FRET-efficiency between various proteolipid constructs and VHA-c (A) or VHA-a (B), respectively. A. thaliana mesophyll protoplasts were co-transfected with VHA-c-YFP (A) or VHA-a-YFP (B) and the denoted VHA-CFP fusion proteins and analysed for energy transfer by quantitative confocal microscopy. The data represent the mean average ± SE (A: VHA-c: n = 80; VHA-c": n = 109; VHA-ctrunc.: n = 78; VHA-c"trunc. n = 63; hybrid proteolipid: n = 88; B: VHA-c: n = 142; VHA-c": n = 117; VHA-ctrunc.: n = 86; VHA-c"trunc.: n = 110; hybrid proteolipid: n = 90).