Auxin regulates lateral meristem activation in developing gametophytes ofCeratopteris richardii

This study investigates the auxin regulation of lateral meristem activation in the gametophytes of the fern Ceratopteris richardii Brongn. Exogenous auxin in the form of α-naphthaleneacetic acid or 2,4,5-trichlorophenoxy-acetic acid repressed the activation of the lateral meristem, and generated a male-like body plan. The auxin antagonist p-chlorophenoxyisobutyric acid reduced activity of both the apical and lateral meristems, and produced a circular-shaped gametophyte. Disrupting auxin transport with 2,3,5-triiodobenzoic acid led to a time lag in lateral meristem activation, while disrupting auxin transport with n-1-naphthylphthalamic acid produced several different body plans generated by the formation of a second lateral meristem. These findings suggest auxin mediates the activation of the lateral meristem and regulates lateral meristem function. In addition, auxin transport may be necessary for communication between the lateral meristem and other regions of the developing gametophyte. Auxin also controls the position of rhizoids produced by the gametophyte, and exogenous auxin interferes with the sexual differentiation of the gametophyte. These results are summarized in a model of how auxin regulates lateral meristem activation and meristem activity during gametophyte development in C. richardii.