Antioxidant protection and PSII regulation mitigate photo-oxidative stress induced by drought followed by high light in cashew plants

Abstract

We tested the hypothesis that effective antioxidant and photoprotective mechanisms are able to avoid photodamage induced by prolonged water deficit (WD) followed by high light (HL). We employed cashew plants (Anacardium occidentale L.), a semiarid adapted species, as a model plant. WD-plants exposed to HL did not show alterations in maximum quantum efficiency of photosystem II (Fv/Fm), cellular integrity, H 2 O 2 and thiobarbituric acid reactive species (TBARS) contents, evidencing that they did not suffered photoinhibition and oxidative stress. These responses were associated with increases in ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities, glutathione (GSH) oxidation and ascorbate (ASC) synthesis. This effective oxidative protection occurred in parallel to strong decrease in photosystem II and I (PSII and PSI) activities, increase in heat dissipation (qE), which was related to enhancement in cyclic electron flux. These favorable photoprotective changes were associated with efficient water use in response to HL, all contributing to avoid excess energy in chloroplasts of drought-exposed leaves. These protective features were associated with a tight regulation in D1 protein accumulation during HL, contributing to avoid reactive oxygen species over-accumulation and a subsequent effective PSII recovery during darkness. Our results indicate that cashew plants are able to avoid photoinhibition, tolerating extreme conditions of drought combined with HL. The displayed mechanisms involve essentially integrated responses to balance energy input and output, avoiding oxidative stress.

Thioredoxin h2 contributes to the redox regulation of mitochondrial photorespiratory metabolism

“…In vivo chlorophyll a fluorescence parameters were also estimated using DUAL PAM 100 (Halz, Germany) using fully expanded leaves from WT and both trxh2 mutants ( trxh2–1 and trxh2–2 ) by the saturation pulse method in light‐ and dark‐adapted leaves (Schreiber, Bilger, & Neubauer, ). The ETR of photosystems I (PSI) and II (PSII) and the induction and relaxation kinetics of nonphotochemical quenching (NPQ = ( F m – F m ′)/ F m ′)) were calculated as described previously (Baker & Rosenqvist, ; Bilger, Schreiber, & Bock, ; Lima et al, ). The maximum quantum yield of photosystem II (PSII) ( F v / F m = ( F m – F o )/ F m ) was measured in dark‐adapted conditions and the effective quantum yield of PSII ( F v '/ F m ′ = ( F m ′– F s / F m ′) measured in leaves exposed to actinic light at 1.000‐μmol·m −2 ·s −1 photosynthetically active photon flux density (PPFD).…”

“…In vivo chlorophyll a fluorescence parameters were also estimated using DUAL PAM 100 (Halz, Germany) using fully expanded leaves from WT and both trxh2 mutants (trxh2-1 and trxh2-2) by the saturation pulse method in light-and dark-adapted leaves (Schreiber, Bilger, & Neubauer, 1995). The ETR of photosystems I (PSI) and II (PSII) and the induction and relaxation kinetics of nonphotochemical quenching (NPQ = ( F m -F m ′)/ F m ′)) were calculated as described previously (Baker & Rosenqvist, 2004;Bilger, Schreiber, & Bock, 1995;Lima et al, 2018). The maximum quantum yield of photosystem II (PSII)…”

Why Are There so Many Plant Species That Transiently Flush Young Leaves Red in the Tropics?

“…The maximum photochemical efficiency of PSII (F v /F m ), which can be used to quantify photo-inhibition (Redondo-Gómez et al, 2006), was then calculated following Figueroa et al (1997) and Lima et al (2018). On the following day (9:00-11:00), after light adaptation for half an hour, chlorophyll a fluorescence traits of the same leaves were estimated with the Li-6400XT portable photosynthesis system.…”

“…After 30 min to allow for dark adaptation, the chlorophyll fluorescence parameters F 0 , F m , and F s of each of the young and mature leaves were measured. F 0 is the minimum chlorophyll a fluorescence after dark adaptation; F m is the maximal fluorescence level in the dark-adapted state, and F s is the steady-state fluorescence yield (Lima et al, 2018).The effective quantum yield of PSII (F PSII ), which can be used for routine assays of plant heath performance and the quantification of environmental stress, was calculated following Redondo-Gómez et al (2006) and Lima et al (2018):…”

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“…& Maehly., 1955). The antioxidant system also maintains organelle stability, preventing damage to the chloroplast membrane and so stabilizing the PSII system (Lima et al, 2018). In addition, stomata are important gas exchange organs of plants, playing irreplaceable roles in the regulation of photosynthesis, respiration, transpiration and temperature (Li et al, 2017, Martin-StPaul et al, 2017).…”