Pollen Germinates Precociously in the Anthers of raring-to-go, an Arabidopsis Gametophytic Mutant

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Abstract
Pollen hydration is usually tightly regulated and occurs in vivo only when desiccated pollen grains acquire water from the female, thus enabling pollen tube growth. Pollen tubes are easily visualized by staining with decolorized aniline blue, a stain specific for callose. We identified a mutant, raring-to-go, in which pollen grains stained for callose before anther dehiscence. Whenraring-to-go plants are transferred to high humidity, pollen tubes dramatically elongate within the anther. As early as the bicellular stage, affected pollen grains in raring-to-goplants acquire or retain water within the anther, and precociously germinate. Thus, the requirement for contact with the female is circumvented. We used pollen tetrad analysis to show thatraring-to-go is a gametophytic mutation, to our knowledge the first gametophytic mutation in Arabidopsis that affects early events in the pollination pathway. To aid in identifyingraring-to-go alleles, we devised a new technique for screening pollen in bulk with decolorized aniline blue. We screened a new M1 mutagenized population and identified several additional mutants with a raring-to-go-like phenotype, demonstrating the usefulness of this technique. Further, we isolated other mutants (gift-wrapped pollen, polka dot pollen, and emotionally fragile pollen) with unexpected patterns of callose staining. We suggest thatraring-to-go and these other mutants may help dissect components of the pathway that regulates pollen hydration and pollen tube growth.