Kaolin Foliar Application Has a Stimulatory Effect on Phenylpropanoid and Flavonoid Pathways in Grape Berries

Abstract

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.

Chitosan Application in Vineyards (Vitis vinifera L. cv. Tinto Cão) Induces Accumulation of Anthocyanins and Other Phenolics in Berries, Mediated by Modifications in the Transcription of Secondary Metabolism Genes

“…This mechanism helps in overcoming the negative effects of high cytosolic accumulation and feedback inhibition of the end product in the cell [26]. The tonoplast transporters (ABCC1 and MATE1), and GST were observed increasingly upregulated in grape berries upon kaolin foliar application towards improved anthocyanin accumulation in berry skins [27]. Recently, the roles of ABCC and MATE transporters in vacuolar accumulation of specific metabolite crocins in saffron stigmas were characterized [28].…”

Grapevine abiotic stress assessment and search for sustainable adaptation strategies in Mediterranean-like climates. A review

“…Phenolic accumulation is also linked with several environmental disturbances (Ferrandino and Lovisolo 2014). Indeed, under high temperatures exposure, the probably increased degradation and inhibition of anthocyanins synthesis may lead to higher H 2 O 2 production with forwarding induction of the antioxidant machinery (Mori et al 2015;Conde et al 2016;Bernardo et al 2017). Flavonoids act as primary antioxidants in plant responses to a wide range of stresses, inhibiting ROS production and reducing ROS levels once they are formed (Agati et al 2012).…”

Silicates of Potassium and Aluminium (Kaolin); Comparative Foliar Mitigation Treatments and Biochemical Insight on Grape Berry Quality in Vitis vinifera L. (cv. Touriga National and Touriga Franca)

“…Moreover, it has been used in controlling pierce's disease in viticulture [14], interception of sun burn in fruits [15,16], and to control photon flux density in tree species [17,18]. Its use has been demonstrated as an effective short-term climate change mitigation strategy in Mediterranean vineyards, e.g., by reflecting infrared radiation [1,16], reducing heat stress [19][20][21], and by improving qualitative characteristics [20,[22][23][24] in grapevine. Kaolin application has been recently recommended for sustainable viticulture for winegrowers to meet various challenges of changing climatic conditions, especially in Mediterranean-like climates [25].…”