Cosmarium botrytis Menegh under the light and scanning electron microscope

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1 Proc. lndian Acad. Sci. (Plant Sci.), Vol. 93, No. 4, September 1984, pp Printed in India. Cosmarium botrytis Menegh under the light and scanning electron microscope VIDYAVATI and G SATHAIAH Department of Botany, Kakatiya University, Warangal , India MS received 28 November 1983; revised 26 June 1984 Abstraet. A detailed study of surface omamentation under light and scanning electron microscope is undertaken. The present observations have added further to the knowledge in taxonomie identification of Cosmarium botrytis Menegh, in particular because the species revealed a va of surface ornamentation based on which va species of Cosmarium ate specifieally identified. Keywords. Taxonomy; Cosmarium botrytis; ornamentation; light microscope; scanning electron microscope. 1. Introduction The genus Cosmarium occupies a very distinct place in the placoderm desmids (Conjugates, Chlorophyceae) of the green algae. As in other fields, SEM may prove of value in the taxonomy of the genus Cosmarium supplementing the data already obtained from LM (West and West 1908). SEM reveals clearly the plasticity of desmid morphology, which is of much importance to taxonomists. SEM studies of desmids were first attempted by Lyon (I 969) who studied the external morphology of the walls of Cosmarium botrytis, Pickett-Heaps (1973) presented stereo-scanning micrographs of two species of Staurastrum, one species of Cosmarium and two species of Micrasterias. Stereo-scanning studies indicate the potential value of this method for developmental studies and taxonomy. The ceil wall of Cosmarium botrytis was studied (Lott et al 1972) using the conventional thin sectioning EM techniques and also SEM and freeze-etching. The freeze-etched preparations shattered the wau and showed overlapping of ribbons of microfibrils oriented randomly (Mix 1975). Recently, Vidyavati and coworkers (Vidyavati 1982a-e, 1983a-d; Vidyavati et al 1983) studied certain species of placoderm desmids under SEM. They also studied the ornamentations along with cell division in species of Cosmarium, Euastrum and Staurastrum under SEM. In this paper a detailed study of surface ornamentation in Cosmarium botrytis under the LM and SEM is undertaken. 2. Material and methods Unialgal clcnal cultures of Cosmarium botrytis, Menegh, (culture centre of Algae and Protozoa, Cambridge, UK) were raised in Chu's 10 (1946) inorganic medium subjected to a temperature of 18-22~ receiving 16/8 hr alternate light and dark periods, respectively. Cells from the actively growing culture were embedded in a 10 ~ glycerine in a watch p 5 459

2 460 Vidyavati and G Sathaiah glass. After one week, slides were prepared to study the front, lateral and top views of the species under the LM. For sera studies, actively growing cells were fixed in 1% glutaraldehyde, made up in the culture medium, for about 1 lar at room temperature. After washing once in the culture medium, these cells were post-fixed for 1 hr in 2 % OSO4, also made up in culture medium. The cells were washed thrice with the culture medium. After fixation, the cells were dehydrated in various grades of acetone, (30, 50, 70, 90 and 100) and finally preserved in 100 % acetone, kept in a desicator. The cells were dried by cpt~ (critical point drying) apparatus and mounted on a stub using double-sticking tape. The cells were coated with carbon and gold and observed through the sera (Jeol JSM- 25 S, at 15 kv). Most of the desmids secrete copious quantities of mucilage and many of the species examined, were too thickly covered with dried material to give good micrographs. Washing fixed cells with warm water sometimes gave good results, but glusulase pretreatment was more effective in removing the mucilage for sera (Pickett-Heaps 1973, 1974; Vidyavati 1983d). 3. Observations and discussion Figures (1-3) show the ceus of various views (front, lateral and top) of Cosmarium botrytis under the LM. The (65-90 #m in length, #m in breadth, q in thickness, breadth of isthmus q cells were about 188 times as long as broad, deeply constricted, sinus narrowly linear with a dilated extremity; semicells ovate pyramidate from a broad, flat base, basal (figures 1-3) angles rounded. Sides convex, apex rather narrowly truncate or subtruncate, apical angles rounded. Side view of semicell broadly elliptic (figure 2). Cell-wall uniformly granulate, granules somewhat small and generally without any definite deposition. In Cosmarium botrytis the two semicells are covered by a variable pattern ofwarts or ridges anda net work of mucilage pores and strands. The secondary walls invariably possess a fairly regular pattern of mucilage deposits over the pores. Mucilage pores were connected by numerous mucilage strands. A number of small fibrils radiate from a mucilage pore (figures 14 and 15). 7: ";'.."."..': "e.*oo " el. ~176 "~~ "o *te',.~g.~ ~ ~ e,4. ao.a~ a~ 1 2 l O 3 Figures 1-3. Cosmarium botrytis under LM ( 1200) showing the 1. front view 2. lateral view 3. top vir

3 Surface ornamentation in Cosmarium botrytis 461 Figures 4-7. Scanning electron microphotographs of Cosmarium botrytis showing 4. cells under various views at lower magnifications (front, lateral and top), 5. cells in front and lateral views, 6. a cell in side view, part of the semicell showing mucilage pores, 7. the mucilagenous strands in the top view of the cell. P --SA

4 462 Vidyat:ati and G Sathaiah ~~ Figures Scanning electron microphotographs of Cosmarium botrytis, showing the ornamentation at the isthmus region, 8, muciiage accumulation at the isthmus, 9. arrangement of mucilagenous strands after glusulase treatment, 10,.ad 11. arrangement of mucilagenous strands at higher magnification.

