ABSTRACT Plant-growth-promoting bacteria of the genus Azospirillum and Herbaspirillum can improve crop yields of maize in tropical environments. The main mechanism proposed for its promotion is related to the auxins produced by these species. The aim of this study was to compare the maize growth response of inoculation using two species, Azospirillum baldaniorum Sp245 (Ab-Sp245) and Herbaspirillum seropedicae ZAE94 (Hs-ZAE94) during the initial growth under controlled conditions. A pot experiment was conducted with five harvests measuring bacterial counts, root morphology, biomass, and nitrogen content, and soluble metabolites for 38 days. Depending on the harvest period, a differential growth response between the two strains test was compared to the control. Plants use the bacterium applied to improve nitrogen acquisition and transform it into higher biomass and nitrogen accumulation, especially for Ab-Sp245. On the other side, Hs-ZAE94 altered the soluble metabolites resulting in higher NO3-, NH4+, and N-amino and lower soluble fractions compared to Ab-Sp245 and the control. The observed plant-bacteria interaction is closely fine-tuned and regulated by the strain used and differences in growth promotion effects cannot solely attributed to the root morphology.

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.

Fatores de transcrição Dof podem atuar como ativadores ou repressores transcricionais envolvidos em diversos processos biológicos exclusivos de vegetais, no entanto muitas de suas funções fisiológicas ainda não foram elucidadas. Neste trabalho, plantas de arroz (Oryza sativa L.) expressando o fator de transcrição OsDof26 mostraram alterações na cinética de absorção e metabolismo de nitrogênio (N) quando submetidas aos tratamentos de 0,2 e 2,0 mM de amônio (NH4+) ou nitrato (NO3-) em solução nutritiva. O delineamento experimental foi inteiramente casualizado, com quatro repetições, em esquema fatorial 2 × 2 × 2, duas plantas (plantas de arroz não transformadas e uma linhagem de arroz expressando o OsDof26, a L24, duas fontes de N (NO3- e NH4+) e duas doses (0,2 e 2,0 mM). Aos 17 dias após a germinação (DAG) foram aplicados os tratamentos e procedeu-se a coleta da solução nutritiva em intervalos de 30 minutos até as 48 horas, afim de estimar os parâmetros cinéticos de absorção de N (Vmax, Km e Cmín). Aos 19 DAG, obteve-se a massa fresca total, sendo parte desse material armazenado para determinação das frações nitrogenadas e açúcares solúveis. A L24 apresentou menor crescimento da parte aérea e raiz em todos os tratamentos analisados quando comparada com a planta não transformada (WT - wild type). e menores teores de NO3-, NH4+ e N-amino, afetando assim o metabolismo de N nas plantas transformadas.

Dof transcription factors can act as transcriptional activators or repressors in several biological processes unique to plants, however many of their physiological functions have not been explained. In this work, rice plants (Oryza sativa L.), expressing the transcription factor OsDof26, showed changes in uptake kinetics and nitrogen (N) metabolism when subjected to treatments of 0.2 and 2.0 mM ammonium (NH4+) or nitrate (NO3-) in a nutrient solution. The experimental design was completely randomised, with four replications in a 2 × 2 × 2 factorial, two plants (nontransformed rice plants and the L24 strain of rice, expressing OsDof26; two sources of N (NO3- and NH4+); and two dosages (0.2 and 2.0 mM). At 17 days after germination (DAG), the treatments were applied and nutrient solution was then collected at intervals of 30 minutes for 48 hours, in order to estimate the kinetic uptake parameters for N (Vmax, Kmand Cmin). At 19 DAG, the total fresh weight was obtained, with part of the material being stored to determine the soluble nitrogen fractions and soluble sugars. The L24 strain showed less growth of shoots and roots for all the treatments studied compared to the untransformed plant (WT - wild type). The lower influx of NO3-and NH4+ in the L24 resulted in unfavourable kinetic parameters and lower levels of NO3-, NH4+ and amino N, thereby affecting the N metabolism in the transformed plants.

O objetivo deste trabalho foi avaliar a dinâmica de decomposição e a liberação de nutrientes da parte aérea de plantas de soja cultivar Celeste, para fins de adubação verde. Utilizou-se o delineamento experimental de blocos ao acaso com cinco repetições. Nas parcelas, as plantas foram cortadas rente ao solo aos 55, 85 e 115 dias após a emergência (DAE) e foram analisadas quanto à decomposição do material vegetal e liberação de N, P, K, Ca e Mg, colocando-se 60 g de matéria fresca da parte aérea em sacos de tela, distribuídos sobre a superfície das parcelas no campo. Nas subparcelas, as taxas de redução de massa de matéria seca e de liberação de nutrientes foram monitoradas mediante análises aos 5, 10, 15, 30, 60, 90, 120 e 150 dias após os cortes das plantas. O modelo exponencial X = X0e-kt demonstrou dinâmicas não muito contrastantes, para os materiais cortados aos 55, 85 e 115 DAE. Apesar de o clima possivelmente ter influenciado na liberação de K, não causou diferenças significativas na decomposição de matéria seca e na liberação de N e fósforo. As plantas de soja, cortadas em diferentes estádios de desenvolvimento, apresentam taxas similares de decomposição e de liberação de nutrientes.

The objective of this work was to evaluate the dynamics of decomposition and release of nutrients from aerial plant parts of the soybean cultivar Celeste used as green manure. A randomized block design was adopted with five replications. Soybean plants were cut close to the soil surface 55, 85 and 115 days after emergency (DAE), and analysed to determine their decomposition and release of N, P, K, Ca and Mg, by placing 60 g of fresh material of the aerial part in nylon screen bags, that were distributed on field plots surface . The rates of loss of dry matter and of nutrient release were monitored in the 5, 10, 15, 30, 60, 90, 120 and 150 days after plant cut. The exponential model X = X0e-kt demonstrated that the dynamics of the material cut in the 55, 85 and 115 DAE were not so contrasting. The climate could have interfered on the results, principally on K release rates, however it did not cause mean differences on the biomass decomposition and N and P release. Soybean plant material from cut plants, at different growth stages, present similar rates of decomposition and nutrient release.