The multiple plant response to high ammonium conditions: The Lotus japonicus AMT1; 3 protein acts as a putative transceptor

Plant evolved a complex profile of responses to cope with changes of nutrient availability in the soil. These are based on a stringent control of expression and/or activity of proteins involved in nutrients transport and assimilation. Furthermore, a sensing and signaling system for scanning the concentration of substrates in the rooted area and for transmitting this information to the plant machinery controlling root development can be extremely useful for an efficient plant response. Ammonium represents for plants either a preferential nitrogen source or the trigger for toxicity symptoms depending by its concentration. We propose a role for the high affinity Lotus japonicus ammonium transporter LjAMT1;3 as an intracellular ammonium sensor to achieve a convenient modulation of the root development in conditions of potentially toxic external ammonium concentration

Toxicity of Cd to signal grass (Brachiaria decumbens Stapf.) and Rhodes grass (Chloris gayana Kunth.)

Given that Cd accumulates within plant tissues to levels that are toxic to animals, it is necessary to understand the role of plants in highly Cd-contaminated systems and their subsequent impact on the health of animals. A solution culture experiment was conducted to elucidate the effects of increasing Cd(2+) activity ({Cd(2+)}) on growth of Rhodes grass (Chloris gayana Kunth.) and signal grass (Brachiaria decumbens Stapf.). The shoot and root fresh mass of both Rhodes grass and signal grass was reduced by 50% at ca. 0.5 A mu M {Cd(2+)}. Elevated {Cd(2+)} resulted in a significant decrease in the tissue Mn concentration for both the shoots and roots, and caused a chlorosis of the veins in the shoots. Root hair growth was prolific even at high {Cd(2+)}, thus root hair growth appeared to be less sensitive to elevated Cd than was root growth per se. The critical shoot tissue concentrations (50% reduction in growth), 230 A mu g g(-1) for Rhodes grass and 80 A mu g g(-1) for signal grass, exceeded the maximum level of Cd tolerated in the diet of animals (ca. 5 A mu g g(-1)). When assessing the risk associated with the revegetation of Cd-contaminated sites with Rhodes grass or signal grass, careful consideration must be given, therefore, to the transfer of toxic concentrations of Cd to grazing animals and through the wider food chain