Since the discovery of auxins as cell division factors a century ago, impressive scientific advances related to phytohormones have revolutionized plant sciences and human progress. This review examines the key features of the ten hormonal groups that operate in plants, here referred to as the ‘classical ten’: auxins, gibberellins (GAs), cytokinins (CKs), abscisic acid (ABA), ethylene (ETH), salicylates (SAs), jasmonates (JAs), brassinosteroids (BRs), peptide hormones (PEPs), and strigolactones (SLs). By leveraging historical data and sharpening the essentials of each hormonal group, their major functions are presented, with a discussion on what makes a compound a phytohormone and how it can be differentiated from hormone-like compounds and other signaling molecules. Hormonal receptors, long-distance transport, and differences between hormonal crosstalk, interactions, and complementation are discussed to illustrate the basics of hormonal action in plants.

Many holoparasitic plants are well-known for their negative impacts on crops, yet the underlying mechanisms behind the interaction between holoparasitic plants and their hosts are still poorly understood. This study investigates the role of stress-induced phytohormones on the relationship between field dodder (Cuscuta campestris) and lentil plants (Lens culinaris), a model for parasitic plant-host interaction in legumes. We evaluated the impact of parasitism on host phenology, vegetative growth, and yield. In addition, stress markers and spatiotemporal variations in endogenous levels of stress-related phytohormones were measured. Parasitism had a drastic effect on yield by accelerating plant phenology, enhancing plant senescence, and deregulating pod maturation. Moreover, an antagonistic relationship between jasmonates and abscisic acid (ABA) was observed in field dodder during the attachment of haustoria to the host, such that the content of the bioactive jasmonate, jasmonoyl-isoleucine (contrary to ABA), was very high in free haustoria (prior to attachment). Finally, the content of jasmonoyl-isoleucine increased in the host plant, although this defense response in young leaves was not sufficient to prevent severe loss of PSII integrity. This demonstrates that jasmonoyl-isoleucine is up-regulated in both free-haustoria field dodder and infested lentil plants, suggesting that this bioactive jasmonate form has a universal protective role in both sides of the interaction between parasitic plant and host.

BACKGROUND:Plant responses to drought stress include a complex variety of processes at the molecular, biochemical, and physiological levels that operate simultaneously in a specific spatiotemporal way at several organizational levels (including organelles, cells, tissue/organs, and the whole-plant level). SCOPE:A roadmap is presented to determine whether drought stress leads to leaf senescence using an integrative approach that considers the process at the whole-plant level. This is essential not only for detecting and monitoring the impact of the drought, but also, more importantly, for identifying whether the plant response is leading to leaf senescence and it is therefore adaptive (protective, indicating stress tolerance) or maladaptive (damaging, indicating vulnerability) to the drought stress. This has important implications for optimizing crop yield and quality (thus requiring urgent attention in current agricultural practices), as well as for environmental management and effective conservation strategies. The detection and monitoring of drought-induced leaf senescence will be discussed, disentangling dubious cases. Furthermore, there will be a focus on drought-induced senescence as an integral plant stress response and whether it indicates damage or protection. CONCLUSIONS:This integrative approach has the potential to help detect, monitor, and fully understand leaf senescence as a protective and adaptive process that plants have evolved to withstand drought stress in agricultural and ecological settings. Exploiting this knowledge and transferring it adequately will help improve crop yield as well as current environmental management programs.

The evolution of parasitic plants has been marked by a progressive relaxation of selective pressures associated with maintaining photosynthesis, resulting in a wide diversity in photosynthetic capacity within this group. In this study, we explored this diversity by examining several hemi- and holoparasitic plants, focusing on photoprotection. Our findings revealed a strongly conserved evolutionary association between vitamin E, PSII activity, and chlorophyll content in parasitic plants, with α-tocopherol consistently being identified as the predominant vitamin E form. To validate the antioxidant and photoprotective role of α-tocopherol in a plant with reduced photosynthetic capacity, we investigated the interaction between the stem holoparasitic plant field dodder (Cuscuta campestris Yunck.), which retains partial PSII activity and low chlorophyll levels, and its host, lentil plant (Lens culinaris Medik). This protective role, essential for controlling lipid peroxidation within chloroplasts, was demonstrated both in planta and in isolated chloroplasts from field dodder exposed to photoinhibitory conditions induced by the synthetic photosensitizer Rose Bengal and light. Notably, our findings highlight the final evolutionary step in the conserved role of vitamin E in photosynthesis and photoprotection as revealed through parasitic plants.

