Leonardo Oliveira Medici

The influence of nitrogen supply on antioxidant enzymes in plant roots

Plants of Zea mays L., Hordeum vulgare L. and Arabidopsis thaliana (L.) Heynh. were grown at different concentrations of nitrogen, as NH4NO3, and the antioxidant enzyme activities and quantities in the roots, were studied. Maize plants were grown at 1 and 10 mM N for 32 d after germination and their roots were analysed by native PAGE for the isoenzymic profiles of glutathione reductase (GR; EC 1.6.4.2), catalase (CAT; EC 1.11.1.6) and superoxide dismutase (SOD; EC 1.15.1.1) and by spectrophotometric assays for total activity of CAT and GR. Barley and A. thaliana plants were grown at five N concentrations (0.25, 0.5, 1, 10 and 20 mM) for 27 and 26 d, respectively, and the isoenzymic profile of the three enzymes were analysed in their roots. The number of GR isoforms in the three plant species was increased at high N supply compared with low N. In addition, the CAT and GR activities detected in the roots were increased in plants grown at higher N. The increase in activity and number of bands of GR at high N in the roots of all three plants studied was not accompanied by a change in activity or the number of SOD isoforms. The possibility that the application of high N promotes the formation of reactive oxygen species by stimulating an increased rate of growth is discussed.

Biochemical responses of glyphosate resistant and susceptible soybean plants exposed to glyphosate

Glyphosate is a wide spectrum, non-selective, post-emergence herbicide. It acts on the shikimic acid pathway inhibiting 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), thus obstructing the synthesis of tryptophan, phenylalanine, tyrosine and other secondary products, leading to plant death. Transgenic glyphosate-resistant (GR) soybean [Glycine max (L.)] expressing an glyphosate-insensitive EPSPS enzyme has provided new opportunities for weed control in soybean production. The effect of glyphosate application on chlorophyll level, lipid peroxidation, catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GOPX) and superoxide dismutase (SOD) activities, soluble amino acid levels and protein profile, in leaves and roots, was examined in two conventional (non-GR) and two transgenic (GR) soybean. Glyphosate treatment had no significant impact on lipid peroxidation, whilst the chlorophyll content decreased in only one non-GR cultivar. However, there was a significant increase in the levels of soluble amino acid in roots and leaves, more so in non-GR than in GR soybean cultivars. Root CAT activity increased in non-GR cultivars and was not altered in GR cultivars. In leaves, CAT activity was inhibited in one non-GR and one GR cultivar. GOPX activity increased in one GR cultivar and in both non-GR cultivars. Root APX activity increased in one GR cultivar. The soluble protein profiles as assessed by 1-D gel electrophoresis of selected non-GR and GR soybean lines were unaffected by glyphosate treatment. Neither was formation of new isoenzymes of SOD and CAT observed when these lines were treated by glyphosate. The slight oxidative stress generated by glyphosate has no relevance to plant mortality. The potential antioxidant action of soluble amino acids may be responsible for the lack of lipid peroxidation observed. CAT activity in the roots and soluble amino acids in the leaves can be used as indicators of glyphosate resistance.

Diallel analysis of maize lines with contrasting responses to applied nitrogen.

Six S5 lines of maize, previously identified as having contrasting responses to nitrogen (N) supply, were used to carry out a complete series of diallel crosses. The resulting 15 hybrids were grown in a field at two N levels. The general combining ability (GCA) and specific combining ability (SCA) were estimated using the method 4, model I analysis of Griffing for grain yield kernel weight, grain number, harvest index, green leaf number, ear leaf area, N utilization efficiency, total plant N, grain N content, anthesis-silking interval, chlorophyll content and prolificacy. For the majority of the traits, GCA was more important than SCA and there was an increase of non-additive effects under low N. Significant interactions were observed between GCA and N levels for grain yield, grain number and chlorophyll content, indicating the selection of different lines for each N level. The lines with the largest effects of N supply per se on grain yield, were those with the largest effects of GCA for this trait. This association indicates that the response of the lines to N supply, should be considered in breeding programmes in order to achieve acceptable hybrids for environments with both high and low N.

Glutamine Synthetase Activity, Relative Water Content and Water Potential in Maize Submitted to Drought

Two maize (Zea mays L.) hybrids, BR 201 and P 6875, were submitted to drought by withholding irrigation at the vegetative or reproductive phases. During water deficit, in both phases, the relative water content (RWC) was higher and leaf water potential (Ψw) was lower in the hybrid P 6875 than in the hybrid BR201. This response indicated a better osmotic adjustment capacity of the hybrid P 6875 when compared to BR 201. Glutamine synthetase activity was not affected by drought even at a RWC of 60 % and Ψw of −1.2 MPa or during rehydration.

