Photosynthesis in chloroplasts rapidly isolated from primary leaves of oat (Avena sativa L.): effects of orthophosphate, metal ion and chelators

Abstract A simple mechanical method for the rapid isolation of chloroplasts with high rates of photosynthesis from young leaves of oat (Avena sativa L.) was described. The photosynthetic activity of these chloroplasts was stable for at least 2 h with rates of CO₂-dependent O₂ evolution of 30–40 μmol g ¹ Chl s ¹. The photosynthetic properties of these chloroplasts were similar to those reported for spinach and pea chloroplasts isolated by mechanical disruption. The pH optimum for photosynthetic O₂ evolution was pH 7.6. The induction time was 0.5–2 min. Maximal rates of photosynthetic O₂ evolution in these chloroplast preparations were obtained in the absence of both divalent cations and EDTA. Addition of divilent cations strongly inhibited photosynthesis which could be partially restored by the subsequent addition of EDTA. But when these cations were not present in the assay medium the addition of EDTA greater than 1 mol m ³ decreased photosynthetic activity. The optimal orthophosphate concentration required for photosynthesis in these chloroplast preparations was 0.2–0.3 mol m ³. In contrast, the addition of pyrophosphate either in the light or dark inhibited photosynthesis. In a comparative study, chloroplasts were also isolated from oat and wheat (Triticum aestivum L., cultivar Hybrid C306) protoplasts. These chloroplast preparations were found to have properties similar to those determined for oat chloroplasts isolated by the mechanical method reported above.