Differential physiological response of the grapevine varieties Touriga Nacional and Trincadeira to combined heat, drought and light stresses

Cytogenetic and Molecular Effects of Kaolin's Foliar Application in Grapevine (Vitis vinifera L.) under Summer's Stressful Growing Conditions

Grapevine varieties from "Douro Superior" (NE Portugal) experience high temperatures, solar radiation, and water deficit during the summer. This summer's stressful growing conditions induce nucleic acids, lipids, and protein oxidation, which cause cellular, physiological, molecular, and biochemical changes. Cell cycle anomalies, mitosis delay, or cell death may occur at the cellular level, leading to reduced plant productivity. However, the foliar application of kaolin (KL) can mitigate the impact of abiotic stress by decreasing leaf temperature and enhancing antioxidant defence. Hence, this study hypothesised that KL-treated grapevine plants growing in NE Portugal would reveal, under summer stressful growing conditions, higher progression and stability of the leaf mitotic cell cycle than the untreated (control) plants. KL was applied after veraison for two years. Leaves, sampled 3 and 5 weeks later, were cytogenetically, molecularly, and biochemically analysed. Globally, integrating these multidisciplinary data confirmed the decreased leaf temperature and enhanced antioxidant defence of the KL-treated plants, accompanied by an improved regularity and completion of the leaf cell cycle relative to the control plants. Nevertheless, the KL efficacy was significantly influenced by the sampling date and/or variety. In sum, the achieved results confirmed the hypothesis initially proposed.

Surviving a Double-Edged Sword: Response of Horticultural Crops to Multiple Abiotic Stressors

Climate change-induced weather events, such as extreme temperatures, prolonged drought spells, or flooding, pose an enormous risk to crop productivity. Studies on the implications of multiple stresses may vary from those on a single stress. Usually, these stresses coincide, amplifying the extent of collateral damage and contributing to significant financial losses. The breadth of investigations focusing on the response of horticultural crops to a single abiotic stress is immense. However, the tolerance mechanisms of horticultural crops to multiple abiotic stresses remain poorly understood. In this review, we described the most prevalent types of abiotic stresses that occur simultaneously and discussed them in in-depth detail regarding the physiological and molecular responses of horticultural crops. In particular, we discussed the transcriptional, posttranscriptional, and metabolic responses of horticultural crops to multiple abiotic stresses. Strategies to breed multi-stress-resilient lines have been presented. Our manuscript presents an interesting amount of proposed knowledge that could be valuable in generating resilient genotypes for multiple stressors.

Use of an automatic fruit-zone cooling system to cope with multiple summer stresses in Sangiovese and Montepulciano grapes

Grapevines are frequently subjected to heatwaves and limited water availability during ripening. These conditions can have consequences for the physiological health of the vines. Moreover, the situation is often exacerbated by intense solar radiation, resulting in reduced yield due to sunburn and a decline in quality. In light of these challenges, our study aimed to develop a fruit-zone cooling system designed to mitigate grape sunburn damage and improve the microclimate conditions within the vineyard. The system comprises a network of proximal sensors that collect microclimate data from the vineyard and an actuator that activates nebulizers when the temperature exceeds the threshold of 35°C. The research was conducted over two years (2022 and 2023) in Bologna (Italy) using potted Sangiovese and Montepulciano vines. These two vintages were characterized by high temperatures, with varying amounts of rainfall during the test period, significantly impacting the evaporative demand, which was notably higher in 2023. Starting from the veraison stage we compared three treatments: Irrigated control vines (WW); Control vines subjected to 50% water restriction during the month of August (WS); WS vines treated with nebulized water in the bunch area during the stress period (WS+FOG). The application of nebulized water effectively reduced the temperature of both the air around the clusters and the clusters themselves. As we expected, Montepulciano showed better single leaf assimilation rate and stomatal conductance under non-limiting water conditions than Sangiovese while their behavior was unaffected under water-scarce conditions. Importantly, for the first time, we demonstrated that nebulized water positively affected gas exchange in both grape varieties. In addition to this, the vines treated with the misting system exhibited higher productivity compared to WS vines without affecting technological maturity. In the 2023 vintage, the activation of the system prevented the ripening blockage that occurred in Montepulciano under water stress. Regarding the concentration of total anthocyanins, a significant increase in color was observed in WS+FOG treatment, suggesting a predominant role of microclimate on anthocyanin biosynthesis and reduction of oxidative phenomena. In conclusion, the fruit-zone cooling system proved to be an invaluable tool for mitigating the adverse effects of multiple summer stresses.

Plant breeding for harmony between sustainable agriculture, the environment, and global food security: an era of genomics-assisted breeding

MAIN CONCLUSION

Genomics-assisted breeding represents a crucial frontier in enhancing the balance between sustainable agriculture, environmental preservation, and global food security. Its precision and efficiency hold the promise of developing resilient crops, reducing resource utilization, and safeguarding biodiversity, ultimately fostering a more sustainable and secure food production system. Agriculture has been seriously threatened over the last 40 years by climate changes that menace global nutrition and food security. Changes in environmental factors like drought, salt concentration, heavy rainfalls, and extremely low or high temperatures can have a detrimental effects on plant development, growth, and yield. Extreme poverty and increasing food demand necessitate the need to break the existing production barriers in several crops. The first decade of twenty-first century marks the rapid development in the discovery of new plant breeding technologies. In contrast, in the second decade, the focus turned to extracting information from massive genomic frameworks, speculating gene-to-phenotype associations, and producing resilient crops. In this review, we will encompass the causes, effects of abiotic stresses and how they can be addressed using plant breeding technologies. Both conventional and modern breeding technologies will be highlighted. Moreover, the challenges like the commercialization of biotechnological products faced by proponents and developers will also be accentuated. The crux of this review is to mention the available breeding technologies that can deliver crops with high nutrition and climate resilience for sustainable agriculture.

Dose differentiation in elevated UV-B manifests variable response of carbon-nitrogen content with changes in secondary metabolites of Curcuma caesia Roxb

Despite acting as environmental stress, UV-B also plays a regulatory role in the plant's growth and secondary metabolism. UV-B-induced changes show variations between and among the species. The present study mainly focuses on variations in carbon and nitrogen contents and their relation with the phytochemical constituents of Curcuma caesia exposed to two different doses of UV-B (ambient ± elevated UV-B for 1 h (2.4 kJ m^-2 day^-1) and 2 h (4.8 kJ m^-2 day^-1)) under natural field conditions. Results showed that increasing the dose of eUV-B leads to high tuber biomass and reduced rhizome biomass (the medicinally important part). Increased expression of compounds at the initial rhizome formation stage might be due to the increased carbon content, whereas no such trend was found at the final growth or rhizome maturation stage. After final harvesting, carbon content was reduced, with an increase of nitrogen content which might be responsible for enhanced production of major components of essential oil (D-camphor and 1,8-cineole) in 2 h of UV-B exposure followed by 1 h. The phytochemical analysis at the final stage showed induction of compounds (15 and 10 in 1 h and 2 h, respectively) after UV-B exposure which was not detected in controls. The present study suggests that the change in carbon-nitrogen played an important role in the fraction of compounds at different stages, and a lower dose of UV-B (1 h) favoured the increased production of essential oil; however, 2 h dose is important for the enhanced production of major active compounds of essential oil.

