Ascending Migration of Endophytic Rhizobia, from Roots to Leaves, inside Rice Plants and Assessment of Benefits to Rice Growth Physiology

Abstract

Rhizobia, the root-nodule endosymbionts of leguminous plants, also form natural endophytic associations with roots of important cereal plants. Despite its widespread occurrence, much remains unknown about colonization of cereals by rhizobia. We examined the infection, dissemination, and colonization of healthy rice plant tissues by four species of gfp-tagged rhizobia and their influence on the growth physiology of rice. The results indicated a dynamic infection process beginning with surface colonization of the rhizoplane (especially at lateral root emergence), followed by endophytic colonization within roots, and then ascending endophytic migration into the stem base, leaf sheath, and leaves where they developed high populations. In situ CMEIAS image analysis indicated local endophytic population densities reaching as high as 9 ؋ 10 10 rhizobia per cm 3 of infected host tissues, whereas plating experiments indicated rapid, transient or persistent growth depending on the rhizobial strain and rice tissue examined. Rice plants inoculated with certain test strains of gfp-tagged rhizobia produced significantly higher root and shoot biomass; increased their photosynthetic rate, stomatal conductance, transpiration velocity, water utilization efficiency, and flag leaf area (considered to possess the highest photosynthetic activity); and accumulated higher levels of indoleacetic acid and gibberellin growthregulating phytohormones. Considered collectively, the results indicate that this endophytic plant-bacterium association is far more inclusive, invasive, and dynamic than previously thought, including dissemination in both below-ground and above-ground tissues and enhancement of growth physiology by several rhizobial species, therefore heightening its interest and potential value as a biofertilizer strategy for sustainable agriculture to produce the world's most important cereal crops.

Promoção de crescimento de arroz por rizóbios em diferentes níveis de adubação nitrogenada

“…Por outro lado, o estímulo dos isolados UFRGS-Lc336 e UFRGS 1-TV na absorção de N foi mais pronunciado em doses elevadas de N. Com a dose de 160kg ha -1 de N, o acúmulo de N na parte aérea das plantas inoculadas com estes dois isolados foi 29% superior ao das plantas do tratamento controle e sem inoculação. Este incremento é muito próximo Tabela 3 -Número de perfilhos por planta de arroz, cultivar 'IRGA 424', em função da inoculação com isolados de rizóbios e aplicação de doses crescentes de N. (BISWAS et al, 2000;YANNI et al, 2001;CHI et al, 2005;MISHRA et al, 2006). Embora o efeito da promoção de crescimento tenha aumentado com o acréscimo da dose de N, os resultados também indicaram que a inoculação de rizóbios proporcionou melhor aproveitamento do N aplicado, pois aumentou o acúmulo deste elemento e proporcionou maior eficiência na adubação.…”

Isolation and characterization of endophytic bacteria isolated from the leaves of the common bean (Phaseolus vulgaris)

“…Postal Code: 365701-000.; Tel. : : 0(55)313899-2971 Fax: 0(55)313899-2573.; E-mail: mvqueiro@ufv.br from 10 2 to 10 9 (6,12,25,39,44) and depends on many factors, including the plant being studied, the part under analysis (31,46), the developmental stage of the plant (17,44), the plant cultivar (genotype) (15,44) and the interaction with other organisms, as well as other environmental-related factors (17).…”

Use of CMEIAS Image Analysis Software to Accurately Compute Attributes of Cell Size, Morphology, Spatial Aggregation and Color Segmentation that Signify in Situ Ecophysiological Adaptations in Microbial Biofilm Communities

“…Nowadays, the unique characteristics of optisectioned confocal imaging make this type of digital microscopy ideal for measuring the biovolume of 3-D microbial aggregates directly by voxel analysis of image stacks acquired using laser scanning confocal microscopy [2,[6][7][8][9][10][11]. Computation of 3-D biovolume of microbes from 2-D projected images acquired by the more commonly used conventional phase-contrast or epifluorescence light microscopy assumes that the shape of the foreground objects of interest (i.e., individual microbial cells) has approximate axial symmetry [12] and they are sampled with sufficient pixel density so their cell periphery can be accurately defined [13].…”