Antioxidant Defenses in Plants

Dear Colleagues,

We are leading the following Special Issue entitled: “Antioxidant Defenses in Plants” in the journal Antioxidants.

A common effect of different environmental stimuli on plants, not necessarily resulting in stressful conditions sensu stricto, is the generation of Reactive Oxygen Species (ROS). For instance, plants face large changes in ROS homeostasis on a daily basis, even when growing under both optimal water and nutrient availability, because of large variation in light irradiance. Deviations from ROS homeostasis become considerable when plants are challenged against multiple environmental pressures, due to their sessile nature (plants do not possess the ‘flight strategy’ displayed by other organisms). Plants faced multiple stress agents from their appearance on land and, hence, are well equipped with a modular and integrated network of antioxidant defenses which is, indeed, much more efficient than that displayed by other organisms. Plants have indeed ‘evolved’ a system of antioxidant defenses to keep the ROS levels within a sub-lethal range, being capable, at the same time, of activating a range of ROS-mediated signaling pathways to offer further protection to stress events. For instance, ROS-mediated signaling pathways are likely the main drivers for the biosynthesis of a wide range of secondary metabolites, the significance of which in countering oxidative stress and damage increases with the severity of stress. It is not surprising that plants have long been used as sources of powerful antioxidants for the care of human health, although most phytochemicals may play roles that go well beyond the mere quenching of ROS. For instance, flavonoids behave as ‘signalling molecules’ capable of modulating ROS-mediated signaling pathways acting not only on ROS, but also on downstream components, such as the large number of protein kinases, including the mitogen-activated protein kinases (MAPK) class family. There is also relatively recent evidence that metabolites synthesized through the methyl D-erythritol 4-phosphate (MEP) pathway, such as isoprene and carotenoids, may effectively counter photooxidative stress because of drought- and heat-induced decline in the use of radiant energy into the photosynthetic process. There is increasing evidence supporting the idea that isoprene and zeaxanthin may serve complementary antioxidant functions depending on drought stress severity, with isoprene acting effectively at mild-to-moderate drought and zeaxanthin offering effective protection at severe drought, when the large pool of violaxanthin cycle pigments fully saturates the binding sites in the light‐harvesting chlorophyll‐protein complexes in the photosystem II.

Signaling pathways following alterations in ROS homeostasis are also long known to activate an integrated network of primary antioxidants, mostly consisting of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, catalase) and metabolites derived from primary metabolism, such as ascorbate and glutathione. So-called soluble carbohydrates, mostly polyols (e.g., mannitol, sorbitol) have long been reported as effective scavengers of ROS, as is the case of mannitol-hydroxyl radical.

The aim of this Special Issue “Antioxidant Defenses in Plants” is to explore the network of antioxidant defenses plants activate in response to the wide range of environmental pressures. Here we are interested in publishing articles focusing on the antioxidant functions of metabolites, originated from both the primary (e.g., soluble carbohydrates, ascorbate and glutathione) and secondary metabolism (e.g., volatile and non-volatile isoprenoids, flavonoids), in plants challenged by stressors of different origin. Papers dealing with the role of antioxidant enzymes in plants exposed to a wide range of stressors are also included in this special issue. Research papers, short (such as opinion pieces) as well as full review articles, both critically reviewing and not merely listing the pertinent literature are welcome.

Dr. Massimiliano Tattini
Prof. Dr. Lucia Guidi
Guest Editors

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• Primary and secondary metabolism
• Abiotic and biotic stressors
• Antioxidant enzymes
• Ascorbate-glutathione cycle
• Climate change
• Oxidative stress and damage
• Photooxidative stress
• Reactive oxygen species
• ROS-mediated signaling pathways
• Sugars