Zinc Biofortification in Vitis vinifera: Implications for Quality and Wine Production

Nowadays, there is a growing concern about micronutrient deficits in food products, with agronomic biofortification being considered a mitigation strategy. In this context, as Zn is essential for growth and maintenance of human health, a workflow for the biofortification of grapes from the Vitis vinifera variety Fernão Pires, which contains this nutrient, was carried out considering the soil properties of the vineyard. Additionally, Zn accumulation in the tissues of the grapes and the implications for some quality parameters and on winemaking were assessed. Vines were sprayed three times with ZnO and ZnSO₄ at concentrations of 150, 450, and 900 g ha^-1 during the production cycle. Physiological data were obtained through chlorophyll a fluorescence data, to access the potential symptoms of toxicity. At harvest, treated grapes revealed significant increases of Zn concentration relative to the control, being more pronounced for ZnO and ZnSO₄ in the skin and seeds, respectively. After winemaking, an increase was also found regarding the control (i.e., 1.59-fold with ZnSO₄-450 g ha^-1). The contents of the sugars and fatty acids, as well as the colorimetric analyses, were also assessed, but significant variations were not found among treatments. In general, Zn biofortification increased with ZnO and ZnSO₄, without significantly affecting the physicochemical characteristics of grapes.

Water Deficit Timing Differentially Affects Physiological Responses of Grapevines Infected with Lasiodiplodia theobromae

Diseases and climate change are major factors limiting grape productivity and fruit marketability. Lasiodiplodia theobromae is a fungus of the family Botryosphaeriaceae that causes Botryosphaeria dieback of grapevine worldwide. Abiotic stress may change host vitality and impact susceptibility to the pathogen and/or change the pathogen's life cycle. However, the interaction between both stress drivers is poorly understood for woody plants. We addressed the hypothesis that distinct morpho-physiological and biochemical responses are induced in grapevine (Vitis vinifera)-L. theobromae interactions depending on when water deficits are imposed. Grapevines were submitted to water deficit either before or after fungus inoculation. Water deficit led to the reduction of the net photosynthetic rate, stomatal conductance, and transpiration rate, and increased the abscisic acid concentration regardless of fungal inoculation. L. theobromae inoculation before water deficit reduced plant survival by 50% and resulted in the accumulation of jasmonic acid and reductions in malondialdehyde levels. Conversely, grapevines inoculated after water deficit showed an increase in proline and malondialdehyde content and all plants survived. Overall, grapevines responded differently to the primary stress encountered, with consequences in their physiological responses. This study reinforces the importance of exploring the complex water deficit timing × disease interaction and the underlying physiological responses involved in grapevine performance.

Modulations in Chlorophyll a Fluorescence Based on Intensity and Spectral Variations of Light

Photosynthetic efficiency is significantly affected by both qualitative and quantitative changes during light exposure. The properties of light have a profound effect on electron transport and energy absorption in photochemical reactions. In addition, fluctuations in light intensity and variations in the spectrum can lead to a decrease in photosystem II efficiency. These features necessitate the use of a simple and suitable tool called chlorophyll a fluorescence to study photosynthetic reactions as a function of the aforementioned variables. This research implies that chlorophyll a fluorescence data can be used to determine precise light conditions that help photoautotrophic organisms optimally function.

Colored Shade Nets Can Relieve Abnormal Fruit Softening and Premature Leaf Senescence of "Jumeigui" Grapes during Ripening under Greenhouse Conditions

High temperature causes premature grape leaf senescence, abnormal berry softening, and shortening of the fruiting period. Furthermore, the fruit quality and yield are severely affected. Here, the "Jumeigui" grape quality and leaf senescence were evaluated under shading; green, blue, black, and gray nets were used for shading, and their spectra were measured. At the same density, the shade-net color significantly affected cooling and shading efficiencies, with gray nets showing the best light transmission and cooling effect. Shading significantly alleviated abnormal heat-induced grape softness. The total soluble solids (TSS) content and grape coloration were affected under gray, blue, and green shade nets. Nonetheless, TSS exceeded 18 °Brix under gray, blue, and green nets, as required of first-class high-quality fruit. The peel color was not significantly affected under gray or blue shade nets, whereas unshaded grapes showed clear heat-stress damage, especially on the edges of unshaded bottom leaves, in which the net photosynthesis rate was significantly lower than that under shading, indicating that high light intensity and heat caused premature leaf senescence. Colored shade nets reduced greenhouse temperature and light intensity, thereby alleviating the premature senescence of grape plants. Grape quality under black shade nets was poor, whereas superior quality was achieved using gray or blue shade nets.

Developmental Regulation of Transcription in Touriga Nacional Berries under Deficit Irrigation

Grapevine (Vitis vinifera L.) is one of the most economically important crops worldwide, especially due to the economic relevance of wine production. Abiotic stress, such as drought, may contribute to low yield, shifts in quality, and important economic loss. The predicted climate change phenomena point to warmer and dryer Mediterranean environmental conditions; as such, it is paramount to study the effects of abiotic stress on grapevine performance. Deficit irrigation systems are applied to optimize water use efficiency without compromising berry quality. In this research, the effect of two deficit irrigation strategies, sustained deficit irrigation (SDI) and regulated deficit irrigation (RDI), in the grape berry were assessed. The effects of different levels of drought were monitored in Touriga Nacional at key stages of berry development (pea size, véraison, and full maturation) through RNA-Seq transcriptome analysis and by specific differentially expressed genes (DEGs) monitoring through RT-qPCR. Handy datasets were obtained by bioinformatics analysis of raw RNA-Seq results. The dominant proportion of transcripts was mostly regulated by development, with véraison showing more upregulated transcripts. Results showed that primary metabolism is the functional category more severely affected under water stress. Almost all DEGs selected for RT-qPCR were significantly upregulated in full maturation and showed the highest variability at véraison and the lowest gene expression values in the pea size stage.