The response of plants to elevated atmospheric [CO2] is highly dynamic and influenced by developmental stage, yet its role in photosynthetic acclimation remains underexplored. This study examines the physiological and molecular responses of wheat (Triticum durum, var. Amilcar) to elevated [CO2] (700 ppm vs. 400 ppm) at two distinct developmental stages: the vegetative stage at the end of the elongation stage and the reproductive stage at the beginning of ear emergence (Z39 and Z51, respectively). Wheat plants at the developmental stage Z39, cultivated under elevated [CO2], maintained photosynthetic rates despite a carbohydrate build-up. However, at Z51, photosynthetic acclimation became more evident as the decline in Rubisco carboxylation capacity (Vcmax) persisted, but also stomatal conductance and diffusion were decreased. This was accompanied by the up-regulation of the CA1 and CA2 genes, likely as a compensatory mechanism to maintain CO2 supply. Additionally, hormonal adjustments under elevated [CO2], including increased auxin and bioactive cytokinins (zeatin and isopentenyl adenine), may have contributed to delayed senescence and nitrogen remobilization, sustaining carbon assimilation despite biochemical constraints. These findings highlight the developmental regulation of photosynthetic acclimation, emphasizing the need for the stage-specific assessments of crop responses to future atmospheric conditions.

Prevention is the most cost-effective strategy for managing plant invasions, which includes defining the potential of exotic species to inhabit different environmental conditions. The limiting similarity hypothesis suggests that resemblance to native species facilitates the establishment and spread of exotics in a non-native range. However, this similarity has rarely been quantified in terms of the physiological strategies used to cope with seasonal environmental variability. Here, we explored for the first time the multivariate ecophysiological similarity between an exotic species and the native community to assess where the invader might succeed. Specifically, we contrasted the physiological annual response of the declared potential invader Aptenia cordifolia relative to six coexistent native species in two contrasting environmental conditions (under canopy and at high irradiance) in a Mediterranean-type ecosystem. The invasive species exhibited distinct physiological responses, demonstrating partial alignment with native traits under specific conditions. At the high irradiance site, the exotic species was the least efficient at counteracting both summer and winter stresses; whereas in the under-canopy habitat, it exhibited greater ecophysiological dissimilarity from the native community. Our results score the potential of multivariate physiological analysis for guiding habitat prioritization in invasion management and biodiversity conservation in Mediterranean-type ecosystems.

The endemic Mediterranean marine angiosperm, Posidonia oceanica, stands out for being a biostructuring sea-grass species with a great importance in trophic relations and coastal erosion protection. This study aimed to understand the physiological response of this emblematic seagrass to multiple stresses, with an emphasis on evaluating the acclimatory capacity of juvenile leaves to low temperatures during winter in three sites with a contrasting exposure to heavy metals of anthropogenic origin in the Mediterranean coast near Cadaques (NE Spain). Heavy metal concentrations together with multiple physiological stress markers, including the capacity of photo-and antioxidant protection and the extent of lipid peroxidation, were evaluated. Shoots from the three studied sites accumulated foliar concentrations of heavy metals that were higher than reference threshold values, especially for Cu, which showed a decreasing concentration gradient from the coast to the open sea. The maximum photochemical efficiency of Photosystem II (PSII) (Fv/Fm ratio) of juvenile leaves was sensitive to low temperatures, despite values attained did not indicate damage to PSII, which was confirmed with studies of recovery of the Fv/Fm ratio and the absence of symptoms of photo-oxidative stress. However, the presence of heavy metals seemed to negatively influence PSII photochemistry, as sites with the highest Cu concentrations also showed the lowest Fv/Fm ratios during spring, even though water temperature had already warmed. Fv/Fm values attained were not recoverable after an extended dark acclimation period, thus indicating damage to PSII. Heavy metals did not seem to exert a negative synergistic effect with low temperatures but rather affected the physiological performance of newly produced juvenile leaves during spring. Despite the great capacity of this species to adapt to multiple stresses, results underscore the need to urgently reduce the current human footprint on seagrass meadows in the Mediterranean basin.

