Nick K. Dokoozlian

The Grape Remote Sensing Atmospheric Profile and Evapotranspiration Experiment

AbstractParticularly in light of California’s recent multiyear drought, there is a critical need for accurate and timely evapotranspiration (ET) and crop stress information to ensure long-term sust...

Metabolomic Measurements at Three Time Points of a Chardonnay Wine Fermentation with Saccharomyces cerevisiae

The transformation of grape juice to wine is a complex metabolic relationship between two species, the grape plant Vitis vinifera and yeast, primarily Saccharomyces cerevisiae. The final molecular composition resulting from the grape–yeast relationship contributes to the flavor, aroma, and mouthfeel of the wine. In this study, we examined this complex relationship by determining the exo- and endo-metabolome (the collection of metabolites present extra- and intracellularly, respectively) of yeast at three time points (days 4, 9, and 15) of a Chardonnay wine fermentation. We identified and tracked 227 metabolites in the exo-metabolome and 404 metabolites in the endo-metabolome, and each metabolite was grouped into metabolic pathways or into metabolite families. Considerable metabolic variation was present at each stage of the fermentation, illuminating metabolic patterns suggesting that regulation of the yeast metabolic pathways is coupled to the fermentation progress. Analysis of the differential utilization and production of primary and secondary metabolites during a wine fermentation in this work provides a key understanding of cell-communication mechanisms relevant to metabolic engineering and industrial biotechnological processes.

MODELING SEASONAL WINE GRAPE DEVELOPMENT USING A MIXTURE TECHNIQUE

Biological growth data typically display an increasing sigmoidal pattern over time. Grape development is no exception and shows a similar general trend. A detailed examination of the growth process in grapes, however, reveals a few systematic deviations from this pattern. Specifically, grape development is often characterized by localized areas of growth plateaus leading to an overall growth pattern referred to as a double sigmoidal curve. Capturing and characterizing these local changes in growth is important as they represent important phases in grape development such as veraison. This paper utilizes a model adapted from the technique of mixture models to estimate the growth curve of grapes. The resulting model provides a more accurate description of the growth process and has parameter estimates directly related to the various phases of grape development. The model is demonstrated using data collected from an experimental trellis tension monitoring system in the Chardonnay grape varietie.

Use of Cordon Wire Tension for Static and Dynamic Prediction of Grapevine Yield

An automated system was used during three growing seasons to monitor the change in tension (ΔT) in the load-bearing wire of a trellis to estimate yield in vineyards. Actual yield varied nearly four-fold among the three study years, but in each year the fruit was uniformly distributed along the length of the wire. The automated sensor detected sequential harvests up to ~12 m to either side of the sensor, or 24 m total wire length, in a nonlinear fashion. Yield was predicted statically from ΔT at the lag phase (L) of berry growth (ΔTL) and dynamically from continuous output of ΔT. Relationships between ΔTL and yield were linear. Estimated yield was not sensitive to the date of ΔTL, within 10 days. In using the ratio between the current year ΔT and that of a specific previous year, the differences between estimated and observed yields depended upon the choice of predictor year(s), where years with similar ΔT were the most accurate. Across an estimation interval of L to harvest, the precision of dynamic estimates was determined by the similarity in the day-to-day shapes of the double-logistic curves of ΔT over time. Due to a catastrophic frost in the second year of the study, an extremely small crop and an uncharacteristic growth curve made it difficult to predict yield either statically or dynamically. In practice, the method requires a grower to collect multiple years of growth curves from which to build a robust linear relationship between ΔTL and yield (static estimates), or to apply an average of multiple years’ ΔT values dynamically.

Timing and order of the molecular events marking the onset of berry ripening in grapevine

A transcriptomic and metabolomic map of grape berry development elucidates timing and order of the key events of the global reprogramming featuring the ripening process. Grapevine (Vitis vinifera) is a model for the investigation of physiological and biochemical changes during the formation and ripening of nonclimacteric fleshy fruits. However, the order and complexity of the molecular events during fruit development remain poorly understood. To identify the key molecular events controlling berry formation and ripening, we created a highly detailed transcriptomic and metabolomic map of berry development, based on samples collected every week from fruit set to maturity in two grapevine genotypes for three consecutive years, resulting in 219 samples. Major transcriptomic changes were represented by coordinated waves of gene expression associated with early development, veraison (onset of ripening)/midripening, and late-ripening and were consistent across vintages. The two genotypes were clearly distinguished by metabolite profiles and transcriptional changes occurring primarily at the veraison/midripening phase. Coexpression analysis identified a core network of transcripts as well as variations in the within-module connections representing varietal differences. By focusing on transcriptome rearrangements close to veraison, we identified two rapid and successive shared transitions involving genes whose expression profiles precisely locate the timing of the molecular reprogramming of berry development. Functional analyses of two transcription factors, markers of the first transition, suggested that they participate in a hierarchical cascade of gene activation at the onset of ripening. This study defined the initial transcriptional events that mark and trigger the onset of ripening and the molecular network that characterizes the whole process of berry development, providing a framework to model fruit development and maturation in grapevine.