CYTOLOGICAL CHARACTERIZATION OF 4 MEIOTIC MUTANTS OF ARABIDOPSIS ISOLATED FROM T-DNA-TRANSFORMED LINES

A secondary screen of the Feldmann collection of T-DNA transformed Ara bidopsis lines identified several meiotic mutants. We used a spreading technique combined with DAPI staining in a detailed cytogenetic analy sis of meiotic chromosome behaviour in four of these mutants, all of w hich are putatively T-DNA tagged and therefore candidates for molecula r and functional analysis of the mutated genes. Two of them are define d as `synaptic' mutants, showing greatly reduced association of homolo gous chromosomes at metaphase I: one is asynaptic, showing failure of synapsis during prophase I, whereas the other is desynaptic and is cha racterized by normal but non-maintained synapsis. Another mutant is de fective in meiotic cell cycle control and undergoes a third meiotic di vision, resembling a second division but without an additional round o f chromosome duplication. A further mutant shows meiosis-limited chrom osome disruption, resulting in extensive chromosome fragmentation comb ined with other defects. All four mutants experience very irregular ch romosome distribution during the meiotic divisions, resulting in abnor mal numbers and/or sizes of microspores, with resulting reduced fertil ity.