ALTERATIONS IN POLYRIBOSOME AND MESSENGER RIBONUCLEIC ACID METABOLISM AND MESSENGER RIBONUCLEOPROTEIN UTILIZATION IN OSMOTICALLY STRESSED PLANT SEEDLINGS (WATER STATUS, GROWTH, HORDEUM VULGARE).

摘要

Polyribosome aggregation state in growing tissues of barley and wheat leaf or stems of pea and squash was studied in relation to seedling growth and water status of the growing tissue in plants at various levels of osmotic stress. It was found to be highly correlated with water potential and osmotic potential of the growing tissue and with leaf or stem elongation rate. Stress rapidly reduced polyribosome content and water status in growing tissues of barley leaves; changes were slow and slight in the non-growing leaf blade. Membrane-bound and free polyribosomes were equally sensitive to stress-induced disaggregation. Incorporation of ³²PO₄³⁻ into ribosomal RNA was rapidly inhibited by stress, but stability of poly(A) ⁺RNA relative to ribosomal RNA was similar in stressed and unstressed tissues, with a half-life of about 12 hours. Stress also caused progressive loss of poly(A) ⁺RNA from these tissues. Quantitation of poly(A) and in vitro messenger template activity in polysome gradient fractions showed a shift of activity from the polysomal region to the region of 20-60 S in stressed plants. Messenger RNA in the 20-60 S region coded for the same peptides as mRNA found in the polysomal fraction. Nonpolysomal and polysome-derived messenger ribonucleoprotein complexes (mRNP) were isolated, and characteristic proteins were found associated with either fraction. Polysomal mRNP from stressed or unstressed plants were translated with similar efficiency in a wheat germ cell-free system; activity of nonpolysomal mRNP was variable, but usually less than that of polysomal mRNP. Deproteinization of mRNP failed to improve its activity. No inhibition of translation of poly(A) ⁺RNA by nonpolysomal mRNP was observed in mixing experiments with the wheat germ cell-free system. It was concluded that no translational inhibitory activity was associated with nonpolysomal mRNP from barley prepared as described.