Secretion of phenolic bodies following fertilisation inDurvillaea potatorum(Durvillaeales, Phaeophyta)

Abstract

Cytological events immediately following plasmogamy in Durvillaea potatorum are described. Eggs contain several types of cytoplasmic vesicle differing in size and appearance. Histochemical tests and measurements are used to characterise and distinguish different types of vesicle containing phenolic compounds, lipids and polysaccharides. Within 2 min of plasmogamy, small phenolic vesicles located just below the egg membrane undergo mass synchronised exocytosis. The contents of these vesicles are discharged as phenolic bodies on the outside of the membrane. Secretion of phenolic bodies precedes secretion of the primary zygote wall by several minutes. Limited secretion of phenolics also occurs in unfertilised eggs. Peripheral phenolic vesicles are distinguishable from physodes, which also 'contain phenolic compounds but which are significantly larger and tend to be localised around the egg nucleus. The possible functional significance of the phenolic bodies is discussed. Coated pits and vesicles are common in zygotes, and their presence is evidence for endocytosis.Key words: Fertilisation, Phaeophyceae, Phenolics, Secretion, Zygote. IntroductionEggs and zygotes of various species of brown algae, mostly fucoids, have been used as model systems in studies of spermatozoid attraction (Maier & M/iller, 1986), fertilisation potential (Brawley, 1987(Brawley, , 1991, polyspermy (Brawley, 1992), cell wall secretion (Evans et al., 1982; Brawley & Bell, 1987;Quatrano, 1992), the development of polarity (Quatrano, 1978;Quatrano et al., 1985;Kropf, 1992) and rhizoid growth (Kropf & Quatrano, 1987, Kropf, 1989. However, despite being the focus of so many investigations, there have been surprisingly few detailed ultrastmctural investigations of the eggs and zygotes of brown algae, possibly due to the notorious problems encountered in the fixation of brown algal tissues. The present study was instigated to examine structural aspects associated with fertilisation in the southern bull kelp, Durvillaea potatorum (Labillardi6re) Areschoug. The study revealed a previously undescribed phenomenon, the mass secretion of phenolic bodies, which occurs immediately following plasmogamy. The possible functional significance of this phenomenon is discussed. Materials and methodsFertile thallus pieces from male and female plants of Durvillaea potatorum were collected at Sorrento, Victoria, and were stored for 24 h without water in polythene bags kept on ice. Release of eggs and spermatozoids was stimulated by washing thallus fragments with chilled seawater. Dense suspensions of eggs and spermatozoids were prepared separately, checked microscopically to ensure they were in good condition, and then used immediately as outlined below. Electron microscopyFor transmission electron microscopy, egg and sperm suspensions were mixed and samples were taken after 2, 15, 30 and 60 min, and 25 h. For comparison, a series of unfertilised eggs (not mixed with spermatozoids) was fixed at the same times. Specimens were preserved in a fixative similar to that us...

Toxicity tests using developmental stages of Hormosira banksii (Phaeophyta) identify ammonium as a damaging component of secondary treated sewage effluent discharged into Bass Strait, Victoria, Australia

“…This concentration greatly exceeded the copper concentration range in effluent, prior to discharge. Tolerance of heavy metals such as copper may well be due to the ongoing synthesis and secretion of the cell wall components, alginate, sulfated polysaccharides and phenolic compounds, associated with brown algal embryo development (Quatrano & Stevens 1976, Clayton & Ashburner 1994, which have an affinity for cations (Skipnes et al 1975, Paskins-Hurlburt et al 1978, Ragan et al 1979, Pellegrini 1980, Lignell et al 1982, Mariani et al 1985, Smith et al 1986, Karez & Pereira 1995, Amado Filho et al 1996, Gledhill et al 1997. Susceptibility to the toxic effects of heavy metals, however, may be enhanced in developing H. banksii embryos, which are stressed due to exposure to other effluent components such as elevated levels of ammonium and to the impact of effluent discharge such as reduced salinity (Andersson & Kautsky 1996).…”

Affiliation of the parasiteHerpodiscus durvillaeae(Phaeophyceae) with the Sphacelariales based on DNA sequence comparisons and morphological observations

“…For transmission electron microscopy, thallus fragments of D. antarctica infected with H. durvillaeae collected in March 2000, were fixed over-night at 4 C in a modified Karnovsky mixture containing 2% glutardialdehyde, 1% paraformaldehyde, and 1% caffeine in cacodylate buffer (0.1M sodium cacodylate, 2% NaCl, 0.1% CaCl 2 , pH 7.2; Clayton & Ashburner, 1994;Schoenwaelder & Clayton, 1998a,b). Samples were rinsed in cacodylate buffer with 1% caffeine and were post-fixed in 1% osmium tetroxide (in cacodylate buffer) for 2 hours at room temperature, before rinsing in cacodylate buffer and water.…”

Storage of nitrogen in the form of protein bodies in the kelp Laminaria solidungula

“…These tissue samples were shipped overnight on ice and then fixed for 4 h in 2% glutaraldehyde, 1% formaldehyde, 2% NaCl, 0.1% CaCl 2 , 1% caffeine in 0.1 M Na cacodylate buffer (pH 7.2) (Clayton & Ashburner 1994). After rinses in pure 0.1 M Na cacodylate buffer, most specimens were postfixed for 4 h in 2% osmium tetroxide, 0.05 M Na cacodylate buffer.…”