Abstract
Main conclusionTimescale analyses suggest the berry shrivel (BS) disorder is induced before veraison with strong effects on anthocyanin biosynthesis, and minor effects on sugar transport and metabolism.Berry shrivel (BS)-affected grapes have low sugar contents, high acidity, less anthocyanins and flaccid berries. To date no pathogenic causes are known, and studies to elucidate the molecular basis leading to symptom induction and development are limited. Here we present a study on pre-symptomatic as well as symptomatic BS berries to characterize early metabolic changes, with focus on anthocyanin biosynthesis and sugars metabolism. Healthy and BS berries from six sampling time points were used (BBCH79–BBCH89). Our objectives are (1) to search for the beginning of BS-related physiological processes; (2) to search for key enzymes and sugar transporters involved in BS induction and development and (3) to understand the consequences on polyphenol biosynthesis. We employed high performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) and liquid chromatography–tandem mass spectrometry (LC–MS/MS) technology for sugar and polyphenol analyses, respectively. Additionally we conducted expression analyses (qPCR) of key genes and enzymatic activity assays. Our results show that BS-related processes start before veraison, as determined by slightly reduced hexose contents and reduced expression levels of a vacuolar invertase (VviGIN1), two monosaccharide transporters (VviTMT2, VviTMT3) and the anthocyanin biosynthesis (VviUFGT, VviMYBA1/2) genes. Lower amounts of delphinidin and cyanidin glycosidic forms were determined, while caftaric acid, quercetin-3-O-glucuronide and (+)-catechin were increased in BS berries. Although not all results were conclusive, especially for the sugar metabolism, our data provide important knowledge to improve the understanding of the highly complex berry shrivel ripening disorder.
Highlights
Grape berry growth and ripening is a process following a double sigmoid developmental curve (Coombe 1992; Conde et al 2006)
Our objectives are (1) to search for the beginning of BSrelated physiological processes; (2) to search for key enzymes and sugar transporters involved in berry shrivel (BS) induction and development and (3) to understand the consequences on polyphenol biosynthesis
Our results show that BS-related processes start before veraison, as determined by slightly reduced hexose contents and reduced expression levels of a vacuolar invertase (VviGIN1), two monosaccharide transporters (VviTMT2, VviTMT3) and the anthocyanin biosynthesis (VviUFGT, VviMYBA1/2) genes
Summary
Grape berry growth and ripening is a process following a double sigmoid developmental curve (Coombe 1992; Conde et al 2006). The complex morphological and physiological processes taking place during ripening can be disturbed leading to physiological ripening disorders (or shrivel disorders) such as bunch stem necrosis (BSN), late-season dehydration and berry shrivel (BS), named sugar accumulation disorder (SAD) (Krasnow et al 2009a) or suppression of uniform ripening (SOUR) (Bondada 2014). These shrivel disorders lead to the same final symptom, shriveled berries, they are distinct in causes, development processes and speed (Bondada and Keller 2012; Griesser et al 2012). The current knowledge suggests no effects on berry development until veraison as seeds are fully developed and able to germinate (Hall et al 2011; Bondada and Keller 2012)
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