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Turgor regulation in Caloglossa leprieurii (Montagne) J. Agardh (Delesseriaceae : Rhodophyta)
235
J. Exp. Mar. Biol. Ecol., 1984, Vol. 81, pp. 235-239 Elsevier
JEM 33 l
TURGOR REGULATION
IN CALOGLOSSA
LEPRIEURIZ
(Montagne)
J. Agardh (DELJZSSERIACEAE : RHODOPHYTA)’
HERMANN
FISCHER
Botanisches Instihlt der Universitiit,Meckenheimer Aliee ilO. D-5300 Bonn I, F.R. G.
Abstract: In cells of Cufoglossa leprieurii (Montagne) J. Agardh after transference to sea water of a higher salinity there is usually no plasmolysis; the only visible result is a swelling of the cell wall. In the course of the following days the cell wall shrinks again; this indicates a turgor regulation similar to that of other intcrtid~ algae. Key words: turgor regulation; salinity; Caloglossa; Bostrychietum
INTRODUCTION
The effect of increased concentrations in the external environment in most marine algae can be seen in plasmolysis, osmotic regulation - caused either by uptake of solutes or by formation of osmotic agents - being visible in deplasmolysis. In many algae the thickness of the cell wall increases in a hypertonic solution; this phenomenon is particularly pronounced in red algae and was explained by Kotte (1915): in a turgid cell turgor pressure compresses the wall but the latter swells on the inside when for any reason turgor is released. In some Rhodophyta of the littoral region, e.g. Bungia and Porphyru, there is no plasmolysis; the wall adheres to the shrinking cell content until osmotic balance has been reached (Walter, 1923). In the cells of those algae that do not show plasmolysis but instead a swelling of the cell wall, restitution of the turgor by an adaptation of internal to external conc~tration must become apparent in an expansion of the cell content, and a shrinking of the cell wall. Like intertidal algae in general, red algae living on the mangrove roots on tropical coasts show remarkable tolerances of high temperatures, dehydration, and variations in salinity (Almodovar & Biebl, 1962; Biebl, 1962; Post, 1963, 1967; Mlintz & Bergmann, 1972). It is not known whether the osmotic tolerance of these algae is due to a high osmotic potential of the ceils and their capacity to tolerate withdrawal of water and possibly plasmolysis, or to an osmotic adjustment. A visit to the Bermuda Biological Station in April and May 1980 provided an opportunity to study a red alga in which the thickness of the cell walls can be easily measured. ’ Contribution No. 994 from the Bermuda Biological Station for Research. 0022-0981/84/$03.00 0 1984 Elsevier Science Publishers B.V.
HERMANN FISCHER
236
MATERIAL
The prop roots of Biological
AND METHODS
Rhizophora mangle L. in the mangrove at Ferry Reach next to the
Station are densely covered
with algae (Bostrychietum);
apart from Bosfry-
chia montagnei Harvey and B. tenella (Vahl) J. Agardh mainly Caloglossa leprieurii
(Montagne) J. Agardh is found. This last species was chosen for the experiments because in its cells the thickness of the walls can be easily measured with a micrometer eye-piece. C. Ieprieurii at Ferry Reach prefers the lower intertidal belt as well as the shadier positions on the roots compared with Bostrychia, and hence is probably exposed to slightly lower variations in external conditions. For the experiments, Petri dishes (5 cm diameter) were used in which the algae were immersed in sea water of higher salinity concentrations and left until the end of the experiment. Salinity levels of up to four times the concentration of sea water (called 1.0, 2.0, 2.5, 3.0, 3.5,4.0 SW) were prepared by evaporation. In the younger cells the walls are thinner; only mature thalli were, therefore, studied, and in these only oblong cells at a distance of at least four rows of cells from the “midrib” (central cells and pericentrals). Cells close to the margin of the thallus were not studied. Older thalli, in which the cell walls may be slightly thicker, were also not used. Measurements were repeated on the successive days in comparable cells. The results shown in Figs. 1 and 2 were means obtained from measurements on 20 cells each in two “leaflets” each; with this number of cells good averages were obtained. RESULTS PRE-TESTS When
CaZoglo.ssathalli are left to dry in air on filter paper it becomes obvious -
especially when observed in paraffin oil-that the cell walls have increased considerably in thickness; these changes were, however, not quantified. Thalli were immersed in 1.0 SW; in the course of several hours, the concentration under the cover glass increased gradually. According to measurements of the length and width of the cells and the cell walls initially the cell content only shrinks as much as the wall swells, just as in cells of Bornetia secundz~ora (Fetzmann & Kusel, 1962); i.e. the total volume does not change to any measurable degree. Only at higher external concentration does the total volume (cell content + cell wall) decrease as a result of withdrawal of water. Plasmolysis only occurs in exceptional cases in cells of very young thalli and with a strong withdrawal of water, but the cell content detaches only in a few places and only to a minor extent. Thus, even in young cells withdrawal of water results mostly in a shrinkage of the cell content and an extension of the cell wall.
