Cytokinin regulation during flower senescence in Petunia x hybrida 'V26' transformed with SAG12-ipt

Previous studies have shown that either exogenous application or increased endogenous production of cytokinins delays senescence in plants. Treatment of petunia flowers with trans-zeatin and trans-zeatin riboside significantly increased flower longevity. Elevated endogenous cytokinin levels have been accomplished by the introduction of the ipt gene from Agrobacterium into plants, and leaves of plants transformed with SAG12-ipt exhibit delayed senescence. In this study, Petunia × hybrida ‘V26’ transformed with SAG12-ipt were used to investigate the role of cytokinins in flower senescence. Two independently transformed lines of petunia have been identified based on increased flower longevity (IPT22 and IPT34). IPT22 and IPT34 flowers exhibited delayed senescence following pollination and during natural senescence, lasting 6 to 9 days longer than non-transgenic Petunia × hybrida ‘V26’ wild type (WT). The presence of the ipt construct in transgenic lines was confirmed by PCR. Ipt transcripts were detected in corollas by RT-PCR in transgenic lines but not wild type. The quantification of ipt expression was accessed by real time RT-PCR. Higher endogenous cytokinin levels were detected in IPT22 and IPT34 corollas compared to corollas from WT. The elevated cytokinin levels resulted in altered ethylene biosynthesis in SAG12- ipt petunia corollas compared to WT. SAG 12-ipt flowers also showed less sensitivity to exogenous ethylene application and required higher concentrations of ethylene to induce wilting and autocatalytic ethylene production. The expression of the senescence-related gene, Phcp1, in SAG12-ipt verses wild type was also investigated, the result was not cytokinin down-regulated as previous study.