High salicylic acid concentration alters the electron flow associated with photosystem II in barley

Abstract

In this study, the effects of exogenously applied salicylic acid (0.5 and 5 mM SA) on the rates of photosystem II (PSII) activity was analysed in 4-week-old barley (Hordeum vulgare‘Bahman’ ) seedlings using chlorophyll (Chl) a fluorescence transient (OJIP) measurements. No evident changes in Chl and carotenoid contents as well as chlorophyll fluorescence transient curves were observed in either of the studied concentrations after 24 h of SA application. After 5 d, low SA concentration (0.5 mM) increased PSII activity, Chl b and carotenoid contents in barley seedlings. In contrary, 5 days after 5 mM SA treatment, the maximal quantum efficiency of PSII (Fv/Fm) and the Performance Index (PIABS), as an indicator of PSII structure and functioning, were significantly decreased. This lower Fv/Fm and PIABS coupled with lower levels of Chl b and carotenoids, and lower values of photosynthetic electron transport chain components including the electron transport flux (φEo) and the inferred oxygen evolving complex activity (Fv/Fo). By monitoring the chlorophyll a fluorescence rise kinetics, from the initial “O” level to the “P” (the peak) level, a dramatic increase in “OJ” phase was detected, which coincides with an increased photo-reduction of QA as a result of blockage of electron flow. This study provided the evidence that the high concentration of SA induced damage to different sites of the PSII.

Keywords

• photosynthetic pigments
• photosynthetic electron flow
• Hordeum vulgare ‘Bahman’
• OJIP transient flourescence
• salicylic acid