Understanding the Sensitivity of Grape Terpenes to Jasmonates Using In Vitro Culture and In Vivo Vineyard Experiments.

Terpene volatiles define the flavor of terpenic grape cultivars. However, grape terpene concentrations can vary 2- to 3-fold across seasons and vineyards, impacting vintage quality. The plant hormone methyl jasmonate (MeJA) stimulates grape terpene production but is expensive and can decrease berry weight and maturity. The synthetic jasmonate prohydrojasmon (PDJ) is cost-effective yet has not been evaluated on grape maturity and terpene production. Here, we performed in vitro (berry culture) and in vivo (vineyard) experiments using Gewürztraminer (Vitis vinifera L.) to evaluate the time- and concentration-dependent sensitivity of maturity parameters and terpene content to MeJA and PDJ. In vitro berry weight was reduced by high MeJA and PDJ concentration across timings. Terpenes were most sensitive to low MeJA concentration at veraison (increased 24-fold) in vitro. Moderate PDJ concentration applied at veraison doubled (increased twofold) terpene concentration in vivo without impacting berry weight or maturity. In conclusion, PDJ may provide a solution to mitigate seasonal variability in terpene production in terpenic grape cultivars.

Juxtaposition of the Source-to-Sink Ratio and Fruit Exposure to Solar Radiation on cv. Merlot (Vitis vinifera L.) Berry Phenolics in a Cool versus Warm Growing Region.

The grapevine source-to-sink ratio and berry exposure to solar radiation both influence grape flavonoid biosynthesis and accumulation. Here, we compared these concepts on cv. Merlot in two different growing locations (Michigan (MI) and Friuli-Venezia Giulia (FVG), IT) to understand whether the environment influences flavonoid sensitivity to these parameters. Three levels of leaf removal (LR0, LR5, LR8) were implemented at the pea-size phenological stage to compare conditions of increased cluster light exposure with a decreasing vine source-to-sink ratio on berry flavonoid accumulation. Treatments did not affect total soluble solids (TSSs) or pH, but titratable acidity (TA) was lower in LR8 at harvest in both locations. LR5 increased anthocyanins and flavonols in MI but decreased most phenolics in FVG. The decreased expression of VviLAR1 and VviF3'5'Hh during ripening supported the lower concentrations of flavan-3-ol monomers and anthocyanins in FVG. In summary, flavonoid biosynthesis and accumulation were more sensitive to solar radiation than the source-to-sink ratio, and the vineyard environment dictated whether solar radiation was beneficial or detrimental to flavonoid biosynthesis.

Impact of hormone applications on ripening-related metabolites in Gewürztraminer grapes (Vitis vinifera L.): The key role of jasmonates in terpene modulation.

Terpenes play a formative role in grape and wine flavor, particularly for high-terpenic cultivars. Differences in terpene profiles influence grape varietal character and vintage quality. Little is known about the endogenous factors controlling terpene biosynthesis in grape. Through multiple experiments, six hormones (abscisic acid, ABA; ethylene, ETH; jasmonic acid, JA; methyl jasmonate, MeJA; indole-3-acetic acid, IAA; 1-naphthaleneacetic acid, NAA) that either promote or repress ripening were applied to Gewürztraminer clusters near veraison to gauge their effect on ripening and terpene biosynthesis. Jasmonates (JA, MeJA) increased terpene concentrations and the expression of terpene genes in grapes. Such increases were not associated to increases of other ripening-related metabolites such as sugars or anthocyanins. MeJA also affected the expression of several hormone related genes, increased IAA levels, and reduced sugar and anthocyanin concentration in grapes. This research provides novel insights into terpene regulation by ripening-related hormones and jasmonates in grapes.

Influence of freezing and heating conditions on grape seed flavan-3-ol extractability, oxidation, and galloylation pattern.

