XVI International Botanical Congess
Our recent findings challenge the idea that cortical microtubules (mts) control cellulose microfibril (mf) alignment. We examined mt and mf orientation and measured cell expansion in the roots of two Arabidopsis mutants, mor1 and rsw1. Both mutants are temperature-sensitive. At 29?C, cortical mts in mor1 shorten and randomize and cellulose synthesis in rsw1 is reduced. Growth anisotropy is inhibited in both mutants. Unexpectedly, field emission SEM revealed that in mor1, mfs were still transversely aligned, well after isodiametric expansion replaced elongation. In rsw1 cells, on the other hand, mts remained transverse but mfs appeared randomized. The loss of growth anisotropy is more severe in mor1-rsw1 double mutants than in mor1 or rsw1 alone, suggesting the genes MOR1 and RSW1 regulate growth anisotropy by independent mechanisms.