Modelling grape growth in relation to whole-plant carbon and water fluxes.

Junqi Zhu,Nathalie Ollat,Michael C T Trought,Gregory A Gambetta,Philippe Vivin,Gilles Vercambre,Stefano Poni,Zhanwu Dai,Serge Delrot,Michel Génard

doi:10.1093/jxb/ery367

Abstract

The growth of fleshy fruits is still poorly understood as a result of the complex integration of water and solute fluxes, cell structural properties, and the regulation of whole plant source-sink relationships. To unravel the contribution of these processes to berry growth, a biophysical grape (Vitis vinifera L.) berry growth module was developed and integrated with a whole-plant functional-structural model, and was calibrated on two varieties, Cabernet Sauvignon and Sangiovese. The model captured well the variations in growth and sugar accumulation caused by environmental conditions, changes in leaf-to-fruit ratio, plant water status, and varietal differences, with obvious future application in predicting yield and maturity under a variety of production contexts and regional climates. Our analyses illustrated that grapevines strive to maintain proper ripening by partially compensating for a reduced source-sink ratio, and that under drought an enhanced berry sucrose uptake capacity can reverse berry shrinkage. Sensitivity analysis highlighted the importance of phloem hydraulic conductance, sugar uptake, and surface transpiration on growth, while suggesting that cell wall extensibility and the turgor threshold for cell expansion had minor effects. This study demonstrates that this integrated model is a useful tool in understanding the integration and relative importance of different processes in driving fleshy fruit growth.

Highlights

The growth of fleshy fruits largely depends on the balance of water influx and efflux (Lang, 1990; Lang and Thorpe, 1989)
The prediction for fruit hexose concentration was less robust than the prediction for Dry weight (DW) and FW as we used a constant kss for estimating the dynamics of p fruit hexose concentration without including specific enzymatic processes
The e predicted hexose concentration agreed well with the observed data for Cabernet Sauvignon (Fig. c 3E), it was lower than observed ones for Sangiovese (Fig. 3F). c Three major internal variables: xylem water potential, phloem sucrose concentration and fruit turgor A pressure

Summary

Introduction

The growth of fleshy fruits largely depends on the balance of water influx and efflux (Lang, 1990; Lang and Thorpe, 1989). The flux of water into a fruit results from a tight coordination between vascular (xylem and phloem) transport and fruit cell expansion. The former is regulated by vascular conductivity and the water potential gradient between plant and fruit, and the latter by cell wall properties and the turgor of fruit cells (Lockhart, 1965; Matthews and Shackel, 2005). It is essential to investigate the regulation and c coordination of water and carbon fluxes during expansive growth as they determine fruit yield and s their ratio largely determines fruit composition, e.g. sugar concentration (Guichard et al, 2001; u Nardozza et al, 2017; Kawasaki and Higashide, 2018). The resumption of rapid berry growth is accompanied by turgor loss,

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