ACCUMULATION OF THE ZRP3 MESSENGER-RNA IN THE ROOT AND COLEORHIZA OF GERMINATING MAIZE (ZEA-MAYS, POACEAE)

The evolutionary origin of the coleorhiza of species of Poaceae is unc lear. The zrp3 gene, which codes for a protein of an as yet unknown fu nction, is expressed in the roots of maize early in development. The s equence of zrp3 is similar to the sequences of three other genes isola ted from dicot species. The pattern of accumulation of ZRP3 mRNA was e xamined in embryos of maize. No ZRP3 mRNA can be detected in the dry s eeds; however, 1.5 d after inbibition, ZRP3 mRNA accumulated in both t he roots and the coleorhiza of the embryo but not in other regions of the seed. In the roots, ZRP3 mRNA accumulates specifically in the cort ical ground meristem and the pro-pith tissues. In the coleorhiza, ZRP3 mRNA accumulates in the parenchymal cells but not in the epidermal ce lls, thus distinguishing two tissue types in this organ. The accumulat ion of ZRP3 mRNA in the coleorhiza as well as in the root is molecular evidence consistent with the homology of these two organs.