Homologues of the pea SBP65, a late embryogenesis abundant (LEA) biotinylated protein that behaves as a putative sink for the free vitamin biotin during embryo development, were characterized biochemically in various plant species, including soybean, lentil, peanut, rape, cabbage, carrot and sugarbeet. Based on sequence homologies, the genome of Arabidopsis thaliana contains a gene putatively encoding a homologue of pea SBP65. These proteins exhibit two remarkable features. First, they only accumulate in seeds, particularly during late stages of embryo development. The results strongly suggest that these seed-specific biotinylated proteins belong to the class of plant proteins called seed maturation proteins, which are presumed to play major roles in embryo development. Secondly, covalent attachment of biotin occurs at a lysine residue within a conserved motif of (V/M)GKF, which shows no resemblance to the highly conserved AMKM tetrapeptide that houses the target lysine residue in the well-characterized biotin-dependent carboxylases and decarboxylases. These findings highlight novel structural features for protein biotinylation.

A model of seed germination is proposed which uses a variable with the units of an osmotic potential (virtual osmotic potential) to integrate the effect of a constant or a varying water potential. This differs from existing models that describe the effects of fixed water potentials on germination, or the effects of fixed priming water potentials on the subsequent germination at a fixed water potential. When a seed is sown, the virtual osmotic potential is assumed to fall at a rate that depends on the ambient water potential, and on the difference between its current and a minimum value. Radicle growth is assumed to initiate when the difference between the ambient water potential and the virtual osmotic potential exceeds a threshold. The germination of carrot and onion seeds at various fixed potentials below 0 MPa was well described by the virtual osmotic potential model. The model was also used to simulate the results of experiments in which seeds were given a single step change in water potential.