Ammonium Uptake, Mediated by Ammonium Transporters, Mitigates Manganese Toxicity in Duckweed, Spirodela polyrhiza

Abstract

Nitrogen is an essential nutrient that affects all aspects of the growth, development and metabolic responses of plants. Here we investigated the influence of the two major sources of inorganic nitrogen, nitrate and ammonium, on the toxicity caused by excess of Mn in great duckweed, Spirodela polyrhiza. The revealed alleviating effect of ammonium on Mn-mediated toxicity, was complemented by detailed molecular, biochemical and evolutionary characterization of the species ammonium transporters (AMTs). Four genes encoding AMTs in S. polyrhiza, were classified as SpAMT1;1, SpAMT1;2, SpAMT1;3 and SpAMT2. Functional testing of the expressed proteins in yeast and Xenopus oocytes clearly demonstrated activity of SpAMT1;1 and SpAMT1;3 in transporting ammonium. Transcripts of all SpAMT genes were detected in duckweed fronds grown in cultivation medium, containing a physiological or 50-fold elevated concentration of Mn at the background of nitrogen or a mixture of nitrate and ammonium. Each gene demonstrated an individual expression pattern, revealed by RT-qPCR. Revealing the mitigating effect of ammonium uptake on manganese toxicity in aquatic duckweed S. polyrhiza, the study presents a comprehensive analysis of the transporters involved in the uptake of ammonium, shedding a new light on the interactions between the mechanisms of heavy metal toxicity and the regulation of the plant nitrogen metabolism.

Duckweeds for Phytoremediation of Polluted Water

“…During biomass accumulation, duckweeds can very efficiently remediate different types of wastewater [ 32 ], and these traits can be further improved not only by selection of the best species or ecotypes [ 7 , 33 , 34 ], but also through optimization of plant’s growth parameters such as ration of nutrients, light intensity, fronds density, etc. [ 35 , 36 , 37 , 38 ]. Biomass accumulation by plants in general strongly depends on efficient use of N, and duckweed plants are extremely efficient at assimilating N. Due to N remobilization and recycling by duckweeds, their nitrogen use efficiency is extremely high, reaching more than 68 kg biomass/kg of N under N limitation [ 39 ].…”

Duckweed: Research Meets Applications

“…Nitrogen availability is not only crucial in the plants’ nutritional status, but may also modulate responses to other stressors, such as the presence of heavy metals. In their study, Kishchenko et al [ 28 ] focused on the mechanisms by which NH 4 + could mitigate manganese toxicity in S. polyrhiza , including the interactions between Mn availability and the transcription of ammonium transporters. Besides remediation, metal accumulation may also gain significance when future duckweed-based feed and food production is considered.…”

Identification and Functional Characterization of MdNRT1.1 in Nitrogen Utilization and Abiotic Stress Tolerance in Malus domestica

“…As a major nutrient element, nitrogen (N) plays a key role in metabolism in various organisms [1][2][3][4][5][6][7][8]. Nitrogen constitutes around 4% of the total dry weight of plants.…”