IN-VITRO ASSEMBLED PLANT MICROTUBULES EXHIBIT A HIGH STATE OF DYNAMICINSTABILITY

Higher plants possess four distinct microtuble arrays. One of these, t he cortical array, is involved in orienting the deposition of cellulos e microfibrils. This plant interphase array is also notable because it contains exceptionally dynamic microtubules. Although the primary seq uence of plant and animal tubulin is similar (79-87% amino acid identi ty overall) there are some regions of divergence. Thus, one possible e xplanation for the high state of polymer assembly and turnover that is observed in plant interphase arrays is that the tubulins have evolved differently and possess a higher intrinsic dynamic character than the ir animal counterparts. This hypothesis was tested using highly purifi ed plant tubulin assembled in vitro. Using high-resolution DIC video-e nhanced microscopy, we quantified the four characteristic parameters o f dynamic instability of plant microtubules and compared them with ani mal microtubules. The elongation velocities between plant and animal m icrotubules are similar. but plant microtubules undergo catastrophes m ore frequently, do not exhibit any rescues, and have an average shorte ning velocity of 195 mu m/min (compared with 21 mu m/min for animal mi crotubules). These data support the hypothesis that plant tubulin form s microtubules that are intrinsically more dynamic than those of anima ls. (C) 1997 Wiley-Liss, Inc.