Cell-free protein synthesis with polysomes from germinating Petunia pollen grains.

1. A cell-free protein synthesizing system was developed, which is able to incorporate amino acids into protein programmed by polysomes from pollen grains. 2. The enzyme system used was a 100,000 g supernatant from rat liver. 3. The characteristics of this mixed "plant-animal" system are described 4. Ungerminated pollen contains only monosomes which have no incorporation activity in the cell-free system. 5. Formation of polysomes starts immediately with the germination accompanied by decrease of the monosomal pool. 6. The rapid synthesis of polysomes suggests the presence of a preformed, masked form of messenger-RNA (mmRNA) in the resting pollen grain. 7. The instantaneous activation of protein synthesis enables pollen germination to proceed to a stage at which the pollen genome is not yet activated.