ORIGINAL PAPER On the mechanism of dormancy release in grapevine buds: a comparative study between hydrogen cyanamide and sodium azide Francisco J. Pe ´rez Æ Ricardo Vergara Æ Etti Or Received: 24 March 2009 / Accepted: 25 June 2009 / Published online: 10 July 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Sodium azide (NaN 3 ), a well-known inhibitor of mitochondrial respiration, stimulated bud-dormancy release in grapevines similar to hydrogen cyanamide (HC), while HC, a well-known dormancy release agent, inhibited the O 2 uptake in isolated grape bud mitochondria similarly to NaN 3 . Additionally, both chemicals induced transcript expression of the antioxidative enzyme glutathione reductase and glu- cose-6-phosphate-dehydrogenase (G6PD), therefore upreg- ulated the ascorbate-glutathione cycle (AGC) and the pentose phosphate pathway, respectively. As a result of AGC activation, the ratio of reduced to oxidized glutathione (GSH/GSSG) increased. Both stimuli also upregulated the transcription of 1,3-b-D-glucanase, a key enzyme in dor- mancy release. Together, these data support mechanistic connection between impaired Mit function and dormancy release, and suggests that as a consequence of O 2 depriva- tion, increases in glycolysis and in ethanolic fermentation could be responsible for activation of downstream stages in the dormancy release mechanisms. Keywords Dormancy release Á Grapevines Á Hydrogen cyanamide Á Sodium azide Introduction Decreasing photoperiod and temperatures in the fall induce grape bud endodormancy (ED) (Lang et al. 1987; Lavee and May 1997). Further development of the bud through the dormancy cycle requires exposure to adequate chill- ing temperatures, which ultimately lead to ED release (Dokoozlian 1999; Lavee and May 1997). Although low compared to other temperate woody perennials, chilling requirements of the grape bud must be fulfilled to allow proper bud break, and maximum bud-break rates improve with increased chilling exposure (Dokoozlian et al. 1995; Dokoozlian 1999; Lavee and May 1997). In warm winter regions, where chilling is often insufficient, prolonged ED is a major obstacle to the commercial production of table grape (Shulman et al. 1983; Saure 1985). Understanding the mechanism of ED release and the role of chilling may assist in developing dormancy-breaking strategies that do not rely on chilling, and enable searching for traits that could be used as informative markers for low chilling requirements in breeding programs. Hydrogen cyanamide (HC), commercially applied to overcome dormancy in warm winter regions, provides controlled, synchronized and relatively rapid induction of bud ED release within a well-characterized time frame, thereby creating a traceable and reliable model system for the identification of biochemical pathways involved in the mechanism of bud ED release (Halaly et al. 2008; Keilin et al. 2007; Nir et al. 1986; Nir and Lavee 1993; Or et al. 2000, 2002; Pang et al. 2007; Pe ´rez and Lira 2005; Pe ´rez et al. 2007, 2008). Using this system, catalase expression and activity have been shown to be inhibited shortly after HC application, with the concomitant increase in the level of H 2 O 2 (Nir et al. 1986; Nir and Lavee 1993; Or et al. 2000, 2002; Pe ´rez and Lira 2005; Pe ´rez et al. 2008). HC F. J. Pe ´rez (&) Á R. Vergara Facultad de Ciencias, Lab. Bioquı ´mica Vegetal, Universidad de Chile, Casilla 653, Santiago, Chile e-mail: frperez@uchile.cl E. Or Department of Fruit Tree Science, Institute of Horticulture, Agricultural Research Organization, The Volvani Center Bet Dagan, P.O. Box, 6, 50250 Bet Dagan, Israel 123 Plant Growth Regul (2009) 59:145–152 DOI 10.1007/s10725-009-9397-5