Effect of steady torque twisting on the orientation of cortical microtubules in the epidermis of the sunflower hypocotyl.

Orientation of cortical microtubules (cMTs) is suggested to be affected by mechanical stress existing in cell walls. However, in mutants exhibiting helical (chiral) growth, there is a correlation between orientation of cMTs in outer tissues and helical growth direction. The aim of this research was to examine the effect of a chiral mechanical stimulation on cMTs. For this purpose, the orientation of cMTs was investigated in hypocotyls subjected to either a right- or a left-handed twist, resulting from a steady torque. cMTs were visualised in fixed material using the immunofluorescence method. The cMTs in untouched control hypocotyls were mostly transverse with respect to the cell long axis. In immobilised, but not twisted control hypocotyls, the transverse orientation was also most frequent, while applied twisting resulted in a change in cMT orientation from transverse to oblique. The data provide additional evidence that changes in tissue stress can be reorganized by cortical microtubules.