A CYTOKINESIS-DEFECTIVE MUTANT OF ARABIDOPSIS (CYT1) CHARACTERIZED BYEMBRYONIC LETHALITY, INCOMPLETE CELL-WALLS, AND EXCESSIVE CALLOSE ACCUMULATION

The genetic control of cell division in eukaryotes has been addressed in part through the analysis of cytokinesis-defective mutants. Two all elic mutants of Arabidopsis (cyt1-1 and cyt1-2) altered in cytokinesis and cell-wall architecture during embryogenesis are described in this report. Mutant embryos appear slightly abnormal at the heart stage an d then expand to form a somewhat disorganized mass of enlarged cells w ith occasional incomplete walls. In contrast to the keule and knolle m utants of Arabidopsis and the cyd mutant of pea, which also exhibit de fects in cytokinesis during embryogenesis, cyt1 embryos cannot be resc ued in culture, are desiccation-intolerant at maturity, and produce ce ll walls with excessive callose as revealed through staining with the aniline blue fluorochrome, Sirofluor. Some cyt1 defects can be partial ly phenocopied by treatment with the herbicide dichlobenil, which is t hought to interfere with cellulose biosynthesis. The distribution of u nesterified pectins in cyt1 cell walls is also disrupted as revealed t hrough immunocytochemical localization of JIM 5 antibodies. These feat ures indicate that CYT1 plays an essential and unique role in plant gr owth and development and the establishment of normal cell-wall archite cture.