MICROTUBULE-ORGANIZING CENTERS IN PLANTS

The organization of microtubules into ordered arrays is essential for cell division and differentiation. Centrosomes have long been recogniz ed as major components of this process in metazoans, Most plant cells, however, do not have such morphologically distinct organelles, althou gh they do have functionally equivalent microtubule-organizing centres , Recent discoveries have shed new light on these mysterious organelle s. A key element is gamma-tubulin, which is ubiquitous in eukaryotes, including plants, Multiprotein complexes with gamma-tubulin -'gamma-so mes' - probaby serve as templates for microtubule initiation. Microtub ules can also self-organize into ordered arrays in the presence of mot or proteins, providing evidence that the organization of microtubule a rrays involves both nucleation and polymer translocation. These exciti ng findings pave the way for elucidating the identity of the diffuse m icrotubule-organizing centres in plants and the principles of microtub ule organization without centrosomes.