Ozone and Reactive Oxygen Species

Abstract

High tropospheric ozone (O 3 ) concentrations affect plant growth and crop yield. O 3 enters leaves through stomata and rapidly degrades in the apoplast into other reactive oxygen species (ROS), which readily interact with surrounding biomolecules. Due to their high reactivity, ROS act as important signalling molecules. Apoplastic ROS perception induces secondary ROS production in other cellular compartments and activates interorganelle signalling pathways towards stress defence. Defence responses include activation of hormonal signalling, the enhancement of antioxidative defence responses, protection of the photosynthetic machinery and induction of cell death processes. Different species prioritise different defence strategies and population studies towards the identification of genetic loci associated with O 3 tolerance are currently the most promising approach for identifying genes involved in O 3 tolerance. Key Concepts While the stratospheric O 3 layer has protective UV‐B screening properties, tropospheric O 3 accumulation near the earth's surface is a health hazard to living organisms. Ozone enters through open stomatal pores in the leaf epidermis and triggers rapid ROS accumulation and complex signalling pathways originating from the apoplastic space between cells. Acute O 3 exposure in sensitive plants results in visible cell death lesions; long‐term chronic exposures to O 3 levels above 40 ppb leads to a reduction in crop yields due to reduced photosynthesis and disruption to metabolism. The photosynthetic activity decreases under O 3 exposure and subsequently causes a reduction in CO 2 fixation and central carbohydrate metabolism. Subsequently, catabolic processes are enhanced to re‐mobilise resources, causing early senescence and a shift in source‐sink relations. ROS are continuously produced during photosynthesis and respiration and ROS production increases under stress conditions. This serves as an important signalling mechanism that initiates defence and acclimation processes. ROS, calcium and hormones accumulate within different intra‐ and extracellular compartments and act together as signals in a dense and complex signalling network under stress conditions. Stomatal closure physically blocks the entry of air pollutants or pathogens. Stomatal closure is a defence response, triggered by O 3 and other types of abiotic and biotic stress, measured through stomatal conductance (g s ). While harsh stress results in passive cell death, programmed cell death (PCD) is an active defence mechanism that can isolate and contain the spread of diseases to smaller areas of tissue in the plant. Strategies to increase the tolerance of plants to O 3 include population studies, transgenic approaches as well as the application of protective chemicals.

Biochemical and economical effect of application biostimulants containing seaweed extracts and amino acids as an element of agroecological management of bean cultivation

“…Frequent abiotic stress leads to the excessive synthesis of reactive oxygen species (ROS), which can cause extensive cell damage. ROS are usually rapidly removed owing to antioxidative mechanisms, however this process may be suppressed by stress 58 , causing an increase in their intracellular concentration and greater damages. However, plant cells are able to prevent or repair such damages through a complex defense system including a series of protective genes associated with the antioxidative stress and leading to changes in the plant's biochemical profile.…”

Histologic, metabolomic, and transcriptomic differences in fir trees from a peri‐urban forest under chronic ozone exposure

“…During the high O 3 period, asymptomatic individuals upregulated some transcripts (Figure 5c , Appendix S6 ) related to plant resistance (NB‐ARC‐domain proteins), plant defense (peroxidases), and the flavonoid biosynthesis (chalcones) pathway (Dao et al., 2011 ; Krasensky et al., 2017 ). In other words, when O 3 concentration increases, asymptomatic trees may be activating mechanisms related to stress response.…”

Increase of apoplastic ascorbate induced by ozone is insufficient to remove the negative effects in tobacco, soybean and poplar

“…plant leaves through open stomata and dissolves in the apoplastic fluid. Once dissolved, the O 3 molecule reacts with H 2 O and solutes to produce several harmful reactive oxygen species (ROS), including hydroxyl radical, singlet oxygen and hydrogen peroxide (Kanofsky and Sima, 1995;Vainonen and Kangasjärvi, 2014;Krasensky et al, 2017). Perception of ROS from its degradation in the apoplast activates several signal transduction pathways that regulate the responses of the cells to the increased oxidative load (Kangasjärvi et al, 2005).…”