Abstract
The pressure-volume technique was employed to compare water relations and moisture stress-induced osmotic adjustment of Periwinkle (Catharanthus roseus) cv. Pink (PC), Oscillatus (REC) and White (WC). Leaf water potential (ψw), osmotic potential (ψs), turgor potential (ψp), bulk modulus of elasticity (ε), bound water (RWCw) and leaf hydration (H), were estimated by exposing the plants to a drying cycle during which well watered plants were dehydrated to zero turgor, and then irrigated. Osmotic adjustment (Δψw100) was calculated by comparing ψa at full hydration (ψa100) in stressed plants after recovery, with ψa100 in control plants. Values of Δψ2100 were 0.76, 0.33 and 0.11 MPa in cv. PC, REC and WC, respectively. Maintenance of ψp at lower ψ3 and relative leaf water content (RWC) in prestressed PC was attributable to a higher alkaloid content and greater leaf cell wall elasticity. RWCW was plotted against ψp to determine its contribution to hydration maintenance at lower ψp. Genotype PC showed greater RWCw at lower ψp compared with REC and WC. The present study has demonstrated that there are cultivar differences in alkaloid accumulation and water relations in acclimated plants and that the relative ranking for drought resistance within periwinkle appeared to correspond with the changes in osmotic properties.
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