Potential Phenotyping Methodologies to Assess Inter- and Intravarietal Variability and to Select Grapevine Genotypes Tolerant to Abiotic Stress

Plant phenotyping is an emerging science that combines multiple methodologies and protocols to measure plant traits (e.g., growth, morphology, architecture, function, and composition) at multiple scales of organization. Manual phenotyping remains as a major bottleneck to the advance of plant and crop breeding. Such constraint fostered the development of high throughput plant phenotyping (HTPP), which is largely based on imaging approaches and automatized data retrieval and processing. Field phenotyping still poses major challenges and the progress of HTPP for field conditions can be relevant to support selection and breeding of grapevine. The aim of this review is to discuss potential and current methods to improve field phenotyping of grapevine to support characterization of inter- and intravarietal diversity. Vitis vinifera has a large genetic diversity that needs characterization, and the availability of methods to support selection of plant material (polyclonal or clonal) able to withstand abiotic stress is paramount. Besides being time consuming, complex and expensive, field experiments are also affected by heterogeneous and uncontrolled climate and soil conditions, mostly due to the large areas of the trials and to the high number of traits to be observed in a number of individuals ranging from hundreds to thousands. Therefore, adequate field experimental design and data gathering methodologies are crucial to obtain reliable data. Some of the major challenges posed to grapevine selection programs for tolerance to water and heat stress are described herein. Useful traits for selection and related field phenotyping methodologies are described and their adequacy for large scale screening is discussed.

Adjustment of K+ Fluxes and Grapevine Defense in the Face of Climate Change

Grapevine is one of the most economically important fruit crops due to the high value of its fruit and its importance in winemaking. The current decrease in grape berry quality and production can be seen as the consequence of various abiotic constraints imposed by climate changes. Specifically, produced wines have become too sweet, with a stronger impression of alcohol and fewer aromatic qualities. Potassium is known to play a major role in grapevine growth, as well as grape composition and wine quality. Importantly, potassium ions (K+) are involved in the initiation and maintenance of the berry loading process during ripening. Moreover, K+ has also been implicated in various defense mechanisms against abiotic stress. The first part of this review discusses the main negative consequences of the current climate, how they disturb the quality of grape berries at harvest and thus ultimately compromise the potential to obtain a great wine. In the second part, the essential electrical and osmotic functions of K+, which are intimately dependent on K+ transport systems, membrane energization, and cell K+ homeostasis, are presented. This knowledge will help to select crops that are better adapted to adverse environmental conditions.

Evaluating Strategies for Adaptation to Climate Change in Grapevine Production-A Systematic Review

In many areas of the world, maintaining grapevine production will require adaptation to climate change. While rigorous evaluations of adaptation strategies provide decision makers with valuable insights, those that are published often overlook major constraints, ignore local adaptive capacity, and suffer from a compartmentalization of disciplines and scales. The objective of our study was to identify current knowledge of evaluation methods and their limitations, reported in the literature. We reviewed 111 papers that evaluate adaptation strategies in the main vineyards worldwide. Evaluation approaches are analyzed through key features (e.g., climate data sources, methodology, evaluation criteria) to discuss their ability to address climate change issues, and to identify promising outcomes for climate change adaptations. We highlight the fact that combining adaptation levers in the short and long term (location, vine training, irrigation, soil, and canopy management, etc.) enables local compromises to be reached between future water availability and grapevine productivity. The main findings of the paper are three-fold: (1) the evaluation of a combination of adaptation strategies provides better solutions for adapting to climate change; (2) multi-scale studies allow local constraints and opportunities to be considered; and (3) only a small number of studies have developed multi-scale and multi-lever approaches to quantify feasibility and effectiveness of adaptation. In addition, we found that climate data sources were not systematically clearly presented, and that climate uncertainty was hardly accounted for. Moreover, only a small number of studies have assessed the economic impacts of adaptation, especially at farm scale. We conclude that the development of methodologies to evaluate adaptation strategies, considering both complementary adaptations and scales, is essential if relevant information is to be provided to the decision-makers of the wine industry.

Sunburn in Grapes: A Review

Sunburn is a physiological disorder that affects the visual and organoleptic properties of grapes. The appearance of brown and necrotic spots severely affects the commercial value of the fruit, and in extreme cases, significantly decreases yield. Depending on the severity of the damage and the driving factors, sunburn on grapes can be classified as sunburn browning (SB) or as sunburn necrosis (SN). Sunburn results from a combination of excessive photosynthetically active radiation (PAR) and UV radiation and temperature that can be exacerbated by other stress factors such as water deficit. Fruit respond to these by activating antioxidant defense mechanisms, de novo synthesis of optical screening compounds and heat-shock proteins as well as through morphological adaptation. This review summarizes the current knowledge on sunburn in grapes and compares it with relevant literature on other fruits. It also discusses the different factors affecting the appearance and degree of sunburn, as well as the biochemical response of grapes to this phenomenon and different potential mitigation strategies. This review proposes further directions for research into sunburn in grapes.

Maize Responses Challenged by Drought, Elevated Daytime Temperature and Arthropod Herbivory Stresses: A Physiological, Biochemical and Molecular View

Maize (Zea mays L.) is one of the main cereals grown around the world. It is used for human and animal nutrition and also as biofuel. However, as a direct consequence of global climate change, increased abiotic and biotic stress events have been reported in different regions of the world, which have become a threat to world maize yields. Drought and heat are environmental stresses that influence the growth, development, and yield processes of maize crops. Plants have developed dynamic responses at the physiological, biochemical, and molecular levels that allow them to escape, avoid and/or tolerate unfavorable environmental conditions. Arthropod herbivory can generate resistance or tolerance responses in plants that are associated with inducible and constitutive defenses. Increases in the frequency and severity of abiotic stress events (drought and heat), as a consequence of climate change, can generate critical variations in plant-insect interactions. However, the behavior of herbivorous arthropods under drought scenarios is not well understood, and this kind of stress may have some positive and negative effects on arthropod populations. The simultaneous appearance of different environmental stresses and biotic factors results in very complex plant responses. In this review, recent information is provided on the physiological, biochemical, and molecular responses of plants to the combination of drought, heat stress, and the effect on some arthropod pests of interest in the maize crop.

Selecting Aragonez Genotypes Able to Outplay Climate Change-Driven Abiotic Stress

High temperatures and extreme drought are increasingly more frequent in Portugal, which represents a strong threat to viticulture in certain regions of the country. These multifactorial abiotic stresses are threatening viticultural areas worldwide, and the problem can hardly be overcome only by changing cultural practices. This scenario has raised a major challenge for plant scientists to find ways to adapt existing varieties to the new conditions without loss of their characteristic flavors, yield, and associated varietal character of wines. Aragonez (syn. Tempranillo) is one such variety, widely cultivated in Portugal and Spain, with specific characteristics associated with terroir. In this context, insight into intravarietal variability to enable its exploitation for selection becomes an important tool to mitigate the effect of multifactorial stresses driven by climate changes. The present work describes an innovative selection approach: selection for abiotic stress tolerance, measured by the leaf temperature of clones under environmental conditions of drought and extreme heat. This evaluation was complemented with values of yield and quality characteristics of the must (pH, acidity, °Brix, and anthocyanins). The application of this methodology was done in an experimental population of 255 clones of Tempranillo for 3 years. The genotypes were then ranked according to their level of tolerance to abiotic stress without loss of yield/quality. To understand the differences at the transcription level that could account for such variability, several of the most tolerant and most sensitive genotypes were analyzed for key genes using reverse transcriptase-quantitative polymerase chain reaction. The results enabled the selection of a group of genotypes with increased tolerance to stress, in relation to the average of the variety, which maintained the typical must quality of Aragonez. In parallel, several transcripts previously acknowledged as markers for abiotic stress tolerance were identified in several clones and are possible targets for plant breeding and genetic modification and/or to develop screening procedures to select genotypes better adapted to the abiotic stress driven by climate change.

