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-NO 3 − ) and the metabolism of nitrogen (N) in rice under conditions of high and low NO 3 − supply. In addition, the kinetic parameters of NO 3 − 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-NO 3 − . 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 NO 3 − under both concentrations. When grown with 0.2 mM NO 3 − , the plants pretreated with HA had lower K m and C min values as well as a higher V max /K m ratio. When grown with 2 mM NO 3 − , the plants pretreated with HA had a higher V max 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 NO 3 − 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 NO 3 − transporters, resulting in a greater efficiency of NO 3 − acquisition by high-and low-affinity systems.

High-affinity ammonium transporters (AMT1) are responsible for ammonium (NH 4 ? ) 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 NH 4 ? acquisition and plant adaptation to environments with low N availability. Transgenic rice plants were obtained to study the activity of the OsAMT1.3 promoter (P OsAMT1.3 :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 K M and C min 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 NH 4 ? supplies.

No abstract

O girassol (Helianthus annuus L.) tem se destacado como cultura promissora, dentre as oleaginosas com importância agroenergética. Considerando-se os nutrientes exigidos pela cultura do girassol, o nitrogênio é o que mais limita a produção, além de afetar seu rendimento de óleo. Este trabalho objetivou avaliar aspectos do metabolismo e a cinética de absorção de nitrogênio (nítrico e amoniacal) na variedade de girassol BRS 324, cultivada em diferentes concentrações desse nutriente, em solução nutritiva, sob condições controladas, em câmara de crescimento. As plantas receberam 0,2 mmol L-1 e 2,0 mmol L-1 de N-NH4+ ou N-NO3-, em delineamento experimental inteiramente casualizado. Foram avaliados os parâmetros cinéticos de absorção (Km e Vmax), massa fresca, acúmulo de frações solúveis nitrogenadas e açúcares. Plantas cultivadas em 2,0 mmol L-1 de N-NH+ apresentaram maior Vmax, indicando maior capacidade de transporte desse íon. O caule apresentou acúmulo preferencial de NO3- e açúcares solúveis, atuando como principal local de reserva energética da planta. Os tratamentos com NH4+ resultaram em correlações negativas entre a massa fresca e a quantidade desse composto no tecido vegetal, o que pode ser responsável por sintomas de toxidez, resultando em redução na relação raiz/ parte aérea.

Fruit maturity stage has direct influence on the post-harvest life and consumer quality. Therefore, the understanding of the maturation process and its quality characteristics for storage are key factors for commercialization. In face of the foregoing, this study aimed to determine shelf life and changes in physical and chemical indexes of cherry tomatoes (Perinha Água Branca (PAB) and Mascot), assessing fruit harvested at four maturity stages and stored at ambient and controlled temperatures. For this, it was used fruit at turning, pink, red and ripe maturity stages, submitted to ambient (25 ± 2 °C) and controlled (12 °C and 90% RH) temperature, and assessed over time the indexes of fresh mass loss, titratable acidity, pH, soluble solids and ascorbic acid. The experimental design was completely randomized design in a factorial scheme of 2×4×7 for ambient temperature and 2×4×8 for controlled temperature. At ambient temperature, a longevity of up to 20 days was observed for PAB and Mascot fruit harvested at turning and pink maturity stages. When harvested at red and ripe stages, the longevity was of 15 days for PAB fruit and of 15 and 11 days, respectively, for Mascot fruit. At controlled temperature, PAB fruit showed longevity of 24 days when harvested at turning and pink stages and of 20 and 7 days, respectively, when harvested at red and ripe stages. A longevity of up to 27 days was observed for Mascot fruit harvested at turning stage and of 24 days for the other stages. The fruit harvested at turning and pink maturity stages, associated with storage under controlled conditions, presented higher longevity and maintenance of physical and chemical indexes of quality. Key words: Solanum lycopersicum. Maturity stage. Post-harvest. ResumoO estádio de maturação do fruto influencia diretamente na sua vida pós-colheita e na escolha por parte do consumidor, por isso o entendimento do processo de maturação e de suas características de qualidade para o armazenamento são fatores fundamentais para a comercialização. Diante disso, este trabalho teve por objetivo determinar o tempo de prateleira e alterações dos índices físicos e químicos em frutos de tomate do grupo cereja (Perinha Água Branca (PAB) e Mascot), colhidos em quatro estádios de maturação e armazenados sob temperatura ambiente e controlada. Para issa, foram utilizados frutos nos estádios de maturação: de vez, rosado, vermelho e maduro, submetidos às temperaturas: ambiente (25 ± 2 °C) e controlada (12 °C e UR de 90%) e avaliados os índices de perda de massa fresca, acidez titulável, pH, sólidos solúveis e ácido ascórbico ao longo do tempo. O delineamento experimental foi