Molybdenum cofactor in nitrate reductase deficient tobacco nicotiana tabacum mutants 3. induction of cofactor synthesis by nitrate

Mendel, R.R.; Alikulov, Z.A.; Mueller, A.J.

Plant Science Letters 27(1): 95-102


Accession: 005920857

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The Mol cofactor (Mo-co) content of cultured cells of N. tabacum was estimated by the ability of the acid and heat treated extract to restore NADPH-nitrate reductase (NR) of Neurospora crassa nit-1. Addition of nitrate to wild-type cells grown on amino acids caused a rapid increase in Mo-co activity concomitant with induction of NADH-NR. Time course experiments revealed the constitutive and the induced levels of Mo-co activity to be dependent on culture age, the maximum occurring during log phase. According to their Mo-co activity, the 12 NR-deficient mutant cell lines tested fall into 3 groups: Group I nia mutants are characterized by a low Mo-co level, which does not increase either during log phase or after addition of nitrate. Group II nia mutants are similar to wild type. The 4 cnx mutants tested display a constitutive-high Mo-co level, being not further inducible by nitrate. Possible mechanisms for the common regulation of Mo-co and NR synthesis are discussed.