Beneath The Bark: The Chemistry of The Olive Tree

Keywords: alternative bearing, phytohormones, phenolic compounds, oleuropein, antioxidant, osmotic adjustment, heat shock proteins, RuBisCO isoforms

Abstract

The olive tree’s long history as a staple tree of the Mediterranean is deeply intertwined with its chemistry. From serving as the backbone to entire cuisines to having astonishing therapeutic uses still shrouded in mystery, Olea europaea has without a doubt shaped the landscapes it populates in more than one way. Yet, beneath its bark, the olive tree employs chemistry in a whirlwind of metabolic processes that allow it to thrive regardless of extreme temperatures, soil conditions and pathogens, all while bearing its characteristic fruit in a timely manner. Pathogens that attempt to weave their way into the tree are met with a defensive wall of phenolics. Drought and salinity are equally ineffective in bringing the tree down, due to its advanced systems of water-retention hormones, osmoprotectants, and antioxidants. If temperatures rise or drop, the olive tree has an array of adapted enzymes and other proteins to preserve membrane integrity and photosynthesis. All these adaptations serve to make Olea europaea a model which we can inspire ourselves from for designs that can revolutionize fields from the food to the healthcare industry.

Introduction

Olea europaea has thrived along the Mediterranean coast since the dawn of some of the earliest civilizations—over 6,000 years ago. Throughout its expansive history, olive trees have gradually been domesticated, as humans selected for traits that facilitated agriculture and produced greater crop yield. There are currently six wild olive subspecies, and their genomes still act as the genetic source for the hundreds of varieties of domesticated olive trees grown today. Although Olea europaea is thought to have originated in the Mediterranean, many of its wild subspecies have expanded their ranges well beyond their native sea, to parts of Africa and Asia (Fig. 1) (Besnard et al., 2018). Inextricably tied to the olive tree’s history is its chemistry. The earliest evidence of olive oil production dates back roughly 6,500 years, making it one of the oldest known plant-derived oils in human history (Hashmi et al., 2015). Yet beyond its role in producing a staple food, Olea europaea has a long history of uses in traditional medicine—many of which are active areas of scientific research today. In fact, the secondary metabolites it produces have been used to treat anything from diabetes and hypertension to respiratory tract infections and intestinal diseases (Hashmi et al., 2015). But why would the olive tree invest in this plethora of chemicals? In other words, what’s in it for the tree itself? To better understand this, we must take a deeper dive into how the olive tree defends itself, endures drought, salinity, cold, and heat, and ultimately produces the distinctive fruit that has shaped human culture for millennia.

Fig. 1. The range of the six wild subspecies of Olea europaea [Adapted from Besnard et al., 2018].

The Olive Tree’s Guide to Making Babies

The goal for a tree (or any species for that matter) is to survive and produce offspring. Although growth and reproduction compete for the same nutrients, the olive tree has developed its own strategy to ensure both, sacrificing neither one for the other. Like many other fruit trees, it does so by undergoing biennial bearing.

This phenomenon, also known as alternative bearing, is characterized by an ON-year and OFF-year. As the name suggests, during the ON-year, a heavy crop of fruits is produced. This large quantity acts as a nutrient sink and consumes carbohydrates, hormones, and nutrients, preventing buds from forming. The tree becomes taxed and undergoes physiological stress. The next year—the OFF-year—the tree takes a break and replenishes its resources, focusing on vegetative growth. It forms new buds, to prepare for the ON-coming year’s fruit crop once again (Fig. 2). In some cases, olive orchards can go from producing 30 tons/ha of fruit to 5 tons/ha. But what drives such a dramatic difference? And why does the olive tree even undergo such a mechanism? Although the physiological underpinnings are still not fully understood, this cycle seems to be an adaptation from the olive tree to avoid nutrient depletion (Dastkar et al., 2020). The guiding mechanism will be explored by examining the endogenous factors; then, we will consider the role of environmental stress; and finally, investigate the advantages of such an evolution.

