Leandro Ferreira Aguiar

Site of nitrate reduction in Jack bean (Canavalia ensiformis) changes from leaf to root during development

Abstract In Jack bean (Canavalia ensiformis), nitrogen metabolism was shown to be drastically altered when different development stages were compared. During development, a change in the location of nitrate reduction and alterations in the relative concentrations of amino acids were observed. Nitrate reductase activity in the roots of C. ensiformis increased during the growth of the plants, being highest at the stage of seed production, whereas leaf nitrate reductase activity showed the reverse pattern, being highest at the vegetative stage and lowest at seed production.

Variation in the ureide content of Jack Bean during the reproductive stages in response to nitrate

Nitrogen is frequently the limiting mineral nutrient for plant productivity and it is essential to obtain an understanding of how this element is assimilated and its metabolism regulated, in crop plants. The objective of this work was to study nitrogen metabolism in the tropical legume Canavalia ensiformis, a plant species used as a green manure. The nitrate dose provided changed the concentrations of ureides exported via the xylem, whilst the developmental stage alterations demonstrated to influence the form of ureide exported via the xylem. Considering the content of ureides as an indicator of N-fixation status, it could be concluded that N-fixation was affected in the presence of nitrate in C. ensiformis.

pH effects on nodulation and biological nitrogen fixation in Calopogonium mucunoides

Calopogonium mucunoides Desv. is able to form nodules, root organs in which biological nitrogen fixation takes place, after a symbiotic interaction with soil bacteria known as rhizobia. Such distinct advantage of some legume species faces different environmental abiotic factors such as acid and alkaline pH conditions of soil. Nodulation and symbiotic nitrogen fixation response in different pH ranges were determined under greenhouse conditions. Plants were cultivated in vermiculite and treated with nutritive solution adjusted to pH 4.0, 5.5, and 7.0, and after three months, the following variables were measured: nodule number, nitrogen fixation, tissue protein, amino acids, total ureides, allantoin, and allantoate. The number of nodules and nitrogen fixation were enhanced under acidic conditions, but nitrogenase activity was drastically decreased at pH 7.0. Acidic conditions decreased the amount of protein, amino acids, total ureides, allantoate, and allantoin in leaves and nodules, but at pH 5.5, only protein content was decreased. Symbiosis with C. mucunoides and biological nitrogen fixation were kept under acidic conditions, but it was negatively affected under conditions that are near to neutral. It is reasonable to conclude that the association between C. mucunoides and nitrogen-fixing bacteria from “Cerrado” evolved in this context, which is supported by the difficulties faced to keep interaction under pH near neutrality.

Changes in soluble amino acid composition during Canavalia ensiformis development: responses to nitrogen deficiency

A limited number of studies focusing nitrogen metabolism have been carried out with plants from Cerrado, the second largest biome of Brazil. Canavalia ensiformes is a legume native from Cerrado and is considered an important forage crop that contributes to soil nitrogen (N) improvement. There are few studies related to amino acid metabolism and growth capacity under nitrogen deficiency for this plant species. Therefore, the objective of this work was to study the profile of soluble amino acids during the growth cycle (from vegetative to the reproductive stage) of Canavalia ensiformis. Major changes in the concentration and composition of soluble amino acids at the beginning of the reproductive stage were observed indicating important alterations in amino acids metabolism. The data revealed that N-stress conditions led to increased aspartate and decreased asparagine contents in most organs and developmental stages of C. ensiformis. A pronounced increase in glutamate concentration during N-stress was also detected. Glutamine, alanine, GABA, threonine, histidine, arginine and glycine metabolisms were probably impaired by N deficiency, which was dependent upon plant developmental stage. The effect of nitrate presence or absence on amino acids metabolism in C. ensiformis is discussed.

Características adaptativas da associação simbiótica e da fixação biológica do nitrogênio molecular em plantas jovens de Lonchocarpus muehlbergianus Hassl., uma leguminosa arbórea nativa do Cerrado

It is well established that mineral nitrogen negatively affects symbioses and molecular nitrogen utilization by crops. Nevertheless, symbiosis and nitrogen fixation of tree species, less studied, has been showed certain tolerance to nitrate. The aim of this work was to evaluated the nitrogen molecular use by nodulated Lonchocarpus muehlbergianus, a Cerrado legume tree, even supplied with mineral nitrogen as nitrate, important feature for symbiotic plants growing in soil where nitrate is the prominent source of nitrogen. For this purpose, the number and dry weight of nodules, shoot and roots, as well as content of xylem sap amino acids, nitrate and ureides, product of symbiotic nitrogen fixation, and nitrate reductase activity were determined. At the end of the experiment, it was observed that the number and dry weight of nodules was not affected by nitrate. Addictionally, it was verified a short increment in shoots and roots treated with nitrate. Similar results were found for amino acids and ureides content and foliar nitrate reductase activity. Our results suggest that Lonchocarpus muehlbergianus is able to utilize at the same time both mineral and molecular nitrogen since transport of ureides from roots to shoots was not reduced when nodulated plants was fed with nitrate.

Boron phytoremediation: Stizolobium aterrimum is tolerant and can be used for phytomanagement of boron excess in soils

ABSTRACT Soil contamination by toxic elements causes concern and is increasing through industrial development, mining activities and the overuse of chemical fertilisers. Some toxic elements, such as boron, also play a structural role. The present study aimed to evaluate the behaviour of S. aterrimum plants growing in boron artificially contaminated soils. It has been found that S. aterrimum is tolerant to low doses of boron, moderately tolerating doses of up to 240 mg.dm−3. But high doses (doses above the adequate zone) cause decreased plant growth and present symptoms of toxicity, such as foliar chlorosis. The dose of 240 mg.dm−3 can already be considered toxic, since the tolerance index (TI) was less than 50%. The species can be used as a phytoextractor in low doses of boron because it presented a high tolerance index (TI) and demonstrated the ability to uptake and accumulate boron in root tissue.