Direct visual screens have been developed in Arabidopsis to identify mutations affecting the male gametophyte, among fast-neutron (Chen and Mc-Cormick 1996), or EMS (Twell and Howden 1998; Park et al. 1998) muta-genized populations. These screens were designed to score early mutants on DAPI-stained mature pollen, a robust and 100% efficient protocol that allowed one to observe pollen grains morphology in microtitre plates (Chapter II). The cloning of the targeted genes in these mutants should bring interesting information on the regulation of pollen tube initiation, along with the analysis of other genes important for pollen cell wall and early pollen/stigma recognition steps (see below, Sect. 3). However, a reliable screen does not yet exist to reasonably allow the isolation of progamic mutants; in vitro pollen germination and tube growth of Arabidopsis is not reproducible enough for this purpose (Johnson-Brousseau and McCormick 2004).
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