TURGOR REGULATION IN CALOGLOSSA MEASUREMENT
237
OF CELL WALLS
In higher salinities the cell walls swell up at once, in 4.0 SW even to three to four times their normal thickness. In the first few hours after this, the thickness of the wall did not change to any measurable degree, but on the next and the following days changes could be seen, As shown in Fig. 1, after 2-5 days in cells that were left in 2.0 and 2.5 SW the
t
I
24 Fig. I. Change of cell
walls
(pm)
60
r
i
79
103 h
with time aRer transference to concentrated sea water.
thickness of the cell wall decreased to that normal in 1.0 SW, whereas in 3.0 SW it did not return to its original value, and in even higher concentrations it changed very little if at all. Five experiments confirmed the existence of a limit at 3.0 SW; the walls thinned markedly, however, the regulation was incompIete. In even higher concentrations it was, at the most, minute. In other algae also, turgor regulation may be reduced if external concentrations are very high, e.g. in Phaeophyta at ~3.0 SW (Biebl, 1938), and also in diatoms (Fischer, unpubl.). In Porphvra umbiEicalis the osmotically non-regulated range begins at ~4.0 SW (Wiencke & Lauchli, 1980). The swelling of the wall of
I
4
23
Ffi
1
I
81
99
h
Fig. 2. Change of cell walls (pm) with time after stepwise transference to concentrated sea water.
238
HERMANNFISCHER
Caloglossa leprieurii was immediately and completely reversible once the algae were re-transferred to 1.0 SW. In order to minimize the potential “osmotic shock” which might impede turgor regulation, in three additional experiments the algae were transferred gradually to higher salinities, i.e. concentration increased at hourly intervals from 1.0 to 2.0, 2.5, 3.0, 3.5 up to 4.0 SW; thus in Fig. 2 the first measurements shown had been taken 4 h after the start of the experiment. Even under these conditions it was only in the lower salinities that the thickness of the walls gradually decreased to their original value or nearly so; from the varying values in the higher concentrations, only a minimal turgor regulation - if any - can be inferred.
