Claessens, Susanne M. C.

Two forms of seed dormancy are distinguished: primary and secondary. Sisymbrium officinale seeds will be used to study induction and breaking of secondary dormancy. In S. officinale changes in seed dormancy coincide with changes in the sensitivity or responsiveness to naturally occurring factors that stimulate germination, such as light and nitrate. This can be best explained by assuming that the number of accessible receptors for light and nitrate fluctuate. When environmental factors change to more optimal conditions for germination the fluidity of the membrane changes and receptors for light and nitrate become more accessible. Membrane fluidity will be studied with electron-spin probe resonance (EPR). Desaturases have been suggested to play a role in the fluidity of the membrane. Expression of genes encoding desaturases will be studied under conditions that showed changed dormancy behaviour. Other mechanisms responsible for dormancy are investigated with a cDNA subtraction library, comparing secondary dormant seeds to seeds that are not dormant, to find differences in gene expression that might explain the dormancy behaviour. A second approach to find differences in gene expression is by proteomics, again comparing secondary dormant seeds to seeds that are not dormant.