Ripening-related occurrence of phosphoenolpyruvate carboxykinase in tomatofruit

Phosphoenolpyruvate carboxykinase (PEPCK) is present in ripening tomato fru its. A cDNA encoding PEPCK was identified from a PCR-based screen of a cDNA library from ripe tomato fruit. The sequence of the tomato PEPCK cDNA and a cloned portion of the genomic DNA shows that the complete cDNA sequence c ontains an open reading frame encoding a peptide of 662 amino acid residues in length and predicts a polypeptide with a molecular mass of 73.5 kDa, wh ich corresponds to that detected by western blotting. Only one PEPCK gene w as identified in the tomato genome. PEPCK is shown to be present in the per icarp of ripening tomato fruits by activity measurements, western blotting and mRNA analysis. PEPCK abundance and activity both increased during fruit ripening, from an undetectable amount in immature green fruit to a high am ount in ripening fruit. PEPCK mRNA, protein and activity were also detected in germinating seeds and, in lower amounts, in roots and stems of tomato. The possible role of PEPCK in the pericarp of tomato fruit during ripening is discussed.