Liliane Santos Camargos

Mycorrhization alters foliar soluble amino acid composition and influences tolerance to Pb in Calopogonium mucunoides

Soil contamination by lead (Pb) is a problem due to the persistence of this element on soil. High amounts of Pb in soil impair plant establishment, however some plants may increase tolerance to heavy metals when colonized by arbuscular mycorrhizal fungi (AMF). The leguminous plant, Calopogonium mucunoides, is Pb-sensitive that is tolerant to Pb when associated to AMF. We performed a chromatographic analysis of foliar free-amino acid in non-mycorrhizal and mycorrhizal plants to determine its relation with Pb tolerance. Mycorrhization caused drastic increase in aspartate, glutamine, glycine, threonine, alanine, isoleucine and gamma-aminobutiric acid (GABA), while depletion of asparagine, histidine and arginine was observed in AMF-associated plants. When grouped according to common metabolic precursor, it was found that amino acids derived from 3-phosphoglicerate and pyruvate was higher in mycorrhizal plants while amino acids derived from glucose-6-phosphate and 2-oxoglutarate were higher in non-mycorrhizal plants; phosphoenolpyruvate and oxaloacetate pathways were not influenced by mycorrhization. Summarizing, mycorrhization changed soluble amino acids profile in C. mucunoides leaves, especially aspartate, alanine and GABA, which may be involved in tolerance to abiotic stress. Additionally the depletion of asparagine, histidine and arginine may be related to a deviation for metabolic pathways not related to protein biosynthesis but to the synthesis of polyamines, especially in the case of arginine. Therefore, we suggest that mycorrhization influence on soluble free amino acid profile in leaves can be one of the factors involved with the attenuation of Pb toxicity in AMF-associated C. mucunoides plants.

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.

Mineral Nitrogen Associated Changes in Growth and Xylem-N Compounds in Amazonian Legume Tree

In nodulated young Inga edulis plants, nodule and plant growth, nitrogen (N) in xylem sap and tissues total contents of amino acid, ureide, and nitrate were determined in response to nutrition with nitrate, ammonium, or no mineral N. Additionally, the amount of soluble sugars in the different plant tissues was quantified. It was found that mineral N improved plant growth in height and diameter especially with ammonium. However, nitrate dramatically reduced nodule dry weight on a root dry weight basis and impaired N organic transport by xylem sap. Additionally, a higher amount of amino acids was observed in the roots and nodules of plants fed with mineral N but sugar levels remained constant. Although nitrate inhibited symbiosis, data support the idea that I. edulis is able to use both molecular and mineral nitrogen during the life cycle.

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.