X-RAY-MICROANALYSIS OF ION CONTENTS IN VACUOLES AND CYTOPLASM OF THE GROWING TIPS OF A HYDROID POLYP AS RELATED TO OSMOTIC CHANGES AND GROWTH PULSATIONS

Growth pulsations (GP) in hydroid polyps are associated with changes i n vacuolar patterns which can be imitated by altering external osmolar ity. With the use of X-ray spectroscopy we measured the elemental cont ents in the vacuoles and cytoplasm of the growing tips of a hydroid po lyp, Podocoryne carnea, under various tonicity conditions. Under hyper tonic condition which arrested the samples at the retraction phase of normal GP, the elemental content within the vacuolar compartment appea red to be similar to that of the external medium, confirming our previ ous conclusion about the dehermetization of the vacuolar compartment u nder these conditions. Under hypotonical condition which arrested samp les at the extension GP phase (vacuoles isolated) element ratio data d isplayed an obvious bimodality. At least one of the data groups could be characterized by a significant increase in the concentrations of so dium and potassium, as related to Cl, Ca and Mg, and in comparison to the same ratios in hypotonical samples and those in the external mediu m. We suggest that under hypotonical conditions the isolated vacuolar compartment is formed by influx of sodium and potassium ions. These ca tions are accompanied by anions other than chloride. Potassium appears to be transferred into the vacuoles from the cytoplasm while the sodi um derives from the external environment.