Proteomic analysis of the enhancement of seed vigour in osmoprimed alfalfa seeds germinated under salinity stress

Alfalfa (Medicago sativa L.) yield is severely compromised by soil salinity, especially at the level of seedling establishment. This question was addressed by proteomics to decipher whether specific changes in protein accumulation correlate with germination performance of alfalfa seeds submitted to a salinity stress as obtained by imbibing seeds in the presence of NaCl. This study used alfalfa seeds submitted to an osmopriming invigoration treatment that proved very efficient in counteracting the negative effect of salinity stress on germination performance. Comparative proteomic analyses disclosed 94 proteins commonly characterizing the response of both the untreated control and osmoprimed seeds to the experimental salinity stress. Remarkably, many of them, representing 84 proteins, showed contrasting accumulation patterns when comparing the untreated control and osmoprimed seeds submitted to the same salt stress. Thus numerous changes observed in the proteome of the untreated control seeds imbibed in the presence of salt, and presumably accounting for the loss in seed vigour associated with salinity stress, can be substantially reversed in osmoprimed seeds undergoing this stress. These data therefore provide a biochemical understanding of the increase in seed vigour generally observed with primed seeds.

Water Permeability of Palaemon Longirostris and other Euryhaline Caridean Prawns

Water permeability [based on the half-time of exchange of body water with the environment (T1/2)] of the upper estuarine prawn Palaemon longirostris was measured in a range of salinities at 4, 12 and 20°C. Prawns acclimated for 7 days were compared with prawns exposed to acute salinity changes. Acclimation to low salinity and low temperature caused a significant reduction in permeability. Transfer of prawns from 34 to 0.5‰ had no immediate effect on permeability; however, transfer from 0.5 to 34‰ caused an immediate significant rise in permeability. Heart rate of P. longirostris acclimated to 0.5 and 34‰ at 4, 12 and 20°C was unaffected by salinity, but was significantly reduced at low temperature. The permeabilities of three other prawn species (Palaemonetes varians, Crangon crangon and Palaemon elegans), which have different horizontal distributions in estuaries and different salinity tolerance ranges, were also studied and compared with the values obtained for P. longirostris. P. varians and C. crangon showed significantly reduced permeabilities at low compared with high salinities; however, the permeability of P. elegans was unchanged at the two salinities used for this species (22 and 34‰). At each experimental salinity, permeabilities followed the sequence: P. longirostris<P. varians<C. crangon<P. elegans. Results show that reduction of permeability is an important physiological adaptation to life in dilute saline regions and may be involved in separating species with overlapping salinity tolerance ranges.