Role of the molecular structure of humified organic matter in rice plant response to environmental lead pollution.

Humified organic matter has been shown to decrease Pb toxicity in plants. However, there are still gaps in our understanding of the mechanism by which this phenomenon occurs. In this study, we aimed to assess the ability of humic substances (HSs), humic acids (HAs), and fulvic acids (FAs) to enhance defense mechanisms in rice plants under lead (Pb)-stressed conditions. HS fractions were isolated from vermicompost using the chemical fractionation methodology established by the International Humic Substances Society. These fractions were characterized by solid-state NMR and FTIR. Chemometric analysis was used to compare humic structures and correlate them with bioactivity. Three treatments were tested to evaluate the protective effect of humic fractions on rice plants. The first experiment involved the application of humic fractions along with Pb. The second comprised pretreatment with humic fractions followed by subsequent exposure to Pb stress. The third experiment involved Pb stress and subsequent treatment with humic fractions. The root morphology and components of the antioxidative defense system were evaluated and quantified. The results showed that HS + Pb, HA + Pb, and FA + Pb treatment preserved root growth and reduced the levels of O2- and malondialdehyde (MDA) in the roots by up to 5% and 2%, respectively. Pretreatment of the plants with humic fractions promoted the maintenance of root growth and reduced the contents of O2-, H2O2, and MDA by up to 48%, 22%, and 20%, respectively. Combined application of humic fractions and Pb reduced the Pb content in plant tissues by up to 60%, while pretreatment reduced it by up to 80%. The protective capacity of humic fractions is related to the presence of peptides, lignin, and carbohydrate fragments in their molecular structures. These results suggest that products could be developed that can mitigate the adverse effects of heavy metals on agricultural crops.

Characteristics of the root system in two Brazilian upland rice varieties which exhibit contrasting behavior towards drought tolerance / Características radiculares de duas variedades brasileiras de arroz de terras altas contrastantes quanto à tolerância ao estresse hídrico

Root system architecture plays a fundamental role in the adaptation of rice to environments subjected to abiotic stresses. This study aimed to characterize the root architecture and morphology of two Brazilian upland rice varieties which display contrasting behavior towards drought tolerance: the tolerant Catetão and susceptible Mira varieties. Two experiments were carried out under greenhouse and growth chamber conditions. The experimental design was completely randomized in a 2 × 2 factorial scheme (varieties × drought stress conditions) with four replicates. Rice varieties were subjected to control and drought conditions for 14 days. Drought stress was applied either by withholding water until the desirable soil tension was achieved or by addition of 20% polyethylene glycol 6000 (PEG) to the nutritive solution. After harvest, the dry weight, root architecture, as well as physiological and root features were assessed. Under drought stress, a higher root biomass was recorded in Catetão compared to Mira. A higher ratio of deep rooting (RDR) was observed for Catetão, while Mira remained stable in response to drought stress. The evaluated physiological features showed that the Catetão variety is less likely to compromise membrane integrity and lipid peroxidation during drought stress. Moreover, analyzed root features exhibited a significant increase in lateral root emission and root density for Catetão in response to drought treatment, which may be considered an important feature when selecting for superior genotypes.(AU)

A arquitetura do sistema radicular exibe um papel fundamental na adaptação do arroz a ambientes sujeitos a estresses abióticos. Por esta razão, este estudo teve como objetivo caracterizar a arquitetura do sistema radicular e sua morfologia em duas variedades de arroz brasileiras de sequeiro contrastantes quanto à tolerância ao estresse hídrico, Catetão (tolerante) e Mira (suscetível). Foram realizados dois experimentos, o primeiro em casa de vegetação e o segundo em câmara de crescimento. O delineamento experimental foi inteiramente casualizado com quatro repetições em um esquema fatorial 2 x 2 (variedades x condições de estresse hídrico). As variedades de arroz foram submetidas a condições controle e estresse hídrico durante 14 dias. O estresse hídrico foi aplicado ao reduzir a lâmina dágua a tensão desejada no solo ou com a utilização de 20% de polietilenoglicol 6000 (PEG) na solução nutritiva. A massa seca, arquitetura do sistema radicular, características fisiológicas e características radiculares foram determinadas após a colheita. A variedade Catetão mostrou maior biomassa radicular comparada a Mira quando submetida ao estresse hídrico. Foi observado maior taxa de raízes profundas (RDR) na Catetão, enquanto a Mira permaneceu estável em resposta ao estresse hídrico. As características fisiológicas avaliadas mostraram que a variedade Catetão está menos sujeita a danos a integridade da membrana e peroxidação de lipídeos durante o estresse hídrico. Além disso, as características radiculares analisadas mostraram que a variedade Catetão apresentou um aumento significativo na emissão de raízes laterais e densidade radicular em resposta ao estresse hídrico, o que pode ser considerado como uma importante característica a ser selecionada em genótipos superiores.(AU)