Fig. 2. The biennial bearing cycle of a fruit tree, illustrated over a 4-year period (Campbell & Kalcsits, 2024).

Internal Signals

The characteristic reproductive cycle in olive trees is an interplay of endogenous hormones and carbohydrates, where a bud—containing huge amounts of differentially expressed genes—must take the crucial decision to become either a flower or a leaf. During an ON-year, the growth of the olive fruit inhibits flower bud differentiation—the process where a plant starts producing flowers instead of leaves. This is because the fruit seed produces inhibiting phytohormones—plant hormones—called gibberellin, which travel to the buds. These gibberellin levels are maintained until harvest (Dastkar et al., 2020). Growing a large crop of fruit is very energy-intensive and depletes the plant’s carbohydrate and mineral reserves. It also triggers the production of the stress hormone, abscisic acid. To manage this internal stress, the olive tree activates pathways such as photorespiration, to prevent damage (Dastkar et al., 2020). The gibberellin phytohormones, combined with energy depletion, suppress the expression of flowering genes. This sets up the subsequent OFF-year, where the plant is allowed to recover. The carbohydrate and mineral resources are thus rebuilt. With the inhibitory signal gone, flowering genes can now be expressed, leading to a bloom that ensures the next ON-year (Campbell & Kalcsits, 2024).

External Factors

Under normal conditions, the alternate bearing cycle is different for each plant, depending on its balance between the ON/OFF-years and its endogenous factors. However, the general framework guiding the phenomenon is not so rigid: it adapts to climate changes. Environmental stressors can damage flowers, cause olive fruits to abort, or affect carbohydrate storage. Frost, drought, or pests can create an energy conflict, and the plant must choose where to invest its limited resources. Drought especially reduces photosynthesis, limiting the tree from replenishing its reserves. Thus, an OFF-year can be induced in a whole orchard, and even in an entire region (Campbell & Kalcsits, 2024). Temperature also plays a part: low temperatures below 9°C are crucial for flower differentiation, bringing flower buds out of their dormant state. Therefore, in warmer regions, periods of chilling temperatures trigger the massive onset of flower buds, leading to synchronized alternate bearing (Lavee, 2007). While stressors create this synchronicity, on the other side of the spectrum, ideal pollination weather can produce a higher-than-normal crop load, thus also reinforcing the ON-OFF cycle (Campbell & Kalcsits, 2024).

It’s Baby-Making Season!

To be able to live up to thousands of years, the olive tree must be extremely long-term oriented. That is why it has learnt to recover from stress by sacrificing consistent fruiting, and instead, focus on growing stronger (Benjeddou et al., 2019). Not only is alternate bearing a strategy for nutrient management, but it also serves other reproductive purposes. In cultivars that undergo this phenomenon, there is greater flower pollination and fruit retention as opposed to annual cultivars. Since olive trees are wind-pollinated, the massive quantities of buds during the ON-year allow the air to be saturated with pollen. This increases the probability of successful cross-pollination, which would lead to more flowers becoming fruit and better-quality seeds (Campbell & Kalcsits, 2024). This cycle is related to that of masting, an adaptation where trees such as oaks produce a massive, synchronized seed drop every few years as a form of resource budgeting (Goldschmidt, 2005). Similarly to masting trees, alternate bearing may be an adaptation to predators—this is called predator satiation. During the ON-year, the massive crop overwhelms predators, leaving them too many fruits to consume. The leftover seeds will have the chance to germinate into new plants. During the OFF-year, little fruit is produced, meaning the predators, looking to eat their fill, find themselves starving. Without food, their population crashes (Bogdziewicz et al., 2024). Thus, alternative bearing can be understood as a homeostasis phenomenon.

