The analysis of ion uptake kinetics is the key experimental procedure for determining the uptake efficiency of different species and varieties. The principal goal of this study was to evaluate phosphorus (P) uptake and its effect on nitrogen (N) metabolism in two maize varieties (Sol da Manhã and Eldorado) and one improved maize cultivar (AG 122®) exposed to a resupply of 10 or 100 μM of P following a period of P deprivation. The experiment was based on a completely randomized design with four replicates, with treatments arranged in a 3x2 factorial scheme consisting of three genotypes and two P doses. The treatments were applied at 16 days after germination (DAG), and samples of nutrient solution were collected over time to estimate the kinetics of P uptake (V max , K M and C min ). At the end of the experiment, a portion of the total fresh weight was stored to determine N fractions and soluble sugars. Under the experimental conditions, the AG 122® cultivar showed the lowest K M and C min values for both P doses, indicating a higher uptake efficiency for these plants. In contrast, the Eldorado and Sol da Manhã varieties showed the highest V max values. An absence of P from the nutrient solution for one day, followed by the addition of 10 μM of P for the same period, did not result in alterations in N metabolism in any of the genotypes. However, it was observed that the Sol da Manhã and Eldorado varieties concentrated their NO 3 --N metabolism in their roots, whereas the AG 122® cultivar concentrated its NO 3 --N metabolism in its shoots. Key words: Zea mays L, nitrate, ammonium, amino-N, soluble sugars ResumoA análise das variáveis cinéticas de absorção de íons é o principal procedimento experimental para a diferenciação da eficiência de absorção entre espécies e variedades. Baseado nisso, o objetivo desse trabalho foi avaliar a absorção de fósforo (P) e o seu efeito no metabolismo de nitrogênio (N) em variedades (Sol da Manhã e Eldorado) e cultivar (AG 122®) de milho (Zea mays L.) submetidos ao ressuprimento com 10 e 100 μM de P. O delineamento experimental utilizado foi inteiramente casualizado, com quatro repetições. Os tratamentos foram dispostos em esquema fatorial 3x2, sendo três genótipos e dois níveis de P. Aos 16 dias após a germinação (DAG) foram aplicados os tratamentos e procedeu-se a coleta da solução nutritiva ao longo do tempo para estimar as variáveis cinéticas de absorção de P (V máx , K M e C mín ) e na coleta final parte da massa fresca total foi armazenada para determinação das frações nitrogenadas e açúcares solúveis. Nas condições do experimento, a cultivar AG 122® apresentou o menor valor de K M e C mín nas duas doses de P, o que indica uma maior eficiência de absorção por essas plantas, enquanto as variedades Eldorado e Sol da Manhã apresentaram os maiores valores de V máx . A omissão de P da solução nutritiva por um dia, seguido da adição de uma dose de 10 μM desse nutriente por igual período não provocou alterações no metabolismo de N entre os genótipos estudados, no entanto, fo...
Nitrogen use efficiency (NUE) is an important characteristic for increasing the yield and quality of rice grains and reducing the use of nitrogen fertilizers. This study evaluated parameters that contribute to NUE in two tropical japonica rice varieties contrasting in nitrogen remobilization efficiency (NRE) and nitrate-uptake kinetics: IAC-47 (bred for high-input farming), and Piauí (a landrace from the state of Maranhão, Brazil). The two varieties were grown with and without N supplementation at anthesis stage. Both varieties received urea equivalent to 60 kg N ha -1 in the first ten days after planting (DAP) and a subset of the two varieties received a supplementation with 40 kg N ha -1 at anthesis stage, composing a treatment with supplementation (Ts). The control treatment (Tc) was constituted of the plants that did not receive nitrogen supplementation at anthesis. We analyzed the nitrogen soluble fractions, soluble sugars, dry matter production, total N, crude protein in grains, NUE parameters, and expression and activity of glutamine synthetase (GS). The N uptake after anthesis affected the total N content in the shoots and grains of both rice varieties. In treatments with and without N supplementation, the nitrogen uptake efficiency (NUpE) was higher in IAC-47 than in Piauí plants. The NRE, a desirable characteristic for plants grown with low N input, was around two times higher in the Piauí plants that were not supplemented with N during anthesis. panicles of piauí plants grouwn without N supplementation presented higher expression of the glutamine synthetase gene OsGS1.3 post-anthesis. The results indicate that NRE is the primary factor contributing to NUE in rice varieties adapted to a low N supply, whereas improved varieties exhibit a higher NUpE.
Nitrogen (N) is one of the mineral elements required in the greatest quantity by plants and the one that most often limits productivity. In addition, the use of N fertilizers may be associated with environmental damage. The rational use of N fertilizers can be achieved by both better management techniques and the use of plant varieties that are more efficient in N use. Two rice (Oryza sativa L.) varieties (Piauí and IAC‐47) with contrasting nitrate‐uptake kinetics (Km and Vmax) were studied through the evaluation of the transcription of genes encoding for the high and low‐affinity nitrate transporters (NRT2 and NRT1, respectively) and NAR2 partner protein needed for NRT2 functional nitrate transporter, as well as the assessment of N soluble fractions (amino‐N, NO$ _3^- $‐N, NH$ _4^+ $‐N) and soluble sugars. The Piauí variety presented higher transcription of the OsNAR2.1, OsNRT2.1, OsNRT2.2 and OsNRT2.3a and accumulated more NO$ _3^- $ in the shoots, sheath and roots when cultivated under low supply of nitrate. OsNRT2.1, OsNRT2.2 and OsNAR2.1 transcription correlated with nitrate concentration in roots, while OsNRT2.1, OsNRT2.2 and OsNRT2.3a correlated with nitrate concentration in leaves. The results of this study indicate that the Piauí variety is adapted to conditions of low natural fertility and seasonal nitrate flux, characteristics of the humid tropics. There is evidence that a portion of this adaptation process maybe due to the differential expression of genes encoding for the high‐affinity nitrate transport proteins, synchronizing plant metabolism with nitrate availability in the soil.
