Microtubule arrays in fucoid zygotes are sensitive to cytoplasmic pH

Abstract

Regulation of microtubule (MT) arrays and embryogenesis by cytoplasmic pH (pH c ) was investigated in zygotes of the brown alga Pelvetia compressa (J. Agardh) De Toni. pH c was clamped to (set to) acidic values using a weak acid, propionic acid (PA), and to alkaline values using a weak base, methylamine (MA). Acidification of pH c from the normal value of 7.4-7.5 to about 7.0 caused disruption of microtubule arrays. The nucleating activity was delocalized from the centrosomes and dispersed over the nuclear envelope, the number of MTs decreased, and MTs failed to extend into the cell cortex. Alkalinization to about pH 8.0 also caused dispersal of nucleating activity, but distinct centrosomes remained. MTs coursed in various directions following MA treatment, giving the array a disorganized appearance. Two MT-dependent processes, rhizoid morphogenesis and cell division, were found to be perturbed by small changes in pH c .