Abstract
BackgroundArabidopsis plants accumulate maltose from starch breakdown during cold acclimation. The Arabidopsis mutant, maltose excess1-1, accumulates large amounts of maltose in the plastid even in the warm, due to a deficient plastid envelope maltose transporter. We therefore investigated whether the elevated maltose level in mex1-1 in the warm could result in changes in metabolism and physiology typical of WT plants grown in the cold.Principal FindingsGrown at 21 °C, mex1-1 plants were much smaller, with fewer leaves, and elevated carbohydrates and amino acids compared to WT. However, after transfer to 4 °C the total soluble sugar pool and amino acid concentration was in equal abundance in both genotypes, although the most abundant sugar in mex1-1 was still maltose whereas sucrose was in greatest abundance in WT. The chlorophyll a/b ratio in WT was much lower in the cold than in the warm, but in mex1-1 it was low in both warm and cold. After prolonged growth at 4 °C, the shoot biomass, rosette diameter and number of leaves at bolting were similar in mex1-1 and WT.ConclusionsThe mex1-1 mutation in warm-grown plants confers aspects of cold acclimation, including elevated levels of sugars and amino acids and low chlorophyll a/b ratio. This may in turn compromise growth of mex1-1 in the warm relative to WT. We suggest that elevated maltose in the plastid could be responsible for key aspects of cold acclimation.
Highlights
To survive in temperate climates, cold-hardy plants such as Arabidopsis make rapid genetic and metabolic changes in response to a reduction in temperature [1], [2]
The most abundant amino acid in wild type (WT) was Gln both before and after acclimation whereas Glu and Pro were in greatest abundance in mex1-1 in warm and cold conditions, respectively
In both treatments GABA was in lowest abundance in mex1-1 and in WT in the warm, after acclimation Ornithine was of lowest abundance in the WT (Table 1)
Summary
To survive in temperate climates, cold-hardy plants such as Arabidopsis make rapid genetic and metabolic changes in response to a reduction in temperature [1], [2]. The importance of starch breakdown in conferring freezing tolerance has been demonstrated using mutants defective in chloroplastic β-amylase, BAM3 (BMY8), which is essential for maltose production, and GLUCAN WATER DIKINASE1 (SEX1), which mediates the phosphorylation of amylopectin In both cases the mutants exhibited a freezing-sensitive phenotype, providing evidence that maltose accumulation is important for cold acclimation [7], [12]. Conclusions: The mex mutation in warm-grown plants confers aspects of cold acclimation, including elevated levels of sugars and amino acids and low chlorophyll a/b ratio. This may in turn compromise growth of mex in the warm relative to WT. We suggest that elevated maltose in the plastid could be responsible for key aspects of cold acclimation
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