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The Mediterranean will be one of the focal points of climate change. The predicted dry and hot summers will lead to water scarcity in agriculture, which may limit crop production and growth. The olive tree serves as a model woody plant for studying drought stress and improving water resource management; thus, it is critical to identify genotypes that are more drought tolerant and perform better under low irrigation or even rainfed conditions. In this study, the metabolomic approach was used to highlight variations in metabolites in stems and leaves of three Italian olive cultivars (previously characterized physiologically) under two and four weeks of drought stress. Phenolic and lipophilic profiles were obtained by gas chromatography-mass spectrometry and ultra-high performance liquid chromatography-mass spectrometry, respectively. The findings identified the leaf as the primary organ in which phenolic variations occurred. The Maurino cultivar exhibited a strong stress response in the form of phenolic compound accumulation, most likely to counteract oxidative stress. The phenolic compound content of ‘Giarraffa’ and ‘Leccino’ plants remained relatively stable whether they were exposed to drought or not. Variations in the lipid profile occurred in leaves and stems of all the cultivars. A high accumulation of compounds related to epicuticular wax components was observed in the leaf of ‘Giarraffa’, while a strong reduction of lipids and long-chain alkanes occurred in ‘Maurino’ when exposed to drought stress conditions. [ABSTRACT FROM AUTHOR]

Highlights • Most abundant lipophilic and phenolic compounds in olive leaves are highlighted. • UV-B radiation and heat differently modulate the lipophilic and phenolic content of olive leaves. • Flavonoids, secoiridoids and monoterpenes are highly responsive to heat and UV-B radiation. • Hydroxycinnamic acids, triterpenes, sterols and fatty acids are little affected by UV-B and heat. Abstract Olea europaea L. is the basis of the olive oil chain value. Olive by-products remain economically underexplored despite their richness in polyphenols and fatty acids. Heat waves and raised UV-B radiation episodes (that increasingly affect Mediterranean orchards) may influence these compounds. Herein we characterize the most relevant leaf lipophilic and phenolic compounds of an important Portuguese cultivar Cobrançosa, immediately and 30 days after exposure to high UV-B radiation or heat shock (HS). Plants were exposed to either UV-B (12 kJ m−2 d-1) or HS (40 °C for 2 h) for two consecutive days. Hydroxycinnamic acids, triterpenes, sterols and fatty acids are less influenced by UV-B and HS, while the amounts of flavonoids, secoiridoids and monoterpenes increased. In particular, after both treatments, quercetin-3- O -glucoside levels increased in leaves, and UV-B stimulated oleuropein levels. HS reduced the amounts of verbascoside, oleuropein and luteolin-7- O -glucoside, while UV-B only decrease apigenin-7- O -rutinoside levels. Thirty days after UV-B and HS relief, these compounds showed different profiles. Whereas UV-B recovering plants showed increased amounts of thymol-β- d -glucopyranoside, in HS recovering plants, the increase was more relevant for oleuropein, chrysoeriol-7- O -glucoside and luteolin-7- O -glucoside. Data evidence that Cobrançosa leaves are particularly rich in luteolin-7- O -glucoside, oleuropein, and oleic and palmitic acids, and that their levels may be stimulated by climate-change related conditions, contributing to the economical valorisation of leaves. [ABSTRACT FROM AUTHOR]

In recent decades, atmospheric pollution led to a progressive reduction of the ozone layer with a consequent increase in UV-B radiation. Despite the high adaptation of olive trees to the Mediterranean environment, the progressive increase of UV-B radiation is a risk factor for olive tree cultivation. It is therefore necessary to understand how high levels of UV-B radiation affect olive plants and to identify olive varieties which are better adapted. In this study we analyzed two Italian olive varieties subjected to chronic UV-B stress. We focused on the effects of UV-B radiation on RubisCO, in terms of quantity, enzymatic activity and isoform composition. In addition, we also analyzed changes in the activity of antioxidant enzymes (SOD, CAT, GPox) to get a comprehensive picture of the antioxidant system. We also evaluated the effects of UV-B on the enzyme sucrose synthase. The overall damage at biochemical level was also assessed by analyzing changes in Hsp70, a protein triggered under stress conditions. The results of this work indicate that the varieties (Giarraffa and Olivastra Seggianese) differ significantly in the use of specific antioxidant defense systems, as well as in the activity and isoform composition of RubisCO. Combined with a different use of sucrose synthase, the overall picture shows that Giarraffa optimized the use of GPox and opted for a targeted choice of RubisCO isoforms, in addition to managing the content of sucrose synthase, thereby saving energy during critical stress points. [ABSTRACT FROM AUTHOR]

