Federico J. Berli

Abscisic acid is involved in the response of grape (Vitis vinifera L.) cv. Malbec leaf tissues to ultraviolet-B radiation by enhancing ultraviolet-absorbing compounds, antioxidant enzymes and membrane sterols.

We investigated the interactions of abscisic acid (ABA) in the responses of grape leaf tissues to contrasting ultraviolet (UV)-B treatments. One-year-old field-grown plants of Vitis vinifera L. were exposed to photosynthetically active radiation (PAR) where solar UV-B was eliminated by using polyester filters, or where PAR was supplemented with UV-B irradiation. Treatments combinations included weekly foliar sprays of ABA or a water control. The levels of UV-B absorbing flavonols, quercetin and kaempferol were significantly decreased by filtering out UV-B, while applied ABA increased their content. Concentration of two hydroxycinnamic acids, caffeic and ferulic acids, were also increased by ABA, but not affected by plus UV-B (+UV-B) treatments. Levels of carotenoids and activities of the antioxidant enzymes, catalase, ascorbate peroxidase and peroxidase were elevated by +ABA treatments, but only if +UV-B was given. Cell membrane beta-sitosterol was enhanced by ABA independently of +UV-B. Changes in photoprotective compounds, antioxidant enzymatic activities and sterols were correlated with lessened membrane harm by UV-B, as assessed by ion leakage. Oxidative damage expressed as malondialdehyde content was increased under +UV-B treatments. Our results suggest that the defence system of grape leaf tissues against UV-B is activated by UV-B irradiation with ABA acting downstream in the signalling pathway.

Solar UV-B and ABA Are Involved in Phenol Metabolism of Vitis vinifera L. Increasing Biosynthesis of Berry Skin Polyphenols

It has been previously found that abscisic acid (ABA) participates in the activation of grapevine leaf tissue defense against potentially damaging effects of solar ultraviolet-B radiation (UV-B), apparently by triggering biosynthesis of phenols that filter the harmful radiation and act as antioxidants. The present work studies the effect of solar UV-B and exogenously applied ABA on berry growth, sugar accumulation, and phenol (anthocyanin and nonanthocyanin) profiles across berry development and ripening of Vitis vinifera L. cv. Malbec in a vineyard at 1450 m of altitude. The grapevines were exposed to relatively high UV-B irradiation (normal sunlight; +UV-B) and also to a reduced UV-B treatment (filter exclusion; -UV-B). These two UV-B treatments were combined with weekly spray applications to the leaves and berries of 1 mM ABA (+ABA) or H(2)O (-ABA). Reduction of UV-B delayed berry development and maturation, whereas the +UV-B and +ABA combined treatment hastened berry sugar and phenol accumulation. +UV-B/+ABA treatments also reduced berry growth and decreased sugar per berry without affecting sugar concentration (°Brix) at harvest. Berry skin ABA levels were higher in the +UV-B and +ABA combined treatment, which also hastened the onset of ripening up to 20 days. Berry skin ABA levels then decreased toward harvest, implying a possible role for ABA in the control of ripening in this nonclimacteric fruit. Under both +UV-B and +ABA treatments berry skin phenols were additively increased with a change in anthocyanin and nonanthocyanin profiles and increases in the proportion of phenols with high antioxidant capacity.

Azospirillum brasilense ameliorates the response of Arabidopsis thaliana to drought mainly via enhancement of ABA levels

Production of phytohormones is one of the main mechanisms to explain the beneficial effects of plant growth-promoting rhizobacteria (PGPR) such as Azospirillum sp. The PGPRs induce plant growth and development, and reduce stress susceptibility. However, little is known regarding the stress-related phytohormone abscisic acid (ABA) produced by bacteria. We investigated the effects of Azospirillum brasilense Sp 245 strain on Arabidopsis thaliana Col-0 and aba2-1 mutant plants, evaluating the morphophysiological and biochemical responses when watered and in drought. We used an in vitro-grown system to study changes in the root volume and architecture after inoculation with Azospirillum in Arabidopsis wild-type Col-0 and on the mutant aba2-1, during early growth. To examine Arabidopsis development and reproductive success as affected by the bacteria, ABA and drought, a pot experiment using Arabidopsis Col-0 plants was also carried out. Azospirillum brasilense augmented plant biomass, altered root architecture by increasing lateral roots number, stimulated photosynthetic and photoprotective pigments and retarded water loss in correlation with incremented ABA levels. As well, inoculation improved plants seed yield, plants survival, proline levels and relative leaf water content; it also decreased stomatal conductance, malondialdehyde and relative soil water content in plants submitted to drought. Arabidopsis inoculation with A. brasilense improved plants performance, especially in drought.