DISCUSSION
Unless they are protected from it by capillary water or water stored in a mucilage layer, the cells of intertidal algae are capable of counteracting a regularly occurring increase in external salinity in various ways. (1) An osmotic potential considerably exceeding that of sea water prevents potentially damaging plasmolysis, or (2) even under natural conditions plasmolysis may occur but is tolerated without major damage, or (3) plasmolysis is reversed or even prevented by the increase of osmotic potential of the cells (for review see Gessner & Schramm, 1971). In red algae, some of which show only a low tolerance of plasmolysis, the swelling of the wall adhering to the contracting cell content may be considered as a protective measure against damage by plasmolysis. Algae with a central vacuole are more or less capable of maintaining their turgor (Cram, 1976); in many red algae this may also be expected. It is possible that because of their special cell structure Bangiales are an exception (Wiencke & Lauchli, 1980). In the experiments with C. leprieurii reported here no decrease of the swelling of the walls could be measured during the day on which the algae had been transferred into higher concentrations, it only occurred on the following day. Thus, turgor regulation does occur, at least in concentrations of up to 3.0 SW. The question remains open, whether this occurs quickly enough to compensate for an increase in concentration caused by tides in the habitat. Without doubt, osmotic stress is reduced in the moss-like Bostrychietum by capillary water stored between the thalli. The capacity for turgor regulation might be more advantageous in the upper littoral during neap tides or in habitats which are more exposed than those in the shade of the mangrove bushes. As in other intertidal algae, in Caloglossa a high osmotic tolerance is combined with a high tolerance of dehydration (Biebl, 1962). Algae of the Bostrychietum endure dehydration for an extraordinary length of time (Post, 1963, 1967). It may depend on habitat conditions which of the two types of tolerance will be of greater importance. Like several Bostrychia species, Caloglossa leprieurii occurs in habitats ranging from sea to fresh water. In this alga as well as in Bostrychia radicans from an estuary Yarish et al. (1979) probably found ecotypes whose growth patterns correlated with the salinity regime of the habitat.
TURGORREGULATIONINCALOGLOSS.4
239
ACKNOWLEDGEMENT
The author is grateful to Dr. Sterrer and the staff of the Bermuda Biological Station for all their kind help.
REFERENCES ALMOD~VAR, L.R. & R. BIEBL,1962. Osmotic resistance of mangrove algae around La Paguera, Puerto Rico. Rev. Algol., Vol. 3, pp. 203-208. BIEBL,R., 1938. Zur Frage der Salzpermeabilitat bei Braunalgen. Protoplasma, Vol. 31, pp. 518-523. BIEBL,R., 1962. Protoplasmatisch-okologische Untersuchungen an Mangrovealgen von Puerto Rico. Protoplasma, Vol. 55, pp. 572-606. CRAM, W. J., 1976. Negative feedback regulation of transport in cells. The maintenance of turgor, volume and nutrient supply. In, Encycl. Plant Physiol., N. S., Vol. 2, Part A, Springer, Berlin, pp. 284-3 16. FETZMANN, E.& H. KUSEL,1962. Uber Bau und Wachstum der Zellwande einiger Ceramiales. Bot. Mar., Vol. 4, pp. 175- 183. GESSNER,F. & H. SCHRAMM,1971. Salinity. Plants. In, Marine ecology, Vol. I, Part 2, edited by 0. Kinne, Wiley Interscience, London, pp. 705-820. KOTTE, H., 1915. Turgor und Membranquellung bei Meeresalgen. Wiss. Meeresunters., Abt. Kiel, N.F., Vol. 17, pp. 115-169. M~~NTz, K. & H. BERGMANN,1972. Resistenz, taxonomische Zugehorigkeit und Proteingehalt einiger Meeresalgen. Arch. Hydrobiol., Suppl. Vol. 41, pp. 94-107. POST, E., 1963. Bostrychiu - nicht tot zu kriegen. Bot. Mar., Vol. 5, pp. 9-18. POST, E., 1967. Zur Gkologie des Bostrychietum. Hydrobiologia, Vol. 29, pp. 263-287. WALTER, H., 1923. Protoplasma- und Membranquellung bei Plasmolyse. Untersuchungen an Bangia fiscopurpurea und anderen Algen. Jahrb. Wiss. Bot., Vol. 62, pp. 145-243. WIENCKE,C. &A. WUCHLI, 1980. Growth, cell volume, and tine structure ofporphyru umbilicalisin relation to osmotic tolerance. Plan&, Vol. 150, pp. 303-311. YARISH, C., P. EDWARDS& S. CASEY, 1979. A culture study of salinity responses in ecotypes of two estuarine red algae. J. Phycol., Vol. 15, pp. 341-346.