Genotype-dependent responses of chickpea to high temperature and moderately increased light

Our aim was to understand how moderately increased light intensities influenced the response of chickpea to high temperature. Three chickpea genotypes (Acc#3, Acc#7 and Acc#8) were treated at control (26 °C and 300 μmol m^-2 s^-1 photosynthetic photon flux density/PPFD), high temperature (38 °C and 300 μmol m^-2 s^-1 PPFD), increased light intensity (26 °C and 600 μmol m^-2 s^-1 PPFD) and combination of increased light and temperature (38 °C and 600 μmol m^-2 s^-1 PPFD). The net photosynthetic rate (P_N) of Acc#3 and Acc#8 significantly decreased at high temperature regardless of light intensity. The P_N of all three genotypes at increased light intensity was significantly higher than that at high temperature. The intracellular CO₂ concentration (C_i), stomatal conductance (g_s) and transpiration rate (E) of Acc#3 and Acc#8 at increased light intensity with or without high temperature significantly decreased in comparison with control and individually high temperature treatment. The relative water content of Acc#3 at high temperature and the combination treatment decreased as compared with control. The relative water content of Acc#7 at control was higher than the other three treatments. The F_v/F_m (Maximum quantum efficiency of photosystem II) of leaves from the three genotypes at 38 °C were lower than at 26 °C regardless of light intensity. The high temperature decreased chlorophyll content in the lower bottom leaf of Acc#7 and Acc#8 than control. In conclusion, chickpeas showed a higher net photosynthetic rate at increased light intensity to withstand heat stress, which was genotype-dependent. Physiological responses of different chickpea genotypes to increased temperature and light intensity indicated that distinct responsive mechanism of photosynthesis. This study provides information on how chickpea respond to high temperature and increased light intensity, which will help us to improve chickpea to deal with future climate changes.

The Interplay between Atmospheric Conditions and Grape Berry Quality Parameters in Portugal

The atmospheric conditions are a strong modulator of grape berry composition, but further research is required to better understand this relationship, which is particularly pertinent under the context of climate change. The present study assesses the relationship between interannual variability in atmospheric conditions (mean, maximum and minimum air temperatures and precipitation totals) on grape berry quality attributes in three main Portuguese wine regions—Douro, Dão and Alentejo—and targets two major varieties growing in Portugal (cv. Touriga Nacional and cv. Aragonez/Tempranillo). Berry weight, titratable acidity (TA), pH, potential alcohol (PA), anthocyanins and total phenols index (TPI) data, collected two to three weeks after the end of the veraison until technological maturity, since 1999 in Douro, 2004 in Alentejo and 2008 in Dão, were selected. Meteorological data were obtained from both automatic weather stations and a climatic database defined at a very-high-resolution grid (<1 km) (PTHRES). The influence of daily mean, maximum and minimum air temperatures (November–October) and precipitation totals (April to June and July to September) on the above-mentioned berry quality parameters were first explored to identify the months/periods more influential to grape berry composition. Different statistical approaches were subsequently carried out to explore in greater detail these relationships. At technological maturity, temperature was negatively correlated to berry weight, titratable acidity, anthocyanins and TPI, but was positively correlated to pH and potential alcohol. Moreover, lowest levels of berry weight and TA (and highest levels of pH) were more frequent in warmer regions, while the opposite was seen in the cooler regions. PA, TPI and anthocyanins at maturity did not show a clear trend across regions. In addition, the maturation parameters of each site were grouped into two clusters—years where the maturation parameter is higher (cluster 1) and years where it is lower (cluster 2)—and significant differences in monthly mean temperatures between clusters were found. Overall, temperatures at veraison and maturation periods (June–August) were more influential in determining grape berry composition at harvest. The influence of precipitation was dependent on location and variety. The results also suggested that berry composition in Alentejo is more sensitive to atmospheric variability, while Aragonez seems more resilient than Touriga Nacional. These outcomes are based on a systematized and unprecedentedly large grape berry quality database in Portugal and provided the grounds for the development of grape quality forecast models, either to be used operationally in each vintage or for assessing potential modifications in berry composition in response to changing climates.

Harnessing sediments of coastal aquaculture ponds through technosols construction for halophyte cultivation using saline water irrigation

The Mediterranean aquaculture has been developed mostly in brackish environment in inactive coastal salt production areas. This study aims to utilise Technosols made with aquaculture sediments for Limonium algarvense Erben cultivation. This species that has nutraceutical potential thrives in halophilic environments in the southwest of the Iberian Peninsula and in Morocco. A microcosm assay was set up with plants grown in bottom sediments (C⁺), commercial substrate (C^-), and Technosols with amendments mixture application at 180 g/kg (Tec180) or at 360 g/kg (Tec360). These plants were irrigated with saline (assay 1) and/or with deionised water (assay 2). The bottom pond sediments, coffee wastes and the estuarine water were evaluated for diverse physicochemical parameters. Plant growth was characterised through a combined methodology using morphometric, SEM and physiological analysis. The Technosols were constructed with bottom sediments and a mixture of organic wastes used as amendments. Results revealed that the bottom sediments had low pH 3.2, C_org and extractable P and K contents, and high electroconductivity (EC) and N-NH₄ concentration. The estuarine water had a neutral pH, high EC and high Cl^-, HCO₃^-, Na⁺, Mg²⁺ and Ca²⁺ but low N-NO₃^- content. The Technosols showed a significant increase of pH, C_org, K and P and a decrease in N-NH₄ and EC in comparison with sediments. Principal component analysis separated the different experiments in three groups: C^-, A1 and A2 assays. The C^- was highly correlated with C_org, P, K, N-NO₃ parameters and total ascorbate. The A1 assay showed a strong association with Na, Ca and EC parameters, whereas the A2 assay presented a strongly correlation with plant growth. Plants from Technosols had greater development when irrigated with deionised water than under salty irrigation as opposed to plants cultivated in unamend sediments. In conclusion, these results support that highly saline sediments could be valorised through Technosols construction to cultivate plants with saline water, with potential application in the agro-food and pharmaceutical industry.

