Ascorbate as a key player in plant abiotic stress response and tolerance

Abstract

During their lifespan, plants are frequently exposed to adverse environmental conditions such as high solar irradiance, drought, heat, chilling, salinity, metal excess, and nutrient deficiency. The effects of these factors on plants are often interrelated and usually result in a decreased capacity of carbon fixation in photosynthesis, disturbed redox homeostasis, and growth arrest. Under severe conditions, increased excitation pressure in the chloroplasts exceeds the antioxidative capacity of plant cells leading to oxidative damage of cellular constituents. Although the plant ascorbate (Asc) level varies depending on external factors, developmental stage, diurnal rhythm, and light, its redox status is related to redox homeostasis in the cell. In chloroplasts, peroxisomes, and cytosol, Asc has a key role in hydrogen peroxide (H2O2) scavenging via Asc peroxidase and is efficiently recycled via the ascorbate-glutathione (Asc-GSH) cycle and directly by monodehydroascorbate reductase activity. In apoplast and vacuoles, Asc is the main reductant of phenolic radicals generated under oxidative stress. Besides its antioxidative role, Asc has an important role in a complex and well-orchestrated plant response network to environmental stress, performing multiple tasks in redox signalling, regulation of enzymatic activities, modulation of gene expression, biosynthesis of phytohormones, and growth regulation. The content of Asc and its redox state is tightly related to cellular compartments. Therefore, it is important to emphasize Asc cellular distribution, which has a great impact on reactive oxygen species regulation and signalling. Numerous studies on transgenic plants with altered endogenous Asc levels and redox status were done with the aim to influence plant growth and improve tolerance to various abiotic stressors. In this chapter, we discuss the current understanding of the involvement of Asc metabolism in abiotic stress response. Moreover, the improved resilience to stressors in transgenic plants with altered enzymes involved in Asc biosynthesis and recycling will be discussed.