Thermochimica Acta 481 (2009) 28–31 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Metabolic activity of low chilling grapevine buds forced to break Marco Antonio Trejo-Martínez a,b , J. Antonio Orozco a , Gustavo Almaguer-Vargas b , Elizabeth Carvajal-Millán a , Alfonso A. Gardea a,∗ a Centro de Investigación en Alimentación y Desarrollo, A.C. Apdo. Postal 1735, Hermosillo, Son. México 83000, Mexico b Universidad Autónoma Chapingo, Km. 38.5 Carr. México-Veracruz, Texcoco, Edo México, Mexico article info Article history: Received 29 April 2008 Received in revised form 19 September 2008 Accepted 22 September 2008 Available online 18 October 2008 Keywords: Vitis vinifera Dormancy Budbreak Isothermal calorimetry Metabolic heat Respiration rate abstract This research documented the metabolic changes associated with the use of budbreak promoter sprays in vineyards. The objective was to evaluate metabolic heat production (R q ) and respiratory (R CO 2 ) rates and water content of Vitis vinifera L. cv. ‘Flame Seedless’ buds during dormancy, and after spraying with the budbreak promoter, hydrogen cyanamide (H 2 CN 2 ), assessing its effect on the developmental response of buds through several phenological phases in the vineyard. The study was conducted in the winter from November 24, 2005 to February 8, 2006 using isothermal calorimetry at 25 ◦ C. Phenological stages mon- itored were dormant bud, swollen bud, half-inch green, first-flat leaf and second-flat leaf. On December 23, when 97 chilling units had accumulated, H 2 CN 2 (0.82 M divided into two applications of 0.47 and 0.35M) was applied and compared with untreated controls. Metabolic heat rates significantly (p ≤ 0.05) increased from endodormant buds to the half-inch green stage, from 2 to 33 W mg -1 dry weight (dw). This occurred from November 24 to January 15. Bud respiration rate showed a similar pattern, increasing from 3.7 to 346 nmoles CO 2 s -1 mg -1 dw, and bud water content increased from 2.2 to 5.6 mg mg -1 dw. In a 27-day period after spraying, treated vines reached 50% budbreak, while controls reached only 7%. Phenological development was heterogeneous due to insufficient chilling, as well as to low temperatures following H 2 CN 2 application. Changes in R q and R CO 2 were detected 12 days in advance compared with changes in bud hydration. © 2008 Elsevier B.V. All rights reserved. 1. Introduction In deciduous species, the dormant phase of development allows winter survival; its induction and fulfillment are genetically con- trolled and are affected by diverse factors, including temperature and photoperiod [1,2]. Traditionally, accumulation of chilling units (CU) has been used as an indicator of dormancy fulfillment to esti- mate dates of budbreak and to determine the need for spraying chemical budbreak promoters. Grapevines require a chilling expo- sure, depending on genotype, ranging between 50 and 400 h at temperatures ≤7 ◦ C for normal bud development [3,4]. Inadequate exposure to low temperatures can cause erratic and/or heteroge- neous budding or a limited number of buds and clusters in different stages of development [3], therefore spraying budbreak promoters becomes a must. The problem turns even more complex in those locations where winters are warm, as in the case of Sonora, Mexico, since productivity is strongly conditioned by the level of budbreak and, unfortunately, chilling accumulation in each crop cycle is irreg- ∗ Corresponding author. E-mail addresses: gardea@ciad.mx, alfonso.gardea@hotmail.com (A.A. Gardea). ular and sometimes even negligible. Deciding whether budbreak promoters should be applied to dormant vines can be a problem since their efficiency and phytotoxicity depend on the stage and intensity of bud dormancy [5–7]. Until now the method used to estimate budbreak, chilling accu- mulation, is based on an environmental variable and does not consider the intensity of bud dormancy [8,9]. Chilling unit accumu- lation has been used in large part because of the absence of visible changes and the lack of endogenous markers that allow determina- tion of bud dormancy stage [9]. However, even though no changes are visible, dormancy is a state physiologically and biochemically active, during which changes occur in bud water content, growth regulators levels and other compounds, although respiration rate is slow [10,11]. Indeed, the events that occur in the bud during this phase and the mechanisms controlling its progress and causing its termination continue to elicit questions [1,12]. It is necessary to find other methods to estimate bud metabolic activity in a comple- mentary fashion, so as to determine the most appropriate moment for the application of growth promoters to improve budbreak and, therefore, productivity. Calorimetry can measure the metabolic response of plant tis- sues as a function of temperature. This technique makes it possible 0040-6031/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2008.09.025