The work originates from Doctoral studies and a BBSRC-funded project on the involvement of the Arabidopsis CNGC19 calcium channel subunit in calcium signalling. Here, roots of wild type plants (Col ecotype) and a cngc19 loss of function mutant (both expressing GCaMP3 as a reporter of cytosolic free calcium) have been exposed to extracellular ATP (or NaCl as a control). Movies 1-6 show representative Arabidopsis thaliana roots expressing GCaMP3 as a cytosolic free calcium reporter. Movie 1 Col (wild type) grown on full phosphate (Pi) medium; response to 0.3 mM ATP. Movie 2 cngc19-1 mutant grown on full Pi medium; response to 0.3 mM ATP. Movie 3 Col grown on full Pi medium; response to 0.6 mM NaCl. Movie 4 cngc19-1 mutant grown on full Pi medium; response to 0.6 mM NaCl. Movie 5 Col grown on no Pi; response to 0.3 mM ATP. Movie 6 cngc19-1 grown on no Pi; response to 0.3 mM ATP. Movie 7 Col grown on no Pi; response to 0.6 mM NaCl. Movie 8 cngc19-1 grown on no Pi; response to 0.6 mM NaCl. Methods For growth on full Pi, surface-sterilised seeds were sown on half-strength Murashige and Skoog medium, 0.8 % (w/v) Bacto-agar pH 5.6 then stratified in darkness at 4 °C for 48 h. The medium contained 0.625 mM KH2PO4 as the sole Pi source. For no Pi, seeds were sown on half-strength custom-made MS excluding Pi, 0.8 % (w/v) Bacto-agar, pH 5.6. KCl was added to compensate. After stratification, plates were transferred to a growth chamber at 21-23 °C with a 16 h light/8 h dark photoperiod (80 µmol m-2 s-1). Plants were grown vertically for 8 to 9 days. A plate with such seedlings growing in situ was placed horizontally under an M205 FA stereo microscope with a DFC365FX camera (Leica) and a Sola SE365 light source (Lumencor). Excitation light was supplied at 470/40 nm, and emission was collected using an ET-GFP filter (Leica) at 525/50 nm. The camera was set to a 500 ms exposure time, a gain of 2.0 and 30× magnification. Images of root tips were taken every 5 s. Control or test solution was applied as a 1 µl aliquot to the root tip after measuring the basal root fluorescence for 50 s. Control solution was 0.6 mM NaCl in either “full Pi” or “zero Pi” half MS solution, pH 5.6. Test solution was 0.3 mM Na2ATP in either medium. Each seedling was genotyped after imaging and only homozygous cngc19-1 seedlings were used for analysis.