Biomedical subjects
M Wolters-Arts
Publications and source records attributed to M Wolters-Arts.
Lipids are required for directional pollen-tube growth.
Successful pollination and fertilization are absolute requirements for sexual reproduction in higher plants. Pollen hydration, germination and penetration of the stigma by pollen tubes are influenced by the exudate on wet stigmas and by the pollen coat in species with dry stigmas. The exudate allows pollen tubes to grow directly into the stigma, whereas the pollen coat establishes the contact with the stigma. Pollen tubes then grow into the papillae, which are covered by a cuticle. The components of the exudate or pollen coat that are responsible for pollen tube penetration are not known. To discover the role of the exudate, we tested selected compounds for their ability to act as functional substitutes for exudate in the initial stages of pollen-tube growth on transgenic stigmaless tobacco plants that did not produce exudate. Here we show that lipids are the essential factor needed for pollen tubes to penetrate the stigma, and that, in the presence of these lipids, pollen tubes will also penetrate leaves. We propose that lipids direct pollen-tube growth by controlling the flow of water to pollen in species with dry and wet stigmas.
Directional guidance of nicotiana alata pollen tubes in vitro and on the stigma
Pollen tubes navigate the route from stigma to ovule with great accuracy, but the cues that guide them along this route are not known. We reproduced the environment on the stigma of Nicotiana alata by immersing pollen in stigma exudate or oil close to an interface with an aqueous medium. The growth of pollen in this culture system mimicked growth on stigmas: pollen grains hydrated and germinated, and pollen tubes grew toward the aqueous medium. The rate-limiting step in pollen germination was the movement of water through the surrounding exudate or oil. By elimination of other potential guidance cues, we conclude that the directional supply of water probably determined the axis of polarity of pollen tubes and resulted in growth toward the interface. We propose that a gradient of water in exudate is a guidance cue for pollen tubes on the stigma and that the composition of the exudate must be such that it is permeable enough for pollen hydration to occur but not so permeable that the supply of water becomes nondirectional. Pollen tube penetration of the stigma may be the most frequently occurring hydrotropic response of higher plants.