Phycomyces: modification of spiral growth after mechanical conditioning of the cell wall.

Mature stage IVb Phycomyces sporangiophores show left-handed spiral growth; that is, viewed from above, the sporangium rotates clockwise. Mechanical conditioning of the cell wall by the Instron technique increases the ratio of the rotational to the elongational growth rate. This result is in agreement with the fibril reorientation model of spiral growth, which suggests that cell wall microfibrils, initially oriented in a nearly transverse right-handed direction in the upper region of the growing zone, are displaced during growth toward the longitudinal axis, causing the observed left-handed spiral growth.