Metabolic and biochemical responses of Potamogeton anguillanus Koidz. (Potamogetonaceae) to low oxygen conditions.

Oxygen availability in water is considered one of the most important factors for growth and productivity in aquatic submerged macrophytes. In the present study, the growth, stress responses, and metabolic changes in Potamogeton anguillanus Koidz. (Potamogetonaceae) were assessed after a 21-day exposure to low (hypoxia; dissolved oxygen, DO < 1 mg/L) or null (anoxia) oxygen concentrations in water. High growth rates and an increased indole acetic acid (IAA) content in P. anguillanus were observed under the hypoxic conditions (4-fold to control) compared to the anoxic conditions. In addition, the activation of glycolysis and fermentation processes was further recorded, given the increase in alcohol dehydrogenase activity and pyruvate concentration on the studied plants that were exposed to low oxygen concentrations. Moreover, the positive correlations of antioxidative enzyme activities, catalase (CAT) and guaiacol peroxidase (POD) with hydrogen peroxide (H2O2) confirmed the species ability to scavenge excess H2O2 under low oxygen stress. The capillary electrophoresis-mass spectrometry (CE-MS) analysis of the metabolome identified metabolite accumulations (e.g., glutamate, glutamine, aspartate, asparagine, valine, malate, lactate, citrate, isocitrate, proline and γ-amino butyric acid) in response to the anoxia.

Biochemical adaptations of four submerged macrophytes under combined exposure to hypoxia and hydrogen sulphide.

A hydroponic experiment was performed to investigate the stress responses and biochemical adaptations of four submerged macrophytes, Potamogeton crispus, Myriophyllum spicatum, Egeria densa, and Potamogeton oxyphyllus, to the combined exposure of hypoxia and hydrogen sulfide (H2S, provided by NaHS). The investigated plants were subjected to a control, hypoxia, 0.1mM NaHS, 0.5 mM NaHS, 0.1 mM NaHS+hypoxia and 0.5 mM NaHS+hypoxia conditions. All experimental plants grew optimally under control, hypoxic and NaHS conditions in comparison to that grown in the combined exposure of hypoxia and hydrogen sulfide. For P. crispus and M. spicatum, significant decreases of total chlorophyll and increases in oxidative stress (measured by hydrogen peroxide, H2O2, and malondialdehyde, MDA) were observed with exposure to both sulfide concentrations. However, the decrease in catalase (CAT) and ascorbate peroxidase (APX) from exposure to 0.5 mM NaHS suggests that the function of the protective enzymes reached their limit under these conditions. In contrast, for E. densa and P. oxyphyllus, the higher activities of the three antioxidative enzymes and their anaerobic respiration abilities (ADH activity) resulted in higher tolerance and susceptibility under high sulfide concentrations.