Dark induction of nitrate reductase in the halophilic algaDunaliella salina

✍ Scribed by M. Jiménez Río; Z. Ramazanov; G. García-Reina

• Publisher: Springer-Verlag
• Year: 1993
• Tongue: English
• Weight: 681 KB
• Volume: 192
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00198690

✦ Synopsis

The effect of nitrogen starvation on the NO 3dependent induction of nitrate reductase (NR) and nitrite reductases (NIR) has been investigated in the halophilic alga Dunaliella salina. When D. salina cells previously grown in a medium with NH + as the only nitrogen source (NH+-cells) were transferred into NO3 medium, NR was induced in the light. In contrast, when cells previously grown in N-free medium were transferred into a medium containing NO 3, NR was induced in light or in darkness. Nitrate-dependent NR induction, in darkness, in D. salina cells previously grown at a photon flux density of 500 lamol, m 2 s 1 was observed after 4 h preculture in N-free medium, whilst in cells grown at 100 ~tmol.m 2 s J NR induction was observed after 7-8 h. An inhibitor of mRNA synthesis (6-methylpurine) did not inhibit NO3-induced NR synthesis when the cells, previously grown in NH + medium, were transferred into NO3 medium (at time 0 h) after 4-h-N starvation. However, when 6-methylpurine was added simultaneously with the transfer of the cells from NH + to NO 3 medium (at time 0 h), NO 3 induced NR synthesis was completely inhibited. The activity of NIR decreased in N-starved cells and the addition of NO 3 to those cells greatly stimulated NIR activity in the light. The ability to induce NR in darkness was observed when glutamine synthetase activity reached its maximal level during N starvation. Although cells grown in NO 3 medium exhibited high NR activity, only 0.33% of the total NR was found in intact chloroplasts. We suggest that the ability, to induce NR in darkness is dependent on the level of N starvation, and that NR in D. salina is located in the cytosol. Light seems to play an indirect regulatory role on NO3 uptake and NR induction due to the expression of NR and NO3transporter mRNAs.