Author
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Sicher Jr, Richard |
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Submitted to: Plant Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/9/2011 Publication Date: 5/28/2011 Citation: Sicher Jr, R.C. 2011. Carbon partitioning and the impact of starch deficiency on the initial response of Arabidopsis to chilling temperatures. Plant Science. 181:167-176. Interpretive Summary: Frost is a threat to crop production. Climate change may increase the risk of frost damage to plants because farmers are likely to expand the growing season. Pre-exposing plants to low temperatures, which is known as cold acclimation, improves frost tolerance. This is partly due to the fact that plants accumulate high concentrations of soluble sugars during growth at low temperatures. This manuscript is concerned with understanding the processes that are responsible for making sugars in response to chilling. The findings were that soluble sugars are mostly products of photosynthesis. However, specific sugars also were made from leaf starch. Additional findings indicated that the ambient carbon dioxide concentration has an important role in the induction of genes involved in frost tolerance. These findings improve our understanding of how plants survive frost and should be of interest to scientists studying plant stress, climate change, and molecular biology. Technical Abstract: Specific metabolites and RNA transcripts were measured in Arabidopsis thaliana leaves in response to chilling temperatures. During the first 24 h of cold treatment eight soluble carbohydrates increased 9.4 fold on average during cold treatment. Except for maltose and raffinose carbohydrate accumulation was not observed when cold treatments were performed in darkness. Most soluble carbohydrates decreased over 24 h and only a trace of maltose accumulated during cold treatments performed in the light with sub ambient (7 Pa) CO2. Leaf starch and maltose were negligible in the pgm1 starchless mutant of Arabidopsis. Glucose and fructose accumulated at low temperatures in the pgm1 mutant but levels of these two hexoses in the mutant never achieved that of the wild type and there was a 6 h or longer delay before these two compounds accumulated in response to cold. Rates of A by excised wild type leaves increased slightly in response to cold when measurements were performed at 38 and 7 Pa CO2. Sucrose, glucose and fructose accumulation consumed 42% of total A acquired in a 24 h period. Moreover, there was insufficient leaf starch to generate the additional soluble carbohydrate that accumulated in response to low temperatures. Expression levels of six stress-induced transcripts increased in response to cold in the wild type when cold acclimation was performed either in the light or dark. Unlike cold treatments with 38 Pa CO2, the induction of transcripts for AtCBF1 and AtHVA22 was almost completely eliminated during cold treatments with 7 Pa CO2. The above results demonstrated that carbohydrate accumulation during cold acclimation was heavily dependent on A. However, maltose and raffinose accumulated under nonphotosynthetic treatment conditions and hexose accumulation in response to 1 d of cold treatment was delayed and/or diminished by the absence of leaf starch. Also, the induction of two of six cold stress related transcripts was inhibited during cold acclimation by photorespiratory cold treatment conditions and this was due to a previously unknown effect of Ci on gene expression. |