Inter-individual variability in fruit and seed production are crucial factors influencing species distribution, community dynamics, and the effective conservation of ecosystems, which often are shaped by complex environmental interactions. We assessed inter-individual variability on fruit and seed production in the Mediterranean shrub Cistus albidus, and how it is influenced by parasitism in a natural population. A huge inter-individual variability was observed in fruit and seed production, as well as in seed viability, without any clear relationship between these parameters in C. albidus plants growing in a Mediterranean ecosystem. However, parasitism reduced both seed production per fruit and seed viability in C. albidus, highlighting the negative impact of C. hypocistis on host reproductive success. Furthermore, identification of plant parasitism in the field unmasked some biases in the effects of nutrients observed in correlative analyses between seed nutrient contents and seed viability loss. This study provides new insights into parasitism, specifically focusing on the detrimental effects of the holoparasitic plant Cytinus hypocistis on the reproductive fitness of its host C. albidus, and highlights the importance of identifying the effects of parasitism in the study of inter-individual variability in fruit and seed production in Mediterranean ecosystems.

The quality of tomatoes is closely linked to their antioxidant content. However, the contribution of vitamin E to the total antioxidant capacity of these fruits remains unknown, along with its relationship with other components that benefit health. This study examined vitamin E content and composition and their correlation with the total antioxidant capacity in commercial tomato varieties, together with their modulation by abiotic stresses. We also assessed their relationship with other quality parameters such as total soluble sugars, titratable acidity, and sodium and potassium contents. A significant correlation was found between vitamin E content and the total antioxidant capacity, which was greatly influenced by the variety and abiotic stress. Furthermore, a strong association was found between vitamin E and potassium contents. We conclude that vitamin E, the total antioxidant capacity and potassium form a triangle of traits that can be coordinately selected to improve tomato quality.

BACKGROUND AND AIMS:The ripening process, characterised by chlorophyll degradation and carotenoids accumulation, culminates in senescence, affecting fruit quality and shelf life. However, certain fruits can undergo regreening, a phenomenon where chlorophyll reaccumulates, opposing the typical senescence process. This study aimed to investigate the influence of phytohormones and light on postharvest regreening in grapefruit (Citrus x paradisi Macfad.) and assess its occurrence in tomatoes (Solanum lycopersicum L.). METHODS:Cherry tomatoes (red and yellow) and grapefruits were treated with phytohormones (gibberellin, cytokinin, and their combination) under fluorescent light with sunlight background to evaluate regreening potential. In yellow tomatoes, additional light conditions (fluorescent, white and blue LED light) were evaluated. Colour changes were monitored using colorimetry. Regreening in yellow tomatoes was further assessed by quantifying chlorophyll and carotenoid contents. Firmness and weight loss were measured as senescence-associated changes in regreened tomatoes. KEY RESULTS:The combination of gibberellin and cytokinin under fluorescent light with sunlight background significantly induced regreening in grapefruits. Furthermore, regreening was observed for the first time in cherry tomatoes, albeit it was exclusively observed in yellow varieties when exposed to fluorescent light with sunlight background. Regreening became apparent after 20 days of light treatment and was characterized by a 45% increase in total chlorophyll content, reversing approximately 42% of the loss of green colouration. Despite restoring green pigmentation, the regreening process did not modulate other senescence-related parameters, such as firmness or weight loss. CONCLUSIONS:These findings highlight that regreening can occur in certain postharvest fruits, including grapefruits and yellow cherry tomatoes, under specific light and hormonal conditions. The absence of regreening in red cherry tomatoes, suggests that regreening is not only species- but also variety-dependent. Notably, this study represents the first observation of regreening in yellow tomatoes, where it results in a clear restoration of green colour through chlorophyll reaccumulation.

Most studies conducted under field conditions commonly contain unusual or deviant observations because of data variability usually driven by environmental stressors. However, due to low replication in most plant physiological studies, these observations are not considered essential to understand plant stress responses. By exploring the hormonal response of the native Mediterranean shrub Cistus albidus to a heat wave occurring in the Mediterranean during the summer of 2023, we found five biological outliers with extraordinarily elevated endogenous concentrations of the bioactive jasmonate, jasmonoyl-isoleucine. Outliers were identified by calculating the median and the interquartile range of the population, with outliers being found beyond the lower and upper boundaries denoting the first (Q1) and third (Q3) quartiles in data distribution. By following the behavior of these outliers during recovery from drought stress in the following months, we observed a differential resilience response in these individuals compared to the rest of the population. Despite outliers (showing sixfold higher jasmonoyl-isoleucine contents during the heat wave) did not exhibit enhanced stress tolerance, they showed a completely differential recovery response during autumn, which was characterized by reduced leaf growth, suggesting a priming effect for future stress acclimation, so that exposure to heat stress improved subsequent plant stress response. Reduced leaf growth during recovery from summer stress may well respond to a more conservative strategy to prevent water loss during subsequent water deficits. These findings underscore the importance of specifically using biological hormonal outliers in ecophysiological studies for a comprehensive understanding of plant stress responses.

