Extra-Cellular But Extra-Ordinarily Important for Cells: Apoplastic Reactive Oxygen Species Metabolism

Abstract

Reactive oxygen species (ROS), by their very nature, are highly reactive, and it is no surprise that they can cause damage to organic molecules. In cells, ROS are produced as byproducts of many metabolic reactions, but plants are prepared for this ROS output. Even though extracellular ROS generation constitutes only a minor part of a cell’s total ROS level, this fraction is of extraordinary importance. In an active apoplastic ROS burst, it is mainly the respiratory burst oxidases and peroxidases that are engaged, and defects of these enzymes can affect plant development and stress responses. It must be highlighted that there are also other less well-known enzymatic or non-enzymatic ROS sources. There is a need for ROS detoxification in the apoplast, and almost all cellular antioxidants are present in this space, but the activity of antioxidant enzymes and the concentration of low-mass antioxidants is very low. The low antioxidant efficiency in the apoplast allows ROS to accumulate easily, which is a condition for ROS signaling. Therefore, the apoplastic ROS/antioxidant homeostasis is actively engaged in the reception and reaction to many biotic and abiotic stresses.

Role of Ascorbic acid, Glutathione and Proline Applied as Singly or in Sequence Combination in Improving Chickpea Plant through Physiological Change and Antioxidant Defense under Different Levels of Irrigation Intervals

“…Some strategies need to be used including osmolytes and antioxidants, to support plant growth under stress such as proline [10], ascorbic acid [11] and glutathione [12]. Ascorbic acid (AsA) acts as the transport of antioxidants and electrons [12]; as an enzyme co-factor and retains physiological and signaling pathways regulated by phytohormones [11], neutralizes ROS directly through the use of secondary antioxidants during the reduction of the oxidized form of α-tocopherol [13] and is a significant plant metabolite and acts as a cell signaling modulator in many physiological processes such as mitosis [14]. In addition, treatment with AsA increased the growth of quinoa plants and alleviates the harmful effects of drought stress [15].…”

The apoplastic antioxidant system and altered cell wall dynamics influence mesophyll conductance and the rate of photosynthesis

“…Furthermore, the activity of enzymes such as NADPH oxidases, peroxidases (POXs) or superoxide dismutases (SODs), which also contribute to apoplastic ROS production, increased in response to either biotic or abiotic stress (Díaz‐Vivancos et al ., ; You and Chan, ). Different studies (De Pinto and De Gara, ; Passardi et al ., ; Podgórska et al ., ) have described that apoplastic POXs are involved in the cross‐linking between CW matrix components and in lignin polymerization. In turn, ascorbic acid (ASC), the most abundant low‐molecular‐weight antioxidant in the apoplast, could have a regulatory effect on POX‐dependent wall stiffening since it removes hydrogen peroxide (H 2 O 2 ) (Ros‐Barceló et al ., ).…”

Photoperiod stress alters the cellular redox status and is associated with an increased peroxidase and decreased catalase activity

“…Noteworthy, AsA is found in the apoplast where it is the major 332 non-enzymatic antioxidant (Shigeoka and Maruta, 2014). A reduction of the AsA content in this 333 compartment would decrease the anyhow low antioxidant-buffering capacity of the apoplast 334 even further (Podgorska et al, 2017). The activities of the enzymes of the AsA-GSH scavenging 335 system (APX, MDHAR, DHAR, GR) were not affected by photoperiod stress (Fig.…”