Estudo da eficiência de uso do nitrogênio em variedades locais e melhoradas de milho

The requirement of nitrogen fertilizers to increase crop productivity risks environmental contamination and increases farmer production costs up to 40% in maize cultivation. The objective of this study was to evaluate physiologic parameters related to nitrogen use efficiency and so contribute to maize breeding programs targeting grain yield in low-N environments. Three maize local varieties (Pedra Dourada, Catetao e Carioca), two improved varieties selected in fertily soil (BR 105 and BR 106) and two improved varieties selected under low N (Nitroflint and Nitrodente) were studied. Plants were supplied with Hoagland nutrient solution with two N levels in the form of nitrate (75%) and ammonium (25%). Low N plants were supplied with 1 mM of N and high N plants with 15 mM of N. The experiment, conducted in greenhouse, was carried out in complete randomized block design with three replicates and 14 factorial treatments. Nitrogen deficiency intensely decreased shoot growth and had a neglectful effect on root system. The biochemical traits studied (pigment contents, nitrate reductase and glutamine synthetase activities) were affected by N supply but did not show variability among genotypes. Dry matter accumulation in nitrogen deficient plants correlated positively (0.86) with the dry matter accumulation in the root system of maize genotypes. Our results suggest that the investigation of root properties may provide important precocious data about nitrogen use efficiency of maize genotypes.

Response of Crotalaria juncea to nickel exposure

A presenca de metais pesados no ambiente e atualmente, um dos principais problemas de contaminacao ambiental, uma vez que, os metais liberados no ambiente contaminam o solo e entram na cadeia alimentar atraves das plantas, causando efeitos toxicos a curto e a longo prazo aos animais e seres humanos. No caso do metal pesado Niquel (Ni), foi constatado que a sua presenca nas plantas pode diminuir o crescimento, reduzir a taxa de fotossintese e provocar alteracoes, tanto nas atividades enzimaticas quanto metabolicas.Pouca informacao esta disponivel na literatura, com referencia a resposta antioxidante das plantas a expressao a esse metal. Neste sentido, os objetivos deste trabalho foram realizar diferentes ensaios para avaliar o efeito fitotoxico do Ni em plântulas de C. juncea. Neste estudo foram analisados parâmetros bioquimicos relativos a atividade das enzimas antioxidantes, Catalase (CAT), Superoxido Dismutase (SOD) e Glutationa Redutase (GR). Constatou-se que, nao houve alteracao da atividade GR e CAT nas raizes. Entretanto, atividades destas enzimas apresentaram aumento significativo na parte aerea. O aumento na atividade da GR, na parte aerea, pode ser explicado pelo fato de ser o ciclo Halliwell-Asada o principal mecanismo que age na desintoxicacao de Especies Ativas de Oxigenio. Quanto a atividade da SOD, quando comparados ambos tecidos, foi constatado que na parte aerea foi pouco alterada, entretanto, a atividade da SOD foi estimulada nas raizes na presenca do Ni. Para aumentar a precisao dos resultados, quantificou-se pela tecnica de Fluorescencia de Raios X, a concentracao de NiCl2 e o seu efeito na absorcao de nutrientes nas plântulas de crotalaria. Nesta analise, observou-se o acumulo do metal nas raizes e baixa translocacao para a parte aerea. Tambem foi analisada a concentracao de Malonaldeido (MDA) na parte aerea de plântulas de C. juncea, sendo constatada, a ocorrencia de peroxidacao lipidica na presenca do Ni. Finalmente, determinou-se o efeito do Ni sobre as concentracoes de aminoacidos soluveis em raizes e na parte aerea, como estrategia desta planta para superar o efeito do Ni , nao tendo sido observadas variacoes significativas nas concentracoes dos mesmos com os diferentes tratamentos com Ni. Palavra?Chave: Aminoacidos, Atividade Enzimatica, Crotalaria, Fitotoxicidade, Niquel, Poluicao Ambiental Abstract

