STUDIES ON CYCLOTELLA MENEGHINIANA KOTZ.

I. and Auxospore Formation*

BY V. N. R. RAO (University Botany Laboratory, Madras-5, India) Received September 18, 1970

(Communicated by Prof. T. V. Desikachary, F.A.SC.)

FOLLOWING Stosch's first report in Melosira mrians (Stosch, 1950, 1951), oogamous sexual reproduction has been observed in a number of Centric (Geitler, 1952; Stosch, 1954, 1956, 1958; Stosch and Drebes, 1964; Steele, 1965, 1966; Holmes, 1966, 1967; see also Findlay, 1969). Earlier studies on few Centric diatoms, especially Cyclotella meneghiniana, have indicated that auxospore formation in these could involve intra-cellular autogamy (Iyengar and Subrahmanyan, 1942, 1944; Erben, 1959). Re- investigation of auxospore formation in Cyclotella meneghiniana revealed an oogamous sexual reproduction in this .

Cells of a particular size of the same unialgal clone (monoecious or homothallic, see Lewin and Guillard, 1963) function as spermatozoid and egg mother cells which are indistinct from vegetative cells of similar sizes. Each spermatozoid mother (3.0-13.5 t~ diameter) produces after reduc- tion division four uniflagellate spermatozoids which are liberated after the two valves of a mother cell break up at the girdle region (Figs. 1 and 2). The body of these varied from 3.0 to 7.5 tz in diameter depending on the size of spermatozoid mother cells. Not always all stages leading to their release are completed within the mother cell. in few instances these are liberated after the first meiotic division. Spermatozoids, at this stage, possess two flagella which move to opposite poles during second nuclear division, taking place externally in the medium. Biflagellate swarmers have been observed in Cyclotella meneghiniana (Schultz and Trainor, 1968; see also Schultz and Trainor, 1970) and a possible involvement of these in oogamous re- production has been suggested in Rhizosolenia hebetata (Seaton, 1970). The biflagellate condition in C. meneghiniana (Fig. 4), observed here and else-

* Memoir No. 89 from the Centre for Advanced Studies in Botany. 285 286 V.N.R. RAo

where, is probably a stage in the formation of uniflagellate spermatozoids. The single is directed backwards during movement of the sper- matozoid. Each egg mother cell (6-0-16.5/z diameter) undergoes reduction division and produces a single non flagellated egg. The spermatozoids swarm round egg mother cells which are in various stages of development. Fertilization has not been observed. In one instance a spermatozoid became attached by the flagellated end to an egg mother cell which appeared enlarged like a developing auxospore (Fig. 3). Diameter of cells derived from auxospores ranged from 19.5 to 43.5 t~. It appears that reproduction in C. meneghi- niana is also oogamous and that spermatozoids are formed from smaller sized cells while eggs from larger ones. It is significant here to note that lyengar and Subrahmanyan (1944) reported that cells less than 10 ~ diameter died away. Such cells, in the present investigation, formed spermatozoids and eggs and especially cells of the smallest diameters (3 "0-4.5/z) produced only spermatozoids. Further studies on the structure and behaviour of spermatozoids are under way. I am grateful to Prof. T. V. Desikachary for guidance, to Prof. T. S. Sadasivan for valuable suggestions and to the University Grants Commission for grant of a Fellowship.

REFERENCES

Erben, K. .. "Untersuchungen fiber Auxosporenentwicklung und Meio- seausl6sung an Melosira nummuloides (DiUw.) C.A. Agardh," Arch. Protistenk., 1959, 104, 165-210. Findlay, I. W. O. •. "Cell size and spore formation in a clone of a Centri¢ diatom Coscinodiscus pavillardii Forti," Phykos., 1969, 8, 3t--41. Geitler, L. .. "Oogamie, Mitose, Meiose und metagame Tedlung bei der zentrischen Diatomee Cyclotella," Ost. Bot. Z., 1952, 99, 506-20• Holmes, R. W. .. "Short-term temperature and light conditions associated with auxospore formation in the marine Centric diatom Cosci- nodiscus concinnus W. Smith," Nature, Lond., 1966, 209, 217-18. .. "Auxospore formation in two marine clones of the diatom genus Coscinodiscus," Am. J. Bot., 1967, 54, t63-q~. Iyensax, M. O. P. and "On reduction division and auxospore formation in Cyclotella Subrahmanyan, R. meneghiniana Kiitz," J. Indian hot. Soc., 1942, 21~ 231-37. .. "On reduction division and auxospore formation in Cyclotella ~wneghiniana KiJtz," Ibid., 1944, 23, 125-52o V. N. R. Rao Proc. Ind. Acad. Sci., B, Vol. LXXII, PI. XII

FIGS. 1-4. Cyclotella meneghiniana.

FIGS. 1 and 2. Uniflagellate spermatozoids. Fro. 3. A spermatozoid attached by the flagella to a developing egg mother cell. FIG. 4. Biflagellate condition during the development of the spermatozoid. Studies on Cyclotella Meneghiniana Kutz--I 287

Lewin, J. C. and Guillard, "Diatoms," A. Rev. Microbiol., 1963, 17, 373--414. R. R. L. Schultz, M. E. and Trainor, "Production of male gametes and auxospores in the Centric F.R. diatoms Cyclotella meneghiniana and C. cryptica," J. Phycol., 1968. 3, 73-77. •. "Production of male gametes and auxospores in a polymorphic clone of the Centric diatom Cyclotella," Can. J. Bot., 1970, 48, 947-51. Seaton, D. D. .. "Reproduction in Rhizosolenia hebetata and its linkage with Rhizosolenia styliformis," J. mar. biol. Ass., t970, 50, 97-106.

Steele, R. L. .. "Induction of sexuality in two Centrie diatoms," Bioscience, 1965, 15, 298. .. In Marine Botany, An Introduction, by E. Y. Dawson, Holt Rinehart and Winston, Inc., New York, t966, 32-33.

Stosch, H. A. v. .. "Oogamy in a Centric diatom," Nature, Lond., 1950, 165, 531. •. "Entwicklungsgeschichtliche Untersuchungen an zentrischen Diatomeen. I. Die Auxosporenbildung von Melosira vorians.," Arch. Mikrobiol., 1951, 16, 101-35. .. "Die Oogamie von Biddulphia mobiliensis und die bisher bekannten Auxosporenbildungen bei den Centrales," Int. hot. Congr. VIII, Paris, 1954, 17, 58-68.

•. "Entwicklungsgeschichtliche Untersuchungen an zentrischen Diatomeen. II. Geschleehtszellenreifung, Befruchtung und Auxosporenbildung einiger grund bewohnender Biddul- phiacean der Nordsee," Arch. MikrobioL, 1956, 23, 327-65. .. "Entwicklungsgeschichtliche Untersuchungen an zentrischen Diatomeen, III. Die Spermatogenese yon Melosira monili. formis Agardh," Ibid., 1958, 31, 274-82. -- and Drebes, G. .. "Entwicklungsgeschichtliche Untersuchungen an zentrischen Diatomeen. IV. Die Diatomee Stephanopyxis turris i/ire Behandlung und Entwicklungsgeschichte," Helgc- lander Wiss. Meeresunters, 1964, 11, 209-57.

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