The changes induced in the physiological, biochemical and anatomical characteristics of Vicia faba by the exogenous application of proline under seawater stress

The depletion of fresh water resources leads to the utilisation of various alternative sources of water, such as seawater. In this regard, the foliar application of proline is one of the alternative shotgun approaches to increase plant stress tolerance. A pot experiment was conducted in the wire house of the National Research Centre, Dokki, Cairo, Egypt, during the winter season of 2010-2011. The experiment consisted of three concentrations of proline (0, 25 and 50 mM) and two concentrations of diluted seawater (3.13 and 6.25 dS m− 1), whereas control plants were irrigated with tap water (0.23 dS m− 1). Diluted seawater caused significant reductions in growth parameters, photosynthetic pigments, some mineral contents (P, K, Ca+ 2), the K+:Na+ ratio and the level of total carbohydrates. In contrast, N, Na+, and Cl− contents, osmoprotectants (soluble carbohydrates, total phenolic concentrations, free amino acids, proline), and activities of antioxidant enzymes (peroxidase and polyphenol oxidase) significantly increased with an increasing salinity level compared with control plants. The foliar application of 25 mM proline caused significant increases in growth parameters, photosynthetic pigments, N, P, K+, and Ca+ 2 %, the K+:Na+ ratio, total carbohydrates, and soluble carbohydrates, accompanied by significant decreases in Na+, Cl−, phenolic contents, free amino acids, proline, and the activities of antioxidant enzymes compared with the control. In addition, 25 mM proline minimised the deleterious effect of salinity on the anatomical structure of the faba bean stem and leaf. The proline treatment at 50 mM was as essentially toxic to faba bean plants as to that of salinity stress. This toxicity was apparent by the reduction of growth parameters, photosynthetic pigments, N, P, K+, and Ca+ 2, K+:Na+ ratio and significant increases in Na+ and Cl− concentrations. Therefore, the exogenous application of proline at a concentration of 25 mM partially alleviated the toxicity of diluted seawater on faba bean plants, whereas the 50 mM proline treatment was toxic.