Singlet Oxygen in Plants: Generation, Detection, and Signaling Roles

Abstract

Singlet oxygen (1O2) refers to the lowest excited electronic state of molecular oxygen. It easily oxidizes biological molecules and, therefore, is cytotoxic. In plant cells, 1O2 is formed mostly in the light in thylakoid membranes by reaction centers of photosystem II. In high concentrations, 1O2 destroys membranes, proteins and DNA, inhibits protein synthesis in chloroplasts leading to photoinhibition of photosynthesis, and can result in cell death. However, 1O2 also acts as a signal relaying information from chloroplasts to the nucleus, regulating expression of nuclear genes. In spite of its extremely short lifetime, 1O2 can diffuse from the chloroplasts into the cytoplasm and the apoplast. As shown by recent studies, 1O2-activated signaling pathways depend not only on the levels but also on the sites of 1O2 production in chloroplasts, and can activate two types of responses, either acclimation to high light or programmed cell death. 1O2 can be produced in high amounts also in root cells during drought stress. This review summarizes recent advances in research on mechanisms and sites of 1O2 generation in plants, on 1O2-activated pathways of retrograde- and cellular signaling, and on the methods to study 1O2 production in plants.

Reactive Oxygen Species and Antioxidant Defense in Plants under Abiotic Stress: Revisiting the Crucial Role of a Universal Defense Regulator

“…However, additional energy from some biochemical reactions, electron transport chains (ETC), ultraviolet-B, and ionizing irradiations assist 3 O2 to get rid of the spin restriction and thus becoming ROS (Figure 1) [24]. In plant cells, ROS can be formed in many compartments including chloroplasts, mitochondria, peroxisomes, and plasma membrane [25]. In the chloroplast, the chlorophyll (chl) pigments absorb light quanta and become excited to their triplet state.…”

“…Some reactions of production and conversions of ROS in the biological system: In plant cells, ROS can be formed in many compartments including chloroplasts, mitochondria, peroxisomes, and plasma membrane [25]. In the chloroplast, the chlorophyll (chl) pigments absorb light quanta and become excited to their triplet state.…”

“…In the chloroplast, the chlorophyll (chl) pigments absorb light quanta and become excited to their triplet state. If this triplet chl is not quenched efficiently, a charge recombination occurs leading 3 O 2 to excited 1 O 2 [ 25 ]. Although its lifetime is very short (3.1–3.9 μs) and diffusion distance is low (190 nm), 1 O 2 diffuses outside the chloroplast to reach the cell wall, targets plasma membrane, tonoplast, or even cytosolic signaling cascades [ 26 ].…”

Acclimation of Chlamydomonas reinhardtii to extremely strong light

“…Studies of both damage and acclimation to high light have largely focused on PSII because PSII is much more sensitive to high light than PSI in strong continuous light (Tyystjärvi et al 1989 ; Sonoike 2011 ), PSII is the major producer of the harmful singlet oxygen ( 1 O 2 ) in photosynthetic organisms (Hideg and Vass 1995 ; Fufezan et al 2002 ; Krieger-Liszkay 2005 ; Krieger-Liszkay et al 2008 ; Cazzaniga et al 2012 ; Telfer 2014 , for recent review on singlet oxygen see Dimitrieva et al 2020 ), and because the rapid turnover of the D1 protein in high light makes PSII specifically sensitive to damage to the translation machinery (Nishiyama Y et al 2001 ). The short lifetimes of excited chlorophylls in PSI (for review, see Chukhutsina et al 2019 ) do not favor production of 1 O 2 in PSI antenna.…”

Blue Light Acclimation Reduces the Photoinhibition of Phalaenopsis aphrodite (Moth Orchid)

“…It easily oxidizes biological molecules and is cytotoxic to plants. The 1 O 2 * production in chloroplasts can activate acclimation to high light or cell death [ 12 ]. In the meantime, plants will turn on reactive oxygen species (ROS) scavenging systems, such as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), to remove toxic ROS molecules [ 13 ].…”