Messenger RNas : their utilization and degradation during pollen germination and tube growth

During pollen germination and tube growth at least 230 new proteins are synthesized, as determined by ³⁵S-methionime labeling and two dimensional gel electrophoretic analysis of the labeled proteins. The same number and pattern of protein spots is seen whether or not actinomycin D is included in the, medium, indicating that the mRNAs present in the unger-minated pollen grain and those newly synthesized code for the same proteins. The genetic program during at least the latter part of pollen maturation prior to anthesis and that during pollen germination and tube growth thus appears to be similar if not identical. During the first hour of pollen tube growth about 500/0 of the protein synthesis that occurs utilizes previously synthesized mRNAs. The remaining 50% occurs on newly made mRNAs. The ungerminated mature pollen grain contains 196 pg of RNA and approximately 6 X 10⁶ molecules of poly(A)+ RNA, i.e. mRNAs. The rate of protein synthesis corrected for internal pool changes in the labeled amino acid used (³H-leucine) is highest during the first 15 min of pollen tube growth. The rate decreases rapidly thereafter for the next 45 min. Concurrent with the reduction in rate of protein synthesis there is a reduction in the poly(A) content of the pollen RNA and in the amount of poly(A) per pollen, grain. The total RNA per pollen grain, however, appears not to change during this period.