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Concerning Chytridium cornutum Braun
[208 ] Trans. Brit. mycol. Soc. 46 (2),208-212 (1963).
CONCERNING CHYTRIDIUM CORNUTUM BRAUN By HILDA M. CANTER (MRS
J.
W. G. LUND)
Freshwater Biological Association, Ambleside, England (With
2
T ext-figures)
A chytrid is described on heterocysts of Aphanizomenon fios-aquae (L.) Ralfs from preserved material of plankton from a pond near Sedlic e, South Bohemia. For the time being it is included provisionally under the binomial Chytridium comutum Braun.
In 1952 Professor B. Fott kindly sent me a sample of preserved plankton from a pond, near Sedlice, South Bohemia, Czechoslovakia (colI. 20 July 1951). It contained Aphanizomenon flos-aquae (L. ) Ralfs, the heterocysts of which were infected by a chytrid. Specimens were not abundant but sufficient is known to warrant a description of the fungus. Many details concerning its morphology and method of dehiscence need confirmation from living material. Because of this I do not propose to diagnose this chytrid as new but include it doubtfully under the binomial Chytridium cornutum Braun, for reasons which become obvious in the discussion . The zoospore having settled on the wall of a heterocyst enlarges, keeping its spherical shape (Fig. 1 a-e). Further growth results in the formation of a more ovoid sporangium (Fig. Ig ). Sporangia range from 8·5P. high x 7'5 p. broad to 13 p. high XII P. broad. The apex of the sporangium is flattened and forms a small lid, which appears refractive in contrast to the rest of the wall. The zoospores (up to sixty ) seem to be fully differentiated in the sporangium for their outline is visible in mature specimens (Fig. 1 g). The zoospore is about 2 p. diam., and its content in preserved material appears to be granular with a few minute refractive globules. That this represents the true nature of the zoospore content is doubtful. Professor B. Fott in a drawing of a mature sporangium, made from living material, shows many globules of equal size and equally spaced. This suggests that the living zoospore contains a single conspicuous refractive globule. The operculum is small, and judging by the narrow opening at the apex of the sporangium it seems likely that the zoospores emerge singly through it. The wall of the empty sporangium does not collapse (Fig. 1 h, i ). Inside th e homogeneous, structureless content of the heterocyst, beneath the sporangium, is a colourless ' bubble-like' region which increases in size as the sporangium grows. It is sph eric al to oval and at first sight resembles a subsporan gial vesicle or sac-like rhizoid. Within it, in some specimens, there appear to be fine threads which probably constitute the rhizoidal system (Fig. 1 b-d,!). The colourless region would then represent a zone of dissolution of the heterocyst content caused by the fungus. No other structural alteration of the heterocyst has been noted. The resting spore is formed after a small male cell (resembling an encysted zoospore) has made direct contact with a larger female cell
•
Chytridium cornutum. Hilda M. Canter "
2°9
b
.;'".
".""'.
e
/:::.~ :=
.....
,~
g
.~~;~:;~:~
~
j
~.".
.
p
Fig.
I .
? Chytridi um cornuturn Braun. a-f, Enlargement of zoospore int o the sporangium;
g, mature sporangium with flatt ened refractive ope rculum at its ap ex ; internally
zoospor es are delim ited ; h, i, empty spo rangia; j , k, ea rly stage in at ta ch ment of male cell to larger femal e bod y ; 1-0, enlargem ent of fema le and developmen t of lobed outline; p-r, fem al e th alli, lobes more attenuated. Male cell visib le in j -m, p, r. All X 1530 . M y c. 46
210
Transactions British Mycological Society c
b
g
k
m
p
o
!2?
d
J» ~
Fig. 2. ?Ch,ytridium cornutum Braun. a, Fully grown female thallus; b, content offemale contracted into the central region; c-j, contracted content now walled forming a resting spore; g, outline of resting spore 'waved' owing to refractive thickenings on the wall; h-l, resting spores (content omitted) lying in variously shaped container walls offemale. Empty male cells seen inj, k, m-t, after Braun (1856). a-I, x 1530; m, x 400; n-t, x 800.