Volatile organic compounds characterized from grapevine (Vitis vinifera L. cv. Malbec) berries increase at pre-harvest and in response to UV-B radiation

Ultraviolet-B solar radiation (UV-B) is an environmental signal with biological effects in plant tissues. Recent investigations have assigned a protective role of volatile organic compounds (VOCs) in plant tissues submitted to biotic and abiotic stresses. This study investigated VOCs in berries at three developmental stages (veraison, pre-harvest and harvest) of Vitis vinifera L. cv. Malbec exposed (or not) to UV-B both, in in vitro and field experiments. By Head Space-Solid Phase Micro Extraction-Gas Chromatography-Electron Impact Mass Spectrometry (HS-SPME-GC-EIMS) analysis, 10 VOCs were identified at all developmental stages: four monoterpenes, three aldehydes, two alcohols and one ketone. Monoterpenes increased at pre-harvest and in response to UV-B in both, in vitro and field conditions. UV-B also augmented levels of some aldehydes, alcohols and ketones. These results along with others from the literature suggest that UV-B induce grape berries to produce VOCs (mainly monoterpenes) that protect the tissues from UV-B itself and other abiotic and biotic stresses, and could affect the wine flavor. Higher emission of monoterpenes was observed in the field experiments as compared in vitro, suggesting the UV-B/PAR ratio is not a signal in itself.

UV-B impairs growth and gas exchange in grapevines grown in high altitude

We previously demonstrated that solar ultraviolet-B (UV-B) radiation levels in high altitude vineyards improve berry quality in Vitis vinifera cv. Malbec, but also reduce berry size and yield, possibly as a consequence of increased oxidative damage and growth reductions (lower photosynthesis). The defense mechanisms toward UV-B signal and/or evoked damage promote production of antioxidant secondary metabolites instead of primary metabolites. Purportedly, the UV-B effects will depend on tissues developmental stage and interplay with other environmental conditions, especially stressful situations. In this work, grapevines were exposed to high solar UV-B (+UV-B) and reduced (by filtering) UV-B (-UV-B) treatments during three consecutive seasons, and the effects of UV-B, developmental stages and seasons on the physiology were studied, i.e. growth, tissues morphology, photosynthesis, photoprotective pigments, proline content and antioxidant capacity of leaves. The +UV-B reduced photosynthesis and stomatal conductance, mainly through limitation in gas exchange, reducing plants leaf area, net carbon fixation and growth. The +UV-B augmented leaf thickness, and also the amounts of photoprotective pigments and proline, thereby increasing the antioxidant capacity of leaves. The defense mechanisms triggered by + UV-B reduced lipid peroxidation, but they were insufficient to protect the photosynthetic pigments per leaf dry weight basis. The +UV-B effects depend on tissues developmental stage and interplay with other environmental conditions such as total radiation and air temperatures.

Gibberellins and Abscisic Acid Promote Carbon Allocation in Roots and Berries of Grapevines

Carbon allocation within grapevines may affect berry growth and development. The plant hormones gibberellins (GAs) and abscisic acid (ABA) control various processes across the plant life and both have been involved in assimilate production and transport in different species. Hence, this work examined the distribution of sugars (sucrose, fructose, and glucose) and starch in grapevines at veraison after foliar applications of GA3, ABA, and an inhibitor of GA biosynthesis, paclobutrazol (PBZ). The results demonstrated that GA3 increased total grapevine mass, with carbon allocated to the whole grapevine (as structural and soluble carbohydrates). Both GA3 and ABA increased monosaccharide (glucose and fructose) levels in berries (up to tenfold) and roots (up to threefold). However, GA3 increased the net carbon fixation whereas ABA did not. PBZ diminished most growth parameters except grapevine mass, and allocated more carbohydrates to roots (up to threefold more sucrose and starch). Such results indicate that GAs promote net carbon fixation and transport, whereas ABA as a stress signal only enhances sugar transport; notwithstanding the two hormones promoted carbon allocation toward roots and berries.

Acclimation mechanisms elicited by sprayed abscisic acid, solar UV-B and water deficit in leaf tissues of field-grown grapevines

The independent and interactive effects of solar ultraviolet-B radiation (UV-B), moderate water deficit and sprayed abscisic acid (ABA) on leaves gas exchange and biochemical aspects of field-grown grapevines of the cv. Malbec were investigated in a high altitude vineyard (1450 m a.s.l.). Two UV-B treatments (ambient solar UV-B or reduced UV-B), two watering treatments (well watered or moderate water deficit) and two ABA treatments (no ABA and sprayed ABA) were given alone and combined in a factorial design. Gas exchange and photosynthesis were reduced by water deficit and highly impaired in the UV-B and water deficit combined treatment. UV-absorbing compounds were stimulated independently by UV-B. The monoterpenes α-pinene, 3-carene and terpinolene, and the sesquiterpene nerolidol were augmented by UV-B, water deficit or sprayed ABA. Levels of the triterpene squalene and the diterpene phytol were significantly higher in the treatment that combined UV-B, water deficit and ABA applications. Environment signals (solar UV-B and moderate water deficit) and sprayed ABA elicited mechanisms of acclimation by augmenting the content of terpenes with antioxidant and antifungal properties, thus enhancing the plant defensive mechanisms towards signals both biotic and abiotic.

