C.J. Geisler-Lee^1,3, Z. Hong³, D.P.S. Verma^2,3

Department of Plant Biology¹, Department of Molecular Genetics², and Plant Biotechnology Center³

Phragmoplastin is localized within phragmoplast during cytokinesis and appears to be critical for cell division. Transgenic plants have been generated which overexpressed normal phragmoplastin (35S::Phr) and a dominant negative allele devoid of GTPase activity (35S::PhrK47M) was obtained. These plants were used to evaluate the role of phragmoplastin in cell plate formation. Our ultrastructural study shows that phragmoplasts in both transgenic plants seem to arrest at a very early stage in cell plate formation. The staining pattern and timing of aniline blue indicator of callose suggests the consequent cell wall maturation is affected. The rate of cell division in root apical meristem (RAM) declined dramatically over time; however, the cell expansion continued in RAM. Eventually there was no cell division in RAM of 35S::Phr plants and the supply of meristematic cells were exhausted to cause the loss of normal RAM anatomy within 4 weeks. We conclude that the arrested growth in the transgenic plants is due to exhaustion of meristematic cells when cell plate formation is delayed.