ABSTRACT
Since the ecosystem is contaminated by lead, decontamination is a difficult and expensive process. Therefore, an alternative would be the use of phytoremediation plants, which have been studied more intensely in recent decades. Astronium graveolens Jacq (Anacardiaceae) is a Cerrado native species and plants of this biome are known to present adaptations and modifications that keep them in this ecosystem. Our aim was to find the tolerance index of A. graveolens to lead doses and to evaluate the morphophysiological alterations of the species when exposed to the heavy metal. The experiment was carried out in a greenhouse in Ilha Solteira-SP, with a completely randomized design and using lead acetate (Pb(C2H3O2)2) as the source of the heavy metal. Samples of the vegetative organs (roots and leaves) were fixed, subsequently dehydrated in an ethyl series, included in hydroxyethyl methacrylate (Leica Historesin) and sectioned for histological slide assembly and subsequent anatomical analysis. The levels of phenolic compounds, protein, amino acid, ammonia, allantoic acid and allantoin were quantified. We calculated the tolerance index for the species. Significant differences were found in leaf and root tissues anatomy, while in relation to the physiology of A. graveolens, a significant difference was observed when the concentration of total ureids in the roots was evaluated. Pb did not interfere with the survivability of the species. In fact, A. graveolens showed a higher secondary growth in the treatment with higher level of lead.
Subject(s)
Adaptation, Physiological/drug effects , Anacardiaceae/drug effects , Lead/toxicity , Soil Pollutants/toxicity , Soil/chemistry , Anacardiaceae/metabolism , Biodegradation, Environmental , Brazil , Ecosystem , Lead/metabolism , Models, Theoretical , Plant Leaves/drug effects , Plant Leaves/metabolism , Plant Roots/drug effects , Plant Roots/metabolism , Soil Pollutants/metabolismABSTRACT
Aspartate kinase (AK, EC 2.7.2.4), homoserine dehydrogenase (HSDH, EC 1.1.1.3) and dihydrodipicolinate synthase (DHDPS, EC 4.2.1.52) were isolated and partially purified from immature Chenopodium quinoa Willd seeds. Enzyme activities were studied in the presence of the aspartate-derived amino acids lysine, threonine and methionine and also the lysine analogue S-2-aminoethyl-l-cysteine (AEC), at 1 mM and 5 mM. The results confirmed the existence of, at least, two AK isoenzymes, one inhibited by lysine and the other inhibited by threonine, the latter being predominant in quinoa seeds. HSDH activity was also shown to be partially inhibited by threonine, whereas some of the activity was resistant to the inhibitory effect, indicating the presence of two isoenzymes, one resistant and another sensitive to threonine inhibition. Only one DHDPS isoenzyme highly sensitive to lysine inhibition was detected. The results suggest that the high concentration of lysine observed in quinoa seeds is possibly due to a combined effect of increased lysine synthesis and accumulation in the soluble form and/or as protein lysine. Nitrogen assimilation was also investigated and based on nitrate content, nitrate reductase activity, amino acid distribution and ureide content, the leaves were identified as the predominant site of nitrate reduction in this plant species. The amino acid profile analysis in leaves and roots also indicated an important role of soluble glutamine as a nitrogen transporting compound.