Eco-Physiological Screening of Different Tomato Genotypes in Response to High Temperatures: A Combined Field-to-Laboratory Approach

High temperatures represent a limitation for growth and development of many crop species. Several studies have demonstrated that the yield reduction of tomato under high temperatures and drought is mainly due to a photosynthetic decline. In this paper, a set of 15 tomato genotypes were screened for tolerance to elevated temperatures by cultivating plants under plastic walk-in tunnels. To assess the potential tolerance of tomato genotypes to high temperatures, measurements of chlorophyll fluorescence, pigments content and leaf functional traits have been carried out together with the evaluation of the final yields. Based on the greenhouse trials, a group of eight putative heat-sensitive and heat-tolerant tomato genotypes was selected for laboratory experiments aimed at investigating the effects of short-term high temperatures treatments in controlled conditions. The chlorophyll fluorescence induction kinetics were recorded on detached leaves treated for 60 min at 35 °C or at 45 °C. The last treatment significantly affected the photosystem II (PSII) photochemical efficiency (namely maximum PSII quantum efficiency, F_v/F_m, and quantum yield of PSII electron transport, Φ_PSII) and the non-photochemical quenching (NPQ) in the majority of genotypes. The short-term heat shock treatments also led to significant differences in the shape of the slow Kautsky kinetics and its significant time points (chlorophyll fluorescence levels minimum O, peak P, semi-steady state S, maximum M, terminal steady state T) compared to the control, demonstrating heat shock-induced changes in PSII functionality. Genotypes potentially tolerant to high temperatures have been identified. Our findings support the idea that chlorophyll fluorescence parameters (i.e., Φ_PSII or NPQ) and some leaf functional traits may be used as a tool to detect high temperatures-tolerant tomato cultivars.

Assessing the Feasibility of Using Sentinel-2 Imagery to Quantify the Impact of Heatwaves on Irrigated Vineyards

Heatwaves are common in many viticultural regions of Australia. We evaluated the potential of satellite-based remote sensing to detect the effects of high temperatures on grapevines in a South Australian vineyard over the 2016–2017 and 2017–2018 seasons. The study involved: (i) comparing the normalized difference vegetation index (NDVI) from medium- and high-resolution satellite images; (ii) determining correlations between environmental conditions and vegetation indices (Vis); and (iii) identifying VIs that best indicate heatwave effects. Pearson’s correlation and Bland–Altman testing showed a significant agreement between the NDVI of high- and medium-resolution imagery (R = 0.74, estimated difference −0.093). The band and the VI most sensitive to changes in environmental conditions were 705 nm and enhanced vegetation index (EVI), both of which correlated with relative humidity (R = 0.65 and R = 0.62, respectively). Conversely, SWIR (short wave infrared, 1610 nm) exhibited a negative correlation with growing degree days (R = −0.64). The analysis of heat stress showed that green and red edge bands—the chlorophyll absorption ratio index (CARI) and transformed chlorophyll absorption ratio index (TCARI)—were negatively correlated with thermal environmental parameters such as air and soil temperature and growing degree days (GDDs). The red and red edge bands—the soil-adjusted vegetation index (SAVI) and CARI2—were correlated with relative humidity. To the best of our knowledge, this is the first study demonstrating the effectiveness of using medium-resolution imagery for the detection of heat stress on grapevines in irrigated vineyards.

Grapevine water relations and rooting depth in karstic soils

Environmental sustainability of viticulture is negatively affected by prolonged droughts. In limestone dominated regions, there is limited knowledge on grapevine water status and on methods for accurate evaluation of actual water demand, necessary to appropriately manage irrigation. During a dry vintage, we monitored plant and soil water relations in old and young vines of Istrian Malvasia on Karst red soil. The vineyard with young vines was additionally subdivided into two areas, based on their soil type, 1) karst silty-clay loam, and 2) mixture of crushed rocks and karst silty-clay loam (stony soil). Seasonal changes in exploited water resources were estimated via analysis of oxygen isotope composition (δ¹⁸O) of rainfall, deep soil water, and xylem sap. We hypothesized that plants are able to thrive during drought thanks to the water stored in deep soil layers, while they rely less on superficial soil horizons. Our results show that vines growing on karstic substrates have deep roots securing the use of stable water sources during summer, with consequent favourable plant water status. In fact, both young and mature vines approached the threshold of severe water stress, but never surpassed it, as midday leaf water potentials were >-1.3MPa in all study sites. Vines roots showed flexible water uptake, i.e. the ability to absorb water from deep or shallow soil horizons during drought and after late-summer thunderstorms, which was particularly evident in vines growing on the stony soil. In fact, precipitations of 20mm were enough for plant water status recovery, due to fast infiltration. On the other hand, at least 50mm of rainfall were necessary to induce water status recovery in more compact soil (karst silty-clay loam). Our findings provide new knowledge on the rooting depth and water needs of vines growing on shallow soils overlying fractured limestone bedrock.

Heat stress tolerance assayed in four wine-producing grapevine varieties using a cytogenetic approach

The degree of tolerance to heat stress (HS) differs among grapevine varieties. HS affects the duration and the regularity of the cell cycle in plants. The cytogenetic studies in grapevine are scarce, and the consequences of HS in the mitosis are barely known. This work intends to evaluate the consequences of induced HS in the mitotic cell cycle and chromosomes of four wine-producing varieties: Touriga Franca (TF), Touriga Nacional (TN), Rabigato and Viosinho using a cytogenetic approach. HS (1h at 42 ºC) was induced in plants of the four grapevine varieties that grew in vitro for 11 months. Plants of the same varieties and with equal age were used as control (maintained in vitro at 25 ºC). Three plants per variety and treatment (control and HS) were analysed. After HS, root-tips were collected in all plants and immediately fixed to be used for the preparation of mitotic chromosome spreads. In total, 6,116 root-tip cells were scored. Among the 5,973 dividing cells, 24.33% showed different types of irregularities in all mitotic phases (prophase, metaphase, anaphase, and telophase). After HS, the mitotic index (MI) decreased in the varieties TF and Viosinho, and increased in TN and Rabigato, relatively to the control. However, the average values of MI did not show statistically significant differences (p ˃ 0.05) among varieties, treatments and for the variety x treatment interaction. The percentage of dividing cells with anomalies (%DCA) increased after HS in all varieties relatively to the control. The average values of %DCA presented statistically significant differences (p < 0.05) only between treatments. As far as we know, this work constitutes the first cytogenetic evaluation of the HS effects in the mitotic cell cycle and chromosomes of grapevine using meristematic cells of root-tips. TN has been considered tolerant to various abiotic stresses (drought and excessive heat and light) based on other methodologies. TF and Viosinho have been referred as tolerant to abiotic stress without deeper studies available, and till the development of our investigation, the sensibility of Rabigato was unknown. Among the varieties analysed in this work, Rabigato revealed to be the less tolerant to HS. This research can be useful for selection of grapevine clones more tolerant to HS for commercialization and for the improvement of the economic sustainability.

