Fig 4. Light-induced DFPM degradation in aqueous solutions and its impact on bioactivity.

A) After 6 hours in the light a clear loss of the yellow color can be detected in an aqueous 30 μM DFPM solution. B) UV-Vis absorbance scans of 30 μM DFPM solution. The fresh solution exhibits a characteristic maximum peak at around 360 nm. This peak was absent if the solution was kept in the light for 6 hours. Less pronounced decay was observed if the solution was protected from light. C) The bioactivity of DFPM is dependent on the presence of light. No growth arrest was found if roots were treated for 24 hours with DFPM in the dark (right), while Col-0 wild type plants treated with DFPM in the presence of light exhibited root growth arrest (left). After 24 hours of DFPM treatment seedlings were retransferred to 1/2 MS without DFPM to recover, and 3 days after retransfer the image was taken. Black horizontal bars indicate the primary root lengths at the time of retransfer. The black vertical bar separates two groups with different light treatments prior to retransferring to the same plate for recovery. D) FDA staining of 1 week-old seedlings treated with 15 μM DFPM for 6 hours. Cell viability was significantly reduced, only if light was present in combination with DFPM. Asterisk stands for P < 0.0001.