Chytridium cornutum, Hilda M. Canter
211
(resembling a young sporangium). Very few of these early stages were found (Fig. t], k). The female continues to enlarge (Fig. I l), at first keeping its smooth outline. Later, however, blunt projections appear and the outline becomes lobed (Fig. Im-o). As development proceeds the lobes frequently become more acute and elongate giving the female a somewhat stellate appearance. There are usually from four to six of these horn-like processes (Fig. 2f-l). Sometimes they are absent (Fig. 2e). The content of the female is dense and contains many refractive globules. To form the resting spore proper the contents contract away from the extremities of the female and form a central spherical or subspherical mass 6'5 x 7 fL-7'5 x 9fL (Fig. 2 b). This becomes surrounded by a smooth wall (Fig. 2 c-f). One specimen was found in which the wall had a wavy appearance due to refractive thickenings (Fig. 2g). This may represent the mature form. The content always retains several large globules. The horn-like processes (measured after contraction of the content) extend up to 6'5 fL in length by 4 fL at the base. They never become solid or refractive. The empty male cell remains as an appendage on the wall of the female. A rhizoidal system, similar to that described for the sporangium, was seen connected to the female (Fig. 2 c). Also beneath the latter within the heterocyst content there is a colourless region. Such a method of resting spore development is unusual among chytrids. A similar contraction of the contents to form the resting spore proper, which then lies in a container, has been shown for Olpidium rotiferum Karling (1946). Also the resting spores of O. granulatum Karling (1946), O. gregarium (Nowak.) Schroeter (in Sparrow, 1960, p. 145) and Cbytridium olla Braun (Scherffel, 1926) may be formed in the same manner. Umphlett & Holland (1960), in describing the resting spore of Phlyctochytrium planicorne Atkinson for the first time, show that it too lies in a container. However they are of the opinion that this is not formed by a process of contraction but more likely by expansion of the container wall. Several chytrids are already known as parasites of planktonic bluegreen algae but only two of them occur on heterocysts (i.e. Phlyctidium megastomum Sparrow [as Rhizophydium sphaerocarpum Raitschenko 1902], and ? Chytridium cornutum Braun). P. megastomum is quite different from the chytrid here described and may infect both the vegetative cells and heterocysts of Anabaena flos-aquae (Lyngb.) Breb, More recently, Miller (1961) has recorded it from Lake Texoma, U.S.A., growing as a saprophyte on sweet-gum pollen bait. ? Chytridium cornutum is apparently confined to the heterocysts of Anabaena circinalis (Kutz.) Hansg. and its horned thalli (Fig. 2 m-t) show a striking resemblance to the resting spore stage I have described above. Although Braun (1856) presumed that the thalli which he so briefly described were sporangia, he found no evidence of zoospores or dehiscence. Therefore the possibility remains that they could be the resting spore stage. Sorokin ( 1 874) identified with ? Chytridium cornutum, horned sporangia which he found on the green alga Hormidium varium. Here, there is no doubt that the thalli described are zoosporangia. That Sorokin's material does in fact relate to Braun's species, in my view, is questionable, more especially since the algae concerned belong to such widely separate groups. 14- 2
212
Transactions British Mycological Society
If in the future numerous examples of a horned stage, which represents a resting spore, are discovered on heterocysts of Aphanizomenon and related genera, then there can be little doubt that? Chytridium cornutum and the fungus here described are identical.
My thanks are due to Prof. B. Fott who provided the material upon which this paper is based and to Dr ]. W. G. Lund, F.R.S. for help with the manuscript and foreign translations. Acknowledgement is made to the Central Research Fund, University of London, for the loan of a microscope used in this investigation. REFERENCES
BRAUN, A. (1856). Uber Chytridium, eine Gattung einzelliger Schmarotzergewachse auf Algen und Infusorien. Abhandl. Berlin Akad. 1855, 21-83. KARLING,]. S. (1946). Brazilian Chytrids, VIII. Additional parasites of Rotifers and Nematodes. Lloydia, 9, 1-12. MILLER, C. E. (1961). Some Aquatic Phycomycetes from Lake Texoma. J. Elisha Mitchell sci. Soc. 77, 293-298. RAITSCHENKO, A. A. (1902). Ueber eine Chytridiacee: R. sphaerocarpum (Zopf) Fischer. Bull. Jard. bot. St-Petersb, 2, 124. SCHERFFEL, A. (1926). Einiges tiber neue oder ungentigend bekannte Chytridineen. (Der 'Beitrage zur Kenntniss der Chytridineen'. Teil 11.) Arch. Protistenk. 54, 167-260. SOROKIN, N. W. (1874). Apercu systematique du groupe des Siphomycetes. Trao. Soc. Nat. Univ. Kasan, 4, 1-26 (in Russian). SPARROW, F. K. (1960). Aquatic phycomycetes, znd rev. ed. Univ. Michigan Press, Ann Arbor, U.S.A. UMPHLETT, C.]. & HOLLAND, M. M. (1960). RestingsporesinPhlyctochytriumplanicorne. Mycologia, 52, 429-435.
