Stimulation of carrot somatic embryogenesis by proline and serine.

Serine and proline, when added in a wide range of concentrations to Daucus carota cultures during pre-growth in the presence of 2,4-D(2,4-dichlorophenoxyacetic acid), extended in time and quantity the mitotic divisions and stimulated significantly the number of embryos regenerated when the hormone subsequently was omitted from the medium. A specific effect of these amino acids on regeneration is suggested, since proline (as hydroxyproline) and serine are the two major constituents of the cell wall glycoprotein, extensin, which thus may have a morphoregulatory function. The significant role of the conditions during pregrowth of the cultures in the presence of hormone is underlined by the effect of hydroxyproline and D-proline which also stimulate embryogenesis, but alter markedly the development of the embryos.

Mutations induced by X-radiation in the yeast Schizosaccharomyces pombe.

Experiments on strains of yeast with different genetic backgrounds were done to evaluate the kinetics of inactivation and mutation induction by X-radiations. A system of forward mutation induction in five loci was used as a specific mutation rate of 0.14-10-minus 8 times locus times rad was evaluated for the wild type.