For many years, the concept “the higher antioxidant activity, the better to plant” has dominated the literature. However, in recent years it has become apparent that plants actively produce ROS as signaling molecules to control numerous physiological processes such as defense responses and cell death, cross tolerance, gravitropism, stomatal aperture, cell expansion and polar growth, hormone action and leaf and flower development. In many cases, production of ROS is genetically programmed, and superoxide and H2O2 are used as second messengers. A new concept of ‘oxidative signaling’ instead of ‘oxidative stress’ was proposed and the positive role of ROS has been reported both at physiological (e.g., regulation of ion channel activity) and genetic (e.g., control of gene expression) levels. This has prompted a need to rethink the above “the more the better” concept and incorporate the signaling role of ROS and a redox state of the cell into the breeding programs aimed to improve biotic and abiotic stress tolerance.

The number of papers linking oxidative stress with stress conditions has increased exponentially over the last two decades. Given the reported increase in antioxidant activity in plants grown in saline conditions, it is hardly surprising that the idea of improving salinity stress tolerance by increased antioxidant production by exogenous applications of hormones, nutrients, and growth regulators is gaining momentum. However, many other reports question the validity of this approach, reporting no or a negative correlation between the activity of antioxidant enzymes and plant salinity stress tolerance. A possible reason for this discrepancy is that some ROS (e.g., H2O2) play an important signaling role in adaptive and developmental responses, and therefore tempering with these ROS may result in pleiotropic effects. It becomes increasingly evident that considerable variations exist in the production of antioxidants, both enzymatic and non-enzymatic, in response to stress in various plant tissues and at various time points. Hence, the inter-specific or intra-specific aspects of ROS production and scavenging should be considered. Finally, the diversity of known antioxidants should be accounted for.

This Research Topic welcomes papers that enhance the mechanistic understanding of the diverse role of antioxidants in stress tolerance. Critical reviews and original research articles that address the potential role of breeding methods, growth regulators, hormones, proteins, and signaling cascades in the ROS scavenging system in plants are also invited.

Manuscripts on the following themes are encouraged:

- Plant biotic and abiotic stress
- Oxidative burst
- Plant nutrition and stress tolerance
- Plant diseases and antioxidant system
- Genotype-specific phenotypic response to ROS scavenging
- Halophytes as key source of gene identification
- Biotechnology interventions

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Frontiers in Plant Science

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