Poster: Hormone synthesis & metabolism

Abs # 466: Ectopic over-expression of a maize β-glucosidase disrupts cytokinin metabolism in transgenic tobacco.

Presenter:	Kiran, Nagavalli S., kiran@sci.muni.cz
Authors	Brzobohaty, Bretislav  (A) (B)  Kiran, Nagavalli S. (B)   Rekova, Alena  (A)   Valkova, Martina  (B)   Malbeck, Jiri  (C)
Affiliations:	(A): Institute of Biophysics AS CR, Brno, Czech Republic (B): Dept. of Functional Genomics and Proteomics, Masaryk University, Brno, Czech Rep. (C): Institute of Experimental Botany AS CR, Prague, Czech Republic

The activity of the phytohormone cytokinin depends on its cellular/tissue location, stability, and metabolism. O-glucosides of zeatin type cytokinins are postulated to be storage and/or transport forms, and may be readily deglucosylated. Tobacco plants overexpressing Zm-p60.1, a β-glucosidase capable of releasing active cytokinins from their O- and N3-glucoside conjugates, show distinct changes due to the presence of the enzyme during seedling development. Transgenic seedlings grown in the presence of exogenous zeatin were indistinguishable from wild type 14 days after sowing (DAS), although root inhibition was apparent. Between 14 and 21DAS, transgenic seedlings growing in short-day conditions increased in fresh weight leading later (21 to 28DAS) to ectopic growths at the base of the hypocotyl. In several cases, fully differentiated true leaves could be seen at 28DAS. The development of ectopic structures correlates with the presence of the enzyme as seen by histochemical staining. Cytokinin quantitation showed that the transgenic seedlings are unable to accumulate zeatin-O-glucoside and this seems to lead to the observed changes. The presence of the enzyme around the base of the hypocotyl and later, in the ectopic structures themselves suggests that the growth of these structures is due to the ectopic presence of Zm-p60.1 and the resultant disruption of zeatin metabolism. Semi-quantitative RT-PCR data for Nicta;CycD3;2 and NT-CAD expression to understand the effect of zeatin metabolism disruption on cell division and differentiation will be presented. Supported by grants from the Ministry of Education of the Czech Republic (Nos. MSM 143100008 and LN00A081), the GA CR (No. GACR 206/96/K188), the AS CR (Z 5004920) and the GA AS CR (No. IAA 5004001).