Regulation of programmed cell death in maize endosperm by abscisic acid

Cereal endosperm undergoes programmed cell death (PCD) during its developme nt, a process that is controlled, in part, by ethylene. Whether other hormo nes influence endosperm PCD has not been investigated. Abscisic acid (ABA) plays an essential role during late seed development that enables an embryo to survive desiccation. To examine whether ABA is also involved in regulat ing the onset of PCD during endosperm development, we have used genetic and biochemical means to disrupt ABA biosynthesis or perception during maize k ernel development. The onset and progression of cell death, as determined b y viability staining and the appearance of internucleosomal DNA fragmentati on, was accelerated in developing endosperm of ABA-insensitive vp1 and ABA- deficient vp9 mutants. Ethylene was synthesized in vp1 and vp9 mutant kerne ls at levels that were 2-4-fold higher than in wild-type kernels. Moreover, the increase and timing of ethylene production correlated with the prematu re onset and accelerated progression of internucleosomal fragmentation in t hese mutants. Treatment of developing wild-type endosperm with fluridone, a n inhibitor of ABA biosynthesis, recapitulated the increase in ethylene pro duction and accelerated execution of the PCD program that was observed in t he ABA mutant kernels. These data suggest that a balance between ABA and et hylene establishes the appropriate onset and progression of programmed cell death during maize endosperm development.