(Accepted for publication 8 June 1962)
CONCERNING CHYTRIDIUM CORNUTUM BRAUN By HILDA M. CANTER (MRS
J.
W. G. LUND)
Freshwater Biological Association, Ambleside, England (With
2
T ext-figures)
A chytrid is described on heterocysts of Aphanizomenon fios-aquae (L.) Ralfs from preserved material of plankton from a pond near Sedlic e, South Bohemia. For the time being it is included provisionally under the binomial Chytridium comutum Braun.
In 1952 Professor B. Fott kindly sent me a sample of preserved plankton from a pond, near Sedlice, South Bohemia, Czechoslovakia (colI. 20 July 1951). It contained Aphanizomenon flos-aquae (L. ) Ralfs, the heterocysts of which were infected by a chytrid. Specimens were not abundant but sufficient is known to warrant a description of the fungus. Many details concerning its morphology and method of dehiscence need confirmation from living material. Because of this I do not propose to diagnose this chytrid as new but include it doubtfully under the binomial Chytridium cornutum Braun, for reasons which become obvious in the discussion . The zoospore having settled on the wall of a heterocyst enlarges, keeping its spherical shape (Fig. 1 a-e). Further growth results in the formation of a more ovoid sporangium (Fig. Ig ). Sporangia range from 8·5P. high x 7'5 p. broad to 13 p. high XII P. broad. The apex of the sporangium is flattened and forms a small lid, which appears refractive in contrast to the rest of the wall. The zoospores (up to sixty ) seem to be fully differentiated in the sporangium for their outline is visible in mature specimens (Fig. 1 g). The zoospore is about 2 p. diam., and its content in preserved material appears to be granular with a few minute refractive globules. That this represents the true nature of the zoospore content is doubtful. Professor B. Fott in a drawing of a mature sporangium, made from living material, shows many globules of equal size and equally spaced. This suggests that the living zoospore contains a single conspicuous refractive globule. The operculum is small, and judging by the narrow opening at the apex of the sporangium it seems likely that the zoospores emerge singly through it. The wall of the empty sporangium does not collapse (Fig. 1 h, i ). Inside th e homogeneous, structureless content of the heterocyst, beneath the sporangium, is a colourless ' bubble-like' region which increases in size as the sporangium grows. It is sph eric al to oval and at first sight resembles a subsporan gial vesicle or sac-like rhizoid. Within it, in some specimens, there appear to be fine threads which probably constitute the rhizoidal system (Fig. 1 b-d,!). The colourless region would then represent a zone of dissolution of the heterocyst content caused by the fungus. No other structural alteration of the heterocyst has been noted. The resting spore is formed after a small male cell (resembling an encysted zoospore) has made direct contact with a larger female cell
•
Chytridium cornutum. Hilda M. Canter "
2°9
b
.;'".
".""'.
e
/:::.~ :=
.....
,~
g
.~~;~:;~:~
~
j
~.".
.
p
Fig.
I .
? Chytridi um cornuturn Braun. a-f, Enlargement of zoospore int o the sporangium;
g, mature sporangium with flatt ened refractive ope rculum at its ap ex ; internally
zoospor es are delim ited ; h, i, empty spo rangia; j , k, ea rly stage in at ta ch ment of male cell to larger femal e bod y ; 1-0, enlargem ent of fema le and developmen t of lobed outline; p-r, fem al e th alli, lobes more attenuated. Male cell visib le in j -m, p, r. All X 1530 . M y c. 46
210
Transactions British Mycological Society c
b
g
k
m
p
o
!2?
d
J» ~
Fig. 2. ?Ch,ytridium cornutum Braun. a, Fully grown female thallus; b, content offemale contracted into the central region; c-j, contracted content now walled forming a resting spore; g, outline of resting spore 'waved' owing to refractive thickenings on the wall; h-l, resting spores (content omitted) lying in variously shaped container walls offemale. Empty male cells seen inj, k, m-t, after Braun (1856). a-I, x 1530; m, x 400; n-t, x 800.