Climate change is affecting fruit tree dormancy progression around the world. Temperature increase during winter could hinder the attainment of the climatic requirements that are needed to have a correct dormancy release. In this context, knowing the chill accumulation needed by each cultivar is essential to make correct decisions on the cultivar selection for each region. Searching for new tools and alternatives is also basic to adapt current cultivars to this new scenario. For this purpose, chill and heat requirements have been assessed for ten relevant apple cultivars using the forcing methodology and their correlation with full bloom date. Bud break response at different chilling accumulations has been modelled with logistic curves. In this work, a climatic study of a highly productive apple region in a Mediterranean agroecosystem revealed a decrease in chill accumulation during the last decade. In this context, cultivars whose chill requirements were below 40 chill portions ('Lory (R)', 'Pink Lady (R)', 'Luiza' and 'Galy (R)') are highly recommended for the future, showing a high bud break percentage at low chilling accumulation. Other cultivars currently grown in the region ('Gala' or 'Fuji') could present problems in the most critical climate change scenarios. Rootstocks did not show any influence on the modulation of chilling requirements. Furthermore, chilling, rather than heat requirement, was the most important parameter determining the flowering date. This study will help growers in decision making for the selection of the most appropriate cultivar under future climatic conditions, thus avoiding problems related with a non-optimal chill accumulation.

Background and Aims Rapid, large-scale monitoring is critical to understanding spatiotemporal plant stress dynamics, but current physiological stress markers are costly, destructive and time-consuming. This study aimed to evaluate the potential of machine learning to non-destructively predict leaf betalains - yellow to reddish pigments unique to Caryophyllales species - for the first time, and to explore intra-individual variation in betalains in a clonal species and its role in responding to stressful periods.Methods We characterized the betalainic profile of an invasive clonal plant for the first time, Carpobrotus edulis (the cape fig), via high-performance liquid chromatography. We measured multiple stress markers over a year, including betalain content using our optimized method, where the species is spreading. Additionally, 3735 digital images at the leaf level were taken. Machine learning regression algorithms were trained to predict betalain accumulation from digital images, outperforming classic spectroradiometer measurements.Key Results Betalain content increased sharply in non-reproductive ramets during extreme abiotic conditions in summer and during senescence in reproductive ramets. The stress markers revealed a strong intra-individual functional mosaic, underscoring the importance of spatiotemporal dimensions in stress tolerance.Conclusions We developed a scalable, non-destructive tool for betalain research that integrates digital imaging with machine learning. This approach opens new possibilities for understanding spatiotemporal stress responses, particularly in clonal plant systems, using artificial intelligence.

Intensive European forestry practices contribute to soil degradation and nutrient depletion, compromising tree health and ecosystem stability. However, the influence of soil nutrient scarcity on tree physiological responses during drought remains unclear, particularly in Pinus radiata D. Don plantations, where it may impair needle function and overall tree health. We investigated how soil nutrient availability influences leaf-level physiological strategies during drought by comparing same-aged needles from two P. radiata stands with contrasting management stages and ages: (i) trees (≈20 years), likely to be clear-cut at 30-35 years (herein managed), and (ii) trees (>45 years) not clear-cut at the typical rotation age (herein abandoned). During the severe summer drought of 2022, both stands exhibited downregulation of the photosynthetic apparatus, indicating impaired photosynthetic performance under drought. However, their leaf-physiological responses to nutrient scarcity diverged. Managed trees exhibited dependence on soil nutrients, with reduced photosynthetic performance under nutrient-poor conditions. In contrast, abandoned trees showed relative independence from soil nutrients, maintaining photosynthetic function even under nutrient-poor conditions. This highlights a trade-off: younger, managed trees may enhance photosynthesis under optimal nutrient conditions but are more susceptible to nutrient imbalances and environmental stress. In turn, older, abandoned trees appeared to buffer the effects of drought and nutrient scarcity through age-related physiological traits. Our findings underscore the physiological value of mature stands. Furthermore, higher soil organic carbon and vegetation diversity in abandoned stands suggest that management cessation may enhance long-term ecosystem resilience. These results emphasise the importance of integrating soil–leaf interactions into sustainable forest management. ### Competing Interest Statement The authors have declared no competing interest. Ministerio de Ciencia e Innovación, https://ror.org/05r0vyz12, PID2020-113244GB-C21, PID2020-113244GA-C22, RED2022-134577-T, RED2024-153822-T EU Horizon 2020, 101000289 Basque Government, https://ror.org/00pz2fp31, BERC 2022-2024, UPV/EHU-GV IT-1648-22

