Lia-Tânia Dinis

Kaolin exogenous application boosts antioxidant capacity and phenolic content in berries and leaves of grapevine under summer stress

Heat waves, high light intensities and water deficit are becoming important threats in many important viticultural areas worldwide, so the implementation of efficient and cost-effective mitigation strategies is crucial for the production of premium wines while maintaining productivity. In this context, the foliar application of kaolin, a chemically inert mineral with excellent reflective properties, is being developed and experimented as a strategy to reduce the impact of heat and drought in Douro vineyards (Northern Portugal), already revealing promising results. In the present study we investigated if an improved antioxidant capacity is part of the beneficial effects of kaolin, by studying changes in the enzymatic and nonenzymatic antioxidant system in leaves and berries (cv Touriga Nacional). Results showed that mature grape berries contained higher amounts of total phenols (40%), flavonoids (24%), anthocyanins (32%) and vitamin C (12%) than fruits from control vines, and important changes were also measured in leaves. In parallel, kaolin application improved the antioxidant capacity in berries, which was correlated with the observed increased content in secondary metabolites. Kaolin application also regulated secondary metabolism at the transcriptional level through the increase in the transcript abundance of genes encoding phenylalanine ammonia lyase and chalcone synthase.

Kaolin-based, foliar reflective film protects photosystem II structure and function in grapevine leaves exposed to heat and high solar radiation

Extreme conditions, such as drought, high temperature, and solar irradiance intensity, are major factors limiting growth and productivity of grapevines. In a field experiment, kaolin particle film application on grapevine leaves was examined during two different summer conditions (in 2012 and 2013) with the aim to evaluate benefits of this practice against stressful conditions hindering photochemical processes. We used chlorophyll a fluorescence to investigate attached leaves. Two months after the application, during the hottest midday, the kaolin-treated plants showed by the JIP test significantly higher quantum yield of PSII photochemistry, flux ratios, maximum trapped excitation flux of PSI, absorption flux, electron transport flux, maximum trapped energy flux per cross section, and performance index than plants under control conditions in the warmer year. On the contrary, the treated plants showed a lower initial slope of relative variable fluorescence and a decrease in the absorption and electron transport per cross section. The JIP test showed higher efficiency of PSII in the plants treated with kaolin mainly in 2013 (higher temperature and drought). Our results supported the hypothesis that the accumulation of active PSII reaction centres was associated with decreased susceptibility to photoinhibition in the kaolin-treated plants and with more efficient photochemical quenching. Grapevines in the Douro Region seems to profit from the kaolin application.

Kaolin foliar application has a stimulatory effect on phenylpropanoid and flavonoid pathways in grape berries

Drought, elevated air temperature, and high evaporative demand are increasingly frequent during summer in grape growing areas like the Mediterranean basin, limiting grapevine productivity and berry quality. The foliar exogenous application of kaolin, a radiation-reflecting inert mineral, has proven effective in mitigating the negative impacts of these abiotic stresses in grapevine and other fruit crops, however, little is known about its influence on the composition of the grape berry and on key molecular mechanisms and metabolic pathways notably important for grape berry quality parameters. Here, we performed a thorough molecular and biochemical analysis to assess how foliar application of kaolin influences major secondary metabolism pathways associated with berry quality-traits, leading to biosynthesis of phenolics and anthocyanins, with a focus on the phenylpropanoid, flavonoid (both flavonol- and anthocyanin-biosynthetic) and stilbenoid pathways. In grape berries from different ripening stages, targeted transcriptional analysis by qPCR revealed that several genes involved in these pathways—VvPAL1, VvC4H1, VvSTSs, VvCHS1, VvFLS1, VvDFR, and VvUFGT—were more expressed in response to the foliar kaolin treatment, particularly in the latter maturation phases. In agreement, enzymatic activities of phenylalanine ammonia lyase (PAL), flavonol synthase (FLS), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) were about two-fold higher in mature or fully mature berries from kaolin-treated plants, suggesting regulation also at a transcriptional level. The expression of the glutathione S-transferase VvGST4, and of the tonoplast anthocyanin transporters VvMATE1 and VvABCC1 were also all significantly increased at véraison and in mature berries, thus, when anthocyanins start to accumulate in the vacuole, in agreement with previously observed higher total concentrations of phenolics and anthocyanins in berries from kaolin-treated plants, especially at full maturity stage. Metabolomic analysis by reverse phase LC-QTOF-MS confirmed several kaolin-induced modifications including a significant increase in the quantities of several secondary metabolites including flavonoids and anthocyanins in the latter ripening stages, probably resulting from the general stimulation of the phenylpropanoid and flavonoid pathways.

