Protein synthetic activity during normal pollen development and during induced pollen embryogenesis in Hyoscyamus niger

Abstract

Protein synthetic activity during maturation, germination, and embryogenic phases of pollen grains of Hyoscyamus niger (L.) was investigated by means of autoradiography of incorporation of [3H]arginine, [3H]leucine, [3H]lysine, and [3H]tryptophan. Silver grain counts showed that during pollen maturation, peaks of incorporation of [3H]arginine and [3H]lysine occurred before the onset of vacuolation in the uninucleate pollen grains and as starch accumulation was initiated in the bicellular pollen grains. In the latter, labeled amino acids were mostly incorporated into the vegetative cell and very little appeared in the generative cell. [3H]leucine and [3H]tryptophan were not incorporated into uninucleate pollen grains at any stage of their development, although they were localized in the vegetative cell of bicellular pollen grains. In germinating pollen grains the nucleus of the vegetative cell, the generative cell, and sperms did not incorporate the isotopes. While the majority of pollen grains incorporated [3H]arginine, [3H]leucine, [3H]lysine, and [3H]tryptophan immediately after culture of anthers, during further periods of culture, protein synthetic activity persisted only in a small number of uninucleate, nonvacuolate, and densely staining "embryogenically determined" pollen grains confined to the periphery of the anther locule. Subsequent division of these pollen grains was accompanied by incorporation of [3H]arginine, [3H]leucine, and [3H]lysine into the vegetative cell or into both the vegetative cell and generative cell. It is suggested that, in contrast to the 3H-labeled amino acid incorporation pattern observed in pollen grains during their normal ontogeny, a significant change associated with embryogenic induction is the incorporation of [3H]leucine and [3H]tryptophan into embryogenically determined uninucleate pollen grains and of [3H]arginine, [3H]leucine, and [3H]lysine into the generative cell of bicellular pollen grains.