Orlando Carlos Huertas Tavares

OsAMT1.3 expression alters rice ammonium uptake kinetics and root morphology

Abstract High-affinity ammonium transporters (AMT1) are responsible for ammonium (NH4+) acquisition and/or perception in the micromolar range, and their expressions can be differentially regulated by nitrogen (N) availability. The present study characterised the functions of the rice (Oryza sativa) OsAMT1.3 transporter to understand its contribution to NH4+ acquisition and plant adaptation to environments with low N availability. Transgenic rice plants were obtained to study the activity of the OsAMT1.3 promoter (POsAMT1.3:GFP:GUS) and the overexpression of the OsAMT1.3 gene (UBIL:OsAMT1.3:3xHA) in plants. The OsAMT1.3 promoter activity was induced strongly in the absence of N and occurred primarily in the zones of lateral root emission and root tips. Anatomical sections of the segment of root tips and the middle third showed a differential pattern of OsAMT1.3 activity. Analysis of the OsAMT1.1–1.3 transporter expression profiles indicated that overexpression of OsAMT1.3 positively affected OsAMT1.2 expression. When subjected to a low N supply, plants overexpressing OsAMT1.3 showed lower KM and Cmin values. Additionally, these lines showed longer roots with a higher area, volume, and number of tips. The data suggested that OsAMT1.3 is involved in the ability of rice plants to adapt to low NH4+ supplies.

Vermicompost humic acids modulate the accumulation and metabolism of ROS in rice plants

This work aims to determine the reactive oxygen species (ROS) accumulation, gene expression, anti-oxidant enzyme activity, and derived effects on membrane lipid peroxidation and certain stress markers (proline and malondialdehyde-MDA) in the roots of unstressed and PEG-stressed rice plants associated with vermicompost humic acid (VCHA) application. The results show that the application of VCHA to the roots of unstressed rice plants caused a slight but significant increase in root ROS accumulation and the gene expression and activity of the major anti-oxidant enzymes (superoxide dismutase and peroxidase). This action did not have negative effects on root development, and an increase in both root growth and root proliferation occurred. However, the root proline and MDA concentrations and the root permeability results indicate the development of a type of mild stress associated with VCHA application. When VCHA was applied to PEG-stressed plants, a clear alleviation of the inhibition in root development linked to PEG-mediated osmotic stress was observed. This was associated with a reduction in root ROS production and anti-oxidant enzymatic activity caused by osmotic stress. This alleviation of stress caused by VCHA was also reflected as a reduction in the PEG-mediated concentration of MDA in the root as well as root permeability. In summary, the beneficial action of VCHA on the root development of unstressed or PEG-stressed rice plants clearly involves the modulation of ROS accumulation in roots.

Humic acid differentially improves nitrate kinetics under low‐ and high‐affinity systems and alters the expression of plasma membrane H+‐ATPases and nitrate transporters in rice

Humic acids (HAs) have a major effect on nutrient uptake, metabolism, growth and development in plants. Here, we evaluated the effect of HA pretreatment applied with a nutrient solution on the uptake kinetics of nitrate nitrogen (N-NO3−) and the metabolism of nitrogen (N) in rice under conditions of high and low NO3− supply. In addition, the kinetic parameters of NO3− uptake, N metabolites, and nitrate transporters (NRTs) and the plasma membrane (PM) H+-ATPase gene expression were examined. The plants were grown in a growth chamber with modified Hoagland and Arnon solution until 21 days after germination (DAG), and they were then transferred to a solution without N for 48 h and then to another solution without N and with and without the addition of HAs for another 48 h. After this period of N deprivation, the plants received new nutrient solutions containing 0.2 and 2.0 mM N-NO3−. Treatment of rice plants with HA promoted the induction of the genes OsNRT2.1-2.2/OsNAR2.1 and some isoforms PM H+-ATPase in roots. The application of HAs differentially modified the parameters of the uptake kinetics of NO3− under both concentrations. When grown with 0.2 mM NO3−, the plants pretreated with HA had lower Km and Cmin values as well as a higher Vmax/Km ratio. When grown with 2 mM NO3−, the plants pretreated with HA had a higher Vmax value, a greater root and shoot mass, and a lower root/shoot ratio. The N fractions were also altered by pretreatment with HA, and a greater accumulation of NO3− and N-amino was observed in the roots and shoots, respectively, of plants pretreated with HA. The results suggest that pretreatment with HA modifies root morphology and gene expression of PM H+-ATPases and NO3− transporters, resulting in a greater efficiency of NO3− acquisition by high- and low-affinity systems.

Assessment of the Use of Natural Materials for the Remediation of Cadmium Soil Contamination.

Rice plants accumulate cadmium (Cd2+) within the grain, increasing the danger of human exposure. Natural materials have been used in soil remediation, but few studies have examined the risks (based on the bioavailability of these metals to plants) of using these materials, so the practice remains controversial. In the present study, we evaluated the effectiveness of biochar produced from sugarcane bagasse, vermicompost (VC), vermicompost solid residue (VCR) and humin for remediation of Cd2+-contaminated soils. We characterized the interactions between these materials and Cd2+ and evaluated their capacity to alter Cd2+ availability to rice plants. Our results show that under the conditions in this study, biochar and humin were not effective for soil remediation. Although biochar had high Cd2+ retention, it was associated with high Cd2+ bioavailability and increased Cd2+ accumulation in rice plants. VC and VCR had high Cd2+ retention capacity as well as low Cd2+ availability to plants. These characteristics were especially notable for VCR, which was most effective for soil remediation. The results of our study demonstrate that in the tested materials, the bioavailability of Cd2+ to plants is related to their structural characteristics, which in turn determine their retention of Cd2+.

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.