5 Surface ornamentation in Cosmarium botrytis 463 Figures Scanning electron microphotographs of Cosmarium botrytis showing 12. enlargement ofisthmus at the time ofdivision, 13. part of the cell wall showing mucilage pores and sheath collars, 14 and 15. typical arrangement of mucilagenous strands.

6 464 Vidyavati and G Sathaiah Figure 4 shows cells under various views at low magnification, and figures 5-7 show the front, lateral and top views along with the cell wall beset with mucilage pores and strands. Whereas figures 8-11 show the cell with thick mucilage and mucilagenous pores and strands at the isthmus region. Figure 12 shows the enlargement of the isthmus during division and figure 13 a part of the inner secondary wall with mucilage potes and sheath collars. The pore is a simple canal with some slight enlargement internally, while externally it was a specially differentiated non-cellulosic cylindrical zone. It is known as 'pore organ' and at the inner surface of the pote entrance there are button-shaped swellings. Figures 14 and 15 show the regular pattern of mucilage deposits around the pores typical for the species. These observations further add to our previous knowledge (Pickett-Heaps 1975; Vidyavati et al 1983). These studies have revealed the detailed surface ornamentation of Cosmarium botrytis, which showed strap-like arrays of parallel microfibrils (figures 14 and 15) like those mentioned in Micrasterias (Lott et al 1972; Mix 1975). However granules, spines or verrucae of varying size and elaboration are characteristic of the cell wall ornamentation of many desmids of the Cosmariae. They are arranged in regular and consistent patterns and can be clearly seen by SEM, which ate significant in desmid taxonomy. However, they are not structures produced from the outer wall layer as is the ornamentation of the genera Closterium, Penium of Gonatozygon, but results from the differentiation of primary and secondary walls being initiated during the latter stages of cell enlargement in Cosmarium botrytis. Thus, they are intimately associated with the development of the cell wall proper. Finally all these observations have further added to the taxonomic identification of Cosmarium botrytis. Acknowledgements The authors ate grateful to Prof. Jafar Nizam and Emeritus Prof. M R Suxena, of Osmania University for help and encouragement. They are extremely thankful to Prof. J D Dodge, of Royal Holloway College, London, UK for the help given during SEM studies. Thanks are also due to Prof. L L Narayana, of Kakatiya University for facilities and to CSIR for financial help. References Chu P 1942 The influence of the mineral composition of the medium on the growth of planktonic algae I. Methods and culture media; J. Ecol Lott J N A, Har G P and Turner C D 1972 The cell wall of Cosmarium botrytis; J. Phycol Lyon T L 1969 Scanning electron microscopy. A new approach to the Desmidiaceae; J. Phycol Mix M 1975 Die Feinstruktur der Zellw/inde der Conjugated und ihre systematische Bedeutung; Beinh. Nova. Hedwigia Pickett-Heaps J D 1973 Stereo SEM of desmids; J. Microsc Piekett-Heaps J D 1974 SEM of some cultured desmids; Trans. Aro. Microsc. Soc Pickett-Heaps J D 1975 The green algae (Sunderland Mass: Sinauer Association) Vidyavati 1982a Cell ornamentation in Cosmarium bioculatum Breb. under SEM; Curr. Sci Vidyavati 1982b Cell division in Staurastrum gracile Ralfs. under the SEM; Proc. lndian Acad Sci. ( Plant Sci.) Vidyavati 1982c Division in Cosmariumformosulum Hoff. under scanning electron microscope; Life. Sci. Adv. l

7 Surface ornamentation in Cosmarium botrytis 465 Vidyavati 1982d Cell ornamentation of Cosmariumformosulum Hoff. under SEM. Proc. Indian Natl. Acad Vidyavati 1982e Staurastrum gracile Ralfs. under SEM; J. lndian. Bot. Soc Vidyavati 1983a Cell division in Cosmarium contractum Kirchn. under SEM; Geobios New Rep Vidyavati 1983b Surface ornamentation in Cosmarium praemorsum Breb; Indian J. Bot Vidyavati 1983c Euastrum verrucosum Ehrenb. Division under SEM; Curr. Sci Vidyavati 1983d Mucilage interference in Cosmarium cucumis (Corda) Ralfs. under SEM. Phykos Vidyavati, Sathaiah G, Rao D B and Reddy R Y 1983 Cosmarium botrytis, Menegh. under SEM; Plant Nature West W and West G S 1908 in A monograph of the British Desmidiaceae. (Cambridge: Univ. Press) Vol. III. pp. 196