Relationship between Inhibition of CO2 Fixation and Glutamine Synthetase Inactivation in Lemna gibba L. Treated with L-Methionine-D,L-Sulphoximine (MSO) |
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Authors: | JOHANSSON LENA; LARSSON CARL-MAGNUS |
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Abstract: | The rate of net CO2 fixation in Lemna gibba L. was decreasedto 50% by 100150 min incubation in the presence of 05mol m3 L-methionine-D,L-Sulphoximine (MSO), an irreversibleinhibitor of glutasnine synthetase (GS). The pattern of inhibitionwas similar in both 21% O2 and 2% O2. The inhibition was accompaniedby increased intracellular levels. Incubation with 10 mol m3 under the same conditions, but without MSO, resulted in even higher levels but the rate of CO2 fixation was unaffected. Additions of glutamine, glutamate, glycine or serine delayedthe MSO-induced inhibition of CO2 fixation. The same amino acidsdelayed the inactivation of GS by MSO. Thus inhibition of CO2 fixation by MSO in Lemna is neither causedby elevated levels nor closely related to photorespiration. Possibly, MSO causes shortage of amino-N formaintenance of the functional integrity of the photosyntheticapparatus. Key words: Methionine sulphoximine, CO2, fixation, Lemna |
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