New foundations for the physical mechanism of variable chlorophyll a fluorescence. Quantum efficiency versus the light-adapted state of photosystem II

Photosystem II (PSII) uses solar energy to oxidize water and delivers electrons to fix CO2. Although the structure at atomic resolution and the basic photophysical and photochemical functions of PSII are well understood, many important questions remain. The activity of PSII in vitro and in vivo is routinely monitored by recording the induction kinetics of chlorophyll a fluorescence (ChlF). According to the 'mainstream' model, the rise from the minimum level (Fo) to the maximum (Fm) of ChlF of dark-adapted PSII reflects the closure of all functionally active reaction centers, and the Fv/Fm ratio is equated with the maximum photochemical quantum yield of PSII (where Fv=Fm-Fo). However, this model has never been free of controversies. Recent experimental data from a number of studies have confirmed that the first single-turnover saturating flash (STSF), which generates the closed state (PSIIC), produces F1 Collapse

Key Words

• F v/Fm
• Chlorophyll a fluorescence induction
• QA-model
• conformational changes
• dielectric relaxation
• electric field effects
• light-adapted charge-separated state
• photochemical quantum efficiency
• photosystem II
• purple bacterial reaction center

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Grants

• Hungarian Ministry of Innovation and Technology
• ANN-144012 National Research, Development and Innovation Fund
• GA ČR 23-07744S Czech Science Foundation
• ELKH KÖ-36/2021 Eötvös Loránd Research Network

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Affiliation(s)

Győző Garab Institute of Plant Biology, Biological Research Centre, Szeged, Hungary Department of Physics, Faculty of Science, University of Ostrava, Ostrava, Czech Republic
Melinda Magyar Institute of Plant Biology, Biological Research Centre, Szeged, Hungary
Gábor Sipka Institute of Plant Biology, Biological Research Centre, Szeged, Hungary
Petar H Lambrev Institute of Plant Biology, Biological Research Centre, Szeged, Hungary

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Synergistic adaptations: freezing tolerance is associated with desiccation tolerance and activation of violaxanthin de-epoxidase in wintergreen ferns

This article comments on: Fernández-Marín B, Arzac MI, López-Pozo M, Laza JM, Roach T, Stegner M, Neuner G, García-Plazaola JI. 2021. Frozen in the dark: interplay of night-time activity of xanthophyll cycle, xylem attributes, and desiccation tolerance in fern resistance to winter. Journal of Experimental Botany 72, 3168–3184.

Positive root pressure is critical for whole-plant desiccation recovery in two species of terrestrial resurrection ferns

Desiccation-tolerant (DT) organisms can lose nearly all their water without dying. Desiccation tolerance allows organisms to survive in a nearly completely dehydrated, dormant state. At the cellular level, sugars and proteins stabilize cellular components and protect them from oxidative damage. However, there are few studies of the dynamics and drivers of whole-plant recovery in vascular DT plants. In vascular DT plants, whole-plant desiccation recovery (resurrection) depends not only on cellular rehydration, but also on the recovery of organs with unequal access to water. In this study, in situ natural and artificial irrigation experiments revealed the dynamics of desiccation recovery in two DT fern species. Organ-specific irrigation experiments revealed that the entire plant resurrected when water was supplied to roots, but leaf hydration alone (foliar water uptake) was insufficient to rehydrate the stele and roots. In both species, pressure applied to petioles of excised desiccated fronds resurrected distal leaf tissue, while capillarity alone was insufficient to resurrect distal pinnules. Upon rehydration, sucrose levels in the rhizome and stele dropped dramatically as starch levels rose, consistent with the role of accumulated sucrose as a desiccation protectant. These findings provide insight into traits that facilitate desiccation recovery in dryland ferns associated with chaparral vegetation of southern California.