Parthenogenesis and apospory in the Laminariales: A flow cytometry analysis

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Abstract
Tissue explants and unisexual cultures of Macrocystis pyrifera, Laminaria saccharina and L. digitata regenerated into various forms, including gametophyte-like filaments, callus-like structures, stipe-like structures and either abnormal or normal sporophytes. The ploidy of the various forms of growth was assessed using flow cytometry analysis of isolated nuclei. Unisexual cultures of female gametophytes of L. digitata gave rise to abnormal parthenogenetic sporophytes, with nuclei exhibiting 2C, 4C and 8C ploidy levels. Aposporous gametophyte-like filaments grown from the tissue explants of M. pyrifera developed into abnormal sporophytes and both forms were diploid. Development of stipe medullary explants of L. saccharina led to the complete regeneration of functional sporophytes, involving the outgrowth of aposporous gametophytes. The regenerated sporophytes were either diploid or tetraploid but only diploid sporophytes were found to be fertile. The developmental and biotechnological significance of these results is discussed.