[Regulation of development and metabolism of the green algae Urospora by temperature]

In the life cycle of Urospora wormskioldii (Mert. in Hornem) Rosenv. and U. vancouveriana (Tilden) Setschell and Gardner unbranched monosiphonous filaments (exceeding 15 cm in length) alternate with microscopic dwarf plants and a unicellular Codiolum stage. The interrelationship between these very different forms and the regulating effect of temperature on this life cycle are shown in Fig. 1. Beyond the morphological differences between the three forms there are large differences in the composition of the cell wall (Fig. 2). While the cell wall of the Codiolum stage is mainly built up of mannans, glucose-containing polysaccharides predominate in the cell wall of the dwarf plants and xylose-containing polysaccharides are abundant in the cell wall of the filamentous plants. Differences in metabolism between dwarf plants and filamentous plants were detected by (14)CO2-incorporating experiments. On the basis of chlorophyll content dwarf plants have a higher total (14)CO2-fixation rate than filamentous plants cultured at either 2°C or 14°C (Fig. 3). Furthermore, a higher rate of synthesis for Calvin-cycle intermediates and other metabolites was generally demonstrated in dwarf plants with one important exception: Uridine diphosphate glucose was synthesized faster in filamentous plants cultured at 2° C (Fig. 4). Studies of (14)CO2-incorporation in filamentous plants cultivated at 2° C or 14° C (at the higher temperature filamentous plants survive only for a limited time) revealed that the latter show a much higher incorporation of (14)C into insoluble substances than the former. On the other hand, pools of soluble substances - especially Calvin-cycle intermediates - are much smaller in 14° C-plants than in 2° C-plants with the exception of that of sucrose, which is accumulated in 14° C-plants in high amounts (more than 70% of the total radioactivity in soluble compounds, Fig. 5). These facts may be explained by temperature-sensitive differential gene expression and/or steps in metabolism (see discussion).