Aerobic organisms are prone to oxidative stress when meeting their metabolic and developmental demands, particularly under stressful environments. Here, we aimed to elucidate survival strategies to withstand an extreme drought stress in a clonal plant species at various organizational levels, including parental and offset rosettes. We explored physiological and morphological mechanisms underlying stress tolerance and offset maintenance in the tolerant plant species houseleek (Sempervivum tectorum) under controlled conditions-where potted plants were exposed to complete water withdrawal for up to 7 mo-and natural habitat conditions. We found an unexpected quiescent-like strategy through the maintenance of low oxidative levels in the leaves under severe stress. Moreover, S. tectorum plants employed a morphological strategy driven by the spatiotemporal senescence pattern along the rosette, thus protecting the apical inner bud under stress. Even with very low resource availability, the parent plant and the associated offspring adjusted their physiology, keeping the stolon-connected offsets alive for as long as required until rooting into the soil (sometimes for several months), without compromising the parental rosette. The quiescent response in the parental rosette is maintained despite an increasing number of unrooted offsets due to photoprotective and morphological adjustments in leaves, with higher endogenous ABA levels. These results revealed the mechanisms through which this species extended its survival during prolonged periods of drought stress without irreversible physiological costs of clonal reproduction for the whole genet.

The advanced molecular tools provide critical inputs in uncovering the regulatory mechanisms underlying plants' adaptation to abiotic stress. Presented holistic studies were done on the barley crown tissue being essential for plant performance under various environmental stimuli. To investigate the effect of brassinosteroids (BRs), the known players in stress management, on molecular response of this tissue to drought, the genotypes with different BRs signal transduction efficiency were employed. Large-scale transcriptomic and proteomic profiling confirmed the specific re-modeling of behavior of the BRs-insensitive barley uzu1.a mutant under drought. On the other hand, a set of genes expressed independently of the genotype was identified, including dehydrin encoding genes. This study also uncovered the candidate genes to be linkers of phytohormones crosstalk. Importantly, we detected the converging upregulation of several proteins and encoding genes under drought, including late embryogenesis abundant proteins and chaperones; they represent a promising target for cereals' improvement. Moreover, the greatest variation between genotypes in accumulation of BRs in the crown tissue exposed to drought was observed for castasterone. Presented multi-omics, high-throughput results enhanced the understanding of molecular response to drought in crown tissue. The new insight was provided into the relationships between gene expression, protein and phytohormone content in barley plants of different BRs signaling.

Malondialdehyde is a three-carbon dialdehyde produced as a byproduct of polyunsaturated fatty acid peroxidation widely used as a marker of the extent of lipid peroxidation in plants. There are several methodological approaches to quantify malondialdehyde contents in higher plants, ranging from the simplest, cheapest, and quickest spectrophotometric approaches to the more complex ones using tandem mass spectrometry. This chapter summarizes the advantages and limitations of approaches followed and provides brief protocols with some tips to facilitate the selection of the best method for each experimental condition and application.

