Assessing the Applicability of Singlet Oxygen Photosensitizers in Leaf Studies

Abstract

Singlet oxygen ((1) O2 ) is of special interest in plant stress physiology. Studies focused on internal, chlorophyll-mediated production are often complemented with the use of artificial (1) O2 photosensitizers. Here, we report a comparative study on the effects of Rose Bengal (RB), Methylene Violet (MVI), Neutral Red (NR) and Indigo Carmine (IC). These were infiltrated into tobacco leaves at concentrations generating the same fluxes of (1) O2 in solution. Following green light-induced (1) O2 production from these dyes, leaf photosynthesis was characterized by Photosystem (PS) II and PSI electron transport and oxidative damage was monitored as degradation of D1, a PSII core protein. Cellular localizations were identified on the basis of the dyes' fluorescence using confocal laser scanning microscopy. We found that RB and NR were both localized in chloroplasts but the latter had very little effect, probably due to its pH-dependent photosensitizing. Both RB and intracellular, nonplastid MVI decreased PSII electron transport, but the effect of RB was stronger than that of MVI and only RB was capable of damaging the D1 protein. Intercellularly localized IC had no significant effect. Our results also suggest caution when using RB as photosensitizer because it affects PSII electron transport.

Oxidative stress and antioxidative systems: recipes for successful data collection and interpretation

“…; Kovacs et al . ). Some of these reagents may have other effects as well as direct photosensitization of singlet oxygen production.…”

“…For instance, rose bengal can inhibit photosynthetic electron transport (Kovacs et al . ). The most physiologically relevant feature of these reagents may be in mimicking endogenous photosensitizers (e.g.…”

“…These include rose bengal, methylene violet, neutral red and indigo carmine. While all produce singlet oxygen following their photoactivation, they do so with different efficiencies and also accumulate in different parts of the cell (Gutiérrez et al 2014;Kovacs et al 2014). Some of these reagents may have other effects as well as direct photosensitization of singlet oxygen production.…”

Reactive oxygen species: Reactions and detection from photosynthetic tissues

“…Different 1 O 2 generators localize in different cellular compartments. For example, Neutral Red and Rose Bengal penetrate to the chloroplast, in contrast to methylene blue [148]. If the sensitizer penetrates weakly to the target tissue, then the amount of 1 O 2 produced may not be physically relevant.…”

“…However, the popular 1 O 2 generators Rose Bengal and methylene blue have been shown to affect PSII electron transfer [148]. Different 1 O 2 generators localize in different cellular compartments.…”