Spring Transition from Grapevine Dormancy

It looks as if spring is finally here in Southeastern Connecticut. Our thoughts are turning to the many tasks ahead of us including that of pruning our grapevines. We did a test pruning on a side shoot about a week ago and found the shoot to have a green interior, a good sign that even thought the temperatures were at times in the negative numbers, they were able to survive. Still, we do have to wait for budbreak to see what the true survival rate will be.
How does a grapevine emerge from dormancy? It's complicated.
In the spring, seemingly dormant grapevines are busily engaged in protein synthesis and chromosome duplication. The nutrient reserves from starch and proteins and the pumping of sugars and amino acids into the xylem creates an osmotic pressure that provides the driving force for the water uptake from the roots and lifts the water up into the vine. This root pressure in turn dissolves and pushes out air bubbles that might have formed in the xylem in the winter and prevents cavitation and restores function to the xylem.
This metabolic activity in the roots marks the beginning of sap flow and is related to soil temperature and soil moisture. The cytokinin delivered from the roots reactivates and rehydrates the dormant buds. Cell division and auxin production in the distal buds stimulates the cambium cells to resume division and differentiation into new phloem and xylem cells.

While all this is occurring, abscisic acid (ABA) declines, awakening the vine from the growth inhibition that protected it through the long cold winter.
References:
1. Markus Keller, The Science of Grapevines Anatomy and Physiology, 2010, Academic Press, pg. 53-54.
2. Illustration modified from Grape Grower's Handbook by Ted Goldammer, Apex Publishers, 2013, pg. 2.