Shimon Lavee

Biotransformations of phenolic compounds in Olea europaea L.

Phenolic compounds are a diverse range of secondary metabolites derived from the shikimate pathway and phenylpropanoid metabolism. Olea europaea L. contains a number of unusual phenolics including various oleosides. The amounts and types of phenolics vary markedly between leaf, fruit, stone, and seed. The metabolic relationships between the various parts and phenolic content are poorly understood. Interest in this area is related to the importance of the phenolic profile to the aesthetics and quality of olive products, and to the use of olive leaves in phytomedicines.

Determination of phenolic compounds in olives by reversed-phase chromatography and mass spectrometry

Abstract A method based on extraction from freeze-dried material and clean up by solid-phase extraction was optimized for recovery of phenolic compounds from olive fruit. The extracted compounds were characterised by reversed-phase liquid chromatography using both ultraviolet, fluorescence and electrospray ionization mass spectral detection. Using this approach, oleuropein was confirmed as the major phenolic in olive fruit. Other compounds whose presence was confirmed include tyrosol, syringic, ferulic and homovanillic acids, quercetin-3-rhamnoside, ligstroside and isomers of verbascoside. Elenolic acid and its glucoside, which are not phenolic but are closely related, were also identified in sample extracts.

Gene-expression profiling of grape bud response to two alternative dormancy-release stimuli expose possible links between impaired mitochondrial activity, hypoxia, ethylene-ABA interplay and cell enlargement.

A grape-bud-oriented genomic platform was produced for a large-scale comparative analysis of bud responses to two stimuli of grape-bud dormancy release, hydrogen cyanamide (HC) and heat shock (HS). The results suggested considerable similarity in bud response to the stimuli, both in the repertoire of responding genes and in the temporary nature of the transcriptome reprogramming. Nevertheless, the bud response to HC was delayed, more condensed and stronger, as reflected by a higher number of regulated genes and a higher intensity of regulation compared to the response to HS. Integrating the changes occurring in response to both stimuli suggested perturbation of mitochondrial activity, development of oxidative stress and establishment of a situation that resembles hypoxia, which coincides with induction of glycolysis and fermentation, as well as changes in the interplay between ABA and ethylene metabolism. The latter is known to induce various growth responses in submerged plants and the possibility of a similar mechanism operating in the bud meristem during dormancy release is raised. The new link suggested between sub lethal stress, mitochondrial activity, hypoxic conditions, ethylene metabolism and cell enlargement during bud dormancy release may be instrumental in understanding the dormancy-release mechanism. Temporary increase of acetaldehyde, ethanol and ethylene in response to dormancy release stimuli demonstrated the predictive power of the working model, and its relevance to dormancy release was demonstrated by enhancement of bud break by exogenous ethylene and its inhibition by an ethylene signal inhibitor.

The effect of yield, harvest time and fruit size on the oil content in fruits of irrigated olive trees (Olea europaea), cvs. Barnea and Manzanillo

Abstract The oil content in olive fruits of different sizes from irrigated high (‘on’) and low (‘off’) yielding olive trees of cvs. Barnea and Manzanillo were determined at different stages of fruit maturation. The fruit size range at all stages of maturation is significantly higher on low yielding ‘off’ trees than on high yielding ‘on’ trees. The oil content in the mesocarp of olive fruits is not yield or fruit size dependent. Only in young fruit at early stages of green maturation is the oil content in the fruit’s mesocarp higher in the low yielding ‘off’ trees than in the high yielding ‘on’ ones. At full black maturation, the relative oil content in the mesocarp is uniform in all fruits regardless of size and level of yield. The final oil content in the fruits is dependent on the interaction between the growing conditions and the genetic potential of the variety. The amount of oil produced by an olive tree seems to be regulated mainly by the amount of mesocarp available for oil biosynthesis. The ratio of mesocarp/endocarp (flesh/pit) within each cultivar is strongly related to fruit size, and thus affected by high and low yields.

Role of carbohydrate reserves in yield production of intensively cultivated oil olive (Olea europaea L.) trees

Olive (Olea europaea) has a very high tendency for year-to-year deviation in yield (alternate bearing), which has a negative economic impact on the olive oil industry. Among possible reasons for alternate bearing, depletion of stored carbohydrates (CHO) during the On-year (high yield) has often been mentioned. The objective of the present study was to verify the role of CHO reserves, as a cause or effect, in the alternate bearing of intensively cultivated olives. A monthly survey of soluble sugar and starch concentrations in the leaves, branches, bark and roots of On- and Off-trees (cv. Barnea) was carried out during a complete reproductive cycle from November 2005 to October 2006. Carbohydrate concentration in the sapwood was determined in January, as well as an estimate of whole-tree biomass. The trunk and limbs possess the largest portion of CHO reserves. The influence of reduced fruit load on CHO reserves was also investigated. Starch, mannitol and sucrose concentrations increased from December to March in all tissues, and then declined along with fruit development. Leaves, branches and bark have a significant role in CHO storage, whereas roots accumulated the lowest CHO concentrations. However, fluctuations in reserve content suggested considerable involvement of roots in the CHO budget. Nevertheless, there were no meaningful differences in the annual pattern of CHO concentration between On- and Off-trees. Even a 75-100% reduction in fruit number brought about only a minor, sluggish increase in CHO content, though this was more pronounced in the roots. Carbohydrate reserves were not depleted, even under maximum demands for fruit and oil production. It is concluded that in olives, the status of CHO reserves is not a yield determinant. However, they may play a significant role in the olives survival strategy, ensuring tree recovery in the unpredictable semiarid Mediterranean environment. This suggests that CHO reserves in olive act like an active sink, challenging the common concept regarding the regulation of CHO reserves in plants.

