Nature Plants 1, 15108 (2015); published online 3 August 2015; corrected 7 October 2015.

In the original version of this Article the y-axis labels in Figs 2b,d and 3f were incorrect. These should have read 'YFP/GFP fluorescence ratio (rel)'. Additionally the Faraday constant (Fa) was mistakenly omitted from Equation (1). These errors have been corrected.