André Marques dos Santos

Effects of Seasonal Nitrate Flush on Nitrogen Metabolism and Soluble Fractions Accumulation in Two Rice Varieties

ABSTRACT Two rice varieties, ‘Piaui’ (a landrace) and ‘IAC-47’ (an improved variety), were grown in nutrient solution containing 20 mg nitrate (NO3 −)-nitrogen (N) L− 1 up to 32 days after germination (DAG). After this, a group of plants received 200 mg NO3 −NL− 1, while the other was kept at 20 mg NO3 −NL− 1 up to 42 DAG. From 42 until 56 DAG, all plants received 5 mg NO3 −NL− 1. Plants were collected at 42 and 56 DAG, soluble fractions, nitrate reductase (NR) and GS enzymatic activities were determined. The nutritional history of the plants affected significantly the uptake and use of nitrogen (N), and should be taken into consideration in the studies of N-use efficiency. The variety ‘Piaui’ was more efficient than ‘IAC-47’ in N-uptake use, accumulating more NO3 − in its tissues at the initial phases of its cycle for subsequent utilization.

Soluble fractions and kinetics parameters of nitrate and ammonium uptake in sunflower (“Neon” Hybrid)

Sunflower plants are source of oilseeds with great importance for agroenergy. Nitrogen deficiency is considered one of the factors limiting growth and yield. The objective of this study was to assess the nitrogen uptake (high and low supply of nitrate and ammonium) and to determine the uptake kinetics parameters (Km and Vmax) of these ions in sunflower plants (Neon hybrid). The experiment was carried out in a growth chamber using a hydroponic system. The following treatments were applied: 0.2 and 2.0 mmol L-1 of N-NO3- and N-NH4+. The two kinetics parameters (Km and Vmax) involved in the uptake of nitrate and ammonium were determined, as well as the soluble fractions (N-NO3-, N-NH4+, amino-N and sugars) and total N, in different plant tissues. The plants grown with ammonium showed higher Vmax than those cultivated with nitrate. High ammonium rates caused reduction of root volume and the plants supplied with 2.0 mmol L-1 of N-NO3- produced more biomass from the roots and aerial part. The highest concentrations of NNO3- were found in the petioles. Analyzed together, the data suggest a greater potential for use of nitric-N as a nitrogen source for fertilization in the cultivation of sunflower.

Efeito da disponibilidade de nitrato em solução nutritiva sobre a absorção de nitrogênio e atividade enzimática de duas cultivares de arroz

Two rice cultivars, Piaui (a landrace) and IAC-47 (an improved variety), were grown in nutrient solution containing 20 mg nitrate (N-NO3-) L-1 up to 32 days after germination (DAG). After this, a group of plants received 200 mg N-NO3- L-1, while the other was kept at 20 mg N-NO3- L-1 up to 42 DAG. From 42 until 56 DAG, all plants received 5 mg N-NO3- L-1 until the end of the cycle. These treatments were applied with the objective to simulate nitrate flush in tropical regions. Plants were collected at 133 DAG and separated in to leaf flag, leaf 2, stem and roots. N contents in amino acids, nitrate and ammonium forms, soluble sugars, nitrate reductase (NR) and glutamine synthetase (GS) enzymatic activities were determined. The evaluated varieties replay in different manner about accumulate and translocation nitrate. The variety Piaui seems to accumulate more NO3- in the tissues at the initial phases of its cycle, allowing subsequent remobilization. Flag leaf and leaf 2 seem to act as preferential sites of N accumulation, being this accumulation more intense in the landrace variety.

Response Mechanisms of Plants to Heavy Metal Pollution: Possibility of Using Macrophytes for Remediation of Contaminated Aquatic Environments

Water contamination by heavy metals is a growing concern among public officials and citizens due to their high potential toxicity to living things and the environment. Macrophytes have been studieds for use in a cleaning up polluted water bodies, due to their favorable characteristics. The various species can respond differently to environments contaminated with heavy metals. They can be sensitive, showing symptoms of toxicity and intolerant of high contamination levels, or tolerant, using extra or intracellular mechanisms to allow them to grow in the presence of these contaminants. In this review, we present the main mechanisms used by plants in response to contamination by heavy metals.

Cinética de absorção de nitrogênio e acúmulo de frações solúveis nitrogenadas e açúcares em girassol

Sunflower ( Helianthus annuus L.) has emerged as a promising crop among oilseed species with agro-energetic importance. Considering the nutrients required by the sunflower crop, nitrogen is the most limiting for yield, besides affecting its oil production. This study aimed to evaluate metabolism aspects and nitrogen absorption kinetics (nitrate and ammonium), in sunflower (BRS 324) grown under different levels of this nutrient in nutritious solution, under controlled conditions, in a growth chamber. Plants were submitted to two nitrogen concentrations (0.2 mmol L -1 and 2.0 mmol L -1 of N-NH 4 + or N-NO 3 - ), in a completely randomized experimental design. The kinetics absorption parameters ( K m and V max ), fresh weight and accumulation of soluble nitrogen fractions and sugars were evaluated. Plants grown in 2.0 mmol L -1 of N-NH 4 + showed a higher V max , indicating a greater capacity for transporting this ion. The stem presented a preferential accumulation of N-NO 3 - and soluble sugars, acting as the main site of energetic reserve of the plant. Treatments with NH 4 + showed negative correlations between fresh weight and amount of this compound in the plant tissue, which may be responsible for symptoms of toxicity, resulting in a reduction in the root/shoot ratio.