Zn stress in Tetradenia riparia. Analysis of physiological responses, interaction with water stress and VOCs emission.

Abiotic stress can affect the growth and development of plants. Environment is a dynamic reality and plant must be able to respond effectively to different stress factors that can occur in combination or separately. Three different experiments were carried out to evaluate the effect of abiotic stress such as zinc excess and water deficit in Tetradenia riparia plant, in order to characterize the emission of volatile organic compounds, observing which compounds were emitted from plant and at what intensity. T. riparia is a plant belonging to the Lamiaceae family and native of South-Africa, known for its essential oil extractable from the leaves. As the essential oils are made for the most part by volatile compounds, this plant can represent an easy-to-study model system to start investigating the relationship between heavy metal stress, drought stress and volatile emission. In the first experiment, it was investigated some physiological responses of T. riparia grown with increasing zinc concentrations in the culture medium. In the second experiment, it was evaluated the combined effect of two types of stress, zinc and drought stress. In the third experiment, it was investigated whether it is possible to induce acclimatization process in plant by means of a previous prolonged exposure to zinc stress. Results showed that zinc adversely affects growth, photosynthetic efficiency and stomatal conductance of T.riparia in a dose dependent manner, but this effect was alleviated by the simultaneous presence of polyethyleneglycol (PEG), simulator of water stress, therefore revealing a not cumulative effect of the presence of both the stresses. Zinc induces a significant greater emissions of volatile organic compounds (VOCs) in Tetradenia riparia, while in the presence of PEG this effect vanishes. Plants grown with both treatments showed an intensity of emission very similar to that of the control plants and plants treated with only PEG, showed an intensity of emission lower than the control plants. Finally no acclimation process was observed in plants primed.