Effects of blue light on cell elongation and microtubule orientation in dark-grown gametophytes of Ceratopteris richardii

Abstract

Gametophytes of Ceratopteris richardii developed into strap-shaped prothalli in the dark. The prothalli had an apical meristem, a subapical elongation zone and a basal zone where no growth occurred. Continuous irradiation of blue light inhibited cell growth of the elongation zone, although red or far-red light had no effect on elongation. Cortical microtubules (MTs) of subapical cells reoriented from transverse to oblique or parallel to the growing axis during blue light inhibition. Each region of the strap-shaped prothallus was irradiated with a microbeam of blue light. Cell elongation in the subapical region was not inhibited by irradiation at the apical meristem. Irradiation of the subapical region inhibited cell elongation to a similar extent as the whole irradiation control. When a single elongating cell at one side of the subapical region was irradiated by a blue microbeam, elongation was inhibited in a cell at the irradiate side only, resulting in a bowing prothallus. Cortical MTs reoriented from transverse to longitudinal to the cell axis in irradiated cells only. The results indicate that each cell in the subapical region perceives blue light by itself, reorients only its cortical MTs and ceases only its cell elongation, independent of surrounding cells.