J. Exp. Mar. Biol. Ecol., 1984, Vol. 81, pp. 235-239 Elsevier
JEM 33 l
TURGOR REGULATION
IN CALOGLOSSA
LEPRIEURIZ
(Montagne)
J. Agardh (DELJZSSERIACEAE : RHODOPHYTA)’
HERMANN
FISCHER
Botanisches Instihlt der Universitiit,Meckenheimer Aliee ilO. D-5300 Bonn I, F.R. G.
Abstract: In cells of Cufoglossa leprieurii (Montagne) J. Agardh after transference to sea water of a higher salinity there is usually no plasmolysis; the only visible result is a swelling of the cell wall. In the course of the following days the cell wall shrinks again; this indicates a turgor regulation similar to that of other intcrtid~ algae. Key words: turgor regulation; salinity; Caloglossa; Bostrychietum
INTRODUCTION
The effect of increased concentrations in the external environment in most marine algae can be seen in plasmolysis, osmotic regulation - caused either by uptake of solutes or by formation of osmotic agents - being visible in deplasmolysis. In many algae the thickness of the cell wall increases in a hypertonic solution; this phenomenon is particularly pronounced in red algae and was explained by Kotte (1915): in a turgid cell turgor pressure compresses the wall but the latter swells on the inside when for any reason turgor is released. In some Rhodophyta of the littoral region, e.g. Bungia and Porphyru, there is no plasmolysis; the wall adheres to the shrinking cell content until osmotic balance has been reached (Walter, 1923). In the cells of those algae that do not show plasmolysis but instead a swelling of the cell wall, restitution of the turgor by an adaptation of internal to external conc~tration must become apparent in an expansion of the cell content, and a shrinking of the cell wall. Like intertidal algae in general, red algae living on the mangrove roots on tropical coasts show remarkable tolerances of high temperatures, dehydration, and variations in salinity (Almodovar & Biebl, 1962; Biebl, 1962; Post, 1963, 1967; Mlintz & Bergmann, 1972). It is not known whether the osmotic tolerance of these algae is due to a high osmotic potential of the ceils and their capacity to tolerate withdrawal of water and possibly plasmolysis, or to an osmotic adjustment. A visit to the Bermuda Biological Station in April and May 1980 provided an opportunity to study a red alga in which the thickness of the cell walls can be easily measured. ’ Contribution No. 994 from the Bermuda Biological Station for Research. 0022-0981/84/$03.00 0 1984 Elsevier Science Publishers B.V.
HERMANN FISCHER
236
MATERIAL
The prop roots of Biological
AND METHODS
Rhizophora mangle L. in the mangrove at Ferry Reach next to the
Station are densely covered
with algae (Bostrychietum);
apart from Bosfry-
chia montagnei Harvey and B. tenella (Vahl) J. Agardh mainly Caloglossa leprieurii
(Montagne) J. Agardh is found. This last species was chosen for the experiments because in its cells the thickness of the walls can be easily measured with a micrometer eye-piece. C. Ieprieurii at Ferry Reach prefers the lower intertidal belt as well as the shadier positions on the roots compared with Bostrychia, and hence is probably exposed to slightly lower variations in external conditions. For the experiments, Petri dishes (5 cm diameter) were used in which the algae were immersed in sea water of higher salinity concentrations and left until the end of the experiment. Salinity levels of up to four times the concentration of sea water (called 1.0, 2.0, 2.5, 3.0, 3.5,4.0 SW) were prepared by evaporation. In the younger cells the walls are thinner; only mature thalli were, therefore, studied, and in these only oblong cells at a distance of at least four rows of cells from the “midrib” (central cells and pericentrals). Cells close to the margin of the thallus were not studied. Older thalli, in which the cell walls may be slightly thicker, were also not used. Measurements were repeated on the successive days in comparable cells. The results shown in Figs. 1 and 2 were means obtained from measurements on 20 cells each in two “leaflets” each; with this number of cells good averages were obtained. RESULTS PRE-TESTS When
CaZoglo.ssathalli are left to dry in air on filter paper it becomes obvious -
especially when observed in paraffin oil-that the cell walls have increased considerably in thickness; these changes were, however, not quantified. Thalli were immersed in 1.0 SW; in the course of several hours, the concentration under the cover glass increased gradually. According to measurements of the length and width of the cells and the cell walls initially the cell content only shrinks as much as the wall swells, just as in cells of Bornetia secundz~ora (Fetzmann & Kusel, 1962); i.e. the total volume does not change to any measurable degree. Only at higher external concentration does the total volume (cell content + cell wall) decrease as a result of withdrawal of water. Plasmolysis only occurs in exceptional cases in cells of very young thalli and with a strong withdrawal of water, but the cell content detaches only in a few places and only to a minor extent. Thus, even in young cells withdrawal of water results mostly in a shrinkage of the cell content and an extension of the cell wall.
