7g). Twenty days after inoculation, the bacteria were found in leaf find more veins (Fig. 7h), indicating that the bacterial cells had invaded the leaf. Thirty days after inoculation, the bacteria were observed in the intercellular spaces of leaves, but no bacterium was found inside the cells (Fig. 7i). In contrast, no GFP-labelled Lu10-1 cells were found in the control plants. In summary, our experiments show that the GFP-labelled bacterial cells infect the roots at the zones of differentiation and elongation and through the cracks formed at the junctions between lateral roots and the
main root and penetrate the cortex, xylem, and pith. The bacteria can migrate from roots to stems and leaves, and are confined mainly to intercellular spaces. Figure 7 Confocal laser scanning microscopic images of colonization of mulberry seedlings by Lu10-1 cells tagged with GFP. (a) Longitudinal section of the primary root showing bacterial cells (arrows) aggregated on root hair and the
zone of elongation and sporadic cells in the zone of differentiation and root tip. (b) Transverse section of primary roots showing the bacteria distributed along root hair one day after inoculation. (c) Longitudinal section of the primary root showing the bacteria concentrated at junctions of lateral BGJ398 order roots with the primary root one day after inoculation. (d) Transverse section of the primary root showing the labelled bacteria distributed in intercellular spaces of primary root cortical parenchyma 3 days after inoculation. (e) Bacteria had progressed towards inner cortex 5 days after inoculation. (f) Bacteria had
colonized the piths of primary roots 7 days after inoculation. (g) Bacteria were found in xylem vessels of stem 11 days after inoculation. (h) Bacteria were found in leaf veins 20 days after inoculation. (i) Bacteria were found in intercellular Adenosine spaces of leaves 30 days after inoculation. Siderophore and indole-3-acetic acid (IAA) production, phosphate solubilization, and nitrogenase activity Both the qualitative determination of siderophore production and phosphate-solubilizing capacity of Lu10-1 on a solid medium showed positive results, indicating that Lu10-1 can produce siderophores and solubilize phosphates. The rate of nitrogenase activity was 1.16 μmol C2H4 mg protein-1 h-1. Thus, strain Lu10-1 possesses all the plant-growth-promoting characters, namely siderophores, IAA production, P solubilization, and nitrogenase activity. Discussion Our results demonstrate that the strain B. cepacia Lu10-1 is an endophyte that can colonize the roots, stems, and leaves of mulberry seedlings rapidly and efficiently following the application of the bacteria by soil drenching. Using GFP-labelled cells B.