Light-induced appearance of polysomal poly(A)-rich messenger RNA during greening of barley plants

Changes in polysomal poly(A)-rich mRNA during greening of etiolated barley plants were studied by the technique of cDNA-mRNa hybridization. Hybridizaiton data of the homologous reactions reveal that in etiolated as well as in greened shoots a complexity of 5 X 10(7) nucleotides or about 33000 different average-sized mRNAs are present. These are organized in different abundancy classes with 94% of the total complexicity present in each of the slowest reacting class representing rare messengers. Heterologous hybridizations indicate that 92% of all polysomal poly(A)-rich mRNAs in etiolated shoots are complementary to those of greened and 82% of 'green' poly(A)-rich mRNAs are complementary to white ones. It is shown that the abundant mRNA clases are essentially responsible for these differences. The prevalent classes making up 15% ('white') and 31% ('green') of the poly(A)-rich mRNA mass but comprising only a complexity of 1.8 X 10(4) and 2.1 X 10(4) nucleotides are identical to 50% with each other. Hybridization of isolated prevalent 'green' cDNA with whole 'white' poly(A)-rich mRNA indicates that the additionally appearing 50% prevalent green messengers must be regarded as green-specific, only present in polysomal poly(A)-rich mRNA after illumination. This conclusion is underlined by the hybridization of the 'green' cDNA with total polysomal RNa of etiolated shoots. Evidently appearance of these prevalent messengers in functional polysomes is not caused by a shift from poly(A)-free mRNA to poly(A)-rich mRNA. The results clearly demonstrate that light induces greening by turning on genes or influencing post-transcriptional processing to produce mature green-specific poly(A)-rich mRNA.