Nickel and Al-excess inhibit nitrate reductase but upregulate activities of aminating glutamate dehydrogenase and aminotransferases in growing rice seedlings
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The present study was undertaken to examine the influence of toxic levels of Ni and Al, on the activities of key nitrogen assimilatory enzymes in roots and shoots of growing rice seedlings. When seedlings of two inbred rice (Oryza sativa L.) cvs. Malviya-36 and Pant-12, sensitive to both Ni and Al, were raised in sand cultures containing 200 and 400 μM NiSO4 or 80 and 160 μM Al2(SO4)3, a marked inhibition in the activities of NO3 − assimilatory enzymes NR and GS was observed in roots as well as shoots during a 5–20 day growth period. Both Ni and Al treatments, in growth medium, stimulated the activity of aminating glutamate dehydrogenase (NADH-GDH) whereas the activity of deaminating GDH (NAD+-GDH) decreased under metal toxicities. The activities of the aminotransferases studied; alanine aminotransferase (AlaAT) and aspartate amino transferase (AspAT) increased due to Ni and Al treatments. Results suggest that both Ni and Al treatments impair N assimilation in rice seedlings by inhibiting the activities of NR and GS and that GDH appears to play a role in assimilation of NH4 + in metal stress conditions. Further, higher activity of aminotransferases in metal stressed seedlings might be helpful in meeting higher demand of amino acids under stressed conditions.
KeywordsNickel Aluminum Toxicity Nitrogen assimilation Oryza sativa L.
PM is grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi, for providing a Junior Research Fellowship.
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