Photosynthetic electron transport activity of light and shade-acclimated field grown grapevine leaves

The light response curves of relativ e electron transport rate (ETR) in field grown grapevine (Vitis vinifer a L.) leaves were studied on different canopy exposure. The daily course of incident photosynthetic photon flux density (PPFD) was measured by means of ceptometer configured in segmented mode and inserted through the canopy. We compared the photosynthetic activity of shaded leaves and leaves exposed to sunlight on the eastern and western sides of canopy by North-South row direction. Moreover, we studied the seasonal influence of change in daily mean temperature and precipitation frequency on ETR light response curves. The different sides of canopy showed significant differences with regard the incident PPFD value, the western side received with 30% higher maximum PPFD values compared to eastern leaves. However, despite these differences we did not find any significant differences in the ETR light response curves between east and west-positioned leaves. The favourable water condition with lower daily mean temperature (<20°C) resulted in significant lower ETR values in all leaf types. Based on seasonal fluctuation of ETR light curves we can hypothesized that low temperature have higher impact on photosynthetic electron transport activities of grapevine leaves than moderate water deficit

Post-harvest UV-B treatment of White Sultanina grapevine berries

The grapevine berries are an important source of phenolic compounds. In this study, White Sultanina berries were treated with UV radiation and followed quantitative change of these secondary metabolites. In the skin of cv. White Sultanina table grapes, a phenolic acid and several mono-glycosilated flavonols were identified by HPLC-DAD. The aim of this work was to alter this profile, to improve antioxidant properties. Resveratrol contents of berry skins have already been successfully increased using UV-C or UV-B radiation (Cantos et al. 2000) in another variety (cv. Napoleon). In this study, we report a UV-B-inducible increase in flavonoid-glycosides observed 2 h after 30 min exposure to 11.5 W/m2 radiation flux (physical dose) from a narrow band source (VL-215M centred at 312 nm, Vilbert Lourmat, France). This was accompanied by higher antioxidant capacities of berry skin extracts, in accordance with the observed strong antioxidant capacities of quercetin-glycosides in vitro (Csepregi et al. 2016, Csepregi and Hideg 2018). Differences between UV-B-treated berries and untreated controls were less pronounced when assayed after a longer storage period following irradiation at 20 ℃ under low fluxes (60 µmol m-2s-1) of photosynthetically active radiation. Berry skin photosynthesis, measured as photochemical yield using imaging PAM (Heinz Walz GmbH, Effeltrich, Germany) temporary increased after the UV-B treatment, then declined, suggesting a possible metabolic source of increased flavonol biosynthesis. These experiments suggest that UV-B irradiation of table grapes can be beneficial in terms of increasing the content of potentially health-promoting flavonol derivatives

Nanostructured titanium dioxide as an antimicrobial agent on grapevine (Vitis Vinifera L.) leaves: a phytotoxicological study

In the past two decades, nanostructured materials including colloidal nanocrystals, semiconductor nanoparticles, nanotubes, nanowires and porous materials have received a great attention thanks to their unique physicochemical properties. Titanium dioxide nanoparticles (TiO2 NPs) excited by UV light can produce different reactive oxygen species (ROS) such as hydroxyl radical, superoxide radical anion and singlet oxygen. This special feature of TiO2 NPs so-called photocatalytic property can be exploited in numerous fields, especially in water treatment technologies for removing toxic compounds or inactivation various pathogens. In this work we applied directly TiO2 NPs on the grapevine (Vitis vinifera cv. Cabernet sauvignon) leaves as potential antimicrobial agent. Experiments were performed under field conditions where the plants were exposed to sunlight. Physiological responses, flavonol profile and micro- macroelements of the leaves were studied. We found that TiO2 NPs with the concentration of 250 3 00 mg kg-1 increased the stomatal conductance whereas decreased the photosynthetic rate. Despite of their negative effect on photosynthesis, flavonol profile as a stress sensitive factor showed only minor changes after the foliar exposure as revealed by HPLC-DAD measurements. Elevated level of K, Mg, Ca, P and B were detected in the treated leaves which may be related to the increased stomatal opening. Our results indicate that TiO2 NPs with the applied concentration can be phytotoxic in the presence of UV irradiation which probably stem from the excess of ROS production of nanoparticles. Consequently, further studies are necessary for determining the parameters which allows safety and efficient field applications of TiO2 NPs

Fotoreaktív nanorészecskék hatása vörösborszőlő-fajták levelének polifenol összetételére és tápelemtartalmára