Characteristics of the root system in two Brazilian upland rice varieties which exhibit contrasting behavior towards drought tolerance / Características radiculares de duas variedades brasileiras de arroz de terras altas contrastantes quanto à tolerância ao estresse hídrico

Root system architecture plays a fundamental role in the adaptation of rice to environments subjected to abiotic stresses. This study aimed to characterize the root architecture and morphology of two Brazilian upland rice varieties which display contrasting behavior towards drought tolerance: the tolerant Catetão and susceptible Mira varieties. Two experiments were carried out under greenhouse and growth chamber conditions. The experimental design was completely randomized in a 2 × 2 factorial scheme (varieties × drought stress conditions) with four replicates. Rice varieties were subjected to control and drought conditions for 14 days. Drought stress was applied either by withholding water until the desirable soil tension was achieved or by addition of 20% polyethylene glycol 6000 (PEG) to the nutritive solution. After harvest, the dry weight, root architecture, as well as physiological and root features were assessed. Under drought stress, a higher root biomass was recorded in Catetão compared to Mira. A higher ratio of deep rooting (RDR) was observed for Catetão, while Mira remained stable in response to drought stress. The evaluated physiological features showed that the Catetão variety is less likely to compromise membrane integrity and lipid peroxidation during drought stress. Moreover, analyzed root features exhibited a significant increase in lateral root emission and root density for Catetão in response to drought treatment, which may be considered an important feature when selecting for superior genotypes.

A arquitetura do sistema radicular exibe um papel fundamental na adaptação do arroz a ambientes sujeitos a estresses abióticos. Por esta razão, este estudo teve como objetivo caracterizar a arquitetura do sistema radicular e sua morfologia em duas variedades de arroz brasileiras de sequeiro contrastantes quanto à tolerância ao estresse hídrico, Catetão (tolerante) e Mira (suscetível). Foram realizados dois experimentos, o primeiro em casa de vegetação e o segundo em câmara de crescimento. O delineamento experimental foi inteiramente casualizado com quatro repetições em um esquema fatorial 2 x 2 (variedades x condições de estresse hídrico). As variedades de arroz foram submetidas a condições controle e estresse hídrico durante 14 dias. O estresse hídrico foi aplicado ao reduzir a lâmina dágua a tensão desejada no solo ou com a utilização de 20% de polietilenoglicol 6000 (PEG) na solução nutritiva. A massa seca, arquitetura do sistema radicular, características fisiológicas e características radiculares foram determinadas após a colheita. A variedade Catetão mostrou maior biomassa radicular comparada a Mira quando submetida ao estresse hídrico. Foi observado maior taxa de raízes profundas (RDR) na Catetão, enquanto a Mira permaneceu estável em resposta ao estresse hídrico. As características fisiológicas avaliadas mostraram que a variedade Catetão está menos sujeita a danos a integridade da membrana e peroxidação de lipídeos durante o estresse hídrico. Além disso, as características radiculares analisadas mostraram que a variedade Catetão apresentou um aumento significativo na emissão de raízes laterais e densidade radicular em resposta ao estresse hídrico, o que pode ser considerado como uma importante característica a ser selecionada em genótipos superiores.

Dark septate endophytic fungi increase the activity of proton pumps, efficiency of 15N recovery from ammonium sulphate, N content, and micronutrient levels in rice plants.

Plants colonised by dark septate endophytic (DSE) fungi show increased uptake of nutrients available in the environment. The objective of the present study was to evaluate the impact of DSE fungi on the activity of proton pumps, nitrogen (N) recovery from ammonium sulphate, and nutrient accumulation in rice plants. Treatments consisted of non-inoculated plants and plants inoculated with two isolates of DSE fungi, A101 and A103. To determine N recovery from the soil, ammonium sulphate enriched with 15N was added to a non-sterile substrate while parameters associated with the activity of proton pumps and with NO3- uptake were determined in a sterile environment. The A101 and A103 fungal isolates colonised the roots of rice plants, promoting 15N uptake, growth, and accumulation of nutrients as compared with the mock control. A103 induced the expression of the plasma membrane H+-ATPase (PM H+-ATPase) isoforms OsA5 and OsA8, the activity of the PM H+-ATPase and H+-pyrophosphatase. Our results suggest that the inoculation of rice plants with DSE fungi represents a strategy to improve the N recovery from ammonium sulphate and rice plant growth through the induction of OsA5 and OsA8 isoforms and stimulation of the PM H+-ATPase and H+-pyrophosphatase.

