Photosynthetic oxygen evolution and chlorophyll fluorescence in intact isolated chloroplasts on a solid support: the influence of orthophosphate.

We devised recently a method to trap intact isolated chloroplasts on a solid support consisting of membrane filters made of cellulose nitrate (Cerović et al., 1987, Plant Physiol. 84, 1249-1251). The addition of alkaline phosphatase to the reaction medium enabled continuous photosynthesis by spinach (Spinacia oleracea L.) chloroplasts to be sustained by hydrolysis of newly produced and exported triose phosphates and recycling of orthophosphate. In this system, simultaneous measurements of chlorophyll fluorescence and oxygen evolution were performed and their dependence on orthophosphate concentration was investigated. Optimal photosynthesis was obtained at a much higher initial orthophosphate concentration (2-4 mM) compared to intact chloroplasts in suspension. Secondary kinetics of chlorophyll fluorescence yield were observed and were shown to depend on the initial orthophosphate concentration.