Improvement of grapevine physiology and yield under summer stress by kaolin-foliar application: water relations, photosynthesis and oxidative damage

Knowledge about short-term climate change adaptation strategies for Mediterranean vineyards is needed in order to improve grapevine physiology and yield-quality attributes. We investigated effects of kaolin-particle film suspension on water relations, photosynthesis and oxidative stress of field-grown grapevines in the Douro region (northern Portugal) in 2012 and 2013. Kaolin suspension decreased leaf temperature by 18% and increased leaf water potential (up to 40.7% in 2013). Maximum photochemical quantum efficiency of PSII was higher and the minimal chlorophyll fluorescence was lower in the plants sprayed by kaolin. Two months after application, net photosynthesis and stomatal conductance at midday increased by 58.7 and 28.4%, respectively, in treated plants. In the same period, kaolin treatment increased photochemical reflectance, photosynthetic pigments, soluble proteins, soluble sugars, and starch concentrations, while decreased total phenols and thiobarbituric acid-reactive substances. Kaolin application can be an operational tool to alleviate summer stresses, which ameliorates grapevine physiology and consequently leads to a higher yield.

The role of nighttime water balance on Olea europaea plants subjected to contrasting water regimes

The climate change scenarios besides foreseeing a severe drought imposition also emphasize the temperature rising in the Mediterranean region, with special prominence at nighttime. Despite the high olive tree tolerance to severe environmental conditions, stomatal nighttime water loss can change plant water relations, and the related consequences and opportunities, especially under water scarcity, must be clarified. A set of 3-year-old potted olive trees were subjected to three cycles of drought, imposed by withholding irrigation, while another group were continuously irrigated. At the end of the latter and more severe drought cycle, daytime gas exchange parameters, water status and membrane integrity was negatively affected by drought imposition. Moreover, the nighttime transpiration rate was far above cuticular water loss, suggesting sustained stomatal aperture during nighttime, leading to substantial water losses, which was higher under drought in the first hours of darkness. The higher nighttime stomatal conductance of droughted plants were related with higher starch concentration in their leaves, a thicker trichome layer and a lower intercellular CO2 concentration, in a closely association with an inferior nighttime respiration. Still, whole-plant transpiration on droughted plants were much lower than leaf transpiration-based estimates, which is interpreted as compensation by water inputs due to dew deposition on leaves. Although unexpected, the increased of stomatal conductance in the first hours of the night, until a certain level of water deficit intensity, could be linked with potential benefits to the plants.

Kaolin particle film application stimulates photoassimilate synthesis and modifies the primary metabolome of grape leaves

Water scarcity is associated with extreme temperatures and high irradiance, and significantly and increasingly affects grapevine yield and quality. In this context, the foliar application of kaolin, a chemically inert mineral that greatly reflects ultraviolet and infrared radiations, as well as, in part, photosynthetically active radiation, has recently been shown to decrease photoinhibition in mature leaves. Here, the influence of this particle film on grapevine leaf metabolome and carbohydrate metabolism was evaluated. Molecular mechanisms underlying photoassimilate synthesis, metabolism and transport capacity were assessed by targeted transcriptional analyses and enzymatic activity assays. Kaolin application increased sucrose concentration in leaves and sucrose transport/phloem loading capacity, as suggested by the stimulation of the transcription of sucrose transporters VvSUC12 and VvSUC27 in these source organs. While the biosynthesis of sucrose increased, as evidenced by higher sucrose content and sucrose phosphate synthase (SPS) activity in leaves, the concentration of transitory starch before the dark period remained unaltered, despite a higher total amylolytic activity in the leaves of kaolin-treated plants. Metabolomic analysis by GC-TOF-MS showed that the application of kaolin enhanced the amounts of simple sugars, including fructose, maltose, xylulose, xylose, sophorose, ribose and erythrose; sugars-phosphate, like mannose-6-Pi, hexose-6-Pi, glucose-6-Pi, glucose-1-Pi, glycerol-α-Pi and fructose-6-Pi; polyols, like xylitol, maltitol, lactitol, glycerol, galactinol and erythritol; organic acids and amino acids.