Kaolin Reduces ABA Biosynthesis Through the Inhibition of Neoxanthin Synthesis in Grapevines Under Water Deficit.

Tommaso Frioni,Alberto Palliotti,Sergio Tombesi,Nieves Lavado Rodas,Cecilia Squeri,Stefano Poni,Paolo Sabbatini

doi:10.3390/ijms21144950

Abstract

In many viticulture regions, multiple summer stresses are occurring with increased frequency and severity because of warming trends. Kaolin-based particle film technology is a technique that can mitigate the negative effects of intense and/or prolonged drought on grapevine physiology. Although a primary mechanism of action of kaolin is the increase of radiation reflection, some indirect effects are the protection of canopy functionality and faster stress recovery by abscisic acid (ABA) regulation. The physiological mechanism underlying the kaolin regulation of canopy functionality under water deficit is still poorly understood. In a dry-down experiment carried out on grapevines, at the peak of stress and when control vines zeroed whole-canopy net CO2 exchange rates/leaf area (NCER/LA), kaolin-treated vines maintained positive NCER/LA (~2 µmol m−2 s−1) and canopy transpiration (E) (0.57 µmol m−2 s−1). Kaolin-coated leaves had a higher violaxanthin (Vx) + antheraxanthin (Ax) + zeaxanthin (Zx) pool and a significantly lower neoxanthin (Nx) content (VAZ) when water deficit became severe. At the peak of water shortage, leaf ABA suddenly increased by 4-fold in control vines, whereas in kaolin-coated leaves the variation of ABA content was limited. Overall, kaolin prevented the biosynthesis of ABA by avoiding the deviation of the VAZ epoxidation/de-epoxidation cycle into the ABA precursor (i.e., Nx) biosynthetic direction. The preservation of the active VAZ cycle and transpiration led to an improved dissipation of exceeding electrons, explaining the higher resilience of canopy functionality expressed by canopies sprayed by kaolin. These results point out the interaction of kaolin with the regulation of the VAZ cycle and the active mechanism of stomatal conductance regulation.

Highlights

Global warming is rapidly changing worldwide agriculture
Leaf-transmitted light was reduced to 6.9% of total photosynthetically active radiation (PAR) in kaolin-treated leaves vs. 8.0% found in control vines
The six vines were randomly divided into two treatments as follows: three vines were sprayed on 23 July (DOY 204) at 9:00 a.m. with a formulation of 100% aluminium silicate (Baïkal, Agrisynergie, Périgueux, France) diluted in water at 3% concentration; the remaining three vines were assigned to the untreated control

Summary

Introduction

Growers are facing general warming trends that intensify extreme events and compromise yield and fruit quality [1,2,3]. Viticulture is one of the most relevant crops in warm and temperate regions and, in Mediterranean wine districts, multiple summer stresses (i.e., the concurrence of prolonged drought, high air temperature and excessive light radiation) are the main causes of vineyard impairments related to climate change [3,4]. The first consequence of multiple summer stresses is the reduction of carbon assimilation and transpiration (E), resulting in the loss of yield and fruit quality, according to the severity and duration of limiting conditions [4,5,6]. Its mechanism of action is primarily related to the increase of light reflection that reduces the radiation absorbed by the leaf [7,8,16]

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