Ecophysiological and transcriptomic responses of oak (Quercus robur) to long-term drought exposure and rewatering

Long-term drought during one and two growing seasons, respectively strongly affected the timing and number of flushes of oak plants (Quercus robur L), and negatively influenced subsequent growth. In contrast, strong compensation growth was observed upon rewatering. The defence response of experimental plants was assessed by analyzing stress metabolites and transcriptome changes. Our data revealed that while during mild and/or short drought stress only readily metabolizable carbohydrates e.g. glucose, fructose, and galactose are accumulated, prolonged drought stress results in accumulation of more stable and protective osmolytes such as quercitol and mannitol. At transcriptome level more than 3% of the expressed sequences tags (ESTs) represented on the microarray were differentially expressed reflecting the activation of defence responses in oak which appear to be stronger in the second year of persisting stress. The transcriptome changes are in good agreement with both the metabolic data as well as morphological observations. We conclude that mild long-term drought stress over two years triggers adaptation processes in oak plants that ensure survival, while irreversible damage is kept low facilitating full recovery upon rewatering. (C) 2011 Elsevier B.V. All rights reserved.