The effects of sulphydryl reagents on morphogenesis in hydroids : I. Metamorphosis and regeneration inHydractinia echinata.

1) The influence of reagents affecting SH or SS groups on morphogenesis has been studied in metamorphosing larvae and in regenerating adult hydranths. The thiol challenges evoke and enhance predominantly the differentiation of basal structures. 2) In larvae undergoing metamorphosis the SS-reducing agent Dithioerythrit (0.12-0.25 mM) brings about a prolongation of the subtentacular part of the body column. Dimercaptopropanol (0.19 mM), among other thiol challenges, enhances specifically stolonization giving rise to highly enlarged stolons. Under the influence of the oxidizing Kosower reagent Diamide (0.075-0.15 mM) transforming larvae develop a hypertrophied hydrorhiza which grows as a closed stolon-plate from the outset. In this way the primary polyps prematurely acquire the developmental state of sexual colonies. A correlation between the rH-values and the particular morphogenetic influences could not be established. 3) According to these "vegetalizing" influences on metamorphosis the thiol challenges cause regenerating hydranths to engage, in contrast to untreated controls, in differentiation of basal structures. The hydranths develop, though only in few cases, basal structures (stalks, stolons), whereas basal parts normally are never restored. In most cases, however, Diamide and especially dimercaptopropanol impose stolonial properties on hydranths as a whole. Such hydranths transform into giant stolons and secrete a periderm without first changing their outward appearance. Thus their state of differentiation becomes totally repolarized. 4) Tryptic dissociation exerts similar effects. Since all thiol reagents, at least in high doses, lead to the separation of the ectoderm and endoderm and to a partial dissociation of the tissue, it is suggested that the enhancement of basal development and the repolarization of the state of differentiation might be due to changes in cell adhesiveness and membrane properties.