engleski

Effects of osmotic stress on antioxidative system of duckweed (Lemna minor L.)

Background and Purpose: It is known that osmotic stress may cause damage to cells by inducing active oxygen species production or by disrupting detoxification mechanisms. We hypothesize that increased activity of antioxidant enzymes in duckweed (Lemna minor L.) provides a mechanism of tolerance to osmotic stress. Material and Methods: Plants were subjected to NaCl- (50 mM), mannitol- (50 and 100 mM) and polyethylene glycol-mediated osmotic stress (PEG, 50 mM) for a period of 15 days. The responses of antioxidative system including also changes in growth, proline content and the extent of oxidative damage in terms of malondialdehyde, H2O2 and chlorophyll a to chlorophyll b (chl a/b) and chlorophyll a+b to carotenoids (chl a+b/car) ratios were studied. Results and Conclusion: Iso-osmolar concentrations of salt and mannitol significantly reduced relative growth rate compared to control plants while osmotic shock mediated by PEG caused complete cessation of growth. Proline content increased with the severity of osmotic stress showing highest values in PEG treated plants. The proline accumulation upon PEG stress was paralleled by equall increase of ascorbic acid pool. Catalase, ascorbate peroxidase and non-specific peroxidase activities showed considerable increase under all osmotic agents, especially PEG. The increased enzyme activities coincided with unchanged H2O2 levels, chl a/b and chl a+b/car under mannitol and salt stress. Despite the highest induction of antioxidative defense, a marked increase in lipid peroxidation and H2O2 level as well as decrease of chl a/b and chl a+b/car accompanied PEG treatment. These results suggested that induction of antioxidant defences is at least one component of the tolerance mechanism of plants to long-term osmotic stress.

oxidative damage; PEG; mannitol; NaCl; antioxidant; proline

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