Relationships of Histones to RNA Synthesis in Plant Tissues

The RNA-synthesizing activity of the tissue, template activity of the chromatin, histones and other parameters were analyzed for young leaves, senescent leaves and the pith tissue of tobacco. The amount, of RNA, DNA and the extent of incorporation of ³²P into RNA was much lower in old leaves and the pith tissue than in young leaves. Furthermore, the ³²P sucrose density gradient patterns of RNA from the three tissues were very different. In old leaves, the label was found mostly in low molecular weight RNA region, presumably as a result of degradation of RNA by soluble and chromatin-associated ribonucleases which were higher in old leaves. — In addition to significant differences in the composition of chromatin, large differences in the ratios of F_I : F_II : F_III : : histone fractions from the three tissues were noted and the fully differentiated old leaves and the pith tissue had proportionately more F_IIand F_III histones than the less differentiated young leaves. The F_III histone of tobacco differed from that of pea and calf thymus in having lys/arg = 1.2. — Although some correlation between RNA-synthesizing activity of the tissue, template activity of chromatin and the histone composition was noted for the pith tissue and the young leaves, the situation with old leaves was more complicated, probably due to the occurrence of chromatin-associated deoxyribonuclease and involvement of other factors which may also effect RNA synthesis.