Calcium/calmodulin affects microtubule stability in lysed protoplasts

Microtubules (Mts) are found in four distinct arrays appearing sequentially in a cell-cycle-dependent fashion within the cells of higher plants. Addition-ally, the cortical Mts of non-cycling cells are spatially altered in a variety of differentiated states. Information regarding the molecular details underlying these Mt-reorientation events in plant cells is scarce. Moreover, it is unclear how cytoskeletal behavior integrates with the myriad of other cellular activities that are altered concomitantly in both differentiating and cycling cells. Data are presented herein to indicate that calcium, in the form of a Ca²⁺/ calmodulin complex, can alter the behavior of Mts in lysed carrot protoplasts. Mechanistically, we show that Ca²⁺/calmodulin most likely interacts with Mts via associations with microtubule associated proteins (MAPs). These results are discussed with reference to how Ca²⁺ may alter the dynamic behavior of Mts during growth and development.