Changes in Photosynthetic Capacity and Photosynthetic Protein Pattern during Tomato Fruit Ripening ¹

Abstract

Levels of polypeptides participating in the photosynthetic light and dark reactions have been measured during fruit ripening in tomato. Photosynthetic proteins were identified by Western blot analysis with heterologous antibodies. The concentrations of proteins of photosystem (PS) I (14 kilodaltons), of PSII (47-kilodalton reaction center protein, 32-kilodalton `Q_B binding' protein and light harvesting complex proteins), of the photosynthetic electron transport chain (ferredoxin-NADP-oxidoreductase and plastocyanin), and of the stroma (ribulose-1,5-bisphosphate carboxylase) decrease during the ripening process. The 32-kilodalton protein and plastocyanin were detectable in pericarp protein preparations of ripe tomato fruits. Absorbance difference spectrophotometry provided information on the relative concentrations of PSII and PSI reaction centers in leaf and green fruit tissue of tomato. These results indicate that green fruit pericarp of tomato is photosynthetically active. Photosynthetic activity decreases during chloroplast/chromoplast differentiation. This is consistent with changes that occur at the transcript level of photosynthesis-specific proteins during the differentiation process.