Evaluating the contribution of fruit photosynthesis toward the biogenesis of olive oil

Abstract

In olive, fruit growth is determined by the turgor and by the сarbon assimilated in photosynthesis. This carbon could come from photoassimilates produced in the leaves (heterotrophic) or produced in the fruit itself (autotrophic). The aim of this work was to evaluate whether the fruit photosynthesis actually represent a substantial contribution to oil synthesis in the fruit. The experiment was carried out in 10-year-old Arbequina olive trees under two irrigation strategies: full irrigation needs (FI) and regulated deficit irrigation (45RDI) applying 45% of the FI treatment. To analyze the origin of photoassimilates, we measured oil content and fatty acid composition in olive mesocarp from fruits in control branches, leafless branches which were also “girdled” (autotrophic), and branches whose fruits were bagged to avoid photosynthesis (heterotrophic). Samples were collected at three different stages of fruit development: immediately after stone lignification; when the olive fruit was completely green and when the olive fruit was yellowish. The 45RDI strategy caused an increase in olive oil content per fruit dry weight compared to the FI at the end of the experiment. However, in both irrigation treatments, autotrophic fruits decreased their oil content and accelerated the maturation process in four weeks. Interestingly, minor changes in fatty acid composition were detected among different treatments and water regimes. In particular, linolenic acid, a precursor of the phytohormone jasmonic acid, increased slightly, although significantly, in the autotrophic treatment.