Reactive Oxygen in Abiotic Stress Perception - From Genes to Proteins

Throughout their life plants have to adapt to variable environmental conditions. Changes in photoperiod, light intensity and quality, nutrient abundance and starvation, drought and flooding, variation in temperature, air and soil pollution and osmotic changes are among the abiotic factors that can cause stress (Apel & Hirt, 2004). To ensure constant monitoring of environmental conditions and a quick and appropriate response, plants have developed elaborate and robust perception and signal transduction mechanisms. The importance of the ability to adapt to a changing environment has been described in numerous research articles and reviews (Hirayama & Shinozaki, 2010). Recent years have seen tremendous progress in our understanding of the mechanisms and processes underlying abiotic stress adaptation and defence in different plant species (Hirayama & Shinozaki, 2010; Jaspers & Kangasjarvi, 2010). Importantly, the analysis of abiotic stress tolerant varieties of Arabidopsis and also rice has led to novel ideas for improving the stress resistance of crop species. The diversity of abiotic stresses implies that there should be a strong specific component in the individual stress responses (Jaspers & Kangasjarvi, 2010). However, there is a striking common component in the general response to all abiotic stresses (Vaahtera & Brosche, 2011). Essentially all abiotic stresses lead to the production of reactive oxygen species (ROS) albeit different forms and in different subcellular compartments (Jaspers & Kangasjarvi, 2010). In contrast to their presumed role as simply damaging agents in cells ROS act as signalling molecules in the regulation of stress adaptation but also in developmental regulation (Apel & Hirt, 2004; Jaspers & Kangasjarvi, 2010; Moller et al., 2007). For reviews on other aspects of abiotic stress we refer to reviews (Jaspers & Kangasjarvi, 2010; Miller et al., 2008; Munns & Tester, 2008; Vaahtera & Brosche, 2011; Zhu, 2002). Despite the wealth of information on abiotic stress defence in plants the mechanisms of stress sensing have remained relatively elusive. In this review we turn our attention to the mechanisms of abiotic stress perception. Generally, stresses, as well as other stimuli, can be perceived in a direct or an indirect manner. In direct perception, the agent causing the stress is perceived through a receptor. Alternatively, in indirect perception, specific effects leading to stress caused by an agent are perceived. Evidence suggests that in abiotic stress perception plants use both modes in parallel. In indirect stress perception ROS are components frequently used as signalling molecules. However, ROS themselves can be