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Summary This study examines the drought-induced mechanisms in Fraxinus excelsior L., a species that exhibits a great tolerance with respect to severe water shortage. Pressure-volume curves obtained from seedlings submitted to an artificially induced drought showed a decrease in the osmotic potential at full turgor and at zero turgor. This osmotic adjustment was also demonstrated in stressed plants by the increase in the level of the main organic compounds, malate and mannitol. By calculating the elastic modulus (e) of the foliar tissues, it was also shown that the cell walls of the stressed plants became less extensible. This adaptative response to water deficit was easily reversed after only 1 day of rehydration. A similar increase in e could be induced in short term experiments by the application of 20 μmol/L ABA to detached well-watered leaves, and counteracted in detached leaves from water-stressed seedlings by treatment with acidic pH buffer. From these data, it is suggested that bonding rearrangements rather than structural modifications of the cell wall are involved in the elastic adjustment. The advantages of the elastic adjustment procedure are discussed in relation to plants water availability. |
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