Invasive Species Compendium

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Abstract

Morphological and biochemical alterations of oomycete fish pathogen Saprolegnia parasitica as affected by salinity, ascorbic acid and their synergistic action.

Abstract

This study investigated the influence of NaCl and ascorbic acid on the morphology of S. parasitica and its metabolic pathways. The vegetative growth of S. parasitica was decreased by increasing the concentration of NaCl and ascorbic acid. Under these conditions, the morphological features of the vegetative hyphae were distinguishable from those used as controls. NaCl and ascorbic acid in combination improved the tolerance of S. parasitica to high levels of salinity. Sporangial formation, release and proliferation were very sensitive to even lower levels of salinity. For instance, at 0.03 M NaCl, sporangia formation was rarely observed. Ascorbic acid alone had a small effect on sporangial formation and release, but when combined with NaCl the developmental processes were improved. Reduction of numbers and plasmolysis of oogonia were found at various NaCl concentrations, whereas ascorbic acid stimulated the formation of these reproductive organs at low concentrations. The synergistic effect of NaCl and ascorbic acid improved and overcame the symptoms of oogonial plasmolysis. Protease activity of S. parasitica was significantly reduced at all NaCl concentrations, whilst ascorbic acid significantly increased and inhibited it at low concentrations and at moderate and high concentrations, respectively. The combination of these compounds reduced protease activity at all tested concentrations, with a significant difference at the highest concentration. The total free amino-acid content of S. parasitica mycelia was significantly reduced at all the NaCl concentrations, whereas ascorbic acid significantly increased it at low but inhibited it at higher concentrations. The combination of NaCl and ascorbic acid significantly increased the accumulation of free amino-acids at low and moderate concentrations, but decreased them at high concentrations. Total protein content was reduced at all tested concentrations of NaCl and ascorbic acid had a similar effect. However, the combined effect of NaCl and ascorbic acid significantly enhanced and reduced total protein content at low and high concentrations, respectively. Treatment with NaCl induced proline accumulation in S. parasitica, which paralleled the salt concentration.