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  • Author: M. D. Guiry x
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Abstract

The vegetative and reproductive development of Polysiphonia lanosa (Linnaeus) Tandy (Rhodomelaceae, Rhodophyta) is reinvestigated based on material from the west coast of Ireland. This species is identified by the following unique combination of characters: a thallus consisting of 17–23 short pericentral cells; short and wide central axial cells; dichotomous branching; a complete absence of cortication; rhizoids generally remaining in contact with pericentral cells; and, its exclusive occurrence as a putative epiphyte of fucoids. Tetrasporangia are arranged in a spiral or sometimes a straight series and produced from the second pericentral cells with two presporangial cover cells. The spermatangial branches in P. lanosa are produced directly from each axial cell in the distal ends of erect branches and are not modified trichoblasts; vegetative trichoblasts are completely absent. The procarp has a four-celled carpogonial branch, as is typical for most members of the Rhodomelaceae, although species with either three- or four-celled carpogonial branches do occur in the genus Polysiphonia Greville. Although the genus Vertebrata S.F. Gray is available, is typified by, and has been used for this species, it is concluded that a molecular investigation is required to assess further the phylogenetic divergence indicated by these characters. The continued inclusion of Vertebrata in Polysiphonia is recommended until this work has been carried out.

Abstract

Both 13C nuclear magnetic resonance (NMR) spectroscopy and High Performance Anion Exchange (HPAE) chromatography were used to examine the alditols mannitol and volemitol found in the brown alga Pelvetia canaliculata (Linnaeus) Decaisne et Thuret (Phaeophycota, Fucales, Fucaceae). Carbohydrates were extracted using either ethanol or distilled water and our investigations have shown that both methods give qualitatively and quantitatively similar results. The ratios of alditols extracted from the seaweed under different growth conditions (temperature and emersion time) were compared. In the laboratory, growth rates of P. canaliculata increased with temperature up to 20 °C and decreased thereafter, but results indicated that the degree to which plants responded to temperature is seasonally dependent. Greater increases occurred during winter and spring, possibly due to low-temperature acclimation of field-collected plants in winter. Mannitol and volemitol concentrations in P. canaliculata increased in culture with temperatures up to 27 °C. Both mannitol and volemitol concentrations remained similar during continuous emersion for 7 d at 10 °C. By contrast, in plants emersed continuously for 8 or 12 d at 25 °C, volemitol concentrations decreased significantly, whilst mannitol concentrations remained similar. But when plants were emersed continuously for varying periods and subsequently re-immersed in seawater, recovery of photosynthesis was complete in plants which had been emersed at 10 °C for up to 7 d. When cultured at 25 °C, photosynthesis recovered only when plants had been emersed for no longer than 4 d. As optimum growth occured at higher temperatures than in other intertidal fucoids and P. canaliculata appeared well adapted to prolonged periods of emersion, even at high temperatures. The accumulation of mannitol and volemitol during growth at higher temperatures when submerged and a decrease during emersion at high temperatures may suggest a possible role for these carbohydrates as stress metabolites. However, further research is required to explain how the unique presence of volemitol in P. canaliculata may contribute to its ability to withstand unfavourable conditions in the intertidal zone during periods of extreme and prolonged dehydration.