Influencia del nitrato en la asimilación del amonio y de la urea en plantas de trigo (Triticum aestivum L. ). Relación con el balance hormonal

Resumo

Influence of nitrate on ammonium and urea assimilation in wheat plants (Triticum aestivum L.). Relation with hormonal balance. Nitrogen is one of the major factors limiting plant growth. It is taken up by the roots principally in the form of nitrate and ammonium, the most abundant nitrogen forms present in soil. Plants can also use urea as a nitrogen source, although its efficiency seems to be lower than that of nitrate and ammonium. However, ammonium nutrition usually has deleterious effects on plant growth and can result in toxicity symptoms in many plants. In addition, urea nutrition can cause negative effects on plant development. A number of studies have shown that presence of nitrate in the nutrient solution corrected the negative effects associated with ammonium and urea nutrition in certain plant species. The main objective of this study is to investigate the nature of the biochemical and physiological events responsible for this beneficial effect of nitrate on ammonium and urea nutrition. The first aim of this study has been to ascertain whether the action of nitrate on ammonium and urea nutrition is associated with the improvement of ammonium and urea uptake and with an enhancement of its assimilation. In this sense, presence of nitrate increases ammonium and urea uptake rates, as well as enhances its assimilation in urea-fed plants. The second part of this work deals with the study of the action of nitrate on plant hormonal balance. Two different nitrate doses has been employed in order to investigate whether the effect of nitrate requires significant doses (nutritional character) or can be promoted by very low doses (pseudo-hormonal character). The results present further evidence that nitrate signal effect involved in its beneficial effect on ammonium-fed plants could be mediated by a coordinated action of the shoot levels of plant hormones.