Table II. Impact of water deficit on osmotic potential, osmotic adjustment, and relative contribution of metabolites.
Osmotic potential [mean and (sd) of 10 replicates] of the rosette sap was measured at the end of the night period (EON) and at the end of the photoperiod (EOP) and expressed as raw values (Ψs[raw]) or after tissue rehydration to account for water loss during drought (Ψs[sat]). Osmotic potential difference at saturation between well-watered and water deficit conditions provides an estimate of osmotic adjustment (OA). The concentration differences of solutes between stressed and nonstressed conditions under saturating conditions were summed, giving an estimation of the osmotic adjustment contributed by metabolites (OA[met]). The proportion of the osmotic adjustment accounted for by metabolites (OA[met]) is indicated in parentheses. The relative contribution of each metabolite given is the average of EON and EOP data. All data originate from plants 10 d after the onset of water deficit.
| Parameter | Period | Unit | Treatment | ||
| Well Watered | Moderate Water Deficit | Severe Water Deficit | |||
| Ψs[raw] | EON | MPa | −0.90 (0.09) | −1.07 (0.05) | −1.42 (0.13) |
| Ψs[sat] | EON | MPa | −0.82 (0.08) | −0.91 (0.05) | −1.03 (0.09) |
| Ψs[raw] | EOP | MPa | −0.94 (0.08) | −1.15 (0.13) | −1.61 (0.15) |
| Ψs[sat] | EOP | MPa | −0.87 (0.08) | −0.98 (0.11) | −1.08 (0.10) |
| OA | EON | MPa | 0.086 | 0.213 | |
| OA[met] | EON | MPa | 0.060 (75%) | 0.181 (91%) | |
| OA | EOP | MPa | 0.112 | 0.214 | |
| OA[met] | EOP | MPa | 0.082 (73%) | 0.182 (91%) | |
| Contribution of metabolites to osmotic adjustment (%) | |||||
| Potassium | 53.8 | 35.9 | |||
| Fumarate | 4.4 | 21.7 | |||
| Malate | 0.3 | 3.6 | |||
| Pro | 3.8 | 13.2 | |||
| Amino acids | 8.4 | 6.3 | |||
| Suc | 4.5 | 5.9 | |||
| Hexose | 0.0 | 2.3 | |||
| Unknown | 24.8 | 11.1 | |||