associations with the European strain of green hydra; this included one strain (NC64A) which released very little maltose at pH 4-5. Althought the relative amounts of algal and host biomass of these experimental associations were very similar under standard culture conditions, large numbers of cells of strain NC64A were regularly expelled from the host. This suggests that the ability of the host to control the growth rate of its symbionts is related to the alga’s capacity for maltose release. The latter characteristic is also correlated with a sensitivity of growth to acid conditions. Of the five cultured strains of symbiotic Chlorella examined, only the two strains that released substantial amounts of maltose at pH 4-5 failed to grow at pH 4.0 and pH 4.5. It is proposed that the regulation of algal cell division in the natural symbiosis is principally mediated through relatively small and temporary changes in the pH of the perialgal vacuole. At more acid values, photosynthetically fixed carbon is primarily directed towards maltose release and little or no algal growth occurs. At higher pH values, maltose release declines sharply and the carbon becomes primarily directed towards symbiont growth. Such a relatively simple hypothetical model, involving stimulation of symbiont growth by temporary alkalinization of the perialgal vacuole, can explain the observed responses to change in environmental conditions, as well as the relation between the timing of symbiont and host cell division.

The green hydra symbiosis and ammonium. II. Ammonium assimilation and release by freshly isolated symbionts and cultured algae

1989 ◽  
Vol 235 (1281) ◽  
pp. 365-382 ◽  
Keyword(s):  
Cell Division ◽  
Nitrogen Deficiency ◽  
Ammonium Assimilation ◽  
Digestive Cell ◽  
Medium Ph ◽  
Detailed Model ◽  
Homeostatic Mechanism ◽  
Green Hydra ◽  
Dark Regime ◽  
Net Release

Freshly isolated symbionts from the European strain of green hydra containing native (E/E) or heterologous algae (E/3N8, E/NC), and the Wytham strain of green hydra (W5) assimilated ammonium at pH 7 in light. Both nitrogen-replete and nitrogen-starved cultures of high (3N813A) and low (NC64A) maltose-releasing strains of Chlorella also assimilated ammonium at pH 7 in light. However, at pH 4, freshly isolated symbionts from E/E, E/3N8 and W5, and nitrogen-replete cultures of the high maltose-releasing strain 3N813A released ammonium, and the rate of release was stimulated in darkness. Freshly isolated symbionts from the association E/NC released ammonium at pH 4 when incubated in darkness but assimilated ammonium in light. Nitrogen-starved cultures of both high and low maltose-releasing strains assimilated ammonium at pH 4 in both light and dark. Ammonium-assimilation characteristics of nitrogen-starved cultures were sufficiently different from those of freshly isolated symbionts to indicate that symbionts are not maintained by the host under nitrogen deficiency at high pH. A detailed model of symbiont regulation is proposed that suggests that the ammonium compensation point (defined as the pH at which there is no net release or assimilation of ammonium) is important as a homeostatic mechanism for maintaining high rates of maltose release in light and as a mechanism for controlling both symbiont cell division and changes in algal number per digestive cell with changes in environmental conditions. Experimental evidence consistent with the model is presented. Nitrogen-replete cultures of the high maltose-releasing strain 3N813A decreased medium pH during ammonium assimilation and increased medium pH during ammonium release. Furthermore, dark-grown animals of the association E/E released ammonium when transferred to a 12 h light : 12 h dark régime and release was stimulated by the photosynthetic inhibitor 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea.

Mechanisms of nutritive endocytosis. I. Phagocytic versatility and cellular recognition in Chlorohydra digestive cells, a scanning electron microscope study

1981 ◽  
Vol 49 (1) ◽  
pp. 311-339
Author(s):  
P.L. McNeil
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Cell Surface ◽  
Surface Coating ◽  
Surface Membrane ◽  
Digestive Cell ◽  
Scanning Electron Microscope Study ◽  
Digestive Cells ◽  
Symbiotic Algae ◽  
Scanning Electron

The quantity of surface membrane internalized during phagocytosis by Chlorohydra digestive cells was estimated for a range of particle types. Challenge with 2 of these particles, freshly isolated symbiotic algae (FIS) and latex spheres (LS), resulted in a greater (2.5 X) quantity of surface membrane interiorized than with heat-treated symbiotic algae (HTS) and free living algae (FA), Chlorella vulgaris. This discriminatory process was investigated further by a scanning electron microscope (SEM) and transmission electron microscope (TEM) comparison of the surface events associated with phagocytosis of each of these 4 particles. Those particles that were avidly phagocytized, FIS and LS, were both enveloped by a tightly fitting extension of digestive-cell surface, and obtained a prominent surface coating after their injection into the gut of Chlorohydra. Phagocytic challenge with FIS resulted, furthermore, in the rapid formation of a dense microvillar cover on digestive-cell surfaces. HTS and FA, on the other hand, were enveloped by a less closely fitting extension of digestive-cell surface, did not obtain a prominent surface coating, and did not induce the formation of microvilli. In addition, SEM revealed that at least 3 morphologically distinct phagocytic modes were utilized by the versatile nutritive phagocyte of Chlorohydra: (I) envelopment by the progressive movement of numerous, overlapping tubular protrusions (microvilli) over the particle (FIS) surface, forming first a network of tubular interlocking members, and finally a continuous but rough enclosing surface; (2) envelopment by a single, smooth-surfaced, funnel-like extension of digestive-cell surface (FIS, LS, HTS, FA); and (3) envelopment by multiple, broad folds, often of unequal size, and with overlapping margins (Artemia particles).

Regulatory mechanisms maintaining the Hydra-Chlorella symbiosis

1983 ◽  
Vol 219 (1215) ◽  
pp. 193-210 ◽  
Keyword(s):  
Light And Electron Microscopy ◽  
Inorganic Nutrients ◽  
Host Cells ◽  
Regulatory Mechanisms ◽  
Digestive Cell ◽  
Digestive Cells ◽  
Symbiotic Associations ◽  
Symbiotic Algae ◽  
Unicellular Algae

In symbiotic associations between unicellular algae and aquatic invertebrates a relatively constant biomass ratio of algae to host is maintained. The mechanisms that maintain this ratio have not been adequately investigated. This study describes aspects of the mechanisms regulating numbers of algae in Hydra viridis digestive cells. Symbiotic digestive cells that acquire supernumerary algae by phagocytosis restore the number to normal levels by several mechanisms. Light and electron microscopy provide evidence showing that excess algae are expelled intact or digested within the host cells. This finding is significant since, under normal circumstances, symbiotic algae are not expelled and avoid digestion by inhibiting phagosome—lysosome fusion. The role of host cell mitosis in the regulation of the number of algae per cell is also investigated. Quantitative data are presented which show that mitosis alone cannot account for the regulation of supernumerary algae. The hypothesis that the supply of inorganic nutrients may influence the regulation of the number of algae per digestive cell is also tested in this study. Enrichment of the maintenance medium with a combination of nutrients enhances growth of the symbiotic algae, the digestive cells become packed with algae, and eventually the host is overgrown and killed by the algae. Therefore regulatory mechanisms controlling the algal population when exogenous inorganic nutrients are limited, are no longer effective when nutrients are available.

Sign in / Sign up

Export Citation Format

Share Document