Contribution of dark septate fungi to the nutrient uptake and growth of rice plants

ABSTRACT The use of dark septate fungi (DSE) to promote plant growth can be beneficial to agriculture, and these organisms are important allies in the search for sustainable agriculture practices. This study investigates the contribution of dark septate fungi to the absorption of nutrients by rice plants and their ensuing growth. Four dark septate fungi isolates that were identified by Internal transcribed spacer phylogeny were inoculated in rice seeds (Cv. Piauí). The resulting root colonization was estimated and the kinetic parameters Vmax and Km were calculated from the nitrate contents of the nutrient solution. The macronutrient levels in the shoots, and the NO3--N, NH4+-N, free amino-N and soluble sugars in the roots, sheathes and leaves were measured. The rice roots were significantly colonized by all of the fungi, but in particular, isolate A103 increased the fresh and dry biomass of the shoots and the number of tillers per plant, amino-N, and soluble sugars as well as the N, P, K, Mg and S contents in comparison with the control treatment. When inoculated with isolates A103 and A101, the plants presented lower Km values, indicating affinity increases for NO3--N absorption. Therefore, the A103 Pleosporales fungus presented the highest potential for the promotion of rice plant growth, increasing the tillering and nutrients uptake, especially N (due to an enhanced affinity for N uptake) and P.

Contribution of dark septate fungi to the nutrient uptake and growth of rice plants

The use of dark septate fungi (DSE) to promote plant growth can be beneficial to agriculture, and these organisms are important allies in the search for sustainable agriculture practices. This study investigates the contribution of dark septate fungi to the absorption of nutrients by rice plants and their ensuing growth. Four dark septate fungi isolates that were identified by Internal transcribed spacer phylogeny were inoculated in rice seeds (Cv. Piauí). The resulting root colonization was estimated and the kinetic parameters Vmax and Km were calculated from the nitrate contents of the nutrient solution. The macronutrient levels in the shoots, and the NO3--N, NH4+-N, free amino-N and soluble sugars in the roots, sheathes and leaves were measured. The rice roots were significantly colonized by all of the fungi, but in particular, isolate A103 increased the fresh and dry biomass of the shoots and the number of tillers per plant, amino-N, and soluble sugars as well as the N, P, K, Mg and S contents in comparison with the control treatment. When inoculated with isolates A103 and A101, the plants presented lower Km values, indicating affinity increases for NO3--N absorption. Therefore, the A103 Pleosporales fungus presented the highest potential for the promotion of rice plant growth, increasing the tillering and nutrients uptake, especially N (due to an enhanced affinity for N uptake) and P.(AU)

Contribution of dark septate fungi to the nutrient uptake and growth of rice plants.

The use of dark septate fungi (DSE) to promote plant growth can be beneficial to agriculture, and these organisms are important allies in the search for sustainable agriculture practices. This study investigates the contribution of dark septate fungi to the absorption of nutrients by rice plants and their ensuing growth. Four dark septate fungi isolates that were identified by Internal transcribed spacer phylogeny were inoculated in rice seeds (Cv. Piauí). The resulting root colonization was estimated and the kinetic parameters Vmax and Km were calculated from the nitrate contents of the nutrient solution. The macronutrient levels in the shoots, and the NO3--N, NH4+-N, free amino-N and soluble sugars in the roots, sheathes and leaves were measured. The rice roots were significantly colonized by all of the fungi, but in particular, isolate A103 increased the fresh and dry biomass of the shoots and the number of tillers per plant, amino-N, and soluble sugars as well as the N, P, K, Mg and S contents in comparison with the control treatment. When inoculated with isolates A103 and A101, the plants presented lower Km values, indicating affinity increases for NO3--N absorption. Therefore, the A103 Pleosporales fungus presented the highest potential for the promotion of rice plant growth, increasing the tillering and nutrients uptake, especially N (due to an enhanced affinity for N uptake) and P.

Development and nitrate reductase activity of sugarcane inoculated with five diazotrophic strains.

