In this study, Mª Dolores Domínguez has compared the effect of ammoniacal nutrition on the metabolism of sensitive plants, such as spinach and on tolerant ones, like the pea. The results indicate that the processes associated with tolerance to ammonia in the pea are multiple with respect to spinach. In the pea plant there is greater regulation of the absorption of ammonia at the roots and control of the ammonium levels, above all in the leaf tissue. Moreover, important changes are observed in relation to the carbon and nitrogen of the majority aminoacids (asparragine in the pea and glutamine in spinach). With respect to the activities of the GS (glutamine synthetase) and GDH (glutamate dehydrogenase) enzymes, responsible for the assimilation of ammonium, this substance is not modified in moderate concentrations in the pea but it is so in spinach. Regarding the main metabolic modifications, these take place in the roots in the case of the pea and in the leaves in the case of spinach. Moreover, in the roots of the pea, morphological changes have been observed which could be indicative of adaptations in order to assimilate the ammonium without modifying its internal processes.
In another part of the study the nature of the stress produced in plants by the use of ammoniacal fertilisers is investigated. The high concentration of ammonium does not carry oxidative stress with it (i.e. the molecules are oxidised due to alteration produced in the enzymes), unlike that which occurs in the majority of these states. The activation of some antioxidant enzymes is reflection of stress that ammonium produces in plants. Mo