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.

Climatic extreme events, like droughts, heatwaves, and floods are becoming recurrent and represent a threat to agriculture, lowering plant growth and productivity. The Mediterranean region is a climate-change hotspot, where traditional agricultural systems, like olive groves, are particularly challenged. Both the traditional and intensive systems of olive culture coexist in the Mediterranean. Both systems differ in their demands for water and agrochemicals, but nowadays, the global inputs of agrochemicals and irrigation have increased to achieve high productivity and profitability. Finding sustainable alternatives to maintain high productivity under the ongoing climate change is urgent to meet the EU-Farm to Fork strategy and climate neutrality. Candidate eco-friendly alternatives include biostimulants. These are substances or microorganisms, that activate signaling cascades and metabolic processes, increasing plant yield, quality, and tolerance to stressors. These benefits include a better growth, nutritional status and water availability, leading to a decreased demand for irrigation and agrochemicals. In this review, we aim to present different types of biostimulants (e.g., seaweed, protein hydrolysates, humic substances, microorganisms and nanomaterials), their mode of action and benefits in agriculture. We also explore the current state-of-the-art regarding the use of biostimulants in olive culture, and their potential benefits to increase tolerance to (a)biotic challenges.

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.