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The grape berry withering process is often seen as a means to concentrate the constituents of the berry via water removal, however, recent molecular studies have indicated that the reprogramming of biosynthetic pathways that impart the unique aroma and flavour of the final wine also occur. Metabolic analysis was performed using GC-MS and LC-MS on Corvina berry dehydrated for up to 108 days. The temporal pattern of metabolic changes and time-series relationship between various classes of metabolites were investigated on berries sampled at 23-time points. Principal component analysis of both GC-MS and LC-MS datasets revealed three distinct phases of post-harvest withering; early (day 0–28), mid (day 35–66) and late (day 69–108) stages. Stress-associated amino acids such as proline, serine, ethanolamine, and leucine accumulated significantly during the mid and late stages of the drying process while phosphorylated glucose and fructose, sucrose, kestose and resveratrol increased massively across time. Unlike most of the identified metabolites, low molecular weight flavanols exhibited a consistent pattern of decline during the withering period. Our network analysis revealed that increased metabolic network connectivity occurred during the middle stage of withering, thus reflecting more coordinated metabolite changes while reduced network connectivity at early and late stages indicates minimal metabolite perturbation during these stages. The current prolonged berry withering experiment revealed the timing of metabolite interconversions in the central metabolism and provided critical clues that link the concentration effect, protein degradation, and the onset of stress-like conditions in drying berries.

Shiraz and Cabernet Sauvignon (Cs) grapevines were grown at near optimal temperatures (25 or 35 °C). Gas exchange, fluorescence, metabolic profiling and correlation based network analysis were used to characterize leaf physiology. When grown at 25 °C, the growth rate and photosynthesis of both cultivars were similar. At 35 °C Shiraz showed increased respiration, non-photochemical quenching and reductions of photosynthesis and growth. In contrast, Cs maintained relatively stable photosynthetic activity and growth regardless of the condition. In both cultivars, growth at 35 °C resulted in accumulations of secondary sugars (raffinose, fucose and ribulose) and reduction of primary sugars concentration (glucose, fructose and sucrose), more noticeably in Shiraz than Cs. In spite of similar patterns of metabolic changes in response to growth at 35 °C, significant differences in important leaf antioxidants and antioxidant precursors (DHA/ascorbate, quinates, cathechins) characterized the cultivar response. Correlation analysis reinforced Shiraz sensitivity to the 35 °C, showing higher number of newly formed edges at 35 °C and higher modularity in Shiraz as compared to Cs. The results suggest that the optimal growth temperatures of grapevines are cultivar dependent, and allow a first insight into the variability of the metabolic responses of grapevines under varied temperatures.

The chemical composition of grape berries is varietal dependent and influenced by the environment and viticulture practices. In Muscat grapes, phenolic compounds play a significant role in the organoleptic property of the wine. In the present study, we investigated the chemical diversity of berries in a Muscat collection. Metabolite profiling was performed on 18 Moscato bianco clones and 43 different red and white grape varieties of Muscat using ultra-performance liquid chromatography–quadrupole time of flight–mass spectrometry (UPLC-QTOF-MS/MS) coupled with SNP genotyping. Principle component analysis and hierarchical clustering showed a separation of the genotypes into six main groups, three red and three white. Anthocyanins mainly explained the variance between the different groups. Additionally, within the white varieties mainly flavonols and flavanols contributed to the chemical diversity identified. A genotype-specific rootstock effect was identified when separately analyzing the skin of the clones, and it was attributed mainly to resveratrol, quercetin 3- O -galactoside, citrate and malate. The metabolite profile of the varieties investigated reveals the chemical diversity existing among different groups of Muscat genotypes. The distribution pattern of metabolites among the groups dictates the abundance of precursors and intermediate metabolite classes, which contribute to the organoleptic properties of Muscat berries.

Postveraison water deficit is a common strategy implemented to improve fruit composition in many wine-growing regions. However, contrasting results are often reported on fruit size and composition, a challenge for generalizing the positive impact of this technique. Our research investigated the effect of water deficit (WD) imposed at veraison on Merlot grapevines, during two experimental seasons (2014-2015). In both years WD resulted in reduced carbon assimilation rates and leaf shedding. However, the treatment effect on the analyzed berry parameters varied between seasons. Modification of skin metabolites was more evident in 2015 than in 2014, despite the similar soil water content and water stress physiological parameters (gas exchange, water potential) recorded in the two experimental years. Higher solar radiation and air temperature in 2015 than in 2014 hint for the involvement of atmospheric parameters in fulfilling the potential effect of WD. Our results suggest that the interaction between water availability and weather conditions plays a crucial role in modulating the grape berry composition.

