Light-induced appearance of polysomal poly(A)-rich messenger RNA [ribonucleic acid] during greening of barley [Hordeum] plants

Changes in polysotnal poly(A)‐rich tnRNA during greening of etiolated barley plants were studied by the technique of cDNA‐mRNA hybridization. Hybridization data of the homologous reactions reveal that in etiolated as well as in greened shoots a complexity of 5 × 107 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 polysotnal 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 classes are essentially responsible for these diferences. 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 × 104 and 2.1 × 104 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 greenspecific, 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 tnRNA.