Great Defenders: Olive Tree Defense Against Herbivores, Pathogens, and Oxidants

Olive trees, like many other plants, need to defend against predators (in this case herbivores), pathogens, as well as stress such as oxidants. The olive tree is a unique tree that has adapted to its specific conditions by using phenolic compounds to fight against these threats to the tree’s survival. Phenolics are a group of chemical compounds characterized by a chemical structure consisting of an aromatic ring and one or more hydroxyl group. This group includes compounds such as oleuropein, hydroxytyrosol, tyrosyl, and verbascoside. Figure 3 depicts the chemical structure of some of the phenolic compounds found within the olive tree.

Fig. 3. Chemical structures of phenolic compounds commonly found in olive trees (Image by Author).

Oleuropein is a phenolic compound of specific importance in the defense of the olive tree. It is a compound consisting of an elenolic acid linked to an ortho-diphenol hydroxytyrosol by an ester bond and bonded to a glucose molecule by a glycosidic bond (Figure 4) (Otero et al., 2020).

Fig. 4. Chemical structure of Oleuropein (Şahin & Bilgin, 2017).

Understanding phenolic compounds, with a focus on oleuropein, allows for a greater understanding of how defense works in the olive tree.

Phenolic Compound Synthesis

To understand the role of phenolic compounds in tree defense, it is essential to first understand how these compounds are synthesized and where they are abundant in the tree. Oleuropein is typically abundant in the leaves of olive trees and can be found in high concentrations in olive leaf extracts (OLEs). A greater concentration of defensive compounds in the leaves is logical since the leaves are typically most vulnerable to stresses and predators. The biosynthesis of oleuropein follows a complex metabolic pathway that starts with mevalonic acid and progresses through intermediates such as geraniol, 10-hydroxygeraniol, iridiol, to yield oleuropein (Otero et al., 2020). This process is depicted in Figure 5, which demonstrates all the compounds that are formed before the final product, oleuropein.

Fig. 5. Metabolic pathway leading to biosynthesis of oleuropein (Otero et al., 2020).

Since this process starts with the synthesis of geraniol, it is catalyzed by geraniol synthases (Hassen et al., 2015). The synthesis of other phenolic compounds are derivatives of pentose phosphate, shikimate, and phenylpropanoid pathways, which are similarly complex pathways (Talhaoui et al., 2015). So, if the biosynthesis of these compounds is complex, what benefit does the olive tree gain from doing so? The answer to this lies in the importance of the defensive phenomena that these compounds enable.

Herbivore Defense

The very thing that makes olive trees so infamous—its delicious fruits—can also be the tree’s downfall. Herbivores like sheep, goats, and cattle enjoy snacking on the leaves of the olive tree, as well as the olive fruit itself. This dilemma means that the olive tree needs to adopt a strategy to defend against these hungry herbivores. Luckily, herbivores do not enjoy eating bitter foods. Thus, the olive trees have developed a bitter taste to lower the number of leaves that are eaten. The bitterness of the leaves can mostly be attributed to compounds found in OLEs. Studies have found that when oleuropein is removed from these OLEs, the bitter taste is eliminated (Ozturk, 2014), leading to the conclusion that oleuropein specifically, is responsible for most of the bitter taste. As the fruits of the tree mature, they become less vulnerable, meaning it is less necessary for them to be bitter. This decrease in vulnerability triggers the oleuropein to be converted to elenolic acid and demethyloeurupein as the fruit ripens (Ozturk, 2014).

