Chloride, glutathiones, and insect-derived elicitors introduced into the xylem trigger electrical signaling.

Ricca assays allow the direct introduction of compounds extracted from plants or the organisms that attack them into the leaf vasculature. Using chromatographic fractionation of Arabidopsis (Arabidopsis thaliana) leaf extracts, we found glutamate was the most active low mass elicitor of membrane depolarization. However, other known elicitors of membrane depolarization are generated in the wound response. These include unstable aglycones generated by glucosinolate (GSL) breakdown. None of the aglycone-derived GSL-breakdown products, including nitriles and isothiocyanates, that we tested using Ricca assays triggered electrical activity. However, we found that glutathione and the GSL-derived compound sulforaphane glutathione triggered membrane depolarizations. These findings identify a potential link between GSL breakdown and glutathione in the generation of membrane depolarizing signals. Noting that the chromatographic fractionation of plant extracts can dilute or exchange ions, we found that Cl- caused glutamate receptor-like3.3 (GLR3.3)-dependent membrane depolarizations. In summary, we show that, in addition to glutamate, glutathione and an adduct with the electrophilic isothiocyanate sulforaphane need to be considered as potential elicitors of membrane potential change. Finally, by introducing aphid (Brevicoryne brassicae) extracts and the flagellin-derived peptide flg22 into the leaf vasculature we extend the use of Ricca assays for the exploration of insect/plant and bacteria/plant interactions.