Effect of Water Deficit on Expression of Stress-related Genes in the Cambial Region of Two Contrasting Poplar Clones

In this study we investigated the effect of prolonged water shortage in the cambial region of two poplar clones, Dvina (Populus deltoides) and I-214 (Populus x canadensis) that differ in their response to water deficit. For this purpose we monitored growth parameters in Dvina and I-214 plants under well-watered and water-stress conditions and after rewatering and analyzed the content of malondialdehyde (MDA) and proline and the expression level of genes coding for antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR) and metallothioneins (MT) by quantitative real-time RT-PCR (RT-qPCR). Water deficit resulted in a significant increase of osmotically active solutes in both clones. No significant increase of MDA level was observed in Dvina, whereas a significant enhancement of lipid peroxidation was detected in I-214, in which also a strong fivefold increase of proline was detected. Transcript analysis of stress-related genes indicated a different ability of the two clones to modulate antioxidant genes under stress. In particular, MT3b was strongly upregulated by water deficit in Dvina thus suggesting an important role for this gene in the maintenance of cellular redox homeostasis in the clone. On the whole, the two clones exhibited changes at the transcription and physiological levels in the cambial region that suggest the occurrence of different strategies of plant protection from prolonged water deficit.