Plant species distribution across ecosystems is influenced by multiple environmental factors, and recurrent seasonal stress events can act as natural selection agents for specific plant traits and limit species distribution. For that, studies aiming at understanding how environmental constraints affect adaptive mechanisms of taxonomically closely related species are of great interest. We chose two Scabiosa species inhabiting contrasting environments: the coastal scabious S. atropurpurea, typically coping with hot-dry summers in a Mediterranean climate, and the mountain scabious S. columbaria facing cold winters in an oceanic climate. A set of functional traits was examined to assess plant performance in these congeneric species from contrasting natural habitats. Both S. atropurpurea and S. columbaria appeared to be perfectly adapted to their environment in terms of adjustments in stomatal closure, CO2 assimilation rate and water use efficiency over the seasons. However, an unexpected dry period during winter followed by the typical Mediterranean hot-dry summer forced S. atropurpurea plants to deploy a set of photoprotective responses during summer. Aside from reductions in leaf water content and F-v/F-m, photoprotective molecules (carotenoids, alpha-tocopherol and anthocyanins) per unit of chlorophyll increased, mostly as a consequence of a severe chlorophyll loss. The profiling of stress-related hormones (ABA, salicylic acid and jasmonates) revealed associations between ABA and the bioactive jasmonoyl-isoleucine with the underlying photoprotective response to recurrent seasonal stress in S. atropurpurea. We conclude that jasmonates may be used together with ABA as a functional trait that may, at least in part, help understand plant responses to recurrent seasonal stress in the current frame of global climate change.

BACKGROUND:Flower load in peach is an important determinant of final fruit quality and is subjected to cost-effective agronomical practices, such as the thinning, to finely balance the sink-source relationships within the tree and drive the optimal amount of assimilates to the fruits. Floral transition in peach buds occurs as a result of the integration of specific environmental signals, such as light and temperature, into the endogenous pathways that induce the meristem to pass from vegetative to reproductive growth. The cross talk and integration of the different players, such as the genes and the hormones, are still partially unknown. In the present research, transcriptomics and hormone profiling were applied on bud samples at different developmental stages. A gibberellin treatment was used as a tool to identify the different phases of floral transition and characterize the bud sensitivity to gibberellins in terms of inhibition of floral transition. RESULTS:Treatments with gibberellins showed different efficacies and pointed out a timeframe of maximum inhibition of floral transition in peach buds. Contextually, APETALA1 gene expression was shown to be a reliable marker of gibberellin efficacy in controlling this process. RNA-Seq transcriptomic analyses allowed to identify specific genes dealing with ROS, cell cycle, T6P, floral induction control and other processes, which are correlated with the bud sensitivity to gibberellins and possibly involved in bud development during its transition to the reproductive stage. Transcriptomic data integrated with the quantification of the main bioactive hormones in the bud allowed to identify the main hormonal regulators of floral transition in peach, with a pivotal role played by endogenous gibberellins and cytokinins. CONCLUSIONS:The peach bud undergoes different levels of receptivity to gibberellin inhibition. The stage with maximum responsiveness corresponded to a transcriptional and hormonal crossroad, involving both flowering inhibitors and inductors. Endogenous gibberellin levels increased only at the latest developmental stage, when floral transition was already partially achieved, and the bud was less sensitive to exogenous treatments. A physiological model summarizes the main findings and suggests new research ideas to improve our knowledge about floral transition in peach.

Tocopherols are lipophilic antioxidants known as vitamin E and synthesized from the condensation of two metabolic pathways leading to the formation of homogentisate and phytyl diphosphate. While homogentisate is derived from tyrosine metabolism, phytyl diphosphate may be formed from geranylgeranyl diphosphate or phytol recycling from chlorophyll degradation. Here, we hypothesized that abscisic acid (ABA) could induce tocopherol biosynthesis in sweet cherries by modifying the expression of genes involved in vitamin E biosynthesis, including those from the phytol recycling pathway. Hence, the expression of key tocopherol biosynthesis genes was determined together with vitamin E and chlorophyll contents during the natural development of sweet cherries on the tree. Moreover, the effects of exogenously applied ABA on the expression of key tocopherol biosynthesis genes were also investigated during on-tree fruit development, and tocopherols and chlorophylls contents were analyzed. Results showed that the expression of tocopherol biosynthesis genes, including VTE5, VTE6, HPPD and HPT showed contrasting patterns of variation, but in all cases, increased by 2- and 3-fold over time during fruit de-greening. This was not the case for GGDR and VTE4, the first showing constitutive expression during fruit development and the second with marked down-regulation at ripening onset. Furthermore, exogenous ABA stimulated the production of both α- and γ-tocopherols by 60% and 30%, respectively, promoted chlorophyll degradation and significantly enhanced VTE5 and VTE6 expression, and also that of HPPD and VTE4, altogether increasing total tocopherol accumulation. In conclusion, ABA increases promote the transcription of phytol recycling enzymes, which may contribute to vitamin E biosynthesis during fruit development in stone fruits like sweet cherries.