Pathogen Defense

It is important for olive trees to be resistant to microbes; as well as their derivatives and the diseases associated with them. Phenolic compounds play a significant role in how the tree executes this. Resistance to pathogens, including Xyella fastidosa and Phythora megasperma, have been associated with phenolic compounds, which include tyrosol and verbascoside (Paskovic et al., 2025). More specifically, pathogen defense can be analyzed through the olive tree’s response to leaf spot disease, which is caused by Spilocaeo oleagina. Spilocaeo oleagina is a pathogen causing widespread fungal disease which weakens olive trees. This is due to premature defoliation, which disrupts photosynthesis and reduces fruit production (Buonaurio et al., 2022). It is implied that phenolic compounds are the main mechanism of defense against Spilocaeo oleagina and other pathogens common to olive trees. With Spilocaeo oleagina, this seems to be due to the inhibition of pectinases, as well as some phenolic compounds being precursors to phytoalexins (Rahioui et al., 2013). Phytoalexins are compounds that are toxic to pathogens and are generally produced on demand in response to detection of infection. Since phenolic compounds can be precursors to phytoalexins, the production of phytoalexins is faster, giving the olive tree a quicker response to pathogens, and ultimately helping in the fight against infection. Olive leaf extracts also seem to help defend against pathogens. A study by Al-Rimawi and colleagues (Al-Rimawi et al., 2024) shows that OLEs, including oleuropein, are effective against a wide range of pathogens, including viruses, bacteria, and even parasites. Specifically, the study found strong antimicrobial activity against both gram-positive and gram-negative bacteria, as well as mycoplasma. These OLEs were particularly effective against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. The reason for the antimicrobial activity is not completely understood. However, it is proposed that it is due to the presence of ortho-diphenic systems (catechins) in OLEs. Furthermore, it is suggested that oleuropein may interfere with production pathways of amino acids associated with the growth of certain microorganisms and may stimulate phagocytosis as an immune response (Al-Rimawi et al., 2024).

Antioxidants

Abiotic stresses such as drought and extreme temperatures can reduce photosynthesis and produce reactive oxygen species, often exceeding the plant's thresholds (Hasanuzzaman & Fujita, 2022). This increase in production demands an increase in antioxidants to counteract the highly reactive oxygen radicals being formed. As climate change increasingly worsens, these abiotic stresses become more prevalent and test the effectiveness of the tree’s antioxidative properties. This is why it is essential for the olive tree (and all plants) to have strong antioxidants. In the olive tree, these antioxidants come in the form of phenolic compounds. The strong antioxidant activity of phenolic compounds can be seen through their strong reducing power and radical scavenging abilities. The strength of the antioxidant is mainly dependent on the number of hydroxyl groups found in the compound (Xie et al., 2015). In oleuropein, the presence of hydroxyl groups prevents oxidation and adds to its electron donating ability, which makes it a strong radical scavenger. Antioxidants also influence gene expression, which can allow plants to adapt better to their surroundings (Kasote et al., 2015).

Allelopathic Effects

Allelopathy is a phenomenon where a plant releases chemical compounds that inhibit the survival of nearby organisms. Allelopathy can be important for the survival of the olive tree, as it can help to eliminate competition between the tree and nearby organisms. Oleuropein and other compounds found in OLEs have been found to have allelopathic effects, specifically with respect to seed germination. This is believed to be attributed to phenolic compounds, as well as alkaloids, amino acids, carbohydrates, terpenoids, and flavonoids (Zairi et al., 2020). These allelopathic effects play just a small but important role in a complex system of phenomena associated with olive tree defense.

Chemical Responses of Olive to Drought, Salinity, and Cold

Osmotic Adjustment and Water Movement

Under salinity or drought, leaf water potential falls, and cells lose water. Osmotic adjustment is an additional adaptive mechanism for olive trees in response to severe conditions. It involves organic compounds such as soluble carbohydrates or amino acids. These compounds, called osmoprotectants, can raise the internal solute concentration so that water potential inside becomes more negative and water is retained. Olive leaves contain many sugars, with glucose and mannitol being the most abundant, and under salinity, mannitol rises strongly while glucose and fructose may show minor change. Mannitol is a six-carbon sugar alcohol whose many hydroxyl groups make it highly soluble in water. In solution, each mannitol molecule is a solute particle that adds to the cytosolic osmolarity without reacting with enzymes or membrane lipids. El Yamani and Cordovilla report from salinity studies in the olive tree that investigators observed early and preferential carbon allocation to mannitol and linked this production with osmotic protection in salt exposed plants. These results identify carbohydrate adjustment, especially mannitol, as a central component of osmotic adaptation in olives under salinity. Proline, which is an amino acid, also functions as an osmoprotectant in olives. Trabelsi reported (as cited in El Yamani & Cordovilla, 2024) that full irrigation of a 26-year-old olive orchard (Chemlali’) with saline water increased proline concentration in several organs, compared to irrigation with tap water. Pot studies with Turkish cultivars Gemlik, Kilis, and Ayvalik likewise found that proline levels rise, under a sodium chloride solution of 100 to 200 mM, over about 14 to 21 days. Additional work notes coordination between proline levels and mannitol dehydrogenase (an enzyme involved in mannitol metabolism) activity, and reports that proline can aid hydration. Responses are not uniform across genotypes, since some cultivars show little change or even a decrease in proline under salt, indicating that osmotic adjustment can also rely on potassium and other organic solutes (El Yamani & Cordovilla, 2024).

