Reactive oxygen species (ROS) are thought to play a dual role in plant biology. They are required for many important signaling reactions, but are also toxic byproducts of aerobic metabolism. Recent studies revealed that ROS are necessary for the progression of several basic biological processes including cellular proliferation and differentiation. Moreover, cell death-that was previously thought to be the outcome of ROS directly killing cells by oxidation, in other words via oxidative stress-is now considered to be the result of ROS triggering a physiological or programmed pathway for cell death. This Opinion focuses on the possibility that ROS are beneficial to plants, supporting cellular proliferation, physiological function, and viability, and that maintaining a basal level of ROS in cells is essential for life.

Summary: Reactive oxygen species (ROS) play a key role in the acclimation process of plants to abiotic stress. They primarily function as signal transduction molecules that regulate different pathways during plant acclimation to stress, but are also toxic byproducts of stress metabolism. Because each subcellular compartment in plants contains its own set of ROS‐producing and ROS‐scavenging pathways, the steady‐state level of ROS, as well as the redox state of each compartment, is different at any given time giving rise to a distinct signature of ROS levels at the different compartments of the cell. Here we review recent studies on the role of ROS in abiotic stress in plants, and propose that different abiotic stresses, such as drought, heat, salinity and high light, result in different ROS signatures that determine the specificity of the acclimation response and help tailor it to the exact stress the plant encounters. We further address the role of ROS in the acclimation of plants to stress combination as well as the role of ROS in mediating rapid systemic signaling during abiotic stress. We conclude that as long as cells maintain high enough energy reserves to detoxify ROS, ROS is beneficial to plants during abiotic stress enabling them to adjust their metabolism and mount a proper acclimation response.

Global warming, climate change, and environmental pollution present plants with unique combinations of different abiotic and biotic stresses. Although much is known about how plants acclimate to each of these individual stresses, little is known about how they respond to a combination of many of these stress factors occurring together, namely a multifactorial stress combination. Recent studies revealed that increasing the number of different co-occurring multifactorial stress factors causes a severe decline in plant growth and survival, as well as in the microbiome biodiversity that plants depend upon. This effect should serve as a dire warning to our society and prompt us to decisively act to reduce pollutants, fight global warming, and augment the tolerance of crops to multifactorial stress combinations.