The isolation and physiological analysis of mutants of the moss, Physcomitrella patens, which over-produce gametophores

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Abstract
Several phenotypically distinct classes of gametophore overproducing mutants have been isolated in P. patens. Mutants belonging to one class resemble the wild-type strain grown on medium containing a high concentration (5–50μM) of exogenously supplied cytokinin. Mutants of this type can increase the production of gametophores in the wildtype strain by cross-feeding it through the culture medium. Mutants belonging to another class resemble the wild-type strain cultured on medium containing a lower concentration (50–500 nM) of exogenous cytokinin. Mutants of this kind cannot cross-feed the wild-type strain through the culture medium. A component, required by the wild-type strain for the initiation of gametophores in response to cytokinin, either is not formed or is not activated in the dark. Gametophore over-producing mutants may also be unable to synthesize/activate this component in the dark and thus, like the wild-type strain, they produce no gametophores in the dark.