TURGOR REGULATION IN CALOGLOSSA MEASUREMENT
237
OF CELL WALLS
In higher salinities the cell walls swell up at once, in 4.0 SW even to three to four times their normal thickness. In the first few hours after this, the thickness of the wall did not change to any measurable degree, but on the next and the following days changes could be seen, As shown in Fig. 1, after 2-5 days in cells that were left in 2.0 and 2.5 SW the
t
I
24 Fig. I. Change of cell
walls
(pm)
60
r
i
79
103 h
with time aRer transference to concentrated sea water.
thickness of the cell wall decreased to that normal in 1.0 SW, whereas in 3.0 SW it did not return to its original value, and in even higher concentrations it changed very little if at all. Five experiments confirmed the existence of a limit at 3.0 SW; the walls thinned markedly, however, the regulation was incompIete. In even higher concentrations it was, at the most, minute. In other algae also, turgor regulation may be reduced if external concentrations are very high, e.g. in Phaeophyta at ~3.0 SW (Biebl, 1938), and also in diatoms (Fischer, unpubl.). In Porphvra umbiEicalis the osmotically non-regulated range begins at ~4.0 SW (Wiencke & Lauchli, 1980). The swelling of the wall of
I
4
23
Ffi
1
I
81
99
h
Fig. 2. Change of cell walls (pm) with time after stepwise transference to concentrated sea water.
238
HERMANNFISCHER
Caloglossa leprieurii was immediately and completely reversible once the algae were re-transferred to 1.0 SW. In order to minimize the potential “osmotic shock” which might impede turgor regulation, in three additional experiments the algae were transferred gradually to higher salinities, i.e. concentration increased at hourly intervals from 1.0 to 2.0, 2.5, 3.0, 3.5 up to 4.0 SW; thus in Fig. 2 the first measurements shown had been taken 4 h after the start of the experiment. Even under these conditions it was only in the lower salinities that the thickness of the walls gradually decreased to their original value or nearly so; from the varying values in the higher concentrations, only a minimal turgor regulation - if any - can be inferred.
