Modulation of photosynthetic energy conversion efficiency in nature: from seconds to seasons

Abstract

Modulation of the efficiency with which leaves convert absorbed light to photochemical energy [intrinsic efficiency of open photosystem II (PSII) centers, as the ratio of variable to maximal chlorophyll fluorescence] as well as leaf xanthophyll composition (interconversions of the xanthophyll cycle pigments violaxanthin and zeaxanthin) were characterized throughout single days and nights to entire seasons in plants growing naturally in contrasting light and temperature environments. All pronounced decreases of intrinsic PSII efficiency took place in the presence of zeaxanthin. The reversibility of these PSII efficiency changes varied widely, ranging from reversible-within-seconds (in a vine experiencing multiple sunflecks under a eucalypt canopy) to apparently permanently locked-in for entire seasons (throughout the whole winter in a subalpine conifer forest at 3,000 m). While close association between low intrinsic PSII efficiency and zeaxanthin accumulation was ubiquitous, accompanying features (such as trans-thylakoid pH gradient, thylakoid protein composition, and phosphorylation) differed among contrasting conditions. The strongest and longest-lasting depressions in intrinsic PSII efficiency were seen in the most stress-tolerant species. Evergreens, in particular, showed the most pronounced modulation of PSII efficiency and thermal dissipation, and are therefore suggested as model species for the study of photoprotection. Implications of the responses of field-grown plants in nature for mechanistic models are discussed.

Drought Adaptation Mechanisms Should Guide Experimental Design

“…Damage avoidance may also have a buffering effect, were a given stress level leads to less damage (Figure 3). Examples include changing leaf orientation away from light [21], heat dissipation of excess absorbed energy by PSII [22], the Mehler reaction or photorespiration [23,24], and altered root to shoot ratios [25]. Damage avoidance is the preferred term as the similar term, stress tolerance, is commonly used in a general manner.…”

“…Dark-adapted maximum photochemical efficiency of PSII (F v /F m ) is a useful indicator of past stress in leaves and acclimation. Low F v /F m can represent damage avoidance due to associated upregulation of excess energy dissipation processes [22]. F v /F m depression is sustained and may decrease photosynthetic rates and thus represent damage too.…”

The effect of methyl jasmonate on selected physiological parameters of copper-treated Phaseolus coccineus plants

“…Moreover, chlorophyll fluorescence has been employed in physiological and ecophysiological studies; since it is considered to be plant species-specific and is emitted only by fluorophores, such as chlorophyll a (Chl a), the fluorescence analysis is a useful tool for in vivo measurement of the stress level in plants (Maksymiec and Krupa 2002;Demmig-Adams et al 2012).…”

Photosynthesis Control: An underrated short-term regulatory mechanism essential for plant viability

“…9 That is obtained through the protonation of two glutamic acid residues in the lumenexposed loop of PsbS protein, [43][44][45] which is a component of PSII, and the activation of the Violaxanthin De-Epoxidase (VDE) that converts violaxanthin into zeaxanthin within the xanthophyll cycle. 13,14,46 Secondly, the pgr5 mutants of both Arabidopsis and rice have also been shown to exhibit an elevated proton conductance of the ATP-synthase, 37,47 as well as an increased amount of the ATP synthase b subunit. 48 It is unclear how the regulation of ATP-synthase activity is perturbed by the pgr5 defect, but activation of ATP-synthase may counteract, to some extent, the reduced supply of ATP for CO 2 fixation in Calvin-BensonBassham cycle.…”

“…optimization of light absorption between PSI and PSII achieved upon phosphorylation and association of the so-called 'mobile pool' of LHCII with either PSI or PSII [6][7][8] ; (ii) "Alternative Electron Transport Routes," i.e., redistribution of electron fluxes through different alternative pathways, including Cyclic Electron Transport (CET) mediated by either the NADH dehydrogenase-like (NDH) complex or the PRG5-PGRL1 protein complex [9][10][11] ; (iii) "Non Photochemical Quenching (NPQ)," i.e. pH-dependent dissipation of excess energy in the LHCII to protect the photosynthetic apparatus against photooxidation [12][13][14] ; (iv) "Photosynthesis Control," i.e., regulation of electron transport by the Cyt b 6 f complex, governed by the pH of thylakoid lumen and stroma. [15][16][17][18] In this review, we will describe the interconnections and the relative importance of these photoprotective mechanisms, with a particular focus on photosynthesis control and its role in the pH-dependent control of plastoquinol (PQH 2 ) oxidation at the Qo-site of the Cyt b 6 f complex, which regulates the overall rate of the intersystem electron transport.…”