Figure 3.

A schematic diagram of retrograde signals and potential mechanisms in regulating plant drought tolerance. Drought can be perceived by chloroplasts. Chloroplast-located ion channels participate in biosynthetic processes of retrograde signals, such as Mg-Protop IX [45], heme [48], ROS [100], and PAP [117], which target either nuclear genes expression (NGE) [48,54,116] or secondary messengers [55]. Secondary messengers and NGE regulate plasma membrane or tonoplast ion transporters [171], triggering the root and shoot responses to drought. Dotted blue arrows: potential interactions. Abbreviations: see legends of Figure 1 and Figure 2.