Quantum efficiency of chloroplasts retained from food by the mixotrophic ciliate Strombidium rassoulzadegani.

This article focuses on the photophysiology of chloroplasts retained by the oligotrich ciliate Strombidium rassoulzadegani, which acquires functional chloroplasts from its algal prey. Using a Fluorescence Induction and Relaxation fluorometer, the study measured the maximum quantum efficiency (QE) of Photosystem II in chloroplasts from two algal foods (a chlorophyte and a cryptophyte) and within the ciliate host, finding that QE in retained chloroplasts was about half that of nutrient-replete algal cultures and declined further under starvation. The PSII inhibitor DCMU significantly reduced ciliate growth, especially in those fed chlorophyte plastids, suggesting that retained chloroplasts contribute to ciliate metabolism beyond photosynthesis. The research highlights the dynamic functionality and ecological significance of kleptoplasts in mixotrophic ciliates and raises questions about the differing roles of chloroplasts from various algal sources within the host.