Ricerche Sulla Flora e Vegetazione dei Fontanili Dell'Agro Milanese

Abstract

Nucleic Acids in Ripening of Castor Bean Endosperm. - I. Quantitative and Qualitative Changes of total RNA. — The ripe Castor Bean seed endosperm (Ricinus Communis var. Sanguinea) has a very low level of nucleic acids and particularly of ribosomal RNA. However, they rapidly increase during the germination of the seed (S. Cocucci et al., Acc. Naz. Lincei, 38, 545, 1965).

The behaviour of the nucleic acids, obtained by phenol extraction from Castor Bean seed endosperm at different ripening stages, is the following:

1. From the moment when the developing seed has reached the maximal fresh weight to the moment of its complete ripening, the RNA content decreases from about 700 μg per seed to about 200 μg.

2. During the same period the DNA level (about 13–15 μg per seed) remains nearly costant.

3. Fractionation by sucrose density gradient of the phenol extracted RNA (H. L. Sanger and C. A. Knight, Biochem. Biophys. Reserch Commun., 13, 445, 1963) shows that during the ripening of the seed the high molecular weight RNA decreases much more than the low molecular weight RNA.

4. Radioactive phosphate injected in the seeds is incorporated in the RNA at all the stages. Fractionation by sucrose density giadient shows that the phosphate is essentially incorporated in low molecular weight RNA and there is pratically no labelling of the heavier RNA after quite a long period (2 hr.).

These data suggest that the decrease of the RNA during the ripening of the seed can be due to a fall in the ability to synthesize high molecular RNA.