In cool-climate viticulture, the short growing season can influence grape seed maturation by reducing the apparent oxidation of flavan-3-ol monomers and associated increase in seed browning. A reduction in seed maturation increases the potential extraction of flavan-3-ol monomers into wine during maceration operations, heightening bitterness. Here, we carried out a 2 × 2 factorial experiment to test the ability of freezing and heating treatments to advance maturation (decrease flavan-3-ol, improve browning) of (Vitis vinifera L.) Pinot noir and Cabernet Sauvignon seeds over a 24-h incubation period. Only freezing significantly increased seed browning in both cultivars. Subsequent correlations with seed flavan-3-ol monomer concentrations suggest that freezing enhanced the oxidation of these compounds. Interestingly, natural ripening and freezing reduced galloylated flavan-3-ol monomers to a greater extent than non-galloylated ones. This study provides new information regarding the susceptibility of flavan-3-ol monomers to freezing and heating, and also suggests that freezing can advance the maturation the seeds of under-ripe red vinifera grapes.

Canopy architecture and fruit microclimate, not ripening-related phytohormones, control phenylpropanoid accumulation in response to early leaf removal in 'Merlot' (Vitis vinifera L.) grapevines.

Early leaf removal (ELR) applied in the grapevine cluster zone at bloom or pre-bloom (PB) is a vineyard practice commonly utilized to reduce fruit disease and yield. In addition, the literature reports that ELR enhances fruit quality, however, little research has deciphered the potential factors regulating this response. In this work, the objective was to understand whether the increase in fruit quality in response to manual or mechanical leaf removal is due to changes in fruit-zone microclimate, vine physiology, or ripening/stress related hormone biosynthesis. In 'Merlot' (Vitis vinifera L.) vines, 60% of leaf area was removed from shoots in three ways: 1) manual removal of 5 leaves (PB-MA), 2) mechanical removal (PB-ME), and 3) simulated mechanical removal (PB-SIM), which was implemented by removing the distal portion of leaves on the first eight nodes to understand whether PB-ME improves fruit quality via enhanced microclimate conditions or plant stress. Yield was reduced in PB-ME and PB-SIM, while total soluble solids was not different at harvest; meaning that ELR decreased the partitioning of carbohydrates to fruit. Anthocyanins and flavonols were enhanced by PB-ME, however neither ABA nor ethylene were similarly altered. Instead, the leaf area at nodes above the fruit-zone was lower in PB-ME compared to non-defoliated ones, which increased post-veraison fruit temperature (+2.8 °C). These parameters correlated with anthocyanins at harvest. In conclusion, skin phenylpropanoid concentrations were influenced by canopy density above the fruit-zone. Additionally, ripening-related phytohormones were not involved in the response of phenylpropanoid biosynthesis in vine subjected to ELR.

Exogenous melatonin improves glutathione content, redox state and increases essential oil production in two Salvia species under drought stress.

This research was conducted to understand the influence of foliar applied melatonin (0, 50, 100, 150 and 200 µM) on two Salvia species (Salvia nemorosa L., and Salvia reuterana Boiss) under conditions of water stress. Water stress was applied using a reduced irrigation strategy based on re-watering at 80%, 60% and 40% of the field capacity (FC). Increasing water stress, while significantly enhancing malondialdehyde (MDA), H2O2, electrolyte leakage, oxidized glutathione (GSSG), and total glutathione (GT), reduced glutathione (GSH), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) activities, which led to a marked reduction in fluorescence (Fv/Fm). Foliar application of melatonin alleviated the oxidative stress by increasing GT, CAT, POD, SOD and GR activities and reducing GSSG. In particular, melatonin heightened GSH content as well as the ratio of GSH/GSSG when compared to non-sprayed water stressed plants. Melatonin-treated plants had significantly lower SOD and POD activities than control plants under drought stress, while the CAT activity was enhanced with the foliar treatment. Essential oil yield of both Salvia species increased with the decrease in irrigation from 80% to 60% FC but diminished with the more severe water deficit (40% FC). Essential oil components of Salvia nemorosa were ß- caryophyllene, germacrene- B, spathulenol, and cis- ß- farnesene, while (E) - ß- ocimene, α- gurjnnene, germacrene-D, hexyl acetate and aromadendrene was the major constituents of Salvia reuterana. When plants were subjected to water deficit, melatonin treatment increased the concentration and composition of the essential oil. In particular, melatonin treatments improved the primary oil components in both species when compared to non-melatonin treated plants. In conclusion, reduced irrigation regimes as well as melatonin treatments resulted in a significant improvement of essential oil production and composition in both Salvia species.

