Pyruvate Orthophosphate Dikinase mRNA Organ Specificity in Wheat and Maize

Polyadenylated RNA was isolated from leaves and seeds of a C(3) plant (Triticum aestivum L. cv Cheyenne, CI 8885) and from a C(4) plant (Zea mays L. cv Golden bantam). Each polyadenylated RNA preparation was translated in vitro with micrococcal nuclease-treated reticulocyte lysate. When the in vitro translation products were probed with antibodies to pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1), two sizes of polypeptide were identified. A 110 kilodalton polypeptide was found in the in vitro translation products of mRNA isolated exclusively from leaves of both wheat and maize. A 94 kilodalton polypeptide, similar to the PPDK polypeptide which can be extracted after in vivo synthesis in maize and wheat leaves and seeds, was found in the in vitro translation products obtained from wheat seeds and maize kernels.These results indicate that the mRNAs for PPDK polypeptides are organ-specific in both a C(4) and a C(3) plant. Hague et al. (1983 Nucleic Acids Res 11: 4853-4865) proposed that the larger size polypeptide of the in vitro translation polypeptide from maize leaf RNA contains a ;transit sequence' which permits entry into the chloroplasts of a polypeptide synthesized in vivo in maize leaf cell cytoplasm. It appears that in wheat leaves also the transit of synthesized PPDK polypeptide through an intracellular membrane may be required, while such a transit sequence seems not to be required within cells of wheat and maize seeds.