Auxospore fine structure and variation in modes of cell size changes in Grammatophora marina (Bacillariophyta)

Abstract

S. Sato, D.G. Mann, T. Nagumo, J. Tanaka, T. Tadano and L.K. Medlin. 2008. Auxospore fine structure and variation in modes of cell size changes in Grammatophora marina (Bacillariophyta). Phycologia 47: 12–27. DOI: 10.2216/07-34.1

Examination of Grammatophora marina from rough and clonal cultures showed that cell size changes were more flexible than is generally reported for diatoms. Allogamous sexual auxosporulation took place through copulation between small male cells and larger female cells, but only in mixed rough culture and never in clonal cultures. Auxospores were also formed without copulation in clonal cultures (‘uniparental auxosporulation’) and these, like sexual auxospores, developed through formation of a perizonium, which consisted of a series of transverse bands. All of these bands, including the primary band, were open. Circular scales were present in the auxospore wall before initiation of perizonium formation and irregular, elongate structures lined the suture of the transverse perizonium. Perizonium and scales resembled those of another araphid pennate diatom, Gephyria media. Initial cells were formed within the perizonium and consisted of an initial epivalve with a simplified structure, an initial hypovalve (formed beneath the perizonium suture) and a third, normally structured valve formed beneath the epivalve; the epivalve was then sloughed off. Initial cells of similar configuration but often aberrant morphology could also be formed through expansion from vegetative cells, without involvement of a perizonium. Vegetative cells were also capable of limited enlargement through simple expansion without formation of an initial cell, and abrupt size reduction. Cell size ranges in populations from different regions suggest that G. marina may contain pseudocryptic species.

Key Words::

• Abrupt cell size reduction
• Auxospore
• Diatoms
• Fine structure
• Grammatophora marina
• Life cycle
• Perizonium
• Scales
• Vegetative cell enlargement

ACKNOWLEDGMENTS

We would like to thank Klaus Valentin and William Wardle for providing us the living samples from France and Texas, respectively, used in this study; Friedel Hinz for support with SEM; Victor Chepurnov for helpful comments and information concerning A.M. Roshchin's work; and Richard Crawford for correction of the manuscript and discussion. This study was supported by DAAD (German Academic Exchange Service) for doctoral research fellowship to S.S.