Emerson Enhancement Effect in Synchronous Scenedesmus Cultures

Abstract

THE photosynthetic activity and quantum efficiency of synchronized cultures of Scenedesmus obliquus maintained on a 14 : 10 h light–dark regime are maximal at the eighth hour after the onset of illumination and minimal at the sixteenth hour just before separation of the mother cells into autospores1. Similar results have been reported in synchronized cultures of Scenedesmus sp.2 and for various strains of Chlorella3,4. The variation apparently resides in photosystem II, for the Hill reaction using quinone as oxidant (a photosystem II reaction) parallels the photo-synthetic activity, whereas photoreduction of CO2 (a photosystem I reaction) is unchanged throughout the life cycle1. We have investigated the level of Emerson enhancement in these synchronized cells to see if this also follows the variation in quantum efficiency and photosynthetic capacity. The literature provides only inferential evidence about the influence of different developmental stages on the effect of the Emerson enhancement5,6.