Main conclusion Drought-acclimated vines maintained higher gas exchange compared to irrigated controls under water deficit; this effect is associated with modified leaf turgor but not with improved petiole vulnerability to cavitation. A key feature for the prosperity of plants under changing environments is the plasticity of their hydraulic system. In the present research we studied the hydraulic regulation in grapevines (Vitis vinifera L.) that were first acclimated for 39 days to well-watered (WW), sustained water deficit (SD), or transient—cycles of dehydration–rehydration—water deficit (TD) conditions, and then subjected to varying degrees of drought. Vine development under SD led to the smallest leaves and petioles, but the TD vines had the smallest mean xylem vessel and calculated specific conductivity (k ts). Unexpectedly, both the water deficit acclimation treatments resulted in vines more vulnerable to cavitation in comparison to WW, possibly as a result of developmental differences or cavitation fatigue. When exposed to drought, the SD vines maintained the highest stomatal (g s) and leaf conductance (k leaf) under low stem water potential (Ψs), despite their high xylem vulnerability and in agreement with their lower turgor loss point (ΨTLP). These findings suggest that the down-regulation of k leaf and g s is not associated with embolism, and the ability of drought-acclimated vines to maintain hydraulic conductance and gas exchange under stressed conditions is more likely associated with the leaf turgor and membrane permeability. Electronic supplementary material The online version of this article (doi:10.1007/s00425-017-2662-3) contains supplementary material, which is available to authorized users.

Background Grape cultivars and wines are distinguishable by their color, flavor and aroma profiles. Omic analyses (transcripts, proteins and metabolites) are powerful tools for assessing biochemical differences in biological systems. Results Berry skins of red- (Cabernet Sauvignon, Merlot, Pinot Noir) and white-skinned (Chardonnay, Semillon) wine grapes were harvested near optimum maturity (°Brix-to-titratable acidity ratio) from the same experimental vineyard. The cultivars were exposed to a mild, seasonal water-deficit treatment from fruit set until harvest in 2011. Identical sample aliquots were analyzed for transcripts by grapevine whole-genome oligonucleotide microarray and RNAseq technologies, proteins by nano-liquid chromatography-mass spectroscopy, and metabolites by gas chromatography-mass spectroscopy and liquid chromatography-mass spectroscopy. Principal components analysis of each of five Omic technologies showed similar results across cultivars in all Omic datasets. Comparison of the processed data of genes mapped in RNAseq and microarray data revealed a strong Pearson’s correlation (0.80). The exclusion of probesets associated with genes with potential for cross-hybridization on the microarray improved the correlation to 0.93. The overall concordance of protein with transcript data was low with a Pearson’s correlation of 0.27 and 0.24 for the RNAseq and microarray data, respectively. Integration of metabolite with protein and transcript data produced an expected model of phenylpropanoid biosynthesis, which distinguished red from white grapes, yet provided detail of individual cultivar differences. The mild water deficit treatment did not significantly alter the abundance of proteins or metabolites measured in the five cultivars, but did have a small effect on gene expression. Conclusions The five Omic technologies were consistent in distinguishing cultivar variation. There was high concordance between transcriptomic technologies, but generally protein abundance did not correlate well with transcript abundance. The integration of multiple high-throughput Omic datasets revealed complex biochemical variation amongst five cultivars of an ancient and economically important crop species. Electronic supplementary material The online version of this article (doi:10.1186/s12864-015-2115-y) contains supplementary material, which is available to authorized users.

Grapevine cultivars possess large variability in their response to water availability, and are therefore considered as a good model to study plant hydraulic adjustments. The current research compared the petiole anatomy of two grapevine (Vitis vinifera L.) cultivars, Shiraz and Cabernet Sauvignon, in respect to hydraulic properties. Hydraulic differences between the cultivar petioles were tested over 3 years (2011–2013). Anatomical differences, hydraulic conductivity and embolism were tested under terminal drought conditions. Additionally, xylem differentiation under well watered (WW) and water deficit (WD) conditions was compared. Shiraz was shown to possess larger xylem vessels that resulted in a significantly higher theoretical specific hydraulic conductivity (Kts), leaf hydraulic conductivity (Kleaf) and maximal petiole hydraulic conductivity (Kpetiole). Under WD, smaller vessels were developed, more noticeably in Shiraz. Results confirmed a link between petiole hydraulic architecture and hydraulic behaviour, providing a simple mechanistic explanation for the higher transpiration rates commonly measured in Shiraz. Smaller xylem vessels in Cabernet Sauvignon could imply on its adaptation to WD, and explains its better performances under such conditions.

