Pollen germinates precociously in the anthers of raring-to-go, an Arabidopsis gametophytic mutant

Pollen hydration is usually tightly regulated and occurs in vivo only when desiccated pollen grains acquire water from the female, thus enabling polle n tube growth. Pollen tubes are easily visualized by staining with decolori zed aniline blue, a stain specific for callose. We identified a mutant, rar ing-to-go, in which pollen grains stained for callose before anther dehisce nce. When raring-to-go plants are transferred to high humidity, pollen tube s dramatically elongate within the anther. As early as the bicellular stage , affected pollen grains in raring-to-go plants acquire or retain water wit hin the anther, and precociously germinate. Thus, the requirement for conta ct with the female is circumvented. We used pollen tetrad analysis to show that raring-to-go is a gametophytic mutation, to our knowledge the first ga metophytic mutation in Arabidopsis that affects early events in the pollina tion pathway. To aid in identifying raring-to-go alleles, we devised a new technique for screening pollen in bulk with decolorized aniline blue. We sc reened a new M, mutagenized population and identified several additional mu tants with a raring-to-go-like phenotype, demonstrating the usefulness of t his technique. Further, we isolated other mutants (gift- wrapped pollen, po lka dot pollen, and emotionally fragile pollen) with unexpected patterns of callose staining. We suggest that raring-to-go and these other mutants may help dissect components of the pathway that regulates pollen hydration and pollen tube growth.