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EXPRESSION OF PHYTOCHROME GENES DURING TROPISTIC CURVATURE IN ARABIDOPSIS.   M.L. Molas⁽¹⁾, E. Fejes⁽²⁾, F. Nagy⁽²⁾, J.Z. Kiss^{(1)   (1)} Dept. of Botany, Miami Univ., Oxford, Ohio, USA ⁽²⁾ Institute of Plant Biology, Biological Research Center, Szeged, Hungary

   Recent work in our laboratory has shown that phytochrome plays a role in a variety of tropisms in Arabidopsis.  For instance, PHYA (phytochrome A) and PHYB directly mediate red-light-induced phototropism in primary roots of seedlings. These two forms of phytochrome also play a role in gravitopism in roots and shoots. In order to determine if there is a differential spatial or temporal expression of phytochrome during tropistic curvature, we have performed preliminary investigations utilizing transgenic plants with PHYA GUS and PHYB GUS reporter genes. Seedlings growing in continuous white light were stained with X-Gluc in order to establish the cell-specific expression of the PHYA and PHYB GUS transgenes in roots. We found different PHYA and PHYB staining patterns in roots exposed to different concentrations of potassium ferricyanide and potassium ferrocyanide. In the 1 mM potassium ferricyanide and potassium ferrocyanide treatment, two different PHYA GUS and one PHYB GUS line showed vascular tissue clearly stained.  In contrast, in 5 mM potassium ferricyanide and potassium ferrocyanide treatment, the same lines were stained mainly in the root cap, and the patterns were irregular. In the 10 mM potassium ferricyanide / potassium ferrocyanide treatment, roots were stained in the root cap in all the lines. Potassium ferricyanide / potassium ferrocyanide can be added to the original GUS protocol as a catalyst that enhances the dimerization that forms the visible indigo dye. Because this reaction is stimulated by oxygen, local variations in oxygen availability during the staining protocol may cause heterogeneous staining. This problem can be minimized by addition of a catalyst like potassium ferricyanide / potassium ferrocyanide. Precise determination of the correct concentration should be made in each tissue in order to determine the accurate expression of phytochromes in GUS reporter systems.  (Funded by NASA  NCC2-1200)