RESUMO:Reduzir as quantidades de fertilizantes nitrogenados e encontrar cultivares com maior eficiência no uso de nitrogênio são os principais objetivos atualmente da nutrição de plantas, pois parte do nitrogênio (N) aplicado ao solo com o intuito de maximizar a produção, pode ser perdido por lixiviação para o lençol freático, lagos e rios ou para a atmosfera causando graves problemas ambientais e aumento no custo de produção. Dentre as estratégias para aumentar a eficiência de uso de N é proposto no presente trabalho superexpressar o transportador de nitrato OsNPF4.11 em arroz. As linhagem transformadas OsNPF4.11 foram cultivadas em solução nutritiva contendo 0,2 mM N-NO 3 -. Foi observado que as plantas transgênicas apresentaram um maior acúmulo de NO 3 -na raiz o que afetou o crescimento das plantas, as quais apresentaram uma menor massa seca de parte aérea e um sistema radicular menos desenvolvido.Palavras-chave: eficiência de uso; nitrogênio; Oryza sativa L. Overexpression of nitrate transporter OsNPF4.11 (OsNRT1.2) affects growth in rice plantsABSTRACT: Reduce the amounts of nitrogen fertilizers and finding varieties with a high nitrogen use efficiency are the main objectives of plant nutrition. A large part of the nitrogen (N) applied to the soil in order to maximize production is lost by leaching to the groundwater, lakes and rivers or to atmosphere by volatilization causing serious environmental impacts and and high production costs. Among the strategies to increase NUE in the present work we propose to overexpression the nitrate transporter OsNPF4.11 in rice. Transformed OsNPF4.11 lines were grown in nutrient solution containing 0.2 mM N-NO 3 -. It was observed that the transgenic plants had a greater NO 3 -accumulation in the root affecting the plants growth, which presented a lower shoot dry mass and a less developed root system.
O presente artigo tem como objetivo apresentar a experiência de agricultores assentados da reforma agrária num intercâmbio com agricultura sintrópica, com vivência realizada na fazenda Ouro Fino. Essa fazenda está localizada no distrito de Itiúba município de Jaguaquara/BA, o intercâmbio teve como proposta vivenciar práticas de manejos da Agricultura Sintrópica. Assim, quebrando paradigmas em relação à capacidade de resiliência de agroecossistemas complexos, a produção de alimentos saudáveis e uso de árvores nos sistemas produtivos. A partir dessa experiência foi possível desmistificar a visão que os agricultores tinham que as árvores nos sistemas agrícolas não “cumprem função nenhuma e só ocupavam espaço que poderia ser cultivado”, compreendendo de fato os preceitos do redesenho e complexidade biológica proposta pela Agroecologia. Com base na experiência vivida pelos participantes, bem como nos relatos coletados e replicação dos arranjos e práticas já iniciadas em seus respectivos lotes da reforma agrária, nos assentamentos agroecológicos, verificou-se que o intercâmbio na fazenda de agricultura sintrópica serviu como ferramenta de construção, sensibilização e impulsionamento das práticas agroecológicas sintrópicas, transformando os agricultores e técnicos em novos agentes multiplicadores deste conhecimento.
Esse estudo teve como objetivo apresentar uma alternativa de uso sustentável ao resíduo do caranguejo-uçá, na perspectiva do cultivo agroecológico de alface americana, bem como a recomendação da dose mais adequada nas condições locais. Para avaliação agronômica da alface, foram aferidos aos 32 dias após o transplantio, a altura da parte aérea, peso fresco da cabeça, diâmetro da cabeça, altura do caule e número de folhas. Onde foi possível identificar o efeito positivo da aplicação da farinha do caranguejo sobre as variáveis avaliadas, onde destaca-se o aumento mais efetivo do peso fresco e diâmetro da cabeça e número de folhas por planta, ao aplicar-se 2 ton./ha em comparação ao tratamento sem aplicação (0 ton./ha), o que possibilitou um ganho de produtividade de 19,1 %. O que aponta o beneficiamento dos resíduos oriundos da mariscagem do caranguejo-uçá como um possível impulsionador da transição agroecológica em comunidades ribeirinhas.
Purpose The expression patterns of the NRT2 genes have been well described, however, it is not well known the role of OsNRT2.4 in root growth. In this study we thus aimed at investigating the role of high-affinity NO3- transport OsNRT2.4 in NO3--regulated and the modulation of root growth.Methods Through the gene silencing technique amiRNA-mediated we successfully obtained osnrt2.4 knockdown lines to study the role of OsNRT2.4 on root growth under low nitrate conditions. We performed real time RT-PCR analysis to investigate the relative gene expression level in root and shoot, soluble metabolites, and measurement of root system.Results Knockdown of OsNRT2.4 did not affect rice growth. In comparison with wild-type (WT) plants showed that knockdown of OsNRT2.4 inhibited root formation under low NO3- supply. We demonstrated that the mutant lines had significantly increased NO3- uptake than WT plants when growth in different nitrate supply; osnrt2.4 knockdown lines showed an alteration in nitrogen metabolism, and this affected the root growth. The downregulation of OsNRT2.4 enhanced the expression of genes response of low external NO3- concentrations.Conclusion Herein we provide new insights in OsNRT2.4 functions. Our data demonstrated that OsNRT2.4 plays a role in root growth, nitrogen metabolic pathway and probably have functions in nitrate transport from root to shoot under low nitrate availability in rice.
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