Fig. 3. Expression of the arginine kinase gene is dependent on the presence of silicic acid. (A-D) Primmorphs were cultivated for 5 days in the absence (-; A,B) or presence of 60 µmol l^-1 silicic acid (SA+; C,D). (E,F) Primmorphs were treated with silicic acid and 100 µmol l^-1 DIDS and in situ hybridization performed with SDAK as the probe. Hybridized cells are stained by brown/black deposits. Magnification: x10 (A,C,E); x20 (B,D,F).