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Abstracts

Best Viticulture Paper

Senior Technical Editor's Note: The authors separated the temperature of developing grapes from the amount of sunlight to which they had been exposed. They did this to determine the role of, and relationship between, heat and incident UV radiation (sunlight) phenolic development, generally, and anthocyanin development, specifically, in the grape skin as the grapes mature.

This research is important because it helps us understand the relationship between the sunlight and temperature conditions and the development of anthocyanins in the grape skin.

Berry Temperature and Solar Radiation Alter Acylation, Proportion, and Concentration of Anthocyanin in Merlot Grapes

Julie M. Tarara¹,* Jungmin Lee², Sara E. Spayd³ and Carolyn F. Scagel⁴

¹ USDA-ARS, 24106 N. Bunn Rd., Prosser, WA 99350; ² USDA-ARS, 29603 U of I Ln., Parma, ID 83660; ³ North Carolina State University, Department of Horticultural Science, Raleigh, NC 27695; and ⁴ USDA-ARS, 3420 N.W. Orchard Ave., Corvallis, OR 97330.

* Corresponding author (email: jtarara@wsu.edu; tel: 509-786-9392)

Am. J. Enol. Vitic. 59:3:235-247 (2008)

Copyright © 2008 by the American Society for Enology and Viticulture.

Using a forced convection system, temperatures of Merlot grape clusters were monitored and controlled between veraison and harvest to produce a dynamic range of berry temperatures under field conditions in both sun-exposed and shaded fruit. Ten combinations of temperature and solar radiation exposure were used to quantify effects on phenolic profiles (anthocyanins and flavonol-glycosides) and on total concentrations of skin anthocyanin (TSA) in the fruit at commercial maturity. Exposure of berries to high temperature extremes for relatively short periods during ripening appears to alter the partitioning of anthocyanins between acylated and nonacylated forms and between dihydroxylated and trihydroxylated branches of the anthocyanin biosynthetic pathway. Specifically, among flavonol-glycosides, quercetin 3-glucoside increased with exposure to solar radiation. Low incident solar radiation alone appeared not to compromise total anthocyanin accumulation; rather, a combination of low light and high berry temperatures decreased TSA. Regardless of exposure to solar radiation, higher berry temperatures led to a higher concentration and a higher proportion of TSA comprised by malvidin-based anthocyanins, driven primarily by increases in the acylated derivatives. Under shade alone and under high temperature extremes in sunlit and shaded fruit, acylated anthocyanins represented a larger proportion of TSA than did nonacylated anthocyanins. At berry temperatures equivalent to those of shaded fruit, exposure to solar radiation decreased the proportion of TSA comprised by acylated forms of the five base anthocyanins and increased the proportion of TSA comprised by dihydroxylated anthocyanins. Results indicate a complex combined effect of solar radiation and berry temperature on anthocyanin composition, synergistic at moderate berry temperatures and potentially antagonistic at high temperature extremes.

Best Enology Paper

Senior Technical Editor's Note: The ability for yeast to move hexoses, simple six-carbon sugars like glucose and fructose, from outside to inside the yeast cell is obviously important for fermentation. The authors of this paper looked at several of the genes responsible for this ability to see which genes, if any, gave yeast the ability to continue to transport sugar across the cell membrane even in the presence of ethanol. They found that yeast lacking a single gene were unable to complete fermentation in 5 percent ethanol. This suggests that this gene may play a crucial role in yeast ethanol tolerance. This research is important because yeast have to tolerate the presence of ethanol in order for fermentation to occur. If we understand what gene or genes are responsible for this ability, we can have a better chance of understanding, predicting and avoiding slow, sluggish and stuck fermentations.

Analysis of the Major Hexose Transporter Genes in Wine Strains of Saccharomyces cerevisiaeM

Jonathan E. Karpel^1,3, Warren R. Place¹ and Linda F. Bisson^2,*

¹ Graduate student, and ² Professor and Maynard A. Amerine Endowed Chair, Department of Viticulture and Enology, University of California, Davis, CA, 95616; ³ current address, Visiting professor, Joint Science Department, The Claremont Colleges, W.M. Keck Science Center, 925 N. Mills Ave., Claremont, CA 91711.

* Corresponding author (email: lfbisson@ucdavis.edu; tel: 530 752-3835; fax: 530 752-0382)

Am. J. Enol. Vitic. 59:3:265-275 (2008)

Copyright © 2008 by the American Society for Enology and Viticulture.

Saccharomyces cerevisiae maintains a large family of hexose transporters encoded by the HXT genes. The major transporter genes, HXT1 through HXT7, were sequenced from four vineyard isolates and two commercial wine yeast strains and compared to the sequences in the Saccharomyces Genome Database for strain S288C and to those available for two additional wine strains V5 and RM11-1a. Base pair changes leading to differences in amino acid sequence were found for all seven transporters. Differences ranged from none to eight amino acid variations for the sequenced strains, depending upon the strain and the gene, in comparison with S288C. In contrast, RM11-1a displayed high degeneracy with multiple in-frame stop mutations for HXT1, HXT4, and HXT6. Several wine strain sequences for the HXT4 gene contained an identical additional 16 amino acids at the C-terminus. Transporter protein levels were analyzed in a wine yeast strain (UCD932) using green fluorescent protein tagging. HXT5, not shown to be expressed in previous studies, was expressed in UCD932 during fermentation. Expression of HXT4, a prominently expressed transporter in laboratory media, was not detected. Deletion of HXT1, HXT3, or HXT5 did not result in a discernable phenotype in UCD932 under the fermentation conditions used in this study as compared with the wild type strain. However, the strain lacking HXT3 was unable to complete the fermentation in media containing 5% exogenous ethanol. This result suggests that correct expression of HXT3 may play a role in ethanol tolerance.