Amino acid and protein profiles of Vicia faba salt-stressed seedlings grown from thermally-stressed seeds

Seeds of Vicia faba L. cv Giza 843 were subjected to 4°C, 25°C (control) and 40°C for 48 h before sowing in clay-loam soil and the seedlings were irrigated with water (control) or 0.1 M NaCl for 35 days (d). Germination percentage, length and fresh and dry weights of 10-d and 35-d old seedlings decreased with the rise of presowing temperature; the decrease was greater when thermal and salinity stresses were combined. In the 10-d-old seedlings, thermal and/or salinity stresses enhanced the assembly of free amino acids into members of the heat shock proteins families Hsp100, Hsp60 and sHsp, which exhausted the free amino acid pool to the point of almost total depletion. The sHsps seem to stabilize the stressdenatured enzymes and structural proteins, thus preparing them for subsequent refolding by members of the Hsp60 and Hsp100 families so that they regain their functional conformations, which might have in turn led to the observed improvement in the germination percentage and in seedling growth. In 35-d-old seedlings, fewer Hsps were synthesized leading to greater accumulation of eight amino acids (proline, glutamic acid, glycine, alanine, methionine, phenylalanine, lysine, arginine) to act as osmoregulators. The strategy for combating abiotic stress seems age-dependent.