Cytokinin Profiles of AtCKX2-Overexpressing Potato Plants and the Impact of Altered Cytokinin Homeostasis on Tuberization In Vitro
Genes encoding cytokinin oxidase/dehydrogenase (CKX) enzymes have been used lately to study cytokinin homeostasis in a variety of plant species. In this study AtCKX2-overexpressing potato plants were engineered and grown in vitro as a model system to investigate the effects of altered cytokinin levels on tuber formation and tuber size. Protein extracts from shoots and roots of transformed potato plants exhibited higher CKX activity compared to control plants. Total endogenous cytokinin levels were generally not decreased in AtCKX2 overexpressors. However, levels of bioactive cytokinins were markedly lowered, which was accompanied by increased levels of O- and N-glucosides in some transgenic lines. The AtCKX2-overexpressing plants displayed reduced shoot growth but other symptoms of the “cytokinin deficiency syndrome” were not recorded. The transgenic plants were able to produce tubers in noninducing conditions. In inducing conditions they developed larger tubers than control. Tubers were also formed on a greater portion of the analyzed AtCKX2 plants, but with a lower number of tubers per plant compared to control. Taken together, our data suggest that cytokinins cannot be regarded simply as positive or negative regulators of tuberization, at least in vitro. Interactions with other plant hormones that play an important role in control of tuberization, such as gibberellins, should be further studied in detail.
KeywordsBioactive cytokinins Cytokinin oxidase/dehydrogenase (CKX) In vitro Potato Transgenic Tuberization
We kindly thank Dr. Thomas Schmülling and Dr. Tomáš Werner from Frei Universität Berlin (Germany) for providing us with the bacterial strains A. tumefaciens GV3101/pBinHTX-AtCKX1 and A. tumefaciens GV3101/pBinHTX-AtCKX2. Dr. Jiří Malbeck is acknowledged for his valuable contribution to HPLC/MS/MS analyses of cytokinins and Marie Korecká for excellent technical assistance. We thank also Dr. Branka Uzelac for editing the English language. The research presented here was funded by the Ministry of Education and Science of the Republic of Serbia (grant No. ON173015), the Czech Science Foundation (P506/11/0774), and the Ministry of Education, Youth and Sports of the Czech Republic (LC 06034).
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