Olive trees also regulate water movement using molecules in membranes and simple chemical signals. Abscisic acid (ABA) is a natural plant hormone that rises during periods of stress and can be applied to leaves to prime this response. In practice, abscisic acid increases soluble sugars while lowering starch, shifting minerals and biomass toward roots, especially potassium, nitrogen, and boron. It also strengthens osmotic adjustment and improves whole-plant water-use efficiency (Brito et al., 2020). For clarity, Figure 6 depicts the chemical structure of abscisic acid, emphasizing the conjugated ring system and terminal carboxyl group that permit receptor binding and trigger signaling pathways affecting carbohydrate and ion partitioning.

Fig. 6. Chemical structure of ABA, highlighting the cyclohexenone core and side chain with carboxyl group. Regions commonly implicated in receptor binding and bioactivity are indicated (Finkelstein, 2013).

Inside the leaf, aquaporins are membrane channel proteins that speed the passage of water, and in some cases, carbon dioxide, across cell membranes. In the olive tree, the plasma membrane aquaporins OePIP1.1 and OePIP2.1 change their expression with drought and recovery in parallel with gas movement through the leaf. Lower leaf water potential during stress can reduce aquaporin activity, which slows water movement between cells and lowers mesophyll conductance to carbon dioxide, so the rate of photosynthesis falls even if stomata are not fully shut. After rewatering, aquaporins reopen, water flow and mesophyll conductance recover quickly, and carbon fixation restarts at a lower water cost (Perez-Martin et al., 2014). ABA priming helps keep solute patterns and aquaporin function stable, shortening the recovery time (Brito et al., 2020).

Antioxidant Defense Activity

When water is scarce or when salinity builds up, olive leaves still capture light, but stomata close to save water, and less carbon dioxide enters. With less carbon dioxide available for the Calvin cycle, the use of captured energy slows. The extra energy is passed to oxygen and forms reactive oxygen species (ROS), such as superoxide and hydrogen peroxide. These signals appear in leaves and sometimes in roots, together with the plant’s own antioxidant responses measured in stressed tissues (El Yamani & Cordovilla, 2024). In cold weather, the situation is similar. Low temperature slows many enzymes and makes photosynthesis less balanced, so oxidative pressure rises and olives respond by turning on antioxidant systems across tissues and cultivars (Petruccelli et al., 2022). Figure 7 shows typical freezing injury in the field, from leaf chlorosis and browning to whole tree defoliation and deep cracks in woody tissues.

Fig. 7. Symptoms of freezing stress in olive. A) leaves chlorotic and brown. B) total defoliation. C) extensive cracks on the trunk. D) extensive cracks on branches. (Petruccelli et al., 2022).

