Environmental and Experimental Botany 72 (2011) 358–367 Contents lists available at ScienceDirect Environmental and Experimental Botany j o ur nal homep age : www.elsevier.com/locate/envexpbot Quantitative and qualitative changes in carbohydrates associated with spring deacclimation in contrasting Hydrangea species Majken Pagter a,∗ , Isabelle Lefèvre c , Rajeev Arora b , Jean-Francois Hausman c a Department of Horticulture, Aarhus University, Kirstinebjergvej 10, DK-5792 Aarslev, Denmark b Department of Horticulture, Iowa State University, Ames, IA 50011, USA c Department EVA Environment and Agrobiotechnologies, Centre de Recherche Public-Gabriel Lippmann, 41, rue du Brill, 4422 Belvaux, Luxembourg a r t i c l e i n f o Article history: Received 2 October 2010 Received in revised form 21 February 2011 Accepted 22 February 2011 Keywords: Climate change Freezing tolerance 1-Kestose Soluble sugars Water status a b s t r a c t Cold deacclimation and associated changes in soluble carbohydrates and water status of two Hydrangea species differing in susceptibility to frost injuries was followed under natural conditions. In fully cold hardy plants of H. macrophylla stem freezing tolerance fluctuated in parallel with changes in air temper- ature, while in a seasonal perspective increased temperatures caused a sigmoid deacclimation pattern in both H. macrophylla and H. paniculata. Timing of deacclimation was approximately synchronized in the two species, but H. paniculata, the hardier species based on mid-winter hardiness, deacclimated faster than H. macrophylla, indicating that deacclimation kinetics were not correlated with mid-winter hardi- ness. In both species concentrations of soluble sugars decreased during deacclimation and were highly correlated with stem cold hardiness and air temperatures. This suggests that sugar hydrolysis may be an important temperature-driven mechanism of deacclimation in Hydrangea. Accumulation patterns of specific carbohydrates differed between the two species, suggesting that they utilize different strategies to overcome cold. In H. paniculata, deacclimation was associated with an increase in stem water content, which occurred shortly before bud burst and hence may be a prerequisite for leafing out. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In temperate perennials cold hardiness is a seasonal process synchronized with the external seasonal changes in temperature and photoperiod. In autumn plants cold acclimate, whereby they become increasingly tolerant to subzero temperatures. Maximum hardiness is reached midwinter, and in spring plants loose accli- mated cold hardiness by deacclimation (Weiser, 1970). Successful over wintering therefore not only requires sufficient maximum freezing tolerance, but also proper timing and rates of acclimation and deacclimation (Suojala and Lindén, 1997). Seasonal timing of acclimation and deacclimation may be an important trait affect- ing mortality, growth and quality of introduced crops cultivated far from their origin. Studies of the kinetics (timing and rates) of cold acclimation and deacclimation in response to the critical environmental stimuli are additionally much needed, given cur- rent predictions of climate change, where growing conditions may favour an altitudinal and poleward shifts in vegetation (Hughes, 2000; Parmesan, 2006). Parallel to cold acclimation in autumn, temperate-zone woody perennials form terminal buds and develop dormancy (Rohde and ∗ Corresponding author. Tel.: +45 89993388; fax: +45 89993496. E-mail addresses: majken.pagter@agrsci.dk (M. Pagter), rarora@iastate.edu (R. Arora), hausman@lippmann.lu (J.-F. Hausman). Bhalerao, 2007). Despite favourable growth conditions dormancy often inhibits or prevents growth and deacclimation (Kalberer et al., 2006); risk of untimely deacclimation is, therefore, a concern for plants that are no longer dormant. Cold deacclimation is strongly dependent on temperature and can occur much faster than cold acclimation (Leionen et al., 1997; Taulavuori et al., 1997; Kalberer et al., 2007). Previous studies indicate that the rate of deacclima- tion is not a linear response but may change as deacclimation progresses. In addition, the rate and/or timing of deacclimation may vary between species, cultivars, ecotypes etc., demonstrating genetic variability for deacclimation kinetics and genetic adapta- tion to the local climate (Leinonen et al., 1997; Suojala and Lindén, 1997; Kalberer et al., 2007). Regulation of cold acclimation in the autumn and the underly- ing physiological, biochemical and molecular responses have been extensively studied (Benedict et al., 2006; Welling and Palva, 2006). Less is known about the process of deacclimation (Kalberer et al., 2006). A close association has been established between accumu- lation of soluble carbohydrates and acquisition of cold tolerance in the autumn (Wanner and Junttila, 1999; Cox and Stushnoff, 2001), whereas the importance of alterations in carbohydrate metabolism in deacclimation is less clear. Some studies have found a corre- lation between decreasing sugar concentrations and the loss of cold hardiness, and suggested a mechanistic role of carbohydrate catabolism in deacclimation (Svenning et al., 1997; Tinus et al., 2000). In contrast, others have noted a decline in soluble carbohy- 0098-8472/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.02.019