Accordingly, we can deduce that stomata have a key role in the Arabidopsis immunity triggered by CP; the guard cells probably possess a receptor for this MAMP. This assumption is in accordance with the role in MAMP sensing attributed to guard cells by Melotto et al., who also hypothesized the presence in these cells of several receptors for multiple MAMPs, and with the actual presence in these cells of the flagellin receptor. At the same time our results do not conflict with the presence of a receptor also in the plasma membrane of NVP-BKM120 epidermal or mesophyll cells, as recently suggested by Frı ´as et al. for the CPP BcSpl1. However, at the level of epidermal cells our results strongly suggest that the stomata are the most responsive to CP. In fact, even when the peels were treated on the underside, i.e. the side devoid of cuticle, the H2O2 production showed the same evolution, namely from guard cells to neighbouring cells, and thus the presence of cuticle cannot be considered the only determinant of the obtained results. Stomata represent a natural entry site for potentially harmful microbes, and the stomatal closure in response to MAMPs is considered as an innate immune response active at the preinvasive level. CP induced a progressive reduction of the stomatal aperture similarly to flagellin-22 and lipopolysaccharides. The generation of H2O2 is crucial to initiate this process and MAMPs rely on RBOHD as the primary NADPH oxidase for ROS production. As found by qPCR, RBOHD was effectively up-regulated by CP but the timing could not explain the early oxidative burst observed. Therefore, we can assume that the rapid generation of H2O2 was caused by this enzyme in the form already present in the cells. Barley is a short-season, early maturing annual grain crop with some degree of tolerance to drought and salinity, which allows its production in a wide range of climatic zones including both irrigated and dryland production areas. Barley In addition to its agronomical relevance and commercial value as a feed or malt grain crop, barley is regaining popularity as human food due to the antioxidant and b-glucan rich grains. Despite its agronomical importance and rising market value, barley acreage in the US has declined from 8.94 million acres in 1991 to 3.48 million acres in 2013. In Washington State alone the acreage has dropped significantly from 500,000 acres planted in 1999 to 180,000 acres in 2013. The significant drop in barley acreage during the last two decades can be partly attributed to the wide scale application of imidazolinone herbicides in combination with the introduction of imidazolinone -resistant crops, and the residual activity of the herbicides of this family. The decline in acreage can also be explained by the overlapping distribution of regions under barley cultivation in the PNW and the regions under extensive application of Imazamox and/or Imazethapyr. Collectively, the major reason for the decline in barley acreage is its sensitivity to commonly used herbicides. Many of the widely used herbicides, which impose barley plant-back restrictions, belong to the group B herbicides. Thus, identification of IMI-resistant mutant in barley.