The role of microtubules in guard cell function

Guard cells are able to sense a multitude of environmental signals and appr opriately adjust the stomatal pore to regulate gas exchange in and out of t he leaf. The role of the microtubule cytoskeleton during these stomatal mov ements has been debated. To help resolve this debate, in vivo stomatal aper ture assays with different microtubule inhibitors were performed. We observ ed that guard cells expressing the microtubule-binding green fluorescent fu sion protein (green fluorescent protein::microtubule binding domain) fail t o open for all major environmental triggers of stomatal opening. Furthermor e, guard cells treated with the anti-microtubule drugs, propyzamide, oryzal in, and trifluralin also failed to open under the same environmental condit ions. The inhibitory conditions caused by green fluorescent protein: :micro tubule binding domain and these anti-microtubule drugs could be reversed us ing the proton pump activator, fusicoccin. Therefore, we conclude that micr otubules are involved in an upstream event prior to the ionic fluxes leadin g to stomatal opening. In a mechanistic manner, evidence is presented to im plicate a microtubule-associated protein in this putative microtubule-based signal transduction event.