The frequency of combined stress events is increasing due to climate change and represents a new threat to olive (Olea europaea) culture. How olive plants modulate their profile of metabolites under multiple stressing agents remains to unveil, although several metabolites affect plants' resilience, and olive production and quality. Young olive plants were exposed to a water deficit (WD) for 30 days and then exposed to a shock of heat and high UVB-radiation (WDHS+UVB treatment) for 2 days. Then, plants were re-watered and grown under optimal conditions (recovery) for 30 days. Leaves were collected after stress and recovery, analysed by liquid and gas chromatography, and the lipophilic and phenolic profiles were characterized. Except for the oleuropein derivatives, the qualitative metabolite profile was similar during stress and recovery. Metabolite increases or decreases in response to stress were stronger when WD was followed by WDHS+UVB treatment. Phenolic compounds (luteolin-7- O -glucoside, quercetin-3- O -rutinoside, apigenin-7- O -glucoside, chrysoeriol-7- O -glucoside, kaempferol derivatives, oleuropein, and lucidumoside C) were the most involved after WD and WDHS+UVB, possibly acting as reactive oxygen species (ROS) scavengers. Lipophilic compounds were more relevant during the recovery period. The catabolism of fatty acids and carbohydrates may provide the necessary energy for plant performance reestablishment, and sterols, long-chain alkanes, and terpenes metabolic pathways may be shifted for the production of compounds with a more important stress protection role. This work highlights for the first time that tolerance mechanisms activated by WD in olive plants are related to metabolite changes, that are adjusted when other stressors are overlapped (WDHS+UVB), and also help the plants recover. This metabolites' plasticity represents an essential contribution to understanding how dry-farming olive orchards may deal with drought combined with high UV-B or heat. [Display omitted] • WD and WDHS+UVB activate the same metabolite responses. • WDHS+UVB induce a stronger metabolite quantity change. • Polyphenols are the most involved to counteract the stress negative effects. • Lipophilic metabolites are more involved in physiological reestablishment after stress. [ABSTRACT FROM AUTHOR]

Extreme climate events are increasingly frequent, and the 2017 summer was particularly critical in the Mediterranean region. Olive is one of the most important species of this region, and these climatic events represent a threat to this culture. However, it remains unclear how olive trees adjust the antioxidant enzymatic system and modulate the metabolite profile under field stress conditions. Leaves from two distinct adjacent areas of an olive orchard, one dry and the other hydrated, were harvested. Tree water status, oxidative stress, antioxidant enzymes, and phenolic and lipophilic metabolite profiles were analyzed. The environmental conditions of the 2017 summer caused a water deficit in olive trees of the dry area, and this low leaf water availability was correlated with the reduction of long-chain alkanes and fatty acids. Hydrogen peroxide (H2O2) and superoxide radical (O2•–) levels increased in the trees collected from the dry area, but lipid peroxidation did not augment. The antioxidant response was predominantly marked by guaiacol peroxidase (GPOX) activity that regulates the H2O2 harmful effect and by the action of flavonoids (luteolin-7-O-glucuronide) that may act as reactive oxygen species scavengers. Secoiridoids adjustments may also contribute to stress regulation. This work highlights for the first time the protective role of some metabolite in olive trees under field drought conditions. [ABSTRACT FROM AUTHOR]

Climate change is increasing the frequency of heat waves accompanied by drought episodes. These challenges are increasing in the Mediterranean basin, where Olea europaea L. has an important ecological and economic role. Olive breeding programs have been focused on highly productive cultivars, while ancient cultivars may present higher tolerance to drought and heat resilience. Therefore, it is important to select traditional cultivars that may give reliable performances under the emerging climate change scenarios. In the present work, the differential physiological response of economically important traditional Portuguese olive cultivars, Cobrançosa, Cordovil de Castelo Branco (C.C. Branco), and Cordovil de Serpa (C. Serpa), to drought combined with heat are evaluated. Stress treatment had lowest impacts on water status in Cobrançosa. Also, this cultivar was less affected regarding pigments content, maximum and effective quantum yield of photosystem II (F v /F m and Φ PSII ) and exhibited higher ability to trigger an antioxidant response. C.C. Branco was the most sensitive cultivar in response to pigments (carotenoids), F v /F m and Φ PSII , and cell membrane stability. Principal component analysis suggested that Cobrançosa has high potential to withstand climate change events, particularly drought combined with heat episodes, followed by C. Serpa and C.C. Branco. [ABSTRACT FROM AUTHOR]

• Cobrançosa olives are richer in organic acids, esters and carbohydrates. • C.Serpa olives present higher levels of phenolic compounds. • Stress modulates olives' phenolic/lipophilic contents in a cultivar-dependent way. • C.Serpa olives have higher stress susceptibility than Cobrançosa and C.C.Branco. • Olives can be enriched in bioactive compounds in response to environmental stresses. The awareness of the functional and nutraceutical properties of olives and olive oil bioactive constituents contributed to oliviculture recent increase. Olives' metabolism and nutritional quality are determined by how the olive-tree is coping to climate change-related episodes, which increasingly occur in the Mediterranean. We characterize the most relevant lipophilic and phenolic compounds of olives from Olea europaea cultivars [Cobrançosa, Cordovil de Castelo Branco and Cordovil de Serpa (C.Serpa)] exposed to drought + heat. Olives from the three cultivars presented a similar qualitative profile but differed in their relative richness. Cobrançosa olives are richer in organic acids, esters and carbohydrates, while C.Serpa olives have higher levels of phenolic compounds, particularly under control conditions. Drought + heat changed the quantitative profile of olives, in a way dependent on the cultivar, and C.Serpa olives showed the highest stress susceptibility. Climate change-related conditions stimulate the accumulation of relevant bioactive compounds in olives, contributing to increasing its nutritional value. [ABSTRACT FROM AUTHOR]