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 (F v /F m ) and the Performance Index (PI ABS ), as an indicator of PSII structure and functioning, were significantly decreased. This lower F v /F m and PI ABS coupled with lower levels of Chl b and carotenoids, and lower values of photosynthetic electron transport chain components including the electron transport flux (φE o ) and the inferred oxygen evolving complex activity (F v /F o ). 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 photoreduction of Q A 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. . Pri spremljanju povečanja fluorescence klorofila a od začetne "O" na največjo vrednost "P" je bilo opazno njeno dramatično povečanje v fazi "OJ", kar je soupadalo s povečano fotoredukcijo Q A kot posledica blokade fotosintezenega elektronskega pretoka. Raziskava dokazuje, da večja koncentracija salicilne kisline povzroči poškodbe na večih mestih PSII.

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“…It suggested that IL 13 caused the PS II center damage leading to decreased excitation energy transfer from the antenna to the reaction center. 48 The damage to PS II center can be detected from the decreases in maximal PS II quantum yield F v /F m and the performance index PI abs . The values of F v /F m and PI abs of IL 13-treated leaves were decreased by 18% and 70%, respectively.…”

“…It provided information about biophysical properties of the photosynthetic energy conversion and transport of electrons. [46][47][48][49][50][51] Some uorescence parameters were highlighted: (a) area: total complementary area between F o and F m (reecting the size of the plastoquinone pool); where F o is minimal uorescence when PSII RCs are all open, F m : maximal uorescence when PSII RCs are all closed; (b) the specic energy uxes per reaction center RC for absorbance (ABS/RC), for transport (ET 0 /RC), for trapping TR 0 /RC and for reduction (RE 0 /RC); (c) the phenomenological energy uxes per excited cross section for absorbance (ABS/CS m ), for transport (ET o /CS m ), for trapping (TR o /CS m ) and for reduction (RE 0 /CS m ); (d) the performance index:…”

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