Gilberto Costa Justino

Estratégias no uso da energia luminosa por plantas jovens de Genipa spruceana Steyerm submetidas ao alagamento

In an attempt to elucidate strategies in the use of light energy by G. spruceana seedlings subjected to flooding, we investigated the capacity of light capture and use of light energy by G. spruceana in three growing conditions: 1- absence of flooding (SA), 2- partially flooded (PA) and 3- totally flooded (TA). Destructive and non-destructive measurements, such as specific leaf area, chloroplast pigment (chlorophyll and carotenoids) content and fluorescence analyses, were made at regular intervals over a period of 90 days. All parameters decreased in seedlings subjected to flooding. Plants of treatment TA dropped all of their leaves after 30 days of complete submergence. Chloroplast pigment content differed between treatments SA and TA after 30 days from the start of the experiment; whereas SA and PA plants only differed for this variable after 90 days. Plants subjected to flooding (PA and TA) exhibited high dissipation of photochemical de-excitation (DIo/ABS), indicating a limited efficiency of light energy use. This fact was proven by the performance index (PIABS) only in analyses after 90 days, and no significant difference was verified for PIABS among treatments up to 30 days. Therefore, considering that G. spruceana seedlings subjected to flooding reduced the chloroplast pigment content more quickly than PIABS, we suggest that the light energetic flux in G. spruceana seedlings subjected to flooding, in the beginning, is more restricted to a decrease in the structures that captures light (reduction chlorophyll pigment content) than how the photosynthetic apparatus functions (alterations in photochemical efficiency of photosystem II).

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.

Drought-stress tolerance in three semi-arid species used to recover logged areas

We subjected seedlings from three tree species from the semi-arid “Caatinga” biome to water deficiency and rehydration. The species were Bauhinia monandra K. and Hymenaea courbaril L., (both Fabaceae), and Tabebuia aurea (Bignoniaceae). Seedlings were kept under water restriction until photosynthesis decreased to values around zero. Plants were rehydrated and photosynthesis measured until its values reached values of well-watered plants. We measured leaf water potential, maximum quantum yield, and chlorophyll index on (1) the first day of the experiment; (2) when photosynthesis decreased to around zero; and (3) after photosynthesis recovery. We then determined biomass and leaf area. To avoid water deficiency B. monandra and T. aurea (but not H. courbaril) reduced their leaf area resulting in lower biomass accumulation. The chlorophyll index was also not affected in H. courbaril, but it was lower for the other two species under stress. Maximum quantum yield was equally decreased in all the tree species as a mechanism to decrease light damage of photosynthetic apparatus. Drought differentially affected the vegetative growths of B. monandra, T. aurea, and H. courbaril when time and intensity were considered, affecting leaf area status leading to the leaf biomass decrease. Decreases in soil moisture led to decreased gas exchange. However, leaves were positively acclimated using chlorophyll strategies by lowering the light harvest in photosystems, which protect photosynthetic reaction centers.