Inorganic nitrogen uptake and related enzymatic activity in the seagrass Zostera noltii

Abstract

The preferential inorganic nitrogen source for the seagrass Zostera noltii was investigated in plants from Ria Formosa, South Portugal. Rates of ammonium and nitrate uptake were determined at different concentrations of these nutrients (5, 25 and 50 μm), supplied simultaneously (NH4NO3) or separately (KNO3 and NH4Cl). The activity of the enzymes nitrate reductase (NR) and glutamine synthetase (GS) was also assessed. The results showed that ammonium is the preferential inorganic nitrogen source for Z. noltii, but, in the absence of ammonium, the species also has a high nitrate uptake capacity. The simultaneous availability of both inorganic nitrogen forms enhanced the uptake rate of ammonium and decreased the uptake rate of nitrate compared to when only one of the nitrogen forms was supplied. The activity of both enzymes was much higher in the leaves than in the roots, highlighting the importance of the leaves as primary reducing sites in the nitrogen assimilation process.

Effects ofCO2enrichment on photosynthesis, growth, and nitrogen metabolism of the seagrassZostera noltii

“…Previous experiments reported elsewhere (Alexandre et al. ) showed no effects of rhizosphere oxygenation on the ammonium and nitrate uptake rates of leaves.…”

Ammonium reduces oxalate accumulation in different spinach (Spinacia oleracea L.) genotypes by inhibiting root uptake of nitrate

“…This suggested that the inhibition of oxalate accumulation in the leaves in the mixed solution was due to the reduced NO 3 À uptake inhibited by NH 4 + ions in the solution. Strong inhibition of NO 3 À uptake into the plants by the presence of NH 4 + has been reported in some other plants (Alexandre, Silva, & Santos, 2010;Garnett, Shabala, Smethurst, & Newman, 2003), which could be caused by the NH 4 + -induced stimulation of a higher NO 3 À efflux (Alexandre et al, 2010;Aslam, Travis, & Huffaker, 1994), or by the down-regulation of some genes involved in NO 3 À assimilation through a nitric oxide-dependent mechanism (Sanz-Luque, Ocana-Calahorro, Llamas, Galvan, & Fernandez, 2013). Although the mechanisms involved in inhibited NO 3 À uptake by NH 4 + in spinach needs to be further elucidated, the results of our study clearly suggest that NH 4 + reduces oxalate accumulation in spinach by inhibiting its root uptake of NO 3 À rather than other strategies.…”

Dissolved inorganic nitrogen uptake kinetics and δ15N of Zostera marina L. (eelgrass) in a coastal lagoon with oyster aquaculture and upwelling influence

“…6-9 mg L −1 and 7.9-8.1, respectively). Although belowground tissues of Z. marina are exposed to a mostly anoxic environment in SQB, rhizomes and roots in these experimental incubations were maintained in partially oxygenated seawater; however previous studies show no effects of rhizosphere oxygenation on the NH 4 + and NO 3 − uptake rates of leaves or belowground tissues (Alexandre et al, 2010(Alexandre et al, , 2011. One entire plant was incubated per chamber, and leaf biomass was 0.5-0.9 g DW in the upper compartment, whereas the belowground biomass in the lower compartment was 0.1-0.4 and 0.05-0.2 g DW for rhizomes and roots, respectively.…”