To limit this chemistry before it damages membranes and photosystems, olive trees increase the activity of antioxidant enzymes that process these reactive molecules. Superoxide dismutase converts superoxide into hydrogen peroxide. Catalase and ascorbate peroxidase then remove hydrogen peroxide in different parts of the cell (Sofo, 2015). Under salt or limited water, olive leaf assays often report higher activity of these enzymes along with better protection of photosynthesis and lower injury in tissue measurements (El Yamani & Cordovilla, 2024). During cold exposure, reviews of olive physiology describe the same antioxidant system. They are described as central parts of acclimation that limit oxidative damage when temperatures drop. Non-enzymatic antioxidants act in parallel with enzymes to buffer reactive oxygen. Ascorbate and glutathione accept and donate electrons to keep ROS scavenging reactions running, and in olive trees, both their total concentrations and redox ratios shift in ways that protect chloroplast pigments and proteins (Petruccelli et al., 2022). Tocopherols in thylakoid membranes limit oxidation of membrane lipids. Carotenoids, including xanthophylls, quench chlorophyll excitation and support non-photochemical quenching, releasing excess light energy as heat and lowering the chance of photo-oxidation (El Yamani & Cordovilla, 2024).

Membrane Lipid Remodeling and Surface Lipids

Stress also leads to the remodeling of membrane lipids that help cells keep working. In cold conditions, the olive tree shows a shift toward a higher share of unsaturated fatty acids. Figure 8 illustrates this routing. Cold raises the activity of OeFAD8, a plastid omega-3 fatty acid desaturase, that introduces an additional double bond and enhances the production of C18:3, a linolenic acid. And OeOSM, a lipid trafficking protein, is also activated, which helps move these lipids so that part enriches membranes to keep them fluid, part goes to storage oil bodies, and part is sent to the surface to build the cuticle (D’Angeli et al., 2016). More double bonds keep membranes fluid at low temperature, support the function of membrane proteins, and reduce leakage. Reviews of the olive tree’s cold physiology present this remodeling as a central element of tolerance and relate it to better maintenance of photosynthetic performance and lower injury scores during chilling or freezing events (Petruccelli et al., 2022). Under salinity, some leaf studies report the opposite trend, with lower synthesis of polar lipids and a reduction in linolenic acid that decreases overall unsaturation, a response linked to ionic and oxidative constraints rather than fluidity demand (Zarrouk et al 1995). With drought, the emphasis shifts toward surface barriers. At the leaf surface, drought brings changes in cuticular wax and related lipids that strengthen the barrier to water loss (see our essay on physics for more about that). In better acclimated leaves, studies also report lower values of lipid peroxidation markers, which link surface chemistry and internal membranes with improved damage control during stress (Parri et al., 2024).

Fig. 8. Cold-induced lipid routing in olive. Cold upregulates OeFAD8 and OeOSM, increasing C18:3 (linolenic acid). C18:3 is partitioned to membrane lipids to maintain fluidity, to plastoglobuli and then oil bodies as triacylglycerols (TAGs), and to cutinosomes that reach the cell wall to support cuticle formation. OeOSM assists with lipid trafficking (D’Angeli et al., 2016).

A Scathing War: How the Olive Tree Deals with Heat Stress

Nestled within the rolling hills of the Mediterranean, Olea europaea experiences summer after summer of scorching temperatures. Although the tree as a whole may seem unfazed, a microscopic battle wages beneath the surface. Within a cell, increased temperatures are catastrophic throughout the cytoplasm: proteins denature and form dangerous aggregates, enzymes stop working, membranes become too fluid, and microtubule networks fall into disarray (Estravis-Barcala et al, 2019). Cells can no longer grow and divide effectively either, as the amount of water they retain is reduced. Heat stress also drastically impairs crucial aspects of photosynthesis, such as the carbon-fixing enzyme RuBisCO, the light-absorbing photosystem II, and the thylakoid membrane (Estravis-Barcala et al, 2019; Haworth et al., 2018). Yet in the face of this cellular calamity, how do the olive tree cells survive, let alone divide and photosynthesize?

The answer lies in a unique array of cellular mechanisms that help the olive tree keep cool when temperatures soar (not literally cool in this case—see our essay on physics for more about that). In fact, Olea europaea maintains up to 80% of its photosynthetic rate at 40°C, and its leaf cuticles remain intact until 55°C—temperature limits that are at least 5°C higher than those of many other species (Bongi & Palliotti, 1994).

