6 Contractile vacuole s in green algae – structure and function

Komsic-Buchmann, Karin; Becker, Burkhard

doi:10.1515/9783110229615.123

Cited by 4 publications

(4 citation statements)

References 72 publications

(106 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…11.2), which allows pinocytotic uptake of external material (Kivic and Vesk 1974a;Bouck 2012;Omodeo 2013). A system of contractile vacuoles (one main vacuole with several accessory vacuoles) is associated with the reservoir, believed to be involved in osmoregulation (Rosati et al 1996;Komsic-Buchmann and Becker 2012). At the base of the reservoir two flagella originate in basal bodies, but only one of them extends as a trailing flagellum from the reservoir while the other one reaches up to the paraxonemal body (PAB, also called paraflagellar body) (Tollin 1973;Piccinni and Mammi 1978), located on the long flagellum half way between the bottom and the opening of the invagination, called pharynx (Frey-Wyssling and Mühlethaler 1960;Kisielewska et al 2015).…”

Section: The Organismsmentioning

confidence: 99%

Photomovement in Euglena

Häder

Iseki

2017

Advances in Experimental Medicine and Biology

View full text Add to dashboard Cite

Motile microorganisms such as the green Euglena gracilis use a number of external stimuli to orient in their environment. They respond to light with photophobic responses, photokinesis and phototaxis, all of which can result in accumulations of the organisms in suitable habitats. The light responses operate synergistically with gravitaxis, aerotaxis and other responses. Originally the microscopically obvious stigma was thought to be the photoreceptor, but later the paraxonemal body (PAB, paraflagellar body) has been identified as the light responsive organelle, located in the trailing flagellum inside the reservoir. The stigma can aid in light direction perception by shading the PAB periodically when the cell rotates helically in lateral light, but stigmaless mutants can also orient with respect to the light direction, and negative phototaxis does not need the presence of the stigma. The PAB is composed of dichroically oriented chromoproteins which is reflected in a pronounced polarotaxis in polarized light. There was a long debate about the potential photoreceptor molecule in Euglena, including carotenoids, flavins and rhodopsins. This discussion was terminated by the unambiguous proof that the photoreceptor is a 400 kDa photoactivated adenylyl cyclase (PAC) which consists of two α- and two β-subunits each. Each subunit possesses two BLUF (Blue Light receptor Using FAD) domains binding FAD, which harvest the light energy, and two adenylyl cyclases, which produce cAMP from ATP. The cAMP has been found to activate one of the five protein kinase s found in Euglena (PK.4). This enzyme in turn is thought to phosphorylate proteins inside the flagellum which result in a change in the flagellar beating pattern and thus a course correction of the cell. The involvements of PAC and protein kinase have been confirmed by RNA interference (RNAi). PAC is responsible for step-up photophobic responses as well as positive and negative phototaxis, but not for the step-down photophobic response, even though the action spectrum of this resembles those for the other two responses. Analysis of several colorless Euglena mutants and the closely related Euglena longa (formerly Astasia longa) confirms the results. Photokinesis shows a completely different action spectrum. Some other Euglena species, such as E. sanguinea and the gliding E. mutabilis, have been investigated, again showing totally different action spectra for phototaxis and photokinesis as well as step-up and step-down photophobic responses.

show abstract

Section: The Organismsmentioning

confidence: 99%

Photomovement in Euglena

Häder

Iseki

2017

Advances in Experimental Medicine and Biology

View full text Add to dashboard Cite

show abstract

“…Despite this structural diversity the basic functions seem to be conserved between different eukaryotes because the same proteins and cellular processes have been found in Amoeba, Dictyostelium, Paramecium, Trypanosoma and green algae [e.g. V-ATPase (Becker and Hickisch, 2005;Fok et al, 2002;Heuser et al, 1993;Montalvetti et al, 2004;Nishihara et al, 2008;Robinson et al, 1998;Wassmer et al, 2005), aquaporin Nishihara et al, 2008), vesicular transport (Becker and Hickisch, 2005;Buchmann and Becker, 2009;Bush et al, 1994;Harris et al, 2001;Kissmehl et al, 2007;Schilde et al, 2006;Stavrou and O'Halloran, 2006); see KomsicBuchmann and Becker for a summary of identified proteins and cellular processes (Komsic- Buchmann and Becker, 2012)]. …”

Section: Introductionmentioning

confidence: 99%

The SEC6 protein is required for function of the contractile vacuole inChlamydomonas reinhardtii

