Metabolomic analysis of extreme freezing tolerance in Siberian spruce (Picea obovata)

Abstract

SummarySiberian spruce (Picea obovata) is one of several boreal conifer species that can survive at extremely low temperatures (ELTs). When fully acclimated, its tissues can survive immersion in liquid nitrogen. Relatively little is known about the biochemical and biophysical strategies of ELT survival.We profiled needle metabolites using gas chromatography coupled with mass spectrometry (GC-MS) to explore the metabolic changes that occur during cold acclimation caused by natural temperature fluctuations.In total, 223 metabolites accumulated and 52 were depleted in fully acclimated needles compared with pre-acclimation needles. The metabolite profiles were found to develop in four distinct phases, which are referred to as pre-acclimation, early acclimation, late acclimation and fully acclimated. Metabolite changes associated with carbohydrate and lipid metabolism were observed, including changes associated with increased raffinose family oligosaccharide synthesis and accumulation, accumulation of sugar acids and sugar alcohols, desaturation of fatty acids, and accumulation of digalactosylglycerol. We also observed the accumulation of protein and nonprotein amino acids and polyamines that may act as compatible solutes or cryoprotectants.These results provide new insight into the mechanisms of freezing tolerance development at the metabolite level and highlight their importance in rapid acclimation to ELT in P. obovata.

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

“…Low temperature acclimation and the development of freezing tolerance are associated with the accumulation of soluble carbohydrates such as Suc (Guy et al, 1992;Uemura and Steponkus, 2003), raffinose (Knaupp et al, 2011), and pinitol (Angelcheva et al, 2014), which are considered cryoprotectants. Our data suggest that raffinose contributes more effectively than pinitol to cold hardening in P. strobus.…”

“…As a consequence, carbon demand in sink tissue decreases toward the end of the growing season, and the bulk of photoassimilate is translocated from source tissues to storage tissues (Hansen and Beck, 1994;Oleksyn et al, 2000). In addition, cryoprotective soluble sugars, including sucrose, raffinose, and pinitol, accumulate in leaf tissues to enhance freezing tolerance (Strimbeck et al, 2008;Angelcheva et al, 2014). Thus, by winter, leaf nonstructural carbohydrates are mainly comprised of mono-and oligosaccharides, and only minimal levels of starch remain (Hansen and Beck, 1994;Strimbeck et al, 2008).…”

Nitrogen Economy and Nitrogen Environmental Interactions in Conifers

“…Conifers growing in cold conditions often exhibit increased respiration rates and accumulate N in their needles [64]. At the biochemical level, changes in the composition of lipids or carbohydrates are evident, as well as in the accumulation of N metabolites and proteins with cryoprotective functions [65]. One of the better-studied responses to temperature in conifers is their cold/freeze acclimatization process.…”

“…It has been proposed that acclimatization to cold or freezing temperatures in plants is not dependent on the synthesis of new compounds but rather on the transient accumulation of certain compounds, including N-containing compounds such as amino acids or proteins [67]. In conifers, some amino acids, such as tryptophan and proline, have been identified as osmolite solutes that exert cryoprotectant functions during cold acclimatization [65,68,69]. The use of tryptophan in these plants is extremely interesting because its synthesis is linked to the secondary metabolism, which is especially well developed in conifers.…”

“…Because conifer forests dominate large boreal regions [12], these plants have developed a unique ability to acclimatize to extremely low temperatures. The tissues of some species, such as Picea obovate, a boreal conifer species that can survive at extremely low temperatures, are able to survive immersion in liquid N [65]. This type of extreme tolerance generally evolves following exposure to sequential stages of cold acclimatization initiated by short photoperiods and non-freezing low temperatures [66].…”