Anisotropic diffuse growth in Arabidopsis thaliana stigma papillae.

Arabidopsis stigma papillae grow by a diffuse growth mechanism rather than by tip growth. In angiosperms, the stigma is the first point of contact between the pollen (male) and pistil (female) during pollination. The stigma facilitates pollen capture and adhesion, compatibility responses, pollen germination, and pollen tube guidance to the transmitting tract. In Arabidopsis thaliana, the stigma is composed of single-celled stigma papillae that initiate from the apex of the carpels. Despite their critical function in plant reproduction, little is known about the cell and molecular mechanisms that govern stigma papillae growth and development. Using morphometric analysis of stigma papillae growth during different stages of floral development, we show that A. thaliana stigma papillae grow via a diffuse growth mechanism. Consistent with this conclusion, several mutants with reduced growth anisotropy in vegetative tissues due to defective cellulose or microtubule function likewise reduce anisotropy in stigma papillae.