| Abstract: | Gas exchange rates, chlorophyll fluorescence, pressure–volume relationships, photosynthetic pigments, total soluble sugars,
starch, soluble proteins and proline concentrations were investigated in five Olea europaea L. cultivars with different geographical origins (Arbequina, Blanqueta, Cobran?osa, Manzanilla and Negrinha) grown under
Mediterranean field conditions. We found considerable genotypic differences among the cultivars. Comparing the diurnal gas
exchange rates, we observed that Cobran?osa, Manzanilla and Negrinha had high photosynthetic rate than Arbequina and Blanqueta.
The first group reveals to be better acclimated to drought conditions, and appears to employ a prodigal water-use strategy,
whereas Blanqueta and Arbequina, with high water-use efficiency, appear to employ a conservative water-use strategy. The degree
of midday depression in photosynthesis was genotype dependent, with a maximum in Arbequina and a minimum in Negrinha. The
reductions in the photosynthetic rate were dependent from both stomatal and non-stomatal limitations. Elastic adjustment plays an important role as drought tolerance mechanism. The group of cultivars that employ a prodigal
water-use strategy revealed high tissue elasticity, whereas Arbequina and Blanqueta revealed high tissue rigidity. We also
identified the existence of drought tolerance mechanisms associated with soluble proteins accumulation in the foliage. The
high levels of soluble proteins in Arbequina may represent an increased activity of oxidative stress defence enzymes and may
also represent a reserve for post stress recovery. In all cultivars, especially in Manzanilla, free proline was accumulated
in the foliage. The discussed aspects of drought stress metabolism may have an adaptative meaning, supporting the hypothesis
that olive cultivars native to dry regions, such as Cobran?osa, Manzanilla and Negrinha, have more capability to acclimate
to drought conditions than cultivars originated in regions with a more temperate climate, like Arbequina and Blanqueta. |
