Physiological responses to drought stress and the emission of induced volatile organic compounds in Rosmarinus officinalis

Aims Drought is one of the numerous environmental factors which affect the growth and development of plants, and it becomes more severe in many regions of the world due to climate change. To examine the mechanisms of responses of the plant Rosemarinus offcinalis to drought stress, we measured the physiological and biochemical changes and volatile organic compounds (VOCs) emission of 2-year-old seedlings of this species under conditions of light drought (LD), intermediate drought (MD) and severe drought (SD). Methods The VOCs emission was measured using the dynamic headspace air-circulation method, and the composition and content of VOCs were analyzed using the thermal desorption system/gas chromatography/mass spectrometer technique (TDS-GC-MS). We measured ion leakage of cell membranes and the content of soluble sugar, soluble protein and malondialdehyde (MDA), activities of lipoxygenase and protective enzymes of R. offcinalis under the different drought treatments. Important findings The content of osmotic adjustment materials in R. offcinalis leaves was significantly influenced by drought stress. The content of soluble sugar was increased by 51.5% and 87.4% (p 0.01) under MD and SD stresses after 12 days, respectively. The content of soluble protein was increased by 82% and 140% (p 0.01), respectively. There were differences among the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in response to drought stress, which was a coordination reaction of those three enzymes to the stress. With prolonged drought stress, the MDA content (p 0.01) and cell injury rate (p 0.05) were increased significantly. Terpenoids were the main components of R. offcinalis VOCs and their relative content was morethan 46% of the total VOCs. Compared with the control, it was increased by 14.4%, 17.0% and 23.7%, respectively, under LD, MD and SD stresses, respectively. Meanwhile, green leaf volatiles (GLVs) and aldehydes were markedly induced by drought stress, and (E)-2-hexenal, leaf alcohol, sorbaldehyde and n-decanal were newly found under the drought stress. The results indicated that R. offcinalis could enhance its drought-resistant ability by adjusting activities of protective enzymes, improving contents of osmotic adjustment materials and releasing VOCs.