Source of nitrogen associated with recovery of relative growth rate in Arabidopsis thaliana acclimated to sustained cold treatment

To determine (1) whether acclimation of carbon metabolism to low temperatures results in recovery of the relative growth rate (RGR) of plants in the cold and (2) the source of N underpinning cold acclimation in Arabidopsis thaliana, we supplied plants with a nutrient solution labelled with ¹⁵N and subjected them to a temperature shift (from 23 to 5°C). Whole-plant RGR of cold-treated plants was initially less than 30% of that of warm-maintained control plants. After 14d, new leaves with a cold-acclimated phenotype emerged, with the RGR of cold-treated plants increasing by 50%; there was an associated recovery of root RGR and doubling of the net assimilation rate (NAR). The development of new tissues in the cold was supported initially by re-allocation of internal sources of N. In the longer term, the majority (80%) of N in the new leaves was derived from the external solution. Hence, both the nutrient status of the plant and the current availability of N from external sources are important in determining recovery of growth at low temperature. Collectively, our results reveal that both increased N use efficiency and increases in nitrogen content per se play a role in the recovery of carbon metabolism in the cold.