Chytridium cornutum, Hilda M. Canter
211
(resembling a young sporangium). Very few of these early stages were found (Fig. t], k). The female continues to enlarge (Fig. I l), at first keeping its smooth outline. Later, however, blunt projections appear and the outline becomes lobed (Fig. Im-o). As development proceeds the lobes frequently become more acute and elongate giving the female a somewhat stellate appearance. There are usually from four to six of these horn-like processes (Fig. 2f-l). Sometimes they are absent (Fig. 2e). The content of the female is dense and contains many refractive globules. To form the resting spore proper the contents contract away from the extremities of the female and form a central spherical or subspherical mass 6'5 x 7 fL-7'5 x 9fL (Fig. 2 b). This becomes surrounded by a smooth wall (Fig. 2 c-f). One specimen was found in which the wall had a wavy appearance due to refractive thickenings (Fig. 2g). This may represent the mature form. The content always retains several large globules. The horn-like processes (measured after contraction of the content) extend up to 6'5 fL in length by 4 fL at the base. They never become solid or refractive. The empty male cell remains as an appendage on the wall of the female. A rhizoidal system, similar to that described for the sporangium, was seen connected to the female (Fig. 2 c). Also beneath the latter within the heterocyst content there is a colourless region. Such a method of resting spore development is unusual among chytrids. A similar contraction of the contents to form the resting spore proper, which then lies in a container, has been shown for Olpidium rotiferum Karling (1946). Also the resting spores of O. granulatum Karling (1946), O. gregarium (Nowak.) Schroeter (in Sparrow, 1960, p. 145) and Cbytridium olla Braun (Scherffel, 1926) may be formed in the same manner. Umphlett & Holland (1960), in describing the resting spore of Phlyctochytrium planicorne Atkinson for the first time, show that it too lies in a container. However they are of the opinion that this is not formed by a process of contraction but more likely by expansion of the container wall. Several chytrids are already known as parasites of planktonic bluegreen algae but only two of them occur on heterocysts (i.e. Phlyctidium megastomum Sparrow [as Rhizophydium sphaerocarpum Raitschenko 1902], and ? Chytridium cornutum Braun). P. megastomum is quite different from the chytrid here described and may infect both the vegetative cells and heterocysts of Anabaena flos-aquae (Lyngb.) Breb, More recently, Miller (1961) has recorded it from Lake Texoma, U.S.A., growing as a saprophyte on sweet-gum pollen bait. ? Chytridium cornutum is apparently confined to the heterocysts of Anabaena circinalis (Kutz.) Hansg. and its horned thalli (Fig. 2 m-t) show a striking resemblance to the resting spore stage I have described above. Although Braun (1856) presumed that the thalli which he so briefly described were sporangia, he found no evidence of zoospores or dehiscence. Therefore the possibility remains that they could be the resting spore stage. Sorokin ( 1 874) identified with ? Chytridium cornutum, horned sporangia which he found on the green alga Hormidium varium. Here, there is no doubt that the thalli described are zoosporangia. That Sorokin's material does in fact relate to Braun's species, in my view, is questionable, more especially since the algae concerned belong to such widely separate groups. 14- 2
212
Transactions British Mycological Society
If in the future numerous examples of a horned stage, which represents a resting spore, are discovered on heterocysts of Aphanizomenon and related genera, then there can be little doubt that? Chytridium cornutum and the fungus here described are identical.
My thanks are due to Prof. B. Fott who provided the material upon which this paper is based and to Dr ]. W. G. Lund, F.R.S. for help with the manuscript and foreign translations. Acknowledgement is made to the Central Research Fund, University of London, for the loan of a microscope used in this investigation. REFERENCES
BRAUN, A. (1856). Uber Chytridium, eine Gattung einzelliger Schmarotzergewachse auf Algen und Infusorien. Abhandl. Berlin Akad. 1855, 21-83. KARLING,]. S. (1946). Brazilian Chytrids, VIII. Additional parasites of Rotifers and Nematodes. Lloydia, 9, 1-12. MILLER, C. E. (1961). Some Aquatic Phycomycetes from Lake Texoma. J. Elisha Mitchell sci. Soc. 77, 293-298. RAITSCHENKO, A. A. (1902). Ueber eine Chytridiacee: R. sphaerocarpum (Zopf) Fischer. Bull. Jard. bot. St-Petersb, 2, 124. SCHERFFEL, A. (1926). Einiges tiber neue oder ungentigend bekannte Chytridineen. (Der 'Beitrage zur Kenntniss der Chytridineen'. Teil 11.) Arch. Protistenk. 54, 167-260. SOROKIN, N. W. (1874). Apercu systematique du groupe des Siphomycetes. Trao. Soc. Nat. Univ. Kasan, 4, 1-26 (in Russian). SPARROW, F. K. (1960). Aquatic phycomycetes, znd rev. ed. Univ. Michigan Press, Ann Arbor, U.S.A. UMPHLETT, C.]. & HOLLAND, M. M. (1960). RestingsporesinPhlyctochytriumplanicorne. Mycologia, 52, 429-435.
(Accepted for publication 8 June 1962)