Morphogenesis in Pterocladiella capillacea (Rhodophyta, Gelidiales): bud differentiation in relation to irradiance-temperature combinations

In Pterocladiella capillacea (Gmelin) Santelices et Hommersand, thallus morphogenesis is controlled by exogenous factors. At 14°C, the adventitious buds arising from the distal pole of frond explants developed into compressed axes, similar to the typical erect shoots of the species, under every irradiance tested. At 19°C and 24°C they developed into compressed axes when irradiance was 20-40 μmol m-2s-1, whereas they developed into terete axes, similar to the typical prostrate thallus, when irradiance was 2.5 to 10 μmol m-2s-1. Buds regenerated from the proximal pole of explants differentiated, as a rule, into terete axes under all conditions, although they may become compressed under the maximum irradiance tested. A hypothesis based on apical dominance is suggested in order to explain the compressed or terete development of the thallus as a response to irradiance and temperature.