Antioxidative Defense Mechanism in Callistemon citrinus (Curtis) Skeels and Viburnum tinus L. ‘Lucidum’ in Response to Seawater Aerosol and Surfactants

In the last decades, resistance to salt stress has been studied intensively in plants. Many ornamental plants have widespread presence in green areas of coastal regions. In such regions, plants are subject to seawater aerosol and surfactants, both of which are frequent in the coastal areas of Mediterranean environment. The objective of this study was to investigate the antioxidant enzyme activities of two ornamental plants, namely, Callistemon and Viburnum, under the effects of these stressful conditions. To analyze the performance of these plants stressed by 8 weeks treatments with seawater aerosol and surfactants, we measured the antioxidative defense mechanism, considered as enzymatic response, Proline (Pro) levels, Chlorophyll (Chl) and MalonDiAldehyde (MDA) contents. To better understand the response mechanisms, two different growing periods were studied: from January to March and from May to July. The higher temperatures of the second period negatively affected the response of the plants. Salt stress considerably reduced the chlorophyll content in both species, especially in the second period. In particular, the sea aerosol treatments caused 29% and about 45% reduction in Callistemon and Viburnum plants, respectively. The amount of Pro in Viburnum was very small (154.35 nmol g-1) compared to Callistemon (1466.94 nmol g-1). An opposite trend was noticed for MDA. ROS-scavenging enzymes, such as SuperOxide Dismutase (SOD), catalase (CAT), and Glutathione Peroxidase (GPX) in plants exposed to treatment with sea aerosol plus anionic surfactant were significantly higher. Between the two species, Viburnum showed more efficient action mechanisms to overcome aerosol stress.