Zinc priming and foliar application enhances photoprotection mechanisms in drought-stressed wheat plants during anthesis

Drought is one of most important limiting factors in wheat productivity worldwide. The need to increase drought tolerance during anthesis is of the utmost importance for high yield potentials and yield stability. Photosynthesis is one of the major physiological processes affected by drought. Damages in the photosynthetic apparatus may also arise due to non-regulated dissipation of excessive energy. Zinc (Zn) is an indispensable micronutrient for plants and is required for a wide range of physiological and biochemical processes. In this work we evaluated the stress mitigation effects of Zn seed priming alone and coupled with Zn foliar application in wheat plants submitted to severe drought during anthesis, followed by a recovery period. Under such severe drought stress, photosynthesis was constrained by both stomatal and non-stomatal limitation. Severe drought also induced an increase in non-regulated energy dissipation and hindered a full recovery of the plant's photosynthetic processes after rewatering. We also report possible activation of transposable elements due to drought stress and Zn application. Yield was severely decreased by drought and Zn treatments were unable to counteract this effect. Although unable to oppose the reduction of net photosynthesis, Zn treatments positively enhance photoprotection. At the end of drought period, Zn priming alone and coupled with Zn foliar application increased, respectively, over 2- and 3- fold the regulated dissipation of excess energy. Zn treatments lessened the non-regulated energy dissipation caused by drought, protected the plants against irreversible damages to the photosynthetic apparatus and enabled a better recovery of wheat plants after stress relief.

Grapevine trunk diseases under thermal and water stresses

Heat and water stresses, individually or combined, affect both the plant (development, physiology, and production) and the pathogens (growth, morphology, dissemination, distribution, and virulence). The grapevine response to combined abiotic and biotic stresses is complex and cannot be inferred from the response to each single stress. Several factors might impact the response and the recovery of the grapevine, such as the intensity, duration, and timing of the stresses. In the heat/water stress-GTDs-grapevine interaction, the nature of the pathogens, and the host, i.e., the nature of the rootstock, the cultivar and the clone, has a great importance. This review highlights the lack of studies investigating the response to combined stresses, in particular molecular studies, and the misreading of the relationship between rootstock and scion in the relationship GTDs/abiotic stresses. Grapevine trunk diseases (GTDs) are one of the biggest threats to vineyard sustainability in the next 30 years. Although many treatments and practices are used to manage GTDs, there has been an increase in the prevalence of these diseases due to several factors such as vineyard intensification, aging vineyards, or nursery practices. The ban of efficient treatments, i.e., sodium arsenite, carbendazim, and benomyl, in the early 2000s may be partly responsible for the fast spread of these diseases. However, GTD-associated fungi can act as endophytes for several years on, or inside the vine until the appearance of the first symptoms. This prompted several researchers to hypothesise that abiotic conditions, especially thermal and water stresses, were involved in the initiation of GTD symptoms. Unfortunately, the frequency of these abiotic conditions occurring is likely to increase according to the recent consensus scenario of climate change, especially in wine-growing areas. In this article, following a review on the impact of combined thermal and water stresses on grapevine physiology, we will examine (1) how this combination of stresses might influence the lifestyle of GTD pathogens, (2) learnings from grapevine field experiments and modelling aiming at studying biotic and abiotic stresses, and (3) what mechanistic concepts can be used to explain how these stresses might affect the grapevine plant status.

The Role of the Plant Antioxidant System in Drought Tolerance

Water deficiency compromises plant performance and yield in many habitats and in agriculture. In addition to survival of the acute drought stress period which depends on plant-genotype-specific characteristics, stress intensity and duration, also the speed and efficiency of recovery determine plant performance. Drought-induced deregulation of metabolism enhances generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which in turn affect the redox regulatory state of the cell. Strong correlative and analytical evidence assigns a major role in drought tolerance to the redox regulatory and antioxidant system. This review compiles current knowledge on the response and function of superoxide, hydrogen peroxide and nitric oxide under drought stress in various species and drought stress regimes. The meta-analysis of reported changes in transcript and protein amounts, and activities of components of the antioxidant and redox network support the tentative conclusion that drought tolerance is more tightly linked to up-regulated ascorbate-dependent antioxidant activity than to the response of the thiol-redox regulatory network. The significance of the antioxidant system in surviving severe phases of dehydration is further supported by the strong antioxidant system usually encountered in resurrection plants.

Changes in grapevine leaf phenolic profiles during the day are temperature rather than irradiance driven

Photosynthesis parameters, adaxial flavonoid index, phenolic profiles and antioxidant capacities of south-facing sun exposed grapevine leaves (Vitis vinifera, Pinot Noir cultivar) were measured hourly between 7 a.m. and 7 p.m. on a clear summer day. Changes in these parameters were statistically compared to changes in environmental conditions, including solar irradiance (photosynthetically active and UV radiations), leaf and air temperature, and relative air humidity. Epidermal UV absorbance, characterised by the flavonoid index, and total extractable phenolic contents were correlated to distinct environmental parameters. The former was positively correlated to irradiance and leaf temperature, while the latter was positively correlated to air temperature. HPLC phenolic profiling identified a positive correlation between air temperature and amounts of the dominant flavonol component, quercetin-3-O-glucuronide. The only phenolic component statistically connected to the flavonoid index was quercetin-3-O-glucoside. This correlation was positive and both parameters decreased during the day, although changes in the amount of this flavonol component showed no correlation to environmental factors. Total antioxidant capacities of leaf extracts were positively correlated to solar UV, and leaf and air temperature, but not to photosynthetically active radiation. Positive correlations of quercetin-3-O-glucoside contents with the flavonoid index, with photosynthesis and with sub-stomatal CO₂ concentration suggest a special protective role of this flavonol. A short-term negative effect of solar UV-A and UV-B on photosynthetic CO₂ uptake was also identified, which was unrelated to changes in stomatal conductance. A hypothesis is presented assuming UV- and photorespiration-derived hydrogen peroxide as the driver of daily changes in leaf antioxidant capacities.

Cutting the Gordian Knot of abiotic stress in grapevine: From the test tube to climate change adaptation

In Mediterranean climate areas, the available scenarios for climate change suggest an increase in the frequency of heat waves and severe drought in summer. Grapevine (Vitis vinifera L.) is a traditional Mediterranean species and is the most valuable fruit crop in the world. Currently, viticulture must adjust to impending climate changes that are already pushing vine-growers toward the use of irrigation, with the concomitant losses in wine quality, and researchers to study tolerance to stress in existing genotypes. The viticulture and winemaking worlds are in demand to understand the physiological potential of the available genotypes to respond to climate changes. In this review, we will focus on the cross-talk between common abiotic stresses that currently affect grapevine productivity and that are prone to affect it deeper in the future. We will discuss results obtained under three experimental stress conditions and that call for specific responses: (1) acclimatization of in vitro plantlets, (2) stress combinations in controlled conditions for research purposes, (3) extreme events in the field that, driven by climate changes, are pushing Mediterranean species to the limit. The different levels of tolerance to stress put in evidence by the plasticity of phenotypic and genotypic response mechanisms, will be addressed. This information is relevant to understand varietal adaptation to impending climate changes and to assist vine growers in choosing genotypes and viticulture practices.