A különleges tulajdonságokkal rendelkező nanoszerkezetű anyagok hasznosítása az iparban, a mezőgazdaságban és gyógyászatban egyaránt folyamatosan növekszik. A fotoreaktív titán-dioxid (TiO2) nanorészecskék sajátsága, hogy UV-fény hatására reaktív oxigén származékokat (ROS generálnak, melyek jelentős antimikrobiális hatással bírnak, így a növényre kijuttatva potenciális növényvédőszerként funkcionálhatnak. A növényekben keletkező ROS a növények élettani folyamatainak szabályozásában is részt vesznek, ezért a mesterségesen, TiO2 nanorészecskék segítségével keltett ROS a célzott antimikrobiális aktivitás mellett a levelek metabolizmusára is hatással lehet. Ez a hatás lehet negatív, mivel a ROS nagy mennyiségben sejtkárosító, de lehet pozitív is, a természetes úton keletkező ROS hatásához hasonlóan a stresszvédő utakat aktiváló. Habár a TiO2, mint alternatív növényvédőszer a gyakorlatban nagy érdeklődésre tarthat számot, ftotoxicitásáról még csak nagyon kevés információ áll rendelkezésünkre. Ebben a munkában azt tanulmányoztuk, hogy a levelek felszínére juttatott és ott napsugárzásnak kitett TiO 2 nanorészecskék miként befolyásolják a szőlőlevelek teljes fenolos tartalmát(antioxidáns kapacitását) és polifenol proflját. Ezek a paraméterek érzékenyen jelzik a növény oxidatív stresszre adott válaszreakcióit.Nyomon követtük továbbá a levelek makro- és mikroelem összetételének változását is. Szabadföldi kísérletben öt vörösborszőlő-fajtát (Cabernet sauvignon, Cabernet franc, Merlot, Kékfrankos és Kadarka) vizsgáltunk. Nagyhatékonyságú folyadékkromatográfás mérésekkel kimutattuk, hogy szőlőfajtától függően a levelek kaftársav és flavonol-glikozid tartalma a kezelést követően szignifkánsan emelkedett. A levelek teljes fenolos tartalmának növekedése szintén szignifkáns volt. Mindemellett ICP-AES méréseink azt mutatták, hogy TiO2 nanorészecskék a levelek főbb makro- és mikroelemeinek (Ca, Mg, K, B és Mn) koncentrációját ugyancsak növelték

Age- and season-dependent pattern of flavonol glycosides in Cabernet Sauvignon grapevine leaves

Flavonols play key roles in many plant defense mechanisms, consequently they are frequently investigated as stress sensitive factors in relation to several oxidative processes. It is well known that grapevine (Vitis vinifera L.) can synthesize various flavonol glycosides in the leaves, however, very little information is available regarding their distribution along the cane at different leaf levels. In this work, taking into consideration of leaf position, the main flavonol glycosides of a red grapevine cultivar (Cabernet Sauvignon) were profiled and quantified by HPLC–DAD analysis. It was found that amount of four flavonol glycosides, namely, quercetin-3-O-galactoside, quercetin-3-O-glucoside, kaempferol-3-O-glucoside and kaempferol-3-O-glucuronide decreased towards the shoot tip. Since leaf age also decreases towards the shoot tip, the obtained results suggest that these compounds continuously formed by leaf aging, resulting in their accumulation in the older leaves. In contrast, quercetin-3-O-glucuronide (predominant form) and quercetin-3-O-rutinoside were not accumulated significantly by aging. We also pointed out that grapevine boosted the flavonol biosynthesis in September, and flavonol profile differed significantly in the two seasons. Our results contribute to the better understanding of the role of flavonols in the antioxidant defense system of grapevine

Managing Phenol Contents in Crop Plants by Phytochemical Farming and Breeding—Visions and Constraints

Two main fields of interest form the background of actual demand for optimized levels of phenolic compounds in crop plants. These are human health and plant resistance to pathogens and to biotic and abiotic stress factors. A survey of agricultural technologies influencing the biosynthesis and accumulation of phenolic compounds in crop plants is presented, including observations on the effects of light, temperature, mineral nutrition, water management, grafting, elevated atmospheric CO2, growth and differentiation of the plant and application of elicitors, stimulating agents and plant activators. The underlying mechanisms are discussed with respect to carbohydrate availability, trade-offs to competing demands as well as to regulatory elements. Outlines are given for genetic engineering and plant breeding. Constraints and possible physiological feedbacks are considered for successful and sustainable application of agricultural techniques with respect to management of plant phenol profiles and concentrations

How do grapevine leaf phenolic contents respond to daily changes in environmental factors?

Grapevine leaves are rich in phenolic compounds, many of which are – among fulfilling other roles – efficient antioxidants (Csepregi et al. 2016, Csepregi and Hideg 2017). The long-term aim of a recently launched project is to explore the functional plasticity of phenolic compounds in grapevine leaves. Here we present results of a pilot study, registering and analysing hour-by-hour changes in photosynthesis, phenolic profiles and antioxidant capacities of South-facing Pinot noir leaves between 7 am and 7 pm during a clear summer day mid-July at Pécs (N46.071, E18.156). During this 12h period, photosynthetically active radiation (PAR) was 80-2130 µmol/m2/s and UV radiation (UV-A+B) varied between 5-46.1 kJ/m2 as physical dose measured on site. Local data were separated into UV-B (280-315 nm) and UV-A (315-400 nm) regions based on a model calculation (NCAR). Total adaxial flavonoid content (measured as Dualex flavonoid index) varied between 88% and 112% of the daily average and showed strong positive correlations with PAR, UV-A, UV-B, leaf temperature and net CO2 assimilation. Stomatal conductance (gs) was positively correlated with PAR, UV-A and UV-B. However, substomatal CO2 concentrations (Ci) were only correlated with PAR (positively) and not with UV. Hourly changes in leaf antioxidant capacities and phenolic profiles measured with HPLC-DAD complete the analysis

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