Komsic-Buchmann¹,

Stephan²,

Becker³

2012

Journal of Cell Science

Self Cite

View full text Add to dashboard Cite

SummaryContractile vacuoles (CVs) are essential for osmoregulation in many protists. To investigate the mechanism of CV function in Chlamydomonas, we isolated novel osmoregulatory mutants. Four of the isolated mutant cell lines carried the same 33,641 base deletion, rendering the cell lines unable to grow under strong hypotonic conditions. One mutant cell line (Osmo75) was analyzed in detail. The CV morphology was variable in mutant cells, and most cells had multiple small CVs. In addition, one or two enlarged CVs or no visible CVs at all, were observed by light microscopy. These findings suggest that the mutant is impaired in homotypic vacuolar and exocytotic membrane fusion. Furthermore the mutants had long flagella. One of the affected genes is the only SEC6 homologue in Chlamydomonas (CreSEC6). The SEC6 protein is a component of the exocyst complex that is required for efficient exocytosis. Transformation of the Osmo75 mutant with a CreSEC6-GFP construct rescued the mutant completely (osmoregulation and flagellar length). Rescued strains overexpressed CreSEC6 (as a GFP-tagged protein) and displayed a modified CV activity. CVs were larger, whereas the CV contraction interval remained unchanged, leading to increased water efflux rates. Electron microscopy analysis of Osmo75 cells showed that the mutant is able to form the close contact zones between the plasma membrane and the CV membrane observed during late diastole and systole. These results indicate that CreSEC6 is essential for CV function and required for homotypic vesicle fusion during diastole and water expulsion during systole. In addition, CreSEC6 is not only necessary for CV function, but possibly influences the CV cycle in an indirect manner and flagellar length in Chlamydomonas.

show abstract

“…Although CV morphologies and behaviors differ among various organisms (see Komsic-Buchman and Becker [5] for a recent comparison of the contractile vacuoles of a variety of protists), the basic mechanism (water uptake into the CV by osmosis) appears to be conserved between different eukaryotes. The same proteins/ cellular processes have been implicated in CV function in Amoeba, Dictyostelium, Paramecium, Trypanosoma, and green algae (e.g., proton pumps and aquaporins) (3,4,6).…”

mentioning

confidence: 99%

The Contractile Vacuole as a Key Regulator of Cellular Water Flow in Chlamydomonas reinhardtii

2014

Self Cite

View full text Add to dashboard Cite

Most freshwater flagellates use contractile vacuoles (CVs) to expel excess water. We have used Chlamydomonas reinhardtii as a green model system to investigate CV function during adaptation to osmotic changes in culture medium. We show that the contractile vacuole in Chlamydomonas is regulated in two different ways. The size of the contractile vacuoles increases during cell growth, with the contraction interval strongly depending on the osmotic strength of the medium. In contrast, there are only small fluctuations in cytosolic osmolarity and plasma membrane permeability. Modeling of the CV membrane permeability indicates that only a small osmotic gradient is necessary for water flux into the CV, which most likely is facilitated by the aquaporin major intrinsic protein 1 (MIP1). We show that MIP1 is localized to the contractile vacuole, and that the expression rate and protein level of MIP1 exhibit only minor fluctuations under different osmotic conditions. In contrast, SEC6, a protein of the exocyst complex that is required for the water expulsion step, and a dynamin-like protein are upregulated under strong hypotonic conditions. The overexpression of a CreMIP1-GFP construct did not change the physiology of the CV. The functional implications of these results are discussed. In hypotonic media, cells/organisms take up water by osmosis. Water uptake occurs only if the water potential inside the cell is more negative than that outside the cell. The amount of water taken up in a given time depends on (i) the water potential gradient between the medium and the cell interior, (ii) the surface area of the plasma membrane (PM), and (iii) the extent to which the PM is permeable to water. Cells can use three strategies to prevent bursting caused by the osmotic influx of water in a hypotonic environment. First, organisms can modify the composition of its interior, its surface area, and/or its PM permeability to limit water uptake. Second, organisms can use a cell wall to generate a cell wall pressure potential (turgor) to balance the osmotic water potential, as many algae, plants, and fungi do. However, many unicellular protists do not possess a rigid cell wall. Instead, these protists use a third strategy: they employ water pumps called contractile vacuoles (CVs) to remove excess water. CVs are specialized vacuoles that slowly accumulate water during diastole and periodically expel the liquid rapidly into the medium (systole) (1-4).Although CV morphologies and behaviors differ among various organisms (see for a recent comparison of the contractile vacuoles of a variety of protists), the basic mechanism (water uptake into the CV by osmosis) appears to be conserved between different eukaryotes. The same proteins/ cellular processes have been implicated in CV function in Amoeba, Dictyostelium, Paramecium, Trypanosoma, and green algae (e.g., proton pumps and aquaporins) (3, 4, 6). However, we still do not know anything about what other factors (ion transport systems) are needed to build up the necessary osmotic gradient in a...

show abstract

6 Contractile vacuole s in green algae – structure and function

Cited by 4 publications

References 72 publications

Photomovement in Euglena

Photomovement in Euglena

The SEC6 protein is required for function of the contractile vacuole inChlamydomonas reinhardtii

The Contractile Vacuole as a Key Regulator of Cellular Water Flow in Chlamydomonas reinhardtii

Contact Info

Product

Resources

About