Protein synthesis in germinating pollen of Petunia: role of proline.

Pollen of Petunia hybrida was germinated in artificial medium. At the beginning of the incubation, a large amount of proline, which comprises about half of the total free amino acid pool, was released into the medium. Part of this proline is reutilized by the pollen. Uptake of radioactive amino acids and their incorporation into proteins were studied. The highest rate of protein synthesis was found directly after the onset of germination. The endogenous free proline pool was found to be compartmentalized; one of the compartments is the protein precursor pool; its size is probably much less than 50% of the total free proline in the pollen.