Fig. 3

a Semi-quantitative RT-PCR analysis of the pkn22 transcripts in absence (lines: 1, 3 and 5) or presence of 100 μM H₂O₂ (lines 2, 4 and 6). One microgram of RNA was used in each experiment. Samples were collected at the exponential phase of the PCR. The expression of the rnpB gene was used as a control. RNAs were extracted from Nostoc wild type strain (WT) or from the pkn22 mutant (WT#pkn22) or from a recombinant strain expressing the pkn22 gene from the petE promoter (WT#pkn22/petE-pkn22). b Absorption spectra for cell suspensions grown with (+) or without (−) iron. The arrows indicate a shift of the 680-nm chlorophyll a absorption peak