3-year old single shoot V. vinifera plants (cultivar Pinot noir 18 Gm grafted on Kober 5BB, 51 plants) potted in 3L pots in a sandy loam soil were used. All plants were well watered (200 mL per day) at the beginning of the experiment (04.06.2010; DAY 0; 5 plants) and water was supplied to all control plants once every day (250 mL per day), whereas water supply of stressed plants was stopped. Physiological measurements and sampling of leaves took place on 07.06.2010 (DAY 3; 5 control, 5 stressed plants), 10.06.2010 (DAY 6; 5 control, 5 stressed plants) and 12.06.2010 (DAY 8; 5 control, 10 stressed plants). Due to very hot weather conditions in June 2010 the experiment was stopped after 8 days and 12 available control plants were used to restart the drought treatment with 6 control and 6 stressed plants on 11.06.2010 and all plants were measured on 15.06.2010 (DAY 5). The mean leaf temperatures at midday were: 25 ℃ (04.06.2010; DAY 0), 31.9 ℃ (07.06.2010; DAY 3), 30.8 ℃ (15.06.2010; DAY 5), 35.8 ℃ (10.06.2010; DAY 6) and 35.7 ℃ (12.06.2010; DAY 8). The mean PAR radiation per day (measured from 6:00 am till 7:00 pm) was 144.1 µmol m^-2 s^-1. Each plant was used only once for physiological measurements and sampling of leaves.On every day of the experiment (day 0, 3, 5, 6, 8) the pot weight and the volumetric soil moisture content (ThetaProbe ML2x and handheld data logger Moisture Meter HH2, Delta-T Devices, Cambridge, United Kingdom) was recorded. The water potential (PWSC Model 3000, Soilmoisture Equipment Corporation, Santa Barbara, USA) was determined for the 6th leaf (representing the insertion level of the shoot from the basis) of every plant and measurement day. Chlorophyll fluorescence and gas exchange parameters of light adapted leaves were determined with the 4th and 5th leaf, whereas dark adaptation was performed only with the 5th leaf. Immediately after these non-invasive measurements, the 5th leaf was harvested, frozen in liquid nitrogen and further used for the measurement of polyphenols, selected primary metabolites and volatiles (VOCs).

The content of different groups of primary and secondary metabolites is significantly influenced by severe drought stress in grapevine leaves. The content of the majority of the metabolites (around 60% of primary metabolites, around 85% of polyphenols and about 40% of the detected and identified VOCs) increased upon drought stress treatment. Among these especially the primary metabolites citric acid and glyceric acid were strongly influenced by the short as well as the prolonged drought stress treatment, whereas all polyphenols were only induced upon the prolonged drought stress treatment.