Activation of ribosomal and messenger RNA synthesis in excised Jerusalem artichoke tuber slices

Rapid appearance of an mRNA correlated with ethylene synthesis encoding a protein ofmolecular weight 35000

Changes in gene expression related to ethylene synthesis were investigated during ripening of tomato fruit, and in unripe fruit and leaves after wounding. Messenger RNA was extracted at different stages of ripening, or at various times after wounding, and translated in vitro. A number of changes in mRNA were noted in all cases, including an increase in one encoding a protein of MW 35000. The mRNA encoding this protein in ripening fruit was hybrid-selected by a ripening-related complementary DNA clone, pTOM13. This clone also selected an mRNA encoding a protein of MW 35000 from RNA extracted from wounded unripe fruit and wounded leaves, but not from unwounded control tissue. During ripening and after wounding the appearance of mRNA for the MW-35000 protein was correlated with increased ethylene synthesis. In unripe fruit, the increase in mRNA for the MW-35000 protein and in ethylene synthesis were detected within 30 min of wounding. In-vivo labelling showed that a protein of MW 35000 was also synthesised rapidly in wounded fruit tissue. We suggest that the mRNAs encoding the MW-35000 proteins that increased during ripening and in response to wounding are the same and may be related to ethylene synthesis.

Molecular cloning and characterisation of cDNAs complementary to mRNAs from wounded potato (Solanum tuberosum) tuber tissue

Five cDNA clones complementary to mRNAs representing different abundances and responses to wounding have been isolated from a library of Sau 3A fragments in the bacteriophage M13 mp8. These were characterised by hybrid-release translation and hybridisation to RNA blots. The levels of RNA complementary to two of the clones show a marked increase during the 24h after wounding, one shows a small increase and two show no appreciable changes except that caused by a general increase in the total amount of polyadenylated RNA per microgram of total RNA which increases 2.5-fold during the same period. The would-induced RNAs are not induced in diluted suspension-culture cells, but RNA complementary to each clone is present in varying levels in stems, leaves and roots of intact potato plants.

Hormonal control of tobacco protoplast nucleic acid metabolism during in vitro culture

Tobacco mesophyll protoplasts cultivated in vitro do not synthesize a measurable quantity of chloroplastic ribosomal RNA, but actively synthesize cytoplasmic ribosomal RNA, polyadenylated RNA, and proteins. These syntheses are essentially independent of the presence of hormones in the culture medium and are thus related to the ageing phenomenon induced by isolation from the plant and in-vitro culture. At all stages of culture and in all culture media, protoplasts incorporate low levels of thymidine into their DNA. However, the incorporation of considerable quantities of thymidine, indicative of the S phase, only takes place after 25-30 h and requires the presence of auxin and cytokinin.

Utilization of stored messenger RNA during early aging of Jerusalem artichoke tuber slices

Using dissociation in 0.8 M KCl, it was established that in freshly excised Jerusalem artichoke (Helianthus tuberosus L.) tuber slices less than 8% of the ribosomes were in polysomes. The first hour of aging in water was the period of most rapid polysome accumulation; over 32% of the ribosomes carried nascent polypeptide chains at the end of this time. Thereafter polysome accumulation continued to increase, but more gradually. While synthesis of high-molecular-weight RNA (presumed mRNA) was inhibited more than 95% by α-amanitin during the first hour of aging, the inhibitor had no effect on polysome formation. As determined by [(3)H]polyuridylic acid hybridization, unaged cells contained polyadenylated RNA with a size range of 6-30S. The amount of polyadenylated RNA did not change during the first hour of aging. In control cells in water the in-vivo rate of protein synthesis increased exponentially during the first 4 h of aging without a comparable increase in polysomes. In α-amanitintreated tissues a similar increase in protein synthesis was not observed despite the presence of near control levels of polysomes. It is suggested that early polysome formation depends on stored mRNA. Inhibition of mRNA synthesis by α-amanitin prevents the normal development of an enhanced rate of protein synthesis which is not directly related to numbers of ribosomes in polysomes.