The goal of this study was to determine the function of cytokinin in the morphological development and gender expression of gametophytes of Osmunda regalis, a member of Osmundales, sister-group to all other extant leptoporangiate fern families. Gametophytes of Osmunda regalis were grown in multispore populations on C-fern nutrient enriched agar containing 0, 1 nM, 1 µM, and 1 mM kinetin. Higher concentrations of exogenous kinetin reduced gametophyte size (area), disrupted correlations observed in the control between rates of apical notch formation and thallus widening, increased the proportions of asexuals and males, decreased the proportion of females in the population, and correspondingly increased male reproductive effort (antheridia per unit thallus area) and decreased female reproductive effort (archegonia per unit thallus area) compared to the control. Low concentrations of exogenous kinetin increased the proportion of females compared to the control. In the control, thalli with a comparatively deep apical notch tended to be wider (relative to their length) and possess a more circular silhouette relative to thalli with a comparatively shallow apical notch; however, these morphological parameters were independent of gametophyte size and gender. Thus, variance in the rate and planes of cell division and patterns of cell expansion and differentiation, most likely genetic in basis, were observed in the control, and the observed effects of exogenous kinetin were more than a simple “push” towards a phenotype already present in the control.
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Vol. 102 • No. 1