Assimilate transport in grapevines -effect of phloem disruption

Abstract

Assimilate translocation in mature grapevines (cv. Gewürztraminer and cv. Harslevelü) under field conditions was investigated during the growth season by quantifying individual sugars and organic acids in mature leaves, shoot bark and berries, as affected by girdling the shoot just above the bunches. Tissue was sampled at berry set, pea size, veraison and ripeness stages of the vine. Invertase activity was determined in the shoot bark at ripeness. In the leaves, malic acid concentrations reached lowest levels at pea size, but increased thereafter. Tartaric acid decreased after peaking at pea size stage. Tartaric acid concentrations increased with girdling. Despite the increase in leaf age, sucrose concentrations remained virtually stable during the season, emphasising the importance of mature leaves for nourishing bunches. Girdling resulted in a build‐up of sucrose in the leaves. In the bark, malic and tartaric acid stayed more or less the same during the growth period, but increased above the girdle. As a result of phloem disruption, sucrose also increased. The increase in glucose and tartaric acid is believed to result from catabolic cleavage of sucrose by invertase. Invertase activity was evident in the bark (of mature Harslevelü vines) at ripeness, which may indicate involvement in osmotic adjustments and gradients in the bark/phloem structure. In the berries, malic and tartaric acids reached peak concentrations at pea size. The volume increase during the ripening period, and in the case of malic acid also respiratory loss, resulted in a decrease in organic acid concentration. Malic acid continued to decrease after the initial decline, whereas tartaric acid stayed virtually stable. Girdling had no marked effect on organic acid accumulation in the berries. Sucrose concentrations were low during the first part of the season, but increased thereafter. Sucrose concentrations during ripening increased with girdling, which may represent a concentration effect and/or import from the rest of the vine. Sucrose concentrations (in mature Harslevelü vines) were indeed lower below than above the girdle. Comparison of sucrose concentrations in the leaves, bark and berries showed the existence of a decreasing concentration gradient, in line with the source:sink transport concept. An equally prominent decrease in sucrose:glucose ratio in the berries from the start of the ripening period indicates that vacuolar integrity (compartmentation) was affected in the ripening berry, most probably allowing hydrolysis of sucrose by invertase and decreasing osmotic potential within the berry. The results provide further evidence for the hypothesis of an osmotic gradient driven transport to the berry.

Integrative Effects of Vine Water Relations and Grape Ripeness Level of Vitis vinifera L. cv. Shiraz/Richter 99. I. Physiological Changes and Vegetative-Reproductive Growth Balances

“…above) were extracted and analysed at all measurement stages by gas liquid chromatography (GLC) (after silylation), as described by Hunter and Ruffner (2001).…”

“…The supply (via photosynthesis) and loading (into the phloem) of sugar (sucrose) in plant sources, sink hierarchy/ priority, phloem transport and unloading in sinks (such as the grape berry) after partitioning, as well as metabolism of sugar in sinks, are critical events in the grapevine growth cycle (Hunter et al, 1994;Hunter, 2000;Hunter & Ruffner, 2001). Despite many attempts based on, e.g., berry dimension responses (after transport disruption by means of girdling and heat treatment) (Lang & Thorpe, 1989;Greenspan et al, 1994Greenspan et al, , 1996, flow of water-soluble dyes (Düring et al, 1987;Findlay et al, 1987;Creasy et al, 1993;Rogiers et al, 2001), monitoring of xylem and phloem mobile mineral transport (Creasy et al, 1993;Rogiers et al, 2000;Etchebarne et al, 2009), hydraulic conductance measurements (Tyerman et al, 2004), the measuring of berry turgor and hydraulic dynamics (Greer & Rogiers, 2009) and xylem tracheary element analyses (Chatelet et al, 2008a), the mechanisms involved in the triggering and regulation of sugar and water import, as well as berry shrinkage at a specific ripeness level (particularly for a highly expressive cultivar like Shiraz),…”

Leaf:Fruit Ratio and Vine Water Status Effects on Grenache Noir (Vitis vinifera L.) Berry Composition: Water, Sugar, Organic Acids and Cations

“…Berry growth and development are supported by the import (from the whole plant) of water, sucrose and mineral nutrients, whereas organic acids are produced inside the berry (Hunter & Ruffner, 2001;Terrier & Romieu, 2001). Variability in berry growth and weight, as a consequence of vine water availability, has been widely reported (Matthews & Anderson, 1988;Poni et al, 1993;Esteban et al, 1999;Ojeda et al, 2002).…”

Integrative Effects of Vine Water Relations and Grape Ripeness Level of Vitis vinifera L. cv. Shiraz/Richter 99. II. Grape Composition and Wine Quality

“…Under the influence of environmental conditions, the physiological activity and prioritising of leaves, roots and berries within the whole plant at different growth stages during the season have a steering effect on yield and grape composition to satisfy the requirements for quality wine or other end products (Hunter, 2000;Hunter & Ruffner, 2001;Hunter et al, 2004;Hunter et al, 2010;Hunter & Bonnardot, 2011;.…”