Fine-tuning of grapevine xanthophyll-cycle and energy dissipation under Mediterranean conditions by kaolin particle-film

Kaolin-particle film has been considered a low-cost technology to mitigate the adverse effects of high light and temperature, and drought in several crops. However, the underlying excess energy absorption and dissipation mechanisms, and related components associated with kaolin photoprotective effects in grapevines are poorly explored. This study aims to understand the interactions between kaolin foliar treatment and photosynthetic pigments accumulation, carotenoids metabolism, xanthophyll cycle regulation, and its putative role on the non-photochemical quenching (NPQ) processes in Touriga-Franca (TF) and Touriga-Nacional (TN) varieties. The experiments were conducted during the 2017 summer season in a commercial vineyard, and measurements were performed at pre-dawn and midday in each sampling date (EL35 – veraison; EL38 – full mature). Overall, TF variety showed higher accumulation of chlorophylls, xanthophylls, and de-epoxidation state (DPS) than TN. Kaolin treatment enhanced TN chlorophyll accumulation up to 114 % at EL35 (veraison) and 123 % at EL38 (full mature), highlighting its protective role on chlorophyll degradation, while no changes were found in TF, which might indicate a lower need for particle-film technology in this variety under the current environmental conditions. Individual carotenoids were mainly higher in the treated leaves of both varieties, as well as the xanthophyll cycle pigments zeaxanthin (Zx) and violaxanthin (Vx). Simultaneously, the DPS and NPQ values were lower in TN and TF treated leaves (1.92 – 2.36) compared to untreated vines (3.19 – 3.24), suggesting that there might be other components influencing NPQ levels beyond Zx, with an indirect role in long-lasting NPQ processes. In addition, in the TF kaolin-treated leaves, violaxanthin de-epoxidase (VvVDE1) and zeaxanthin epoxidase (VvZEP1) gene expression were respectively 3-fold and 4-fold upregulated at stage EL35, while VvZEP1 gene expression decreased at stage EL38 in TN kaolin-treated leaves, indicating an optimised regulation of the xanthophyll cycle. These findings suggest that kaolin treatment promoted a fine-tuning of grapevine summer stress responses under sustained summer stress factors, by managing xanthophyll cycle dynamics, and pigments accumulation.
This work was supported by National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020, the Clim4Vitis project – "Climate change impact mitigation for European viticulture: knowledge transfer for an integrated approach", funded by European Union's Horizon 2020 research and innovation programme, under grant agreement no. 810176. Authors acknowledge Rui Flores from “Herdade do Esporão”, for the collaboration and efforts in making the vineyard facilities available for this study, as well as BASF collaboration, namely Paulo Matos. The technical assistance of Inmaculada Carbonell (IATA-CSIC) in pigment analysis is also gratefully acknowledged. Sara Bernardo acknowledges the financial support provided by the FCT-Portuguese Foundation for Science and Technology (PD/BD/ 128273/2017), under the Doctoral Programme "Agricultural Production Chains – from fork to farm", and Dinis L.-T. thanks the FCT and UTAD for the research contract (D.L. Law no. 57/2017).