Studies on reproduction inEctocarpus siliculosus

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Abstract
For more than 6 years clonal cultures of Ectocarpus siliculosus from Naples, Italy, have been used for studying problems concerning re production. Three aspects will be discussed here: 1, alternation of generations, 2, mechanism of sex determination, 3, attempts to isolate and identify a sperm-attractive substance. 1. Two growth-forms can be distinguished: gametophytes and sporophytes. They differ in their morphology and their reproductive capacity. Gametophytes have been observed in the haploid and diploid nuclear phase. Sporophytes occur in haploid, diploid and tetraploid forms. All these stages are interconnected by a number of processes: fertilization, meiosis, parthenogenesis, spontaneous multiplication of chromosome number and heteroblasty. 2. Analysis of the products of meiosis in diploid heterozygous sporophytes shows that sex determination is genotypic. The sex of haploid plants is determined, although in haploid sporophytes it is not expressed directly. Diploid and tetraploid plants can be either homo- or heterozygous. Diploid heterozygous gametophytes show that the male factors are dominant. 3. Female gametes produce an odorous, highly volatile substance which has been shown to induce chemokinesis and Chemotaxis in male gametes. The compound was collected, purified and obtained in milligram quantities. Application of gaschromatography, mass-nuclear magnetic resonance—infrared—and ultraviolet-spectroscopy, gave information about structural details. It is an olefinic hydrocarbon, molecular weight 148, empiric formula C11 H16, with 3 unconjugated double bonds, one methyl group, and a ring-configuration with 7 carbons atoms.