The First Line of Defense - Heat Shock Proteins

Heat shock proteins (HSPs) are a class of chaperone protein, meaning they assist in the proper folding of proteins (Estravis-Barcala et al, 2019). HSPs are highly evolutionarily conserved across animals and plants alike and are essential to protein folding as a whole—even under normal conditions, the folding of some proteins would be impossible without them (Araújo et al., 2019). However, under heat stress, the heat shock transcription factors (HSFs) that regulate HSP expression are activated in greater numbers. This increases the cellular concentration of HSPs, which helps slow the denaturation and aggregation of proteins, and can even increase membrane integrity (Al-Whaibi, 2011). 

Plants have many types of HSPs that can be classified according to their size: HSP100, HSP90, HSP70, HSP60, and small heat shock proteins (sHSPs) (Al-Whaibi, 2011). Broadly speaking, they all work in a similar fashion: by binding the exposed hydrophobic patches of denatured proteins, HSPs halt the process of misfolding and give proteins a chance to refold correctly (Fig. 9) (Lodish et al., 2021). Oftentimes, HSPs work together in larger complexes to accomplish this goal. Some HSPs, such as sHSPs, also play a role in degrading proteins that are irreparably misfolded (Al-Whaibi, 2011).

Fig. 9. The general mechanism by which an ATP-dependent heat shock protein (in this case, Hsp70) refolds a misfolded protein: 1) A misfolded protein binds Hsp70 in its open, ATP-bound conformation; 2) ATP is hydrolyzed to ADP, inducing a conformational change that closes Hsp70; 3) The misfolded protein is now locked in place and is given a chance to refold properly; 4) ADP leaves as a new ATP binds Hsp70, releasing the protein; 5) If the protein is still misfolded, the cycle may repeat [Adapted from Lodish et al., 2021].

But if nearly all organisms express HSPs, how do they allow olive trees to withstand significantly greater temperatures? After all, there is nothing remarkable about olive tree HSPs: the mechanism by which they help fold proteins is the same as for any other plant. What is astounding, however, is the olive tree’s HSP diversity. In fact, this tree has 12 genes that encode specifically for HSP90, which is nearly twice as many as other common plants, such as cottonwood and tomato (Bettaieb et al., 2020). Moreover, these 12 genes do not produce identical HSP90 mRNA transcripts—rather, each transcript results in a slightly different protein (Fig. 10) (Bettaieb et al., 2020). 

Fig. 10. 3D structures of the 12 olive tree HSP90 (OeHSP90). Spirals represent α-helices, strips with arrows are β-sheets, and thin loops are coils. Note the small differences in each of their structures, especially in their coils (Bettaieb et al., 2020).

This slight difference in the HSP90 structures may allow each protein to bind unique co-chaperones or to home in on specific organelles, which suggests that each is adapted to a particular role. Perhaps some are best at breaking up cytosolic protein aggregates, whereas others efficiently increase membrane integrity. Some may be more important during critical stages in the early development of the olive tree—others may only shine once the tree has fully matured. The point is that through duplication of what was likely one HSP90 gene, functional redundancy was slowly introduced into the olive tree’s genome. This allowed one of the genes to mutate as the other conserved its initial function. Eventually, the mutating gene would be selected for, as it fulfilled some function of HSP90 more efficiently than the original one (Bettaieb et al., 2020). The final product of this evolutionary dance is a varied bank of HSP90 genes at the olive tree’s disposal—reinforcing its first line of defense against an endless onslaught of heat.

A Tactical Decision — UV-Resistant Forms of RuBisCO

RuBisCo is the enzyme that catalyzes the fixation of CO₂ onto a sugar molecule. It is thus central to photosynthesis in all plants, which is why it is also the most abundant protein on Earth (Prywes et al., 2023). However, RuBisCO has a fatal flaw: its affinity for both CO₂ and O₂. When temperatures increase, plants are forced to close their stomata and absorb less CO₂. RuBisCO will thus begin binding more O₂ as CO₂ becomes scarcer and will catalyze a different reaction known as photorespiration. This reaction produces ROS that can accumulate and damage proteins. The increased UV radiation typically associated with heat stress only serves to worsen the problem by producing even more ROS. Under this barrage of oxidative stress, RuBisCO is eventually damaged, which dramatically impairs a plant’s ability to photosynthesize (Prywes et al., 2023).

