MOLECULAR CHARACTERIZATION OF PLASTID PYRUVATE-KINASE FROM CASTOR AND TOBACCO

Clones encoding two different forms of plastid pyruvate kinase (PKp; EC 2.7.1.40) have been isolated from both castor and tobacco seed cDNA libraries. One form, designated PK(p)A, from castor was described in a previous report, and the tobacco homologue of PK(p)A has now been isolated. In addition, a second cDNA, designated PK(p)G, has been identified and sequenced in both species. Western blot analysis, using antibodies raised against protein overexpressed from these clones, indicates that they encode the two predominant polypeptides of plastid pyruvate kinase from developing castor endosperm; In castor, both PK(p)A and PK(p)G are encoded by single genes. In the allotetraploid Nicotiana tabacum, there are two copies of each, one derived from each of the progenitors of this species. The expression of the genes for PK(p)A and PK(p)G was examined in various tissues from both castor and tobacco. In castor, both forms are expressed in developing and germinating endosperm and in the root but neither is expressed in the leaf. In tobacco, bothforms are expressed in developing seeds but in mature tissues, PK(p)A is most abundant in roots and PK(p)G in leaves.