The dark side of 5,10,15,20-(tetra-4-sulfonatophenyl)-porphyrin tetra-ammonium (TPPS) on Botrytis cinerea mycelium growth

Abstract

The powerful inhibitory effect of a photoactivated anionic porphyrin (TPPS) on the mycelium growth of a phytopathogenic fungus Botrytis cinerea, was previously demonstrated, suggesting a new agricultural application of photodynamic treatment. In this context, it was also needed to investigate the effect of non-photoactivated TPPS onB. cinerea. Unexpectedly, TPPS tested at 3.5 [Formula: see text]M, induced a delay of the Botrytis cinerea mycelium growth that was later recovered under dark conditions. This delay, compared to the control, was low and suggested that the stress was induced by TPPS. This hypothesis was also confirmed at phenotypical level by Environmental Scanning Electron Microscopy analysis. Further tests at a biochemical level: total proteins, thiols and proline content determinations; and at cellular level, by monitoring cell leakage, gave more evidence for the presence of this stress. Nevertheless, TPPS induced a very short-lived effect on B. cinerea, suggesting that the mycelium was able to induce a rapid defense mechanism that involved medium acidification. A 4-day-old mycelium acidified the culture medium from a pH of 8 to less than 4. This acidic medium thus induced changes in the TPPS chemical structure that became protonated in its inner core. To our knowledge, this is the first paper that reports a dark effect of TPPS on Botrytis cinerea mycelium growth that could be rapidly counteracted by the protonation of TPPS leading to its no-longer dark toxicity.