Academic journal article The American Midland Naturalist

Low Temperature Tolerance in the Perennial Sunflower Helianthus Maximiliani

Academic journal article The American Midland Naturalist

Low Temperature Tolerance in the Perennial Sunflower Helianthus Maximiliani

Article excerpt

Introduction

Freezing temperatures represent an important abiotic stress for plants and limit species distribution patterns and opportunities for dispersal and colonization (Woodward, 1987). Geographical variation in low temperature extremes can drive local adaptation within species as well, especially for taxa distributed broadly (Green, 1969; Casier et aL, 2004; Saenz-Romero and Tapia-Olivares, 2008; Zhen and Ungerer, 2008a; Lee et aL, 2012). Because of their sessile lifestyle and inability to escape ambient climate conditions, plants provide a powerful experimental system to examine strategies of coping with low temperature stress, with direct relevance to ecological and evolutionary population dynamics and agriculture.

For many temperate plant species, maximum freezing tolerance is enhanced via acclimation to low but nonfreezing temperatures. This phenomenon, known as cold acclimation, is marked by major cellular biochemical changes enabling plants to withstand temperatures several degrees colder than non cold- acclimated controls (Guy, 1990; Xin and Browse, 2000; Iba, 2002; Smallwood and Bowles, 2002; Guy et al" 2008). Cold- acclimation represents an inducible change and likely evolved in response to seasonal changes in which low, nonfreezing temperatures portend colder temperatures that are potentially more harmful. Genes and gene pathways regulating plant cold- acclimation have been identified in the model plant species Arabidopsis thaliana (Gilmour et aL, 1998; Liu et aL, 1998; Xin and Browse, 2000; Chinnusamy et aL, 2003; Vogel et aL, 2005; Agarwal et aL, 2006; Van Buskirk and Thomashow, 2006; Doherty et aL, 2009; Thomashow, 2010) with some genes shown to exhibit functional variability among natural A. thaliana accessions subjected to different historical selection pressures for freezing tolerance (Zhen and Ungerer, 2008b).

Avoidance mechanisms also represent feasible means through which organisms can cope with abiotic stress. Such mechanisms are relevant to plant species via seasonal growth patterns and reproductive timing events that minimize the probability of encountering stressful environments and/or conditions (Heide, 1994; Bennington and Mcgraw, 1995; Griffith and Watson, 2005; Heschel and Riginos, 2005). Tolerance and avoidance mechanisms of abiotic stress need not be mutually exclusive and both may function in natural plant populations (Geber and Dawson, 1997; Heschel and Riginos, 2005).

Helianthus maximiliani is a diploid perennial sunflower species that flowers in late summerfall (Heiser et aL, 1969; Schilling, 2006). Though distributed widely in North America, populations are found in highest concentration in mid-continental regions between Texas, U.S.A. and Manitoba, CA (Schilling, 2006). Helianthus maximiliani exhibits steep latitudinal dines in multiple morphological and life history traits that are hypothesized to be driven by variation in photoperiod and climate (Kawakami et aL, 2011). A role for natural selection in shaping clinal variation in this species is supported by patterns of phenotypic differentiation among populations that exceed neutral expectations estimated from putatively neutral molecular markers, i.e., Qst - Fst analysis (Leinonen et aL, 2013). None of these previously studied phenotypes, however, are directly related to low temperature tolerance or low temperature adaptation.

In the current report, we test whether H. maximiliani populations from three climatically diverse regions in central North America (Texas, Kansas and Manitoba) differ in their tolerance to freezing temperatures and whether effects of cold acclimation treatment differentially impacts freezing tolerance among these groups. We explore basic genetic aspects of cold acclimation in H. maximiliani by examining cold acclimation capacity and freezing tolerance of FI hybrids derived from a cross between Manitoba and Texas plants. We demonstrate plants from the northernmost population (Manitoba) predictably display highest freezing tolerance under most treatment combinations but that cold acclimation effects persist for plants from warmer regions (Texas and Kansas). …

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