Physiological and biochemical response of water lettuce (Pistia stratiotes) to short-term mild saline stress

This current work describes the response of Pistia stratiotes (water lettuce) to moderate saline stress under controlled conditions. Plant biomass as well as the levels of aldehydes, phenolics, chlorophylls and carotenoids was evaluated after a week of stress. Following the first experiment (up to 80mM NaCl), high levels of mortality were observed. Hence, a second trial was undertaken where lower salt concentrations were tested, i.e. 0, 5, 10, 15 and 20mM NaCl. Small changes in biomass were observed with some necrosis evident. Biochemical evaluations indicated the accumulation of lipid peroxidation products in response to the saline stress, indicative of oxidative damage. Furthermore, water lettuce plants were unable to accumulate phenolics (soluble and bound) or carotenoids, both regarded as antioxidants that play an important role in mitigating against the adverse effects of damage caused by oxidative stress. Hence, water lettuce appeared to be sensitive to saline stress with adverse effects evident even at low exposure levels. One of the reasons proposed for the inability of water lettuce to tolerate saline stress might be the inefficient antioxidant systems which led to the accumulation of damage. This requires further investigation. In addition, it is recommended that future studies consider the ability of water lettuce to tolerate longer term mild stress as this might allow plants to adapt suitable protective mechanisms to promote survival and have implications on their spread and weed status.