Physiological responses of Populus przewalskii to oxidative burst caused by drought stress

We measured dry matter accumulation and allocation to the roots, leaf gas exchange, chlorophyll fluorescence, antioxidant enzymes, and ABA and polyamine (PA) contents in Populus przewalskii under three different watering regimes (100, 50, and 25% of the field capacity) to investigate the morphological and physiological responses to water deficit in woody plants. The results showed that drought stress retarded P. przewalskii as evident from a decreased biomass accumulation and the reduced increment of shoot height and basal diameter. Drought stress also affected the biomass partition by higher biomass allocated to the root systems for water uptake. The contents of ABA and PAs especially were increased under stressful conditions. Drought stress caused oxidative burst indicated by the accumulation of peroxide (H2O2), and fluorimetric detection also confirmed the increased accumulation of H2O2. The antioxidant enzymes, including superoxide dimutase, peroxidase, ascorbate peroxidase, and reductase, were activated to bring the reactive oxygen species to their homeostasis; however, oxidative damages to lipids, proteins, and membranes were significantly manifested by the increase in total carbonyl (C=O) and electric conductance (EC).