Abstract
Reactive oxygen species (ROS) are constantly produced by metabolically active plant cells. The concentration of ROS may determine their role, e.g., they may participate in signal transduction or cause oxidative damage to various cellular components. To ensure cellular homeostasis and minimize the negative effects of excess ROS, plant cells have evolved a complex antioxidant system, which includes ascorbic acid (AsA). AsA is a multifunctional metabolite with strong reducing properties that allows the neutralization of ROS and the reduction of molecules oxidized by ROS in cooperation with glutathione in the Foyer-Halliwell-Asada cycle. Antioxidant enzymes involved in AsA oxidation and reduction switches evolved uniquely in plants. Most experiments concerning the role of AsA have been performed on herbaceous plants. In addition to extending our understanding of this role in additional taxa, fundamental knowledge of the complex life cycle stages of woody plants, including their development and response to environmental factors, will enhance their breeding and amend their protection. Thus, the role of AsA in woody plants compared to that in nonwoody plants is the focus of this paper. The role of AsA in woody plants has been studied for nearly 20 years. Studies have demonstrated that AsA is important for the growth and development of woody plants. Substantial changes in AsA levels, as well as reduction and oxidation switches, have been reported in various physiological processes and transitions described mainly in leaves, fruits, buds, and seeds. Evidently, AsA exhibits a dual role in the photoprotection of the photosynthetic apparatus in woody plants, which are the most important scavengers of ozone. AsA is associated with proper seed production and, thus, woody plant reproduction. Similarly, an important function of AsA is described under drought, salinity, temperature, light stress, and biotic stress. This report emphasizes the involvement of AsA in the ecological advantages, such as nutrition recycling due to leaf senescence, of trees and shrubs compared to nonwoody plants.
Highlights
Plants are immobile organisms and are exposed to stress factors of both biotic and abiotic origin
Ascorbic acid (AsA) and glutathione may be contemplated as the leading antioxidants and constituents of redox signaling; another group of biomolecules that should be mentioned in this context are polyamines (PAs), implicated in many of the ascorbic acid (AsA) functions, such as nitrogen recycling and woody plant stress responses [14]
Both studies revealed that compensatory antioxidant mechanisms were activated in ascorbate peroxidase (APX) mutants, but deficiency in AsA to dehydroascorbic acid (DHA) switches contributed to growth abnormalities
Summary
Plants are immobile organisms and are exposed to stress factors of both biotic and abiotic origin. Ascorbic acid (AsA) and glutathione may be contemplated as the leading antioxidants and constituents of redox signaling; another group of biomolecules that should be mentioned in this context are polyamines (PAs), implicated in many of the AsA functions, such as nitrogen recycling and woody plant stress responses [14]. PAs are positively charged molecules protecting the cell against oxidative damage, both directly and indirectly They function as antioxidants themselves, scavenging free radicals, and indirectly, they have been reported to adjust the levels of enzymatic and/or non-enzymatic antioxidants inside the plant cell. The redox buffering capability of the apoplast is low, regardless of the existence of further antioxidant molecules, such as PAs and flavonoids, and mainly depends on the AsA content due to the lack of glutathione and nicotinamide adenine dinucleotide phosphate [16].
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