The high performance liquid chromatography HPLC. Dionex DX 500 system consisting of an AS40 Autosampler, GP40 gradient pump, AD20 UV/Visible absorbance detector, ED40 electrochemical detector, and LC20 chromatography enclosure was used to quantify levels of compatible solutes in plants. Immediately following harvest, the leaf sap was extracted as described for osmotic potential measurement. One ml of methanol:chloroform:water (60:25:15 by vol) was added to each sample and the samples were vortexed for 1 min before centrifugation for 10 min at 10 000 g at 4 °C. The supernatant was removed and the samples were freeze-dried. The samples were resuspended in 200 μl of milliQ water prior to injection into the HPLC. A mixture of standards (glycine betaine, sucrose, glucose, fructose, mannitol, trigonelline, and sorbitol), was prepared in methanol:water (50:50, v:v) at 0.5 μg μl−1 for glycine betaine and 2.5 μg μl−1 for the remaining solutes. Ten μl of the standard solution was injected into the HPLC while running each batch of samples. The contribution of organic and inorganic ions to leaf osmotic potential was determined using the van’t Hoff equation, where the calculated contribution of individual solutes to measured Ψs, was based on solute concentration on a molar basis