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Isopentenyl transferase (IPT) is an enzyme encoded by a bacterial gene that catalyzes the rate-limiting step in cytokinin biosynthesis. Under the control of senescence-associated promoter (pSAG12), isolated from Arabidopsis thaliana, it has been shown to delay senescence in several herbaceous species. Cytokinin synthesis begins at the onset of senescence and is then stopped when senescence ceases. This auto regulatory control of the transgene ensures normal development and morphology of the transformed plant, which may be affected in plants constitutively expressing ipt. In this study, it was investigated if an altered cytokinin metabolism, as a result of transformation by pSAG12: ipt, will display a decayed ageing phentopye in a deciduous tree species as has been demonstrated in herbaceous species. This was carried out using various physiological assays and several transgenic lines were shown to display the symptoms of a plant exhibiting delayed senescence. A parallel study was carried out, investigating recombinant protein leakage during senescence (in detached leaves from tobacco plants containing the pSAG12: ipt cassette in the nucleus and gfp in the chloroplast). pSAG12: ipt was found to be efficient in maintaining the integrity of the chloroplast and thus preventing leakage and degradation of the recombinant chloroplast protein.
McEvoy, I.:The Effect of an Altered Cytokinin Metabolism on Plant Development and C ell Aging in Crop Plants. Doctoral Thesis. Dublin Institute of Technology, 2004.