Comparison of photomixotrophic and heterotrophic callus and suspension cultures of Pinus elliottii. 1. Photosynthetic properties and ultrastructural evidence for coexistence of starch granules and secondary metabolites

Photomixotrophic callus and suspension cultures of salsh pine (Pinus elliottii var. elliottii Engelm.) have been established. Callus tissues contained up to 2.76 g chlorophyll mg^-1 dry wt and suspensions 2.98 g chlorophyll mg^-1 dry wt. Maximum photosynthetic oxygen evolution was 25–32 mol O₂ h^-1 mg^-1 chlorophyll for callus and 35–39 mol O₂h^-1 mg^-1 chlorophyll for suspension, respectively. Photomixotrophic callus was friable with a high moisture content during early and exponential growth, but evolved into a compact and dense tissue during the latter stage of growth. Compact photomixotrophic callus accumulated and deposited secondary metabolites in the central vacuole and developed large starch granules in the chloroplasts. Secondary metabolites were not observed in photomixotrophic suspensions or in heterotrophic calli and suspensions. Photomixotrophic callus contained numerous mitochondria closely associated with well-developed chloroplasts containing 2–6 thylakoids per granum. Heterotrophic callus was characterized by a poorly developed cytoplasm and cup-shaped mitochondria.