Metabolism of poly (A) in plant cells: Discrete classes associated with free and membrane-bound polysomes [Peas]

In the subapical region of dark-grown pea epicotyls about 40% of the total polysomes are associated with membranes. The presence of poly(A) in polysomal mRNA was detected by hybridization of unlabeled RNA with 3H-poly(U). Both free mRNA and messenger ribonucleoprotein particles in polysomes hybridize with 3H-poly(U) quantitatively. The binding of 3H-poly(U) to polysomes is increased by treatment with the detergent sodium dodecyl sulfate. Since detergent influenced the 3H-poly(U) binding more in membrane-bound polysomes than in free, there may be more protein(s) associated with the poly(A) portion of the mRNA in membrane-bound polysomes. Analysis of the poly(A) segments isolated from the mRNA of these two classes of polysomes indicates that there are discrete classes of poly(A) and they appear to be differentially associated with free and membrane-bound polysomes. Mean size distribution of poly(A) in free polysomes is larger than in membrane-bound polysomes. Following treatment (2 days) with the plant growth hormone indole-acetic acid, there is a gradual decrease in the mean length of total poly(A), which appears to correspond to a decrease in the size of the polysomes and their associated mRNA.