Joseph Schmidt, Amy Olsen, and Laurent Deluc* 
*Oregon State University, 2750 SW Campus Way, Agriculture and Life Sciences Building 4121, Corvallis, OR 97331 (laurent.deluc@oregonstate.edu)

Two common, yet expensive, practices used in viticulture are cluster thinning and cluster-zone leaf removal, which are intended to alter environmental conditions in hopes of causing the vine to respond in a favorable manner (e.g., improved fruit quality or disease management). Because the vine’s response to environmental changes is principally hormone-mediated, we profiled the active forms, conjugates, and precursors of auxin and abscisic acid to understand the physiological effects of cluster-thinning and leaf removal on dynamic accumulation of these compounds in the berry. Clusters were thinned to 0.5 clusters/shoot in cluster-thinned vines and all cluster-zone leaves were removed in leaf-removal vines. Similarly-developing berries were identified at eight time points during the growing season and each individual berry’s developmental profile was examined using multivariate analysis tools. The tissues of the berries were separated (seed, pulp, and skin) and pooled by their vine of origin in preparation for metabolite extraction. Phytohormones were extracted using a targeted method developed within our laboratory and analyzed using HPLC-MS/MS under selective reaction monitoring mode. Data collected over two growing seasons indicate a clear spatial and temporal distribution of the bioactive and conjugate forms of the analytes: the accumulation of most correlated with major developmental transitions. Analysis of the precursors, conjugates, and catabolites of the bioactive analytes revealed specific regulatory pathways used in grape berries. We quantified the effects of the two practices on the two hormones responsible for ripening initiation. The most notable effect was consistent reduction of ABA in seeds of leaf-removal vines, which correlated strongly with elevated accumulation of the conjugated form, ABA-GE The data suggest an impact of either light or temperature in modulating conversion of ABA into its glycosylated form.

Funding Support: American Vineyard Foundation