Composition and synthesis of raphide crystals and druse crystals in berries of Vitis vinifera L. cv. Cabernet Sauvignon: Ascorbic acid as precursor for both oxalic and tartaric acids as revealed by radiolabelling studies

Copyright © 2008 Australian Society of Viticulture and Oenology Inc.Biomineralisation in the fleshy pericarp of berries of Vitis vinifera L. gives rise to crystals of two distinct forms, viz. raphides and druses, which are found in exocarp and endocarp cells respectively. Druses have generally been considered as crystalline aggregates of calcium oxalate. However, the organic moiety of raphide crystals has been commonly accepted as tartrate, although we have found no analytical data to support that assumption. We now present TEM and X-ray powder diffraction analysis data showing that raphide crystals of V. vinifera berries are composed of calcium oxalate monohydrate. This work also established ascorbic acid as the biosynthetic precursor of both oxalic and tartaric acids. When ascorbic acid labelled with ¹⁴C at position 1 was introduced into berries via the rachis, 21% and 52% of the added radiolabel was recovered as oxalic and tartaric acids respectively. Purified crystals from the radiolabelled grape berries contained approximately 20% of the original radioactivity, further confirming the role of ascorbic acid in oxalic acid biosynthesis. To our knowledge, this is the first evidence to be published on the formation of oxalic and tartaric acids from ascorbic acid via two distinct pathways operating within the same physiological entity (organ).Seth Debolt, Jim Hardie, Steve Tyerman and Christopher M. For

Quantifying phenotypic plasticity of berry traits using an allometric-type approach: A case study on anthocyanins and sugars in berries of Cabernet Sauvignon

The definitive version is available at www.blackwell-synergy.comIn this paper we advance a novel allometric-type approach to quantify the stability of key berry traits viz. anthocyanins and sugars. To test the concept, we used data from Cabernet Sauvignon grown in a hot environment of South Australia. Sources of variation in berry traits included water supply, fruit load, seasonal conditions and their interactions. Anthocyanins and sugars were measured in berry samples taken 7–8 times between veraison and harvest. Rates and durations of accumulation of anthocyanins and sugars per berry were derived from a bi-linear model between amount of compound and thermal time. We develop a framework based on ‘α’ a parameter representing the slope of the regression between rate and duration in a log-log scale. This relationship accommodates three conditions viz. (a) potentially plastic, rate-driven trait (α –1), (b) potentially plastic, duration-driven trait (α < –1), and (c) a stable trait, whereby variation in rate and variation in duration cancel each other (α = –1). Under our experimental conditions, amount of anthocyanins (range of variation 148%) was more plastic than amount of sugars per berry (range of variation 37%). The slope α captured the differential plasticity of these traits: α was significantly greater than –1 for anthocyanins and statistically undistinguishable from –1 for sugars. The rate-dominated accumulation of anthocyanins explained the relatively large variation in this constituent whereas the tightly coupled, inverse relationship between duration and rate (α –1) explained the relative stability of sugars per berry. We conclude that our allometric-type relationship between rate and duration allows for the quantification of cultivar-environment specific plasticity of important berry traits.V.O. Sadras, R.M. Stevens, J.M. Pech, E.J. Taylor, P.R. Nicholas, M.G. McCarth