Changes in microtubule and microfibril arrangement during polarotropism inAdiantum protonemata

Abstract

Polarotropism was induced inAdiantum (fern) protonemata grown under polarized red light by turning the electrical vector 45 or 70 degrees. One hour after the light treatment, tropic responses became apparent in many cells as a slight distortion of the apical dome. Changes in the position of the circumferentially-arranged cortical microtubule band (Mt-band) (Murataet al., 1987) and the arrangement of microfibrils around the subapical part of protonemata were investigated in relation to the polarotropic responses. Twenty minutes after turning the electrical vector, preceding the morphological change of cell shape, the Mt-band began to change its orientation from perpendicular to oblique to the initial growing axis. After 30 min, the Mt-band changed its orientation further under 45 degrees polarized light, but under light rotated 70 degrees, it began to disappear. In phototropic responses induced by local irradiation of a side of the subapical part of a protonema with a non-polarized red microbeam, the Mt-band on the irradiated side disappeared or became faint within 20 min, but neither disappearance nor a change of orientation of Mts occurred on the non-irradiated side. One hour after turning the electrical vector 45 degrees, in half of the cells tested, the innermost layer of microfibrils in the subapical part of the protonema changed its orientation from perpendicular to oblique to the growing axis, corresponding to the changes in the orientation of the Mt-band. After 2 hr, those changes were obvious in all cells examined. The same basic results on the orientation of microfibrils were obtained with protonemata cultured for 2 hr under 70 degrees polarized light. The role of the Mt-band in tropic responses is discussed.