Analysis of extracellular pH
Extracellular alkalinisation can be used as a rapid readout for the activation of plant immunity, because it reports the co-import of proton with calcium as an earliest known event of signalling (Felix et al., 1993), and was measured as described by Qiao et al. (2010), after pre-equilibrating the cells on an orbital shaker for around 60 min, before adding 200 µM AlCl3 either with or without 20 µM GdCl3 as compared to a control without added compounds and a further control with 20 µM GdCl3 alone.