Background Grapevine metabolism in response to water deficit was studied in two cultivars, Shiraz and Cabernet Sauvignon, which were shown to have different hydraulic behaviors (Hochberg et al. Physiol. Plant. 147:443–453, 2012). Results Progressive water deficit was found to effect changes in leaf water potentials accompanied by metabolic changes. In both cultivars, but more intensively in Shiraz than Cabernet Sauvignon, water deficit caused a shift to higher osmolality and lower C/N ratios, the latter of which was also reflected in marked increases in amino acids, e.g., Pro, Val, Leu, Thr and Trp, reductions of most organic acids, and changes in the phenylpropanoid pathway. PCA analysis showed that changes in primary metabolism were mostly associated with water stress, while diversification of specialized metabolism was mostly linked to the cultivars. In the phloem sap, drought was characterized by higher ABA concentration and major changes in benzoate levels coinciding with lower stomatal conductance and suberinization of vascular bundles. Enhanced suberin biosynthesis in Shiraz was reflected by the higher abundance of sap hydroxybenzoate derivatives. Correlation-based network analysis revealed that compared to Cabernet Sauvignon, Shiraz had considerably larger and highly coordinated stress-related changes, reflected in its increased metabolic network connectivity under stress. Network analysis also highlighted the structural role of major stress related metabolites, e.g., Pro, quercetin and ascorbate, which drastically altered their connectedness in the Shiraz network under water deficit. Conclusions Taken together, the results showed that Vitis vinifera cultivars possess a common metabolic response to water deficit. Central metabolism, and specifically N metabolism, plays a significant role in stress response in vine. At the cultivar level, Cabernet Sauvignon was characterized by milder metabolic perturbations, likely due to a tighter regulation of stomata upon stress induction. Network analysis was successfully implemented to characterize plant stress molecular response and to identify metabolites with a significant structural and biological role in vine stress response.

Drought stress is known to limit photosynthesis rates and to inflict photo-oxidative damage in grapevines. Grapevines, which are considered drought-tolerant plants, are characterized by diverse hydraulic and photosynthetic behaviors, depending on the cultivar. This research compared the photosynthesis and the photorespiration of Cabernet Sauvignon (Cs) (isohydric) and Shiraz (anisohydric) in an attempt to acquire a wider perspective on the iso/anisohydric phenomenon and its implications. Shiraz and Cs were subjected to terminal drought in the greenhouse. Soil water content (θ), leaf water potential (Ψl ) and stomata conductance (gs ) were measured to determine the cultivars' hydraulic behavior. Gas exchange and fluorometry measurements were taken at 21 and 2% O2 to acquire photosynthesis and photorespiration characteristics. Cs was found to behave in a near isohydric manner whereas Shiraz behaved in a near anisohydric manner. Compared to Shiraz, the reduced stomata conductance values of Cs were accompanied by higher water use efficiency and photorespiration rates, as well as photosystem II photochemical potential (Fv /Fm ). As compared with Shiraz, Cs compensated for lower stomata conductance by higher photosynthesis and photorespiration. These two processes contributed to higher electron flow rates that might have a role in photoinhibition avoidance, which was observed in the stability of Fv /Fm under drought stress.

Background Seed of Shismus arabicus, a desert annual, display a seasonal tolerance to dehydration. The occurrence of a metabolic seasonal rhythm and its relation with the fluctuations in seed dehydration tolerance was investigated. Results Dry seeds metabolism was the least affected by the season, while the metabolism of germinated and dehydrated seeds exhibit distinct seasonal patterns. Negative associations exist between amino acids, sugars and TCA cycle intermediates and seed survival, while positive relations exist with seed germination. In contrast, associations between the level of secondary metabolites identified in the dehydrated seeds and survival percentage were evenly distributed in positive and negative values, suggesting a functional role of these metabolites in the establishment of seed dehydration tolerance. Conclusion Our results indicate the occurrence of metabolic biorhythms in germinating and dehydrating seeds associated with seasonal changes in germination and, more pronouncedly, in seed dehydration tolerance. Increased biosynthesis of protective compounds (polyphenols) in dehydrating seeds during the winter season at the expenses of central metabolites likely contributes to the respective enhanced dehydration tolerance monitored. Electronic supplementary material The online version of this article (doi:10.1186/s12870-015-0421-9) contains supplementary material, which is available to authorized users.