The control of the annual growth cycle in raspberry

Summary Priming treatments (osmoconditioning), which can considerably improve seed germination performance, are widely applied by seed companies to increase the rate and uniformity of seedling establishment of commercial vegetable and flower seeds. Advancement of embryonic root tip cells into S and G2 phases of the cell cycle, as measured by the increase in the percentage of nuclei showing a 4C DNA content, has been observed to occur after osmoconditioning of pepper (Capsicum annuum L.) seeds. Here we report the relationship between osmoconditioning effects and the activation of DNA replication as well as the accumulation of p-tubulin, a constitutive element of microtubules, in the embryo root tips during priming in PEG 6000 solutions, at the osmotic potentials of ‒1.1 and ‒1.5 MPa. With dry seeds, flow cytometric profiles indicated that most of the cells were arrested at Gi phase of the cell cycle while β-tubulin was not detectable on western blots. During priming, β-tubulin appeared to be synthesized de novo and its accumulation preceded DNA replication. Within each priming condition, the time courses and amounts of DNA replication and p-tubulin accumulation were found to correlate with improved seed germination performance. Their potential use as molecular markers for discriminating a priori priming effectiveness is discussed.