Culture studies ofChorda tomentosa(Phaeophyta, Laminariales)

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Abstract
The complete life history of Chorda tomentosa Lyngbye from northern Norway has been followed in culture. Under relatively high temperatures (10–15°C) or low irradiance, zoospores develop into filamentous monoecious gametophytes with unlimited vegetative growth. Formation of oogonia and antheridia was induced by transfer to strong white fluorescent light and low temperatures (1–5°C). By variation of these environmental factors the degree of fertility can be controlled. In a light-dark regime, egg release occurs exclusively during the dark periods. Freshly released eggs secrete a sexual hormone which effects explosive discharge of spermatozoids from the antheridia and subsequent chemotaxis towards the egg. Plasmogamy occurs immediately. Chromosome staining reveals interesting nuclear activities during karyogamy. Frequently, unfertilized eggs develop parthenogenetically. The resulting sporophytes are haploid and show the same developmental pattern as those originating from fertilized eggs. All sporophytes produce sporangia and release zoospores within 60 to 90 days after egg discharge.