Polyadenylylation of Stored mRNA in Cotton Seed Germination

Abstract

This chapter discusses that much of the mRNA used by germinating cotton cotyledons in the first several days of germination is transcribed in embryogenesis but not used until germination begins. It considers the body of mRNA to code for proteins unique to the germination process rather than representing mRNA functioning in embryogenesis and carried over undergraded into germination. In fact, a specific enzyme, unique to germination, arises from this “stored” mRNA. The chapter attempts to determine by several methods whether preexisting mRNA is polyadenylylated during the first 24 hours of germination. The first of these involved measuring the relative extent of incorporation of [ 32 P] phosphate and [2- 3 H] adenosine into the mRNA portion and poly (A) portion of mRNA (A,) of cotyledons during the hours 10–20 of germination. This was done by isolating mRNA (A n ) from extracts of the tissue on oligo( dT)-cellulose columns using standard techniques. The mRNA portion of the molecules was digested with ribonucleases A and T 1 and the poly (A) portion was recovered by oligo (dT)-cellulose chromatography. The chapter summarizes that the values obtained in the experiments for the true mass-average mRNA chain-length and for the relative amounts of preexisting and newly synthesized mRNA that is polyadenylylated during the first day of germination. Although there is considerable variation in the latter values depending on the method of evaluation used, in every case the polyadenylylation of preexisting RNA is suggested.