Diazotrophs are able to stimulate plant growth. This study aimed at evaluating the effect of inoculation of five diazotrophic strains on growth promotion and nitrate reductase (NR, EC 1.7.1.1) activity in sugarcane. An experiment was carried out from three stages of cultivation: sprouting, tubes, and in hydroponics. On the first two stages, seven treatments were adopted: uninoculated control; mixed inoculation with five strains; and individual inoculation with Gluconacetobacter diazotrophicus (Gd), Herbaspirillum rubrisubalbicans (Hr), Herbaspirillum seropedicae (Hs), Nitrospirillum amazonense (Na), and Paraburkholderia tropica (Pt). The four treatments showing the best performance were transferred to the hydroponic system for analysis of NR activity. Hs, Pt, and the mixture of all strains led to the highest seedling biomass in tubes, followed by Hr. In hydroponics, the mixture and the strain Hr had the highest growth-promoting effect. NR activity was influenced by inoculation only under low N supply conditions, with positive effect of Hr, Pt, and the mixture.

Involvement of Hormone- and ROS-Signaling Pathways in the Beneficial Action of Humic Substances on Plants Growing under Normal and Stressing Conditions.

The importance of soil humus in soil fertility has been well established many years ago. However, the knowledge about the whole mechanisms by which humic molecules in the rhizosphere improve plant growth remains partial and rather fragmentary. In this review we discuss the relationships between two main signaling pathway families that are affected by humic substances within the plant: one directly related to hormonal action and the other related to reactive oxygen species (ROS). In this sense, our aims are to try the integration of all these events in a more comprehensive model and underline some points in the model that remain unclear and deserve further research.

Phosphorus uptake kinetics and nitrogen fractions in maize grown in nutrient solutions / Cinética de absorção de fósforo e frações nitrogenadas em milho cultivado em solução nutritiva

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 (Vmax, KM and Cmin). 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 KM and Cmin 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 Vmax 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 NO3--N metabolism in their roots, whereas the AG 122® cultivar concentrated its NO3--N metabolism in its shoots.(AU)

A 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 (Vmáx, KM e Cmín) 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 KM e Cmín 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 Vmáx. 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, foi observado que as variedades Sol da manhã e Eldorado têm preferência para o metabolismo de N-NO3- na raiz quando comparadas a cultivar AG 122® que o faz preferencialmente na parte aérea.(AU)

Phosphorus uptake kinetics and nitrogen fractions in maize grown in nutrient solutions / Cinética de absorção de fósforo e frações nitrogenadas em milho cultivado em solução nutritiva

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 (Vmax, KM and Cmin). 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 KM and Cmin 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 Vmax 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 NO3--N metabolism in their roots, whereas the AG 122® cultivar concentrated its NO3--N metabolism in its shoots.

A 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 (Vmáx, KM e Cmín) 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 KM e Cmín 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 Vmáx. 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, foi observado que as variedades Sol da manhã e Eldorado têm preferência para o metabolismo de N-NO3- na raiz quando comparadas a cultivar AG 122® que o faz preferencialmente na parte aérea.

Isoforms of plasma membrane H(+)-ATPase in rice root and shoot are differentially induced by starvation and resupply of NO3⁻ or NH4+.

The goal of this study was to evaluate the effects of nitrogen starvation and resupply in 10 PM H+-ATPase isoforms and the expression of NO3⁻ and NH4+ transporters in rice. The net uptake of both forms of NO3⁻-N or NH4+-N was increased with its resupply. Resupply of NO3⁻ resulted in induction of the following PM H+-ATPase isoforms, OsA1, OsA2, OsA5 and OsA7 in the shoots and OsA2, OsA5, OsA7 and OsA8 in the roots. Resupply of NH4+ resulted in the induction of the following OsA1, OsA3 and OsA7 isoforms in the roots while OsA1 was induced in the shoots. It was observed that increased PM H+-ATPase activity also resulted in increased net uptake of NO3⁻ and NH4+. In the roots, OsNRT2.1 and OsNRT2.2 were induced by NO3⁻ resupply, while OsAMT1.1 and OsAMT1.2 were induced by NH4+ deficiency. The results showed that the expression of PM H+-ATPase isoforms is related to NO3⁻ and NH4+ transporters as well as in which section of the plant it takes place. PM H+-ATPase isoforms OsA2 and OsA7 displayed the strongest induction in response to N resupply, therefore indicating that these genes could be involved in N uptake in rice.