Lettuce seeds were germinated at 20 C in the dark in water and sampled at various intervals during the first 18h of germination to determine quantitative and qualitative differences in proteins. The soluble protein fraction was partitioned into albumins and globulins by dialysis and the proteins of the globulin fraction were visualized by SDS-PAGE. Heat stable proteins were obtained by boiling the proteins, cooling on ice, and resuspending in buffer.
The soluble protein content remained constant during the first 8h of germination. Thereafter protein content decreased and was 6% of the amount present in unimbibed seed in 21 day old seedlings. The ratio of heat stable to heat unstable proteins decreased during the germination process. No differences in banding patterns were observed when the soluble protein fraction were run on SDS-PAGE. However, on gels run with the globulin fraction a 57 kD protein appeared 4 and 8 h after imbibition and had disappeared by 12 h after imbibition. The role of proteins and heat-stable proteins during germination and prevention of dessication during early seedling growth is discussed.