Figure 8.

Model for the molecular, cellular, and anatomical bases of the systemically transmitted wound-induced electrical potentials in Arabidopsis thaliana. Wild type A. thaliana plants generate 2 major types of electrical signals upon wounding that can be recorded in unwounded leaves, namely an action potential (AP) in the SE/CC network of the phloem, and a long potential (LP) in unknown cell populations, outside of the SE/CC network. The model proposes that GLR3.3 and GLR3.6 have a redundant function in sending the AP to unwounded leaves via the SE/CC network. GLR3.5 functions as an off-switch that blocks the transmission of the AP to non-neighbor leaves. However, the AP sent to the neighbor leaf in this mutant is significantly small, compared with that of wild type plants (c. 30 mV), and therefore, it may act as a partial on-switch for the transmission of the AP between neighbor leaves. This is not shown in the model, as it emphasizes “all or none” phenotypes. GLR3.6 is essential for the occurrence of the wound-induced long potential. The model proposes that the GLR3.6-dependent LP is not independently propagated between leaves, but induced locally by the phloem-propagated AP. Therefore, the AP represents primary excitation, and the LP represents secondary excitation. This model suggests that the fine coordination of the expression of these GLR channels results in a highly regulated spatial distribution of stimulus-induced electrical signals in plants.