Malbec grape (Vitis vinifera L.) responses to the environment: Berry phenolics as influenced by solar UV-B, water deficit and sprayed abscisic acid

High-altitude vineyards receive elevated solar ultraviolet-B (UV-B) levels so producing high quality berries for winemaking because of induction in the synthesis of phenolic compounds. Water deficit (D) after veraison, is a commonly used tool to regulate berry polyphenols concentration in red wine cultivars. Abscisic acid (ABA) plays a crucial role in the acclimation to environmental factors/signals (including UV-B and D). The aim of the present study was to evaluate independent and interactive effects of high-altitude solar UV-B, moderate water deficit and ABA applications on Vitis vinifera cv. Malbec berries. The experiment was conducted during two growing seasons with two treatments of UV-B (+UV-B and -UV-B), watering (+D and -D) and ABA (+ABA and -ABA), in a factorial design. Berry fresh weight, sugar content, fruit yield, phenolic compounds profile and antioxidant capacity (ORAC) were analyzed at harvest. Previous incidence of high UV-B prevented deleterious effects of water deficit, i.e. berry weight reduction and diminution of sugar accumulation. High UV-B increased total phenols (mainly astilbin, quercetin and kaempferol) and ORAC, irrespectively of the combination with other factors. Fruit yield was reduced by combining water deficit and high UV-B or water deficit and ABA. Two applications of ABA were enough to induced biochemical changes increasing total anthocyanins, especially those with higher antioxidant capacity.

UV-B and abscisic acid effects on grape berry maturation and quality

This review provides an overview of existing literature on the effects of ultraviolet-B (UV-B) radiation and abscisic acid (ABA) on physiological and biochemical aspects affecting grape berry (Vitis vinifera L.) growth, maturation and their quality for winemaking. The UV-B (280-315 nm) comprises only a small fraction of sunlight that reaches the Earths surface, but has enough energy to cause large photobiological effects on higher plants. The UV-B levels are greater in the tropics than in upper latitudes and also increase with altitude, hence some vineyards are exposed to high UV-B but photoprotection and repair mechanisms are usually sufficient to prevent the occurrence of damage in grapevine tissues. ABA is a phytohormone that, aside to control stomatal aperture, regulates acclimation to adverse environmental conditions, and controls grape berry maturation (non-climacteric). A promotive effect of UV-B on ABA biosynthesis has been found in grapevine leaves. Accumulation of phenols (namely phenolic acids, stilbenes and flavonoids) is an acclimation and protective response against UV-B, either directly by absorbing UV-B in epidermal tissues and/or by reducing its penetration through underlying tissues, or indirectly by scavenging free radicals so acting as antioxidants. High UV-B and ABA applications increase total phenols in grape berries, but those with higher antioxidant capacity (i.e. dihydroxylated anthocyanidins and flavonols like quercetin) are increased relatively more. These treatments also hasten berry sugar and phenol accumulation, but reduce berry growth and sugar per berry at harvest, and therefore decrease yield. The quality of grape berries for winemaking integrates various aspects, but for red wines, it has a high correlation with accumulation of phenolics stimulated by UV-B and ABA.

High Altitude Solar UV-B and Abscisic Acid Sprays Increase Grape Berry Antioxidant Capacity

It has been proposed that ultraviolet-B (UV-B) radiation activates the antioxidant defense system in grapevines and that abscisic acid (ABA) acts downstream in the signaling pathway. Here, we studied the effects of solar UV-B and ABA sprays on berry quality indicators and fruit yield in Vitis vinifera L. cv. Malbec grown in a high-altitude vineyard, for five developmental stages and three growing seasons. Grapevines were exposed to elevated ambient solar UV-B (+UV-B) or to UV-B-filtered sunlight (−UV-B) from 15 days before flowering, combined with weekly sprays of 1 mM ABA (+ABA) or water (−ABA) from 27 days before veraison. The concentration of phenols (anthocyanins and total polyphenols) in berry skin was increased by +UV-B and +ABA, and there was a significant interaction between UV-B and ABA. For a given increase in sugar content, antioxidant capacity and phenolic contents were higher in berries in the +UV-B/+ABA treatment than in berries in the −UV-B/−ABA treatment. +UV-B and +ABA interacted to lessen the number of berries, possibly because of higher ethylene emissions, and additively reduced cluster weight without affecting sugar concentration at harvest. Antioxidant compounds, which are protective for plants, were triggered by +UV-B/+ABA at the expense of sugar accumulation, berry retention, and growth (fruit yield). Effects of UV-B and ABA on sugar accumulation and berry growth were dependent on the developmental stage. In high-altitude vineyards, solar UV-B and ABA application interact to increase quality indicators in red grape berries. The effects of UV-B and ABA on berry quality indicators are significant on a concentration basis (important from a winemaking standpoint) and additive on a per-berry basis.