Mechanistic Insights on Salicylic Acid Mediated Enhancement of Photosystem II Function in Oregano Seedlings Subjected to Moderate Drought Stress

Abstract

Dramatic climate change has led to an increase in the intensity and frequency of drought episodes and, together with the high light conditions of the Mediterranean area, detrimentally influences crop production. Salicylic acid (SA) has been shown to supress phototoxicity, offering photosystem II (PSII) photoprotection. In the current study, we attempted to reveal the mechanism by which SA is improving PSII efficiency in oregano seedlings under moderate drought stress (MoDS). Foliar application of SA decreased chlorophyll content under normal growth conditions, but under MoDS increased chlorophyll content, compared to H2O-sprayed oregano seedlings. SA improved the PSII efficiency of oregano seedlings under normal growth conditions at high light (HL), and under MoDS, at both low light (LL) and HL. The mechanism by which, under normal growth conditions and HL, SA sprayed oregano seedlings compared to H2O-sprayed exhibited a more efficient PSII photochemistry, was the increased (17%) fraction of open PSII reaction centers (qp), and the increased (7%) efficiency of these open reaction centers (Fv′/Fm′), which resulted in an enhanced (24%) electron transport rate (ETR). SA application under MoDS, by modulating chlorophyll content, resulted in optimized antenna size and enhanced effective quantum yield of PSII photochemistry (ΦPSII) under both LL (7%) and HL (25%), compared to non-SA-sprayed oregano seedlings. This increased effective quantum yield of PSII photochemistry (ΦPSII) was due to the enhanced efficiency of the oxygen evolving complex (OEC), and the increased fraction of open PSII reaction centers (qp), which resulted in an increased electron transport rate (ETR) and a lower amount of singlet oxygen (1O2) production with less excess excitation energy (EXC).

Comparative Study of Photosynthesis Performance of Herbicide-Treated Young Triticale Plants during Drought and Waterlogging Stress

“…Mainly, the maximal quantum yield of PSII (F v /F m ) and the electron transport outside Q A − (F v /F 0 ) are used as important reliable indicators reflecting the performance of PSII under an unfavorable environment [24]. Under drought stress conditions, an overexcitation of PSII occurs, because the absorbed light energy exceeds the capabilities of the chloroplasts to utilize it, which in turn causes further photoinhibition and photodamage, as indicated by decreased maximal quantum yield of PSII (F v /F m ) [25,26]. PSII photodamage can happen through photooxidative stress, either at the acceptor side or at the donor side via inactivation of the oxygen-evolving complex [27,28].…”

“…PSII photodamage can happen through photooxidative stress, either at the acceptor side or at the donor side via inactivation of the oxygen-evolving complex [27,28]. Under drought stress conditions, the availability of water for oxidation is limited, which reduces the efficiency of the oxygen-evolving complex at the donor side (F v /F 0 ) [25,29]. Our results indicate that additional oxidative damage could take place because of limited photoprotection as a consequence of decreased carotenoids content in drought-treated plants (Figure 2).…”

Mechanistic Insights on Salicylic Acid-Induced Enhancement of Photosystem II Function in Basil Plants under Non-Stress or Mild Drought Stress

“…Exogenously applied SA in oregano seedlings has been reported to enhance PSII functionality under NS conditions only under HL and not under low light (LL) [ 79 ]. However, under mild drought stress (MiDS), it improved PSII photochemistry at both LL and HL conditions [ 79 ].…”

“…Exogenously applied SA in oregano seedlings has been reported to enhance PSII functionality under NS conditions only under HL and not under low light (LL) [ 79 ]. However, under mild drought stress (MiDS), it improved PSII photochemistry at both LL and HL conditions [ 79 ]. Since it has been suggested that the mode of action of SA varies with plant species [ 50 , 56 , 79 ], we evaluated the responses of basil plants to exogenously applied SA under the same experimental conditions.…”

Early-Stage Detection of Biotic and Abiotic Stress on Plants by Chlorophyll Fluorescence Imaging Analysis

“…Global climate change has quickly turned into a huge issue in the agricultural industry due to increased episodes of drought and elevated temperature that, together with the longer sunlight hours of the Mediterranean area, detrimentally influence crop production [ 1 , 2 , 3 , 4 ]. For example, leguminous lentil in the Mediterranean region is affected by huge fluctuations in seasonal precipitation, with intensive rainfalls in winter, and drought and high-temperature stress from March to May [ 5 , 6 ].…”