Abstract
The IPT gene encodes isopentenyl pyrophosphate transferase, a key enzyme in cytokinin biosynthesis. We introduced IPT under the control of the CaMV35S promoter into Asakura-sanshoo (Zanthoxylum piperitum (L.) DC. f. inerme Makino) via stable Agrobacterium tumefaciens-mediated transformation. Three of 3-year-old transgenic Asakura-sanshoo lines Y5, Y16, and Y17 were used to evaluate the effects of IPT expression on the morphological characteristics, leaf senescence, and essential oil composition. Introduced IPT into Asakura-sanshoo stimulated an increase in cytokinin content and a decrease in auxin level. The increase in the cytokinin/auxin ratio affected the tree architecture in 3-year-old transgenic lines. The phenotypes of transgenic lines included reduced stem elongation, decreased leaf surface area, increased branching, and delayed leaf senescence. The expression of IPT in Asakura-sanshoo also affected the leaf essential oil composition. The amount of oxygenated sesquiterpenoid compounds in Y5 and Y16 was 21.1 and 15.8 % higher, respectively, than that in wild type (WT). The amount of aromatic compounds in Y5 and Y16 was 2.9 and 24.6 % lower, respectively, than that in WT. These results show that ipt expression in Asakura-sanshoo conferred desirable traits, including a dwarf growth habit, delayed senescence, and increased concentrations of some sesquiterpenoid compounds.Electronic supplementary materialThe online version of this article (doi:10.1007/s11105-015-0948-9) contains supplementary material, which is available to authorized users.
Highlights
Cytokinins regulate many biological processes in plant growth and development
The IPT gene under the control of 35S promoter was introduced to Asakura-sanshoo plants, and more than 1000 kanamycin-resistant shoots were obtained
Addition of 2.0 mg/L indole-3butyric acid (IBA) reduced the inhibition of root formation, and the rooting frequency in transgenic shoots increased to 75.0 % (Table 1)
Summary
Cytokinins regulate many biological processes in plant growth and development. They stimulate cell division, reduce apical dominance and plant elongation, delay plant senescence, prolong the post-harvest shelf-life, and increase production of secondary metabolites (DiCosmo and Misawa 1985; Ha et al 2012; Hirose et al 2008; Namdeo 2007; Santoro et al 2013; Somasundaram 2013; Vankova 2014). Genetic modification is one strategy to increase the amount of cytokinin in plants This has been achieved by introducing the IPT gene into the plant genome (Honda et al 2011; Khodakovskaya et al 2009). Plants overexpressing IPT can result in the accumulation of cytokinin, which alters certain morphological and physiological characteristics of the plant, showing delayed leaf senescence, increased abundance of flowers, increased branching, increased secondary metabolite production, restricted root formation, and reduced plant height (Honda et al 2011; Khodakovskaya et al 2005; Khodakovskaya et al 2006; Li et al 1992)
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