Impacts of Pre-bloom Leaf Removal on Wine Grape Production and Quality Parameters: A Systematic Review and Meta-Analysis.

Wine grape (Vitis vinifera L.) is the most widely cultivated fruit crop in the world. However, the climactic characteristics in some growing regions are suboptimal for grape production, including short season length and excess precipitation. Grape growers can utilize an array of methods to mitigate these issues, including "early leaf removal," a management practice involving the removal of leaves from selected basal nodes along shoots around bloom. This meta-analysis reviews the extensive literature on this practice, with specific regards to application at "pre-bloom" (PB). One hundred seventy-five publications on the topic of "early leaf removal" were identified using key terms and subsequently narrowed via eight data curation steps. The comparison between treated (PB) and control plants in these studies revealed two important results. First, PB lowered bunch rot disease (-61%), partially through reducing the compactness of clusters. Second, PB promoted a significant increase in fruit total soluble solids (°Brix, +5.2%), which was related to the increase in the leaf-to-fruit ratio. Furthermore, cultivar and rootstock were found to have a large influence on the success of PB, while the contribution of climate was smaller. In conclusion, PB significantly lowers yield and bunch rot disease and increases °Brix, both of which improve grape and wine quality.

Increase in seed tannin extractability and oxidation using a freeze-thaw treatment in cool-climate grown red (Vitis vinifera L.) cultivars.

Grape seed maturation involves the gradual oxidation of tannins, decreasing excessive bitterness and astringency in wine. In cool climates, this process is limited by the short growing season, affecting wine quality. A "freeze-thaw" treatment on seeds of red vinifera cultivars at veraison and harvest was used to evaluate the effect of oxidation and extractability on seed phenolic fractions. Freezing increased the extraction of total phenolics and o-diphenols quantified from fractionation (fraction 1, vacuolar tannins; fraction 2, hydrogen bonded tannins; fraction 3, covalently bonded tannins), especially at harvest. Despite this, colorimetry, microscopy, oxidation reactivity index (ORI), and correlations between the color index and fractions indicated that freezing disrupted vacuole integrity, enhancing oxidation in the seed coat. In conclusion, vacuolar tannins (which are the main seed phenolics extracted during fermentation) were highly correlated with seed color change, potentially providing information for winemaking in cool climate regions.

Enhancement of Fruit Technological Maturity and Alteration of the Flavonoid Metabolomic Profile in Merlot ( Vitis vinifera L.) by Early Mechanical Leaf Removal.

Removal of basal leaves near blooms inevitably affects grapevine balance and cluster microclimate conditions, improving fruit quality. Mechanization of this practice allows growers to save time and resources, but to our knowledge, it has not yet been compared with the manual application of this practice in a cool-climate region where seasonal temperatures frequently limit fruit technological maturity and phenolic ripening in red Vitis vinifera cultivars. In our research, berry sugar concentration was highest with prebloom mechanical treatment (PB-ME). Furthermore, metabolomics analysis revealed that PB-ME favored the accumulation of significantly more disubstituted anthocyanins and flavonols and OH-substituted anthocyanins compared with manual application. Given that vine balance was similar between treatments, increased ripening with PB-ME is likely due to enhanced microclimate conditions and higher carbon partitioning through a younger canopy containing basal leaf fragments proximal to fruit. This information provides an important strategy for consistently ripening red Vitis vinifera cultivars in cool climates.