Acquisition of freezing tolerance in Vaccinium macrocarpon Ait. is a multi-factor process involving the presence of an ice barrier at the bud base

Authors: VILLOUTA, CAMILO - Harvard University; WORKMASTER, BETH ANN - University Of Wisconsin; Livingston, David; ATUCHA, AMAYA - University Of Wisconsin

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2022
Publication Date: 5/4/2022
Citation: Villouta, C., Workmaster, B., Livingston, D.P., Atucha, A. 2022. Acquisition of freezing tolerance in Vaccinium macrocarpon Ait. is a multi-factor process involving the presence of an ice barrier at the bud base. Frontiers in Plant Science. 13:891488. https://doi.org/10.3389/fpls.2022.891488.
DOI: https://doi.org/10.3389/fpls.2022.891488

Interpretive Summary: The winter survival of cranberry buds that are formed the previous summer and fall is crucial for the production of fruit the following season. In this study, the freezing process was monitored using an infrared camera that can follow ice formation in plants. We found that cranberries have a barrier just below the bud that can inhibit freezing into the bud by several degrees. This is one reason cranberry is considered to be a winter hardy fruit species. Using light microscopy it was determined that very small pours in water conducting vessels at the base of the bud is one reason for the delay in freezing. In addition, we used antibodies to detect pectin, the "glue" that keeps cells in contact with each other, and found that one form of pectin was prevalent between cells and likely also restricted ice from entering the bud. If variation between cranberry varieties for these characteristics can be identified breeders could develop new, even more winter hardy varieties.

Technical Abstract: Bud freezing survival strategies have in common the presence of an ice barrier that impedes the propagation of lethally damaging ice from the stem into the internal structures of buds. Despite ice barriers’ essential role in buds freezing stress survival, the nature of ice barriers in woody plants is not well understood. High-definition thermal recordings of Vaccinium macrocarpon Ait. buds explored the presence of an ice barrier at the bud base in September, January, and May. Light and confocal microscopy were used to evaluate the ice barrier region anatomy and cell wall composition related to their freezing tolerance. Buds had a temporal ice barrier at the bud base in September and January, although buds were only freezing tolerant in January. Lack of functionality of vascular tissues may contribute to the impedance of ice propagation. Pith tissue at the bud base had comparatively high levels of de-methyl-esterified homogalacturonan (HG), which may also block ice propagation. By May, the ice barrier was absent, xylogenesis had resumed, and de-methyl-esterified HG reached its lowest levels, translating into a loss of freezing tolerance. The structural components of the barrier had a constitutive nature, resulting in an asynchronous development of freezing tolerance between anatomical and metabolic adaptations.