Combined drought and virus infection trigger aspects of respiratory metabolism related to grapevine physiological responses

In the Mediterranean region, grapevines usually deal with drought during their summer growth season. Concurrently, grapevines are hosts to a large number of viruses from which grapevine leafroll associated virus-3 is one of the most widespread and provokes considerable economic losses in many vineyards. However, information concerning grapevine metabolic responses to the combination of drought and viral infection is scarce. Gas-chromatography coupled to mass-spectrometry based metabolite profiling was used in combination with growth analysis, viral loads and gas exchange data to perform an integrative study of the effects of individual and combined stress in two Majorcan grapevine varieties at two experimental years. Metabolic responses of both varieties to the combination of water stress and virus infection were specific and not predicted from the sum of single stress responses. Correlations between respiration, biomass and key metabolites highlight specific adjustments of respiratory and amino acid metabolism possibly underlying the maintenance of carbon balance and growth in grapevines under stress combination.

Effects of heat stress in the leaf mitotic cell cycle and chromosomes of four wine-producing grapevine varieties

Grapevine varieties respond differentially to heat stress (HS). HS ultimately reduces the photosynthesis and respiratory performance. However, the HS effects in the leaf nuclei and mitotic cells of grapevine are barely known. This work intends to evaluate the HS effects in the leaf mitotic cell cycle and chromosomes of four wine-producing varieties: Touriga Franca (TF), Touriga Nacional (TN), Rabigato, and Viosinho. In vitro plants with 11 months were used in a stepwise acclimation and recovery (SAR) experimental setup comprising different phases: heat acclimation period (3 h-32 °C), extreme HS (1 h-42 °C), and two recovery periods (3 h-32 °C and 24 h-25 °C), and compared to control plants (maintained in vitro at 25 °C). At the end of each SAR phase, leaves were collected, fixed, and used for cell suspensions and chromosome preparations. Normal and abnormal interphase and mitotic cells were observed, scored, and statistically analyzed in all varieties and treatments (control and SAR phases). Different types of chromosomal anomalies in all mitotic phases, treatments, and varieties were found. In all varieties, the percentage of dividing cells with anomalies (%DCA) after extreme HS increased relative to control. TF and Viosinho were considered the most tolerant to HS. TF showed a gradual MI reduction from heat acclimation to HS and the lowest %DCA after HS and 24 h of recovery. Only Viosinho reached the control values after the long recovery period. Extrapolating these data to the field, we hypothesize that during consecutive hot summer days, the grapevine plants will not have time or capacity to recover from the mitotic anomalies caused by high temperatures.

Arbuscular Mycorrhizal Symbiosis as a Promising Resource for Improving Berry Quality in Grapevines Under Changing Environments

Climate change and their resulting impacts are becoming a concern for winegrowers due to the high socioeconomic relevance of the winemaking sector worldwide. In fact, the projected climate change is expected to have detrimental impacts on the yield of grapevines, as well as on the quality and properties of grapes and wine. It is well known that arbuscular mycorrhizal fungi (AMF) can improve the nutritional quality of edible parts of crops and play essential roles in the maintenance of host plant fitness under stressed environments, including grapevines. The future scenarios of climate change may also modify the diversity and the growth of AMF in soils as well as the functionality of the mycorrhizal symbiosis. In this review, we summarize recent research progress on the effects of climate change on grapevine metabolism, paying special attention to the secondary compounds involved in the organoleptic properties of grapes and wines and to the levels of the phytohormones implied in the control of berry development and fruit ripening. In this context, the potential role of AMF for maintaining fruit quality in future climate change scenarios is discussed.

Regulation of citrus responses to the combined action of drought and high temperatures depends on the severity of water deprivation

Plants grown in natural environment are regularly subjected to different combinations of abiotic stresses. Recent studies revealed that citrus plants subjected to a combination of severe drought and high temperatures displayed specific physiological, hormonal, molecular and metabolic responses. In the present study, we have performed a long-term experiment combining moderate drought and heat in Cleopatra mandarin to evaluate the impact of the stress-sequence, intensity and duration. Our results support previous observation of high sensitivity of Cleopatra mandarin to abiotic stresses that include high temperatures. In this sense, a combination of drought and heat stress negatively impacts Cleopatra seedlings independently of the drought intensity. However, some responses to combined drought and heat depend on drought intensity, especially those involved in stomatal regulation. The intricate natural environment, abiotic stress combinations and global climatic changes increase the complexity of studying plant responses to stress factors in the laboratory. Consequently, new experimental approaches taking in consideration different stress combinations should be implemented to study the viability of Cleopatra mandarin as a rootstock in a rapidly changing environment.

Physiological and agronomical responses to environmental fluctuations of two Portuguese grapevine varieties during three field seasons

Extensive agricultural losses are attributed to heat, often combined with drought. These abiotic stresses occur in the field simultaneously, namely in areas with Mediterranean climate, where grapevine traditionally grows. The available scenarios for climate change suggest an increase in the frequency of heat waves and severe drought events in summer, also affecting the South of Portugal. In this work we monitored several production-related parameters and evaluated the state of the oxidative stress response apparatus of two grapevine varieties, Touriga Nacional (TN) and Trincadeira (TR), with and without irrigation, during three field seasons (2010 to 2012). Overall, results point to a high correlation of most yield and stress-associated parameters with the specific characteristics of each variety and to each season rather than the irrigation treatments. In the season with the driest winter, 2012, the lack of irrigation significantly affected yield in TR, while in the two other seasons the impact of the irrigation regime was much lower. In 2012, the yield of TN was affected by environmental conditions of the previous season. The irrigation treatments significantly affected berry size rather than quality.

Kaolin modulates ABA and IAA dynamics and physiology of grapevine under Mediterranean summer stress

The foliar exogenous application of kaolin, a radiation-reflecting inert mineral, has proven to be an effective short-term climate change mitigation strategy for Mediterranean vineyards. In this work, we address the hypothesis that kaolin could improve both the hormonal dynamics and physiological responses of grapevines growing in Douro Region, northern Portugal. For this purpose, the leaf water potential, gas exchange and chlorophyll a fluorescence parameters were monitored, as well as the abscisic acid (ABA) and indole-3-acetic acid (IAA) quantification and immunolocalization were assessed. The study revealed a slight decrease in ABA and an increase in IAA in the kaolin treatment, which in turn were associated with the improvement of physiological performance. A month after spraying, kaolin improves the water potential respectively, 30% and 17% in the predawn and midday periods. Besides, plants treated with kaolin showed higher values of stomatal conductance, net CO₂ assimilation rate and intrinsic water use efficiency. Kaolin also ameliorates the effective PSII efficiency (67%), as well as the maximum quantum efficiency of photosystem II and the photosynthetic electron transport rate (>73%). These results were consistent with the higher photochemical quenching and the lower non-photochemical quenching observed in treated leaves and with the better performance obtained by the JIP test parameters. Physiological and hormonal analysis confirmed that kaolin effectively enhance grapevine summer stress tolerance.

