Cytokinins in Rosa hybrida in relation to bud break.

To assess the role of endogenous cytokinins in growth and development of Rosa hybrida, their concentrations in bleeding sap and in roots, stem, leaves, axillary shoots and bottom breaks in three stages of development were quantified. Cytokinins were purified by means of immunoaffinity chromatography and HPLC, and identified by retention time, UV spectrum and GC‐MS. The major translocation form in the xylem was zeatin riboside (ZR). In all mature tissues, cytokinins of the zeatin‐type were predominant, amounting to 80–90% of the total cytokinin concentration. The stems contained high concentrations of cytokinins, probably caused by lateral movement of ZR from the xylem to adjacent stem tissue and the ability of the stem to metabolize cytokinins. In young leaves the contribution of isopentenyl adenine (iP)‐type cytokinins to the total cytokinin pool was about 50%, indicating that these leaves might be capable of de novo synthesis of cytokinins. In older leaves, the concentration of an unidentified cytokinin‐like compound increased to more than 50% of total cytokinins. This compound, which was also found in the roots, might be a storage form of cytokinins. In young axillary shoots, about 50% of the cytokinins are iP‐compounds, suggesting either import of iP‐type cytokinins via the phloem or de novo synthesis of cytokinins. In buds forming bottom breaks, ZR and zeatin riboside monophosphate (ZRMP) are the main cytokinins, indicating that these buds receive their cytokinins from the roots.<br/

Identification and functional characterization of the candidate tumor suppressor gene TRIT1 in human lung cancer

tRNA-isopentenyltransferase (tRNA-IPT) catalyses the addition of N6-isopentenyladenosine (i6A) on residue 37 of tRNA molecules that bind codons starting with uridine. Post-transcriptional modifications of tRNA molecules have been demonstrated to be essential in maintaining the correct reading frame of the translational machinery, thus improving fidelity and efficiency of protein synthesis. We show here that the human tRNA-isopentenyltransferase (TRIT1) gene encodes a complex pattern of mRNA variants through alternative splicing in both normal and tumor lung tissue and that the nonsense suppressor activity of tRNA-IPT is maintained only in the full-length mRNA isoform, as revealed by gene complementation in yeast. Expression of the full-length transcript was down-regulated 6-14-fold in lung adenocarcinomas as compared to normal lung tissue. A549 lung cancer cells transfected to express the functional TRIT1 gene formed significantly smaller colonies with reduced scattering on the edges and had only limited ability to induce tumors in nude mice. Our findings raise the possibility of TRIT1 as a candidate lung tumor suppressor