Fruit growth and sink strength in olive (Olea europaea) are related to cell number, not to tissue size.

The relationship between tissue (mesocarp and endocarp) growth and either tissue initial (i.e. in the ovary at bloom) size or cell number was studied using the olive cultivar Leccino (L) and its mutated clone (LC), which produces tetraploid fruits. LC ovaries were 2.7 times the volume of L ovaries, but contained an overall similar number of much larger cells. This allowed decoupling cell number and ovary size, which are normally closely correlated. With this decoupling, cell number in the ovary correlated with tissue growth in the fruit while tissue size in the ovary did not. Cell size in the ovary was inversely correlated with the tissue relative growth from bloom to harvest (i.e. the ratio between final and initial tissue size). These results support the hypothesis that cell number and not tissue size are related to fruit growth and sink strength, and that cell size in the ovary tissues is a good predictor of tissue growth, across cultivars and tissues, even when cell size is strongly affected by ploidy.

Effect of agronomical practices on carpology, fruit and oil composition, and oil sensory properties, in olive (Olea europaea L.).

We examined whether some agronomical practices (i.e. organic vs. conventional) affect olive fruit and oil composition, and oil sensory properties. Fruit characteristics (i.e. fresh and dry weight of pulp and pit, oil content on a fresh and dry weight basis) did not differ. Oil chemical traits did not differ except for increased content of polyphenols in the organic treatments, and some changes in the acidic composition. Sensory analysis revealed increased bitterness (both cultivars) and pungency (Frantoio) and decreased sweetness (Frantoio) in the organic treatment. Fruit metabolomic analysis with HRMAS-NMR indicated significant changes in some compounds including glycocholate, fatty acids, NADPH, NADP+, some amino acids, thymidine, trigonelline, nicotinic acid, 5,6-dihydrouracil, hesanal, cis-olefin, ß-D-glucose, propanal and some unassigned species. The results suggest that agronomical practices may have effects on fruit composition that may be difficult to detect unless a broad-spectrum analysis is used.

Olive phenolic compounds: metabolic and transcriptional profiling during fruit development.

BACKGROUND: Olive (Olea europaea L.) fruits contain numerous secondary metabolites, primarily phenolics, terpenes and sterols, some of which are particularly interesting for their nutraceutical properties. This study will attempt to provide further insight into the profile of olive phenolic compounds during fruit development and to identify the major genetic determinants of phenolic metabolism. RESULTS: The concentration of the major phenolic compounds, such as oleuropein, demethyloleuropein, 3-4 DHPEA-EDA, ligstroside, tyrosol, hydroxytyrosol, verbascoside and lignans, were measured in the developing fruits of 12 olive cultivars. The content of these compounds varied significantly among the cultivars and decreased during fruit development and maturation, with some compounds showing specificity for certain cultivars. Thirty-five olive transcripts homologous to genes involved in the pathways of the main secondary metabolites were identified from the massive sequencing data of the olive fruit transcriptome or from cDNA-AFLP analysis. Their mRNA levels were determined using RT-qPCR analysis on fruits of high- and low-phenolic varieties (Coratina and Dolce d'Andria, respectively) during three different fruit developmental stages. A strong correlation was observed between phenolic compound concentrations and transcripts putatively involved in their biosynthesis, suggesting a transcriptional regulation of the corresponding pathways. OeDXS, OeGES, OeGE10H and OeADH, encoding putative 1-deoxy-D-xylulose-5-P synthase, geraniol synthase, geraniol 10-hydroxylase and arogenate dehydrogenase, respectively, were almost exclusively present at 45 days after flowering (DAF), suggesting that these compounds might play a key role in regulating secoiridoid accumulation during fruit development. CONCLUSIONS: Metabolic and transcriptional profiling led to the identification of some major players putatively involved in biosynthesis of secondary compounds in the olive tree. Our data represent the first step towards the functional characterisation of important genes for the determination of olive fruit quality.

Tissue size and cell number in the olive (Olea europaea) ovary determine tissue growth and partitioning in the fruit.

The relationship between tissue size and cell number in the ovary and tissue size in the fruit, was studied in eight olive (Olea europaea L.) cultivars with different fruit and ovary size. All tissues in the ovary increased in size with increasing ovary size. Tissue size in the fruits correlated with tissue size in the ovary for both mesocarp and endocarp, but with different correlations: the mesocarp grew about twice as much per unit of initial volume in the ovary. Tissue size in the fruit also correlated with tissue cell number in the ovary. In this case, a single regression fitted all data pooled for both endocarp and mesocarp, implying that a similar tissue mass was obtained in the fruit per initial cell in the ovary, independent of tissues and cultivars. Tissue relative growth from bloom to harvest (i.e. the ratio between final and initial tissue size) differed among cultivars and tissues, but correlated with tissue cell size at bloom, across cultivars and tissues. These results suggest that in olive, tissue growth and partitioning in the fruit is largely determined by the characteristics of the ovary tissues at bloom, providing important information for plant breeding and crop management.