DISCUSSION
Unless they are protected from it by capillary water or water stored in a mucilage layer, the cells of intertidal algae are capable of counteracting a regularly occurring increase in external salinity in various ways. (1) An osmotic potential considerably exceeding that of sea water prevents potentially damaging plasmolysis, or (2) even under natural conditions plasmolysis may occur but is tolerated without major damage, or (3) plasmolysis is reversed or even prevented by the increase of osmotic potential of the cells (for review see Gessner & Schramm, 1971). In red algae, some of which show only a low tolerance of plasmolysis, the swelling of the wall adhering to the contracting cell content may be considered as a protective measure against damage by plasmolysis. Algae with a central vacuole are more or less capable of maintaining their turgor (Cram, 1976); in many red algae this may also be expected. It is possible that because of their special cell structure Bangiales are an exception (Wiencke & Lauchli, 1980). In the experiments with C. leprieurii reported here no decrease of the swelling of the walls could be measured during the day on which the algae had been transferred into higher concentrations, it only occurred on the following day. Thus, turgor regulation does occur, at least in concentrations of up to 3.0 SW. The question remains open, whether this occurs quickly enough to compensate for an increase in concentration caused by tides in the habitat. Without doubt, osmotic stress is reduced in the moss-like Bostrychietum by capillary water stored between the thalli. The capacity for turgor regulation might be more advantageous in the upper littoral during neap tides or in habitats which are more exposed than those in the shade of the mangrove bushes. As in other intertidal algae, in Caloglossa a high osmotic tolerance is combined with a high tolerance of dehydration (Biebl, 1962). Algae of the Bostrychietum endure dehydration for an extraordinary length of time (Post, 1963, 1967). It may depend on habitat conditions which of the two types of tolerance will be of greater importance. Like several Bostrychia species, Caloglossa leprieurii occurs in habitats ranging from sea to fresh water. In this alga as well as in Bostrychia radicans from an estuary Yarish et al. (1979) probably found ecotypes whose growth patterns correlated with the salinity regime of the habitat.
TURGORREGULATIONINCALOGLOSS.4
239
ACKNOWLEDGEMENT
The author is grateful to Dr. Sterrer and the staff of the Bermuda Biological Station for all their kind help.
REFERENCES ALMOD~VAR, L.R. & R. BIEBL,1962. Osmotic resistance of mangrove algae around La Paguera, Puerto Rico. Rev. Algol., Vol. 3, pp. 203-208. BIEBL,R., 1938. Zur Frage der Salzpermeabilitat bei Braunalgen. Protoplasma, Vol. 31, pp. 518-523. BIEBL,R., 1962. Protoplasmatisch-okologische Untersuchungen an Mangrovealgen von Puerto Rico. Protoplasma, Vol. 55, pp. 572-606. CRAM, W. J., 1976. Negative feedback regulation of transport in cells. The maintenance of turgor, volume and nutrient supply. In, Encycl. Plant Physiol., N. S., Vol. 2, Part A, Springer, Berlin, pp. 284-3 16. FETZMANN, E.& H. KUSEL,1962. Uber Bau und Wachstum der Zellwande einiger Ceramiales. Bot. Mar., Vol. 4, pp. 175- 183. GESSNER,F. & H. SCHRAMM,1971. Salinity. Plants. In, Marine ecology, Vol. I, Part 2, edited by 0. Kinne, Wiley Interscience, London, pp. 705-820. KOTTE, H., 1915. Turgor und Membranquellung bei Meeresalgen. Wiss. Meeresunters., Abt. Kiel, N.F., Vol. 17, pp. 115-169. M~~NTz, K. & H. BERGMANN,1972. Resistenz, taxonomische Zugehorigkeit und Proteingehalt einiger Meeresalgen. Arch. Hydrobiol., Suppl. Vol. 41, pp. 94-107. POST, E., 1963. Bostrychiu - nicht tot zu kriegen. Bot. Mar., Vol. 5, pp. 9-18. POST, E., 1967. Zur Gkologie des Bostrychietum. Hydrobiologia, Vol. 29, pp. 263-287. WALTER, H., 1923. Protoplasma- und Membranquellung bei Plasmolyse. Untersuchungen an Bangia fiscopurpurea und anderen Algen. Jahrb. Wiss. Bot., Vol. 62, pp. 145-243. WIENCKE,C. &A. WUCHLI, 1980. Growth, cell volume, and tine structure ofporphyru umbilicalisin relation to osmotic tolerance. Plan&, Vol. 150, pp. 303-311. YARISH, C., P. EDWARDS& S. CASEY, 1979. A culture study of salinity responses in ecotypes of two estuarine red algae. J. Phycol., Vol. 15, pp. 341-346.