The floral biology of the olive: effect of flower number, type and distribution on fruitset

Abstract The effect of flower number and distribution on the fruiting behavior of various olive cultivars was studied over a period of 10 years. The number of staminate flowers within each cultivar had no significant effect on fruitset. Pre-bloom removal of up to 50% of the flowers did not affect fruitset. Variation in prebloom flower-removal position resulted in similar fruitset per inflorescence, whether flowers were removed along the inflorescence axis or from the distal half of each inflorescence. Removal of half of the inflorescences resulted in doubling the fruit set on the remaining ones, except in cv. Koronaiki which normally sets more than one fruit on most of its inflorescences. The distal fruitful inflorescence set more than one fruit (mostly two) on 70–80% of the shoots of various cultivars. In cv. Santa Caterina a clear increase in fruitset per shoot was observed when 80% of the flowers per inflorescence were removed. In this cultivar the lateral flowers were significantly more fruitful than the king flower. This however, was not the case with cv. Manzanillo.

Photosynthetic activity during olive (Olea europaea) leaf development correlates with plastid biogenesis and Rubisco levels

Olive leaves are known to mature slowly, reaching their maximum photosynthetic activity only after full leaf expansion. Poor assimilation rates, typical to young olive leaves, were previously associated with low stomata conductance. Yet, very little is known about chloroplast biogenesis throughout olive leaf development. Here, the photosynthetic activity and plastids development throughout leaf maturation is characterized by biochemical and ultrastructural analyses. Although demonstrated only low photosynthetic activity, the plastids found in young leaves accumulated both photosynthetic pigments and proteins required for photophosphorylation and carbon fixation. However, Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase), which catalyzes the first major step of carbon fixation and one of the most abundant proteins in plants, could not be detected in the young leaves and only slowly accumulated throughout development. In fact, Rubisco levels seemed tightly correlated with the observed photosynthetic activities. Unlike Rubisco, numerous proteins accumulated in the young olive leaves. These included the early light induced proteins, which may be required to reduce the risk of photodamage, because of light absorption by photosynthetic pigments. Also, high levels of ribosomal L11 subunit, transcription factor elF-5A, Histones H2B and H4 were observed in the apical leaves, and in particular a plastidic-like aldolase, which accounted for approximately 30% of the total proteins. These proteins may upregulate in their levels to accommodate the high demand for metabolic energy in the young developing plant tissue, further demonstrating the complex sink-to-source relationship between young and photosynthetically active mature leaves.

In vitro germination of embryos for speeding up seedling development in olive breeding programmes

Abstract The germination potential of olive seeds without the sclerified endocarp (stoneless seeds) and growth of the seedlings were compared with germination and growth of excised and in vitro cultured embryos of ten olive cultivars. The number of empty stones and the number of stones with two seeds were also determined for each of the cultivars. Isolated embryos of all the cultivars germinated uniformly within 10–14 days in culture, while the mean germination time of stoneless seeds was 55–95 days depending on the cultivar. The percentage of embryo germination was 3–15 fold higher than that of stoneless seeds according to cultivar. Root growth was more rapid in plants originating from seeds than from excised embryos. The growth of plantlets derived from in vitro germinated embryos in the greenhouse was normal. Thus, embryo culture would increase the efficiency and shorten the time for starting initial progeny evaluation of olive breeding programmes.

Possible juvenile-related proteins in olive tree tissues

Comparisons of protein composition between juvenile and adult organs of olive trees were made by SDS-polyacrylamide gel electrophoresis analysis. Plant material included leaves, bark and bud tissues obtained from juvenile and adult organs within the same plant as well as from separate plants of both the same and different genetic origin. The amount of protein loaded onto the gels was standardized by adjusting the volume of the extract applied to the gel. The protein population of both juvenile and adult tissue from the same or separate trees was qualitatively similar but at least one group of 29 kDa polypeptides, is more abundant in the juvenile leaf tissues. In contrast, a protein group of 35 kDa is more strongly expressed in the adult tissue. Similar relations between the proteins of juvenile and adult tissues were obtained in various cultivars of different genetic origin. Thus, differences in protein composition between juvenile and adult tissues, although only quantitative, are consistent across genotypes. Although, some protein groups, e.g. 63 kDa might be clone-specific some other protein groups also differ quantitatively between adult and juvenile tissues but to a lesser extent.

Identification and seasonal changes of glucose, fructose and mannitol in relation to oil accumulation during fruit development in Olea europaea (L.)

Abstract The amounts of glucose, fructose and mannitol, the main sugars in olive fruits, were determined in ‘Kadesh’, ‘Uovo di Piccione’ and ‘Manzanillo’ which have 8, 15 and 20% oil, respectively, at full black maturation. The sugars were separated by high-pressure liquid chromatography and characterized by ultraviolet detection after derivatization with nitrobenzoate. The total amount of sugar in ‘Kadesh’ was more than double that in the two other cultivars. A parallel rise in oil and sugar levels was noticed at the beginning of the fruit ripening period of ‘Kadesh’, while the sugar level of the other cultivars decreased during most of that period. Glucose was the predominant sugar in all cultivars, followed by fructose and mannitol. The relative amounts of mannitol were only 2% in ‘Kadesh’ and 10% in ‘Manzanillo’ and ‘Uovo de Piccione’. It is suggested that mannitol levels and oil accumulation are related.