Yet the olive tree can maintain greater photosynthetic rates than other species at high temperatures—so what is its secret? Olea europaea is capable of adjusting its RuBisCO to be less susceptible to oxidative stress. This can be achieved by inducing certain point mutations in the gene coding for RuBisCO (Pinheiro et al., 2014). However, certain olive tree varieties take this a step further. By post-translationally modifying RuBisCO under heat stress, they are able to decrease its susceptibility to ROS. In fact, the Giarraffa olive tree variety generates a multitude of RuBisCO isoforms—proteins with small modifications that slightly alter RuBisCO’s structure and function, allowing only the most stable and efficient isoforms to persist. These post-translational modifications, such as changes in oxidation state, folding, or carbamylation, help protect the enzyme from degradation and preserve its catalytic activity in the face of rising temperatures. Thus, by selectively retaining or producing isoforms better suited to stressful conditions, Giarraffa can sustain carbon fixation when most plants would experience severe photosynthetic inhibition. This mechanism of molecular resistance is a key tactic in combating heat-induced oxidative stress, especially in certain olive tree varieties (Piccini et al., 2021).

Conclusion

The olive ensures its overall survival by alternating between growing and reproducing, minimizing the depletion of its nutrients. Across fruiting, defense, and stress physiology, the olive tree’s success rests on a common chemical logic: it manages water, electrons, and membranes to keep cells functional while guiding reproduction. During fruit development and dispersal, the tree times hormone signals and metabolite flow to build oil-rich drupes, tune bitterness and aroma, and control germination. These chemical controls influence when animals eat the fruit, where seeds land, and when seedlings emerge. The same metabolic currency, including carbohydrates, phenolics, lipids, and small hormones, powers defense and stress tolerance. Phenolics such as oleuropein deter herbivores and microbes and scavenge radicals. Osmoprotectants like mannitol and proline help cells retain water. Abscisic acid and aquaporins coordinate water movement. Antioxidant systems and membrane remodeling keep photosystems and transport proteins intact under drought, salinity, and cold. Under heat, molecular chaperones from diverse heat shock protein families stabilize folding and limit aggregation, and adjustments to core enzymes, as UV-resistant or modified RuBisCO isoforms, help preserve carbon fixation. These strategies require metabolic investment and can divert carbon and minerals away from growth and reproduction. Expression varies with cultivar, stress intensity, and timing, which explains why traits such as proline accumulation or antioxidant capacity are not universal. Several of the same molecules that protect the tree, including oleuropein, hydroxytyrosol, tocopherols, and carotenoids, also benefit human health through antioxidant and anti-inflammatory activity.

Building on these findings, several accessible design ideas emerge across food, agriculture, materials, and healthcare. From the defense chemistry section, polyphenols with exposed hydroxyl groups suggest simple antioxidant additives for foods and beverages, gentler skincare preservatives, and supportive ingredients in wellness products. Bitter olive leaf extracts point to natural herbivore deterrents or seed coatings, and phenolics as precursors to phytoalexins inspire mild priming sprays that help crops mobilize pathogen defenses faster. From the drought, salinity, and cold section, mannitol and context dependent proline accumulation motivate selecting or breeding stress tolerant lines, exploring low cost osmoprotectant foliar feeds, and formulating edible oils or packaged foods with carotenoids and tocopherols to slow oxidation. Aquaporin inspired concepts include comparing water flow through small pore filters in school or community water projects, and cuticle mimicking wax sprays suggest simple leaf surface protectants. From the heat stress section, greater diversity of heat shock proteins supports short heat priming at the seedling stage to strengthen chaperone responses, and UV resistant Rubisco ideas motivate shade management and UV filter films to protect photosynthesis.