The Biosynthesis of Phenolic Compounds Is an Integrated Defence Mechanism to Prevent Ozone Injury in Salvia officinalis

Alessandra Marchica,Lorenzo Cotrozzi,Cristina Nali,Maike Petersen,Rebecca Detti,Elisa Pellegrini,Giacomo Lorenzini

doi:10.3390/antiox9121274

Alessandra Marchica, Lorenzo Cotrozzi + Show 5 more

Open Access

https://doi.org/10.3390/antiox9121274

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Journal: Antioxidants	Publication Date: Dec 14, 2020
Citations: 20	License type: CC BY 4.0

Affiliation: University of Pisa, Philipps University of Marburg

Abstract

Specialized metabolites constitute a major antioxidant system involved in plant defence against environmental constraints, such as tropospheric ozone (O3). The objective of this experiment was to give a thorough description of the effects of an O3 pulse (120 ppb, 5 h) on the phenylpropanoid metabolism of sage, at both biochemical and molecular levels. Variable O3-induced changes were observed over time among the detected phenylpropanoid compounds (mostly identified as phenolic acids and flavonoids), likely because of their extraordinary functional diversity. Furthermore, decreases in the phenylalanine ammonia-lyase (PAL), phenol oxidase (PPO), and rosmarinic acid synthase (RAS) activities were reported during the first hours of treatment, probably due to an O3-induced oxidative damage to proteins. Both PAL and PPO activities were also suppressed at 24 h from the beginning of exposure, whereas enhanced RAS activity occurred at the end of treatment and at the recovery time, suggesting that specific branches of the phenolic pathways were activated. The increased RAS activity was accompanied by the up-regulation of the transcript levels of genes like RAS, tyrosine aminotransferase, and cinnamic acid 4-hydroxylase. In conclusion, sage faced the O3 pulse by regulating the activation of the phenolic biosynthetic route as an integrated defence mechanism.

Highlights

Plants, being sessile organisms, are persistently exposed to environmental stresses, which usually have negative impacts on their growth and productivity [1]
Plants possess a forceful and multifarious antioxidant system composed of enzymatic reactions and non-enzymatic compounds, which are involved in detoxification, removal, and/or neutralization of reactive oxygen species (ROS) overproduction due to biotic and abiotic stresses [3]
Chlorogenic acid showed the lowest concentration of all observed compounds (Figure 2B) and did not show a clear trend; it significantly decreased at 1 h from the beginning of exposure (FBE) (−67% in comparison with controls), was higher than controls at 2 h FBE (+43%), did not show significant differences between treatments at the end of exposure, and significantly decreased again at the recovery time (−63%)

Summary

Introduction

Plants, being sessile organisms, are persistently exposed to environmental stresses, which usually have negative impacts on their growth and productivity [1]. Secondary metabolites—classified into, e.g., terpenoids, phenylpropanoids, and nitrogen containing compounds, based on their biosynthetic origin [4]—are well suited to constitute a major antioxidant system with a central role in plant defence against environmental constraints by (i) avoiding the generation of ROS (e.g., catalyzing oxygenation reactions through formation of metallic complexes reducing/inhibiting the activities of oxidizing enzymes), and (ii) quenching ROS once they are formed [5] These specialized molecules are produced by plants to respond to a large number of diverse signals, both internal ones and those emanating from the environment, which are critical for their survival and adaption as sessile organisms. Accumulation of these compounds is usually a consistent feature in the plant defence mechanisms as they can increase the tolerance and adaptability to different stresses [5]

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Conclusion