https://orcid.org/0000-0001-9959-1362
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Amna Mhamdi, Scott Hayes, Highlighting the Fast Signals that Establish Remote Metabolite Profiles, Plant Physiology, Volume 178, Issue 4, December 2018, Pages 1434–1435, https://doi.org/10.1104/pp.18.01327
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They say you can get too much of a good thing, and for plants that is certainly true. Light is essential for growth, but excessive light causes an overloading of the plant’s photosynthetic machinery. This excess energy can spill out and, through formation of reactive oxygen species (ROS), damages the cell. To protect against this, plant tissues that have previously experienced high light levels undergo a process of acclimation that involves changes to gene and metabolite profiles (Suzuki et al., 2012; Foyer et al., 2017). These are particularly important because they can take place in a matter of minutes, quickly protecting against the effects of future light damage.
Acclimation responses are often studied in the tissue that perceives the original stress, but there is growing interest in how light stress experienced by one tissue can affect acclimation in distant tissues. This process is known as systemic acquired acclimation (SAA). In this issue of Plant Physiology, Choudhury et al. (2018) study SAA in Arabidopsis (Arabidopsis thaliana) by subjecting one rosette leaf to extremely high light intensities and then recording changes in the metabolome across time in distant parts of the plant. The authors identify a set of metabolites that are mainly increased in a particular tissue or that have similar responses in more than one specific tissue. Remarkably, changes in the metabolome occur within a very short time, 1–2 min in tissues that are at least 12 cm from the site of high light exposure (Fig. 1). The authors show that respiratory burst oxidase protein D (RBOHD) is required for the rapid accumulation of at least some of these metabolites (Fig. 1). Because RBOHD generates ROS in the apoplast, the authors propose that a ROS wave facilitates the propagation of systemic acclimation to high light. This is in agreement with previous reports showing that a ROS wave is required for leaf-to-leaf communication and stomatal closure (Devireddy et al., 2018). The authors then further investigate the origins of this ROS wave and its interaction with cytosolic ROS-related systems. Through interrogation of their metabolomic data, they identify a rapid systemic decrease in citric acid along with a rapid increase in 2-oxo-glutaric acid. This is relevant as the conversion of citric acid to 2-oxo-glutaric acid is coupled to the production of NADPH, the ultimate substrate for ROS production (at least by RBOHs). The authors show that mutants for the cytosolic NADP‐dependent isocitrate dehydrogenase, one of the sources for NADPH, are partially deficient in the acclimation of systemic leaves.