Identification of Maize Lines with Contrasting Responses to Applied Nitrogen

ABSTRACT A better understanding of how maize responds to nitrogen (N) supply is required for both economic and environmental purposes. Contrasting genotypes are indispensable for genetic and physiological studies of any trait, and the identification of the response of a range of lines of maize to two N level, was the aim of this work. One S4 and seven S5 lines, originating from two commercial hybrids, were studied for agronomic traits related to nitrogen-use efficiency (NUE). Two field experiments with two levels of N (10 and 110 Kg N/ha in 2000 and 10 and 130 Kg N/ha in 2001) were carried out. In the first experiment, in which the lines 2, 3, 4, 5, 6, 10, 13, and 17 were tested, the N supplied appeared to be excessive because the maize controls and most of the lines did not show an increase in grain yield at the high N level when compared with the low-N treatment in this experiment. The high N level increased the grain yield only in line 2, decreased grain yield in line 13, but increased the chlorophyll content in all lines except line 3. The second experiment, in which the lines 2, 3, 4, 5, 6, and 10 were tested, showed a severe N deficiency because the maize controls and most of the lines exhibited reduction in grain yield at the low N level when compared with the high-N treatment in this experiment. This severe N deficiency caused a reduction in grain yield in lines 2, 3, 5, and 10, prolificacy (ears plant− 1) in lines 2, 3, 4,and 5, grain N content in all lines (except line 10), and total plant N in lines 2, 3, and 5. On the other hand, this severe N deficiency also caused an increase in 100-kernel weight in line 2 and anthesis-silking in lines 3 and 5. The interactive behavior of all the traits cited indicates that they have different genetic controls at each N level. The existence of genotype-environment interaction may mean that the best genotype at a low N level is not the best at a high N level, and that the physiological mechanisms as well the genes required for high performance are to some extent different. These results also demonstrate that the response to N of these traits is under separate controls for each one, because they did not exhibit consistency in the lines tested. The correlations indicated that the anthesis-silking interval and prolificacy were associated more with grain yield at low-N availability, supporting the idea that these traits can be used to select maize tolerant to low-N soils. The contrasting responses to N availability indicate that these lines are important plant materials for use in further studies of NUE.

Automatic controller to water plants

A despeito da enorme demanda por agua na irrigacao de plantas, existem poucos aparelhos para automacao deste processo sendo usados na agricultura. Avaliou-se um acionador automatico para irrigacao, o qual pode ser confeccionado com materiais comerciais de baixo custo, pois sao produzidos em larga escala. Este acionador e composto por uma capsula cerâmica usada em filtros de agua domesticos; um tubo plastico com cerca de um metro e meio de comprimento e um pressostato de maquinas de lavar roupas domesticas. A capsula e o pressostato sao conectados pelo tubo de forma que todo o espaco interno seja preenchido com agua. A capsula e o sensor do acionador e deve ser posicionada dentro do substrato das plantas. O pressostato deve ser posicionado abaixo do sensor e quanto mais baixo ele estiver, maior e a tensao da agua que aciona a irrigacao, pois quanto mais baixo estiver o pressostato, maior e a coluna de agua acima do mesmo e, portanto, maior e a tensao na capsula cerâmica para puxar para cima a coluna de agua. O acionador foi avaliado no controle da irrigacao por gotejamento em pequenos potes preenchidos com substrato orgânico comercial ou solo. Regressoes lineares explicaram a relacao entre a posicao do pressostato e a tensao maxima no substrato comercial (p < 0,0054) e no solo (p < 0,0001). Entre as posicoes do pressostato de 0,30 a 0,90 m abaixo do sensor, a tensao da agua variou de 1 a 8 kPa para o substrato comercial e de 4 a 13 kPa para o solo. Este simples acionador pode ser util para cultivar plantas, aplicando agua automaticamente em funcao da tensao da agua no substrato das plantas.

Nutritional Quality of Sorghum Seeds: Storage Proteins and Amino Acids

One sorghum commercial genotype (MASSA 03) and nine ICRISAT high-lysine genotypes from India were analyzed for storage protein content, distribution profile, and soluble amino acid concentrations. Storage proteins fraction were extracted and separated by SDS-PAGE. Soluble amino acids contents were determined by HPLC. Variations in intensity and appearance and disappearance of protein bands were observed among the sorghum genotypes suggesting genetic variability. Amino acid profile also indicated large variations in the amino acid concentrations. The high lysine and threonine soluble concentrations observed in the seeds of the sorghum genotypes encouraged the use of these genotypes as potential food source due to the better balanced amino acids profile.

Distribution of soluble amino acids in maize endosperm mutants

For human nutrition the main source of vegetable proteins are cereal and legume seeds. The content of total soluble amino acids in mature endosperm of wild-type, opaque and floury maize (Zea mays L.) mutants were determined by HPLC. The total absolute concentration of soluble amino acids among the mutants varied depending on the mutant. The o11 and o13 mutants exhibited the highest average content, whereas o10, fl3 and fl1 exhibited the lowest average content. In general, the mutants exhibited similar concentrations of total soluble amino acids when compared to the wild-type lines, with the clear exception of mutants o11 and fl1, with the o11 mutant exhibiting a higher concentration of total soluble amino acids when compared to its wild-type counterpart W22 and the fl1 mutant a lower concentration when compared to its wild-type counterpart Oh43. For methionine, the mutants o2 and o11 and wild-type Oh43 exhibited the highest concentrations of this amino acid. Significant differences were not observed between mutants for other amino acids such as lysine and threonine. The high lysine concentrations obtained originally for these mutants may be due to the amino acids incorporated into storage proteins, but not those present in the soluble form.