Conditional male fertility in maize

Abstract

This study compares conditional male fertility (CMF) in maize and petunia. CMF is a reversible defect in pollen germination or tube growth; pollen is nonfunctional in self-crosses but fully functional in outcrosses or when supplied with specific flavonol aglycones at pollination. CMF occurs in maize and petunia mutants that lack chalcone synthase (CHS) activity and therefore do not synthesize flavonols. In maize CMF seedlings and developing male florets, CHS transcripts accumulate to high levels, yet western blot analysis using an anti-CHS antiserum does not detect any CHS protein. This is in contrast to CMF petunia, where no CHS RNA is detected (Vogt et al. 1994). While CMF petunia pollen requires flavonols to germinate, CMF maize pollen germinates and grows both in vivo and in vitro without the addition of flavonols. However, pollen tubes abort after 12 h of growth which explains the lack of seed set in self crosses (Mo et al. 1992). Pollen tubes of CMF maize have an unusual morphology in vivo, with heavy callose deposits throughout the tube and tips that burst within the silk. Normal tube morphology and seed set are restored by adding flavonols to the silks at pollination. As previously shown with petunia, fecundity (seed set) may be enhanced in maize by adding quercetin and kaempferol at pollination.