Reactive oxygen species, abiotic stress and stress combination

Reactive oxygen species (ROS) play a key role in the acclimation process of plants to abiotic stress. They primarily function as signal transduction molecules that regulate different pathways during plant acclimation to stress, but are also toxic byproducts of stress metabolism. Because each subcellular compartment in plants contains its own set of ROS-producing and ROS-scavenging pathways, the steady-state level of ROS, as well as the redox state of each compartment, is different at any given time giving rise to a distinct signature of ROS levels at the different compartments of the cell. Here we review recent studies on the role of ROS in abiotic stress in plants, and propose that different abiotic stresses, such as drought, heat, salinity and high light, result in different ROS signatures that determine the specificity of the acclimation response and help tailor it to the exact stress the plant encounters. We further address the role of ROS in the acclimation of plants to stress combination as well as the role of ROS in mediating rapid systemic signaling during abiotic stress. We conclude that as long as cells maintain high enough energy reserves to detoxify ROS, ROS is beneficial to plants during abiotic stress enabling them to adjust their metabolism and mount a proper acclimation response.

Design of a Custom RT-qPCR Array for Assignment of Abiotic Stress Tolerance in Traditional Portuguese Grapevine Varieties

Widespread agricultural losses attributed to drought, often combined with high temperatures, frequently occur in the field, namely in Mediterranean climate areas, where the existing scenarios for climate change indicate an increase in the frequency of heat waves and severe drought events in summer. Grapevine (Vitis vinifera L.) is the most cultivated fruit species in the world and the most valuable one and is a traditional Mediterranean species. Currently, viticulture must adjust to impending climate changes that are already pushing vine-growers toward the use of ancient and resilient varieties. Portugal is very rich in grapevine biodiversity, however, currently, 90% of the total producing area is planted with only 16 varieties. There is a pressing need to understand the existing genetic diversity and the physiological potential of the varieties/genotypes available to be able to respond to climate changes. With the above scenario in mind, an assembly of 65 differentially expresses genes (DEGs) previously identified as responsive to abiotic stresses in two well studied genotypes, 'Touriga Nacional' and 'Trincadeira,' was designed to scan the gene expression of leaf samples from 10 traditional Portuguese varieties growing in two regions with distinct environmental conditions. Forty-five of those DEGs proved to be associated to "abiotic stress" and were chosen to build a custom qPCR array to identify uncharacterized genotypes as sensitive or tolerant to abiotic stress. According to the experimental set-up behind the array design these DEGs can also be used as indicators of the main abiotic stress that the plant is subjected and responding to (drought, heat, or excess light).

Melatonin enhances thermotolerance by promoting cellular protein protection in tomato plants

Melatonin is a pleiotropic signaling molecule that provides physiological protection against diverse environmental stresses in plants. Nonetheless, the mechanisms for melatonin-mediated thermotolerance remain largely unknown. Here, we report that endogenous melatonin levels increased with a rise in ambient temperature and that peaked at 40°C. Foliar pretreatment with an optimal dose of melatonin (10 μmol/L) or the overexpression of N-acetylserotonin methyltransferase (ASMT) gene effectively ameliorated heat-induced photoinhibition and electrolyte leakage in tomato plants. Both exogenous melatonin treatment and endogenous melatonin manipulation by overexpression of ASMT decreased the levels of insoluble and ubiquitinated proteins, but enhanced the expression of heat-shock proteins (HSPs) to refold denatured and unfolded proteins under heat stress. Meanwhile, melatonin also induced expression of several ATG genes and formation of autophagosomes to degrade aggregated proteins under the same stress. Proteomic profile analyses revealed that protein aggregates for a large number of biological processes accumulated in wild-type plants. However, exogenous melatonin treatment or overexpression of ASMT reduced the accumulation of aggregated proteins. Aggregation responsive proteins such as HSP70 and Rubisco activase were preferentially accumulated and ubiquitinated in wild-type plants under heat stress, while melatonin mitigated heat stress-induced accumulation and ubiquitination of aggregated proteins. These results suggest that melatonin promotes cellular protein protection through induction of HSPs and autophagy to refold or degrade denatured proteins under heat stress in tomato plants.

Transcriptomic comparison between two Vitis vinifera L. varieties (Trincadeira and Touriga Nacional) in abiotic stress conditions

BACKGROUND

Predicted climate changes announce an increase of extreme environmental conditions including drought and excessive heat and light in classical viticultural regions. Thus, understanding how grapevine responds to these conditions and how different genotypes can adapt, is crucial for informed decisions on accurate viticultural actions. Global transcriptome analyses are useful for this purpose as the response to these abiotic stresses involves the interplay of complex and diverse cascades of physiological, cellular and molecular events. The main goal of the present work was to evaluate the response to diverse imposed abiotic stresses at the transcriptome level and to compare the response of two grapevine varieties with contrasting physiological trends, Trincadeira (TR) and Touriga Nacional (TN).

RESULTS

Leaf transcriptomic response upon heat, high light and drought treatments in growth room controlled conditions, as well as full irrigation and non-irrigation treatments in the field, was compared in TR and TN using GrapeGene GeneChips®. Breakdown of metabolism in response to all treatments was evidenced by the functional annotation of down-regulated genes. However, circa 30 % of the detected stress-responsive genes are still annotated as «Unknown» function. Selected differentially expressed genes from the GrapeGene GeneChip® were analysed by RT-qPCR in leaves of growth room plants under the combination of individual stresses and of field plants, in both varieties. The transcriptomic results correlated better with those obtained after each individual stress than with the results of plants from field conditions.

CONCLUSIONS

From the transcriptomic comparison between the two Portuguese grapevine varieties Trincadeira and Touriga Nacional under abiotic stress main conclusions can be drawn: 1. A different level of tolerance to stress is evidenced by a lower transcriptome reprogramming in TN than in TR. Interestingly, this lack of response in TN associates with its higher adaptation to extreme conditions including environmental conditions in a changing climate; 2. A complex interplay between stress transcriptional cascades is evidenced by antagonistic and, in lower frequency, synergistic effects on gene expression when several stresses are imposed together; 3. The grapevine responses to stress under controlled conditions are not fully extrapolated to the complex vineyard scenario and should be cautiously considered for agronomic management decision purposes.