Metabolism of Poly(A) in Plant Cells

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Abstract
In the subapical region of dark-grown pea [Pisum sativum] 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 2 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 IAA, 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.

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