Sugarbeet seed priming:: effects of priming conditions on germination, solubilization of 11-S globulin and accumulation of LEA proteins

The relationship between initial mobilization of 11-S globulin storage protein (leading to solubilization of its B-subunit) and germination performance after priming was studied in sugarbeet (Beta vulgaris L.) seeds. Priming was conducted for 2 d either in water (hydropriming) or in -2.0 MPa polyethylene glycol-8000 (osmopriming), at various temperatures ranging from 5 to 40 degreesC and oxygen concentrations in the atmosphere ranging from 0 to 21%. For both types of pre-treatments, the range of temperatures and the concentrations of oxygen which were effective in priming were very similar to those which allowed solubilization of the B-subunit of 11-S globulin, supporting the robustness of this protein marker for optimization of sugarbeet seed priming. Furthermore, the temperature and oxygen dependence of priming efficiency closely paralleled that for germination of the untreated seeds, reinforcing the finding that the beneficial effect of priming corresponded to the advancement of germination sensu stricto (i.e. phase II of the germination process). For priming times longer than 2 d, particularly for osmopriming, there was a very dramatic decrease in germination of the treated seeds. For instance, following a 14 d osmopriming at 25 degreesC as much as 60% of the pre-treated seed population failed to germinate when transferred to water. This loss in germination performance quite closely paralleled degradation of LEA (late embryogenesis abundant) proteins, notably a heat-stable seed-specific protein of about 60 kDa and a seed-specific biotinylated LEA protein.