ALANINE UPTAKE BY ISOLATED ZOOXANTHELLAE OF THE MANGROVE JELLYFISH, CASSIOPEA XAMACHANA. II. INHIBITION BY HOST HOMOGENATE FRACTION

¹ Department of Biology, Georgetown University, Washington, DC 20057

A low molecular weight fraction (Inhibitory Fraction, IF) was isolated from whole animal homogenates of the symbiotic jellyfish, Cassiopea xamachana. This fraction (2-10 kDa) strongly inhibited the uptake of L-(U-¹⁴C)alanine by isolated zooxanthellae at concentrations as low as 5 µg protein ml^-1. The magnitude of suppression was unaffected by the length of exposure time to IF prior to monitoring uptake. Uptake rates were linear for control and experimental cell suspensions, suggesting that algal metabolic integrity was maintained in the presence of IF. Zooxanthellae incubated in IF, and then washed free of this fraction, continued to show suppressed alanine uptake with only partial recovery. These cells, when placed in culture media, exhibited normal morphology, continued to grow and divide, and developed flagellated stages. The possible regulation of nutrient exchange between symbionts by symbiosis-specific host factors is discussed.