Root surface colonization of non-cereal crop plants by pleomorphic Azospirillum brasilense Cd

Abstract

Root surface colonization by Azospirillum brasilense Cd of tomato, pepper and cotton plants under normal growth conditions and soybean plants under normal and water-stress conditions was monitored by scanning electron microscopy and bacterial counts. A. brasilense Cd was capable of efficiently colonizing the elongation and root-hair zones of all four plant species tested. In these zones, the bacteria mainly colonized the root surface (tomato, soybean), root-hairs (pepper), or both (cotton), by single cells (tomato, soybean), micro-aggregates (pepper), or a combination of the two (cotton). All inoculated plants demonstrated (i) larger amounts of mucigel-like substance on the root surface than non-inoculated plants and (ii) fibrillar material which anchored the bacterial cells to the root surface and established connections between cells within bacterial aggregates. On non-water-stressed soybean plants, most A. bradense Cd cells in the rhizosphere occurred as vibroid forms whereas those on water-stressed plants (wilting) were cyst-like. A lower rhizosphere bacterial population was observed on water-stressed plants. When water-stress conditions were eliminated, the bacterial cells reverted to the vibroid form and a concomitant increase in the bacterial population was observed. It is suggested that cyst-like formation is a natural response for A. brasilense Cd in the rhizosphere of water-stressed plants.

Transformation of Azospirillum brasilense Cd with an ACC Deaminase Gene from Enterobacter cloacae UW4 Fused to the Tet r Gene Promoter Improves Its Fitness and Plant Growth Promoting Ability

“…Other studies on root colonization by Azospirillum have revealed the presence of fibrillar material that anchors the bacterial cells to the root surface and establishes connections between cells within bacterial aggregates [3,4,30]. In these images, bacteria are closely packed but clearly embedded in an amorphous material that is presumably composed of exopolysaccharides of bacterial origin.…”

“…8a-f) show that all of the Azospirillum strains examined can colonize leaves forming aggregates, a prominent feature of the colonization of leaf surfaces [4,7,30].…”

“…Heinz 1439 VF) were surface disinfected as described above and incubated for 2-3 h at 30°C with 10 mL of either 0.03 M MgSO 4 or a bacterial suspension in 0.03 M MgSO 4 . The bacterial suspension was prepared by growing the bacteria overnight in Luria broth (supplemented with 20 lg ml )1 tetracycline in case of the Azospirillum transformants), washing the cells twice with 0.03 M MgSO 4 , resuspending them in the same solution, and adjusting the concentration of cells to 10 8 cfu mL )1 .…”

Biocontrol of Fusarium wilt of banana: Key influence factors and strategies

“…To achieve ideal biocontrol efficacy, the antagonists must colonize the rhizosphere soil and sustainedly occupy favorable ecological sites in the environment. Previous studies have illustrated that the long-term colonization of antagonists is correlated to soil moisture (or the water content of soil), temperature, soil aeration, pH, soil salinity, as well as the continuous supply of nutrients (Sessitsch et al, 2004;Bashan et al, 1991;Bevivino et al, 2005;Cavaglieri et al, 2005;de-Bashan and Bashan, 2008).…”

Growth and yield response of cowpea to multiaction bioinoculants

“…The increase in K nutrient uptake might be due to the synergistic effect of higher N uptake (Srinivasan Rao et al, 1997). The preferential potassium accumulation in the leaves as a result of bacterial inoculation might be also related to changes in membrane activity and subsequently proton efflux in roots (Bashan et al, 1991).…”