Fig. 2. Major types of signalling for plants during drought and salt stress. Representative cascades, output and biological functions are shown. Type I signalling involves the generation of ROS scavenging and anti-oxidant compounds as well as osmolytes. The involvement of MAPK pathway in the production of osmolytes in plants has not been demonstrated experimentally. Type II signalling involves the production of stress-responsive proteins mostly of undefined functions. Type III signalling involves the SOS pathway which is specific to ionic stress. Signalling events for homologs of SOS3 (SCaBP) and SOS2 (PKS) are tentatively grouped with SOS3 and SOS2. Primary sensors are shown to be localized in the membrane. Receptors for secondary signalling molecules (2nd SM) are not shown (Xiong et al., 2002b).
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