SUMMARYNitrogen fixing nodules are formed on the roots and stems of the tropical legume Sesbania rostrata by A orhi obium caulinodans as a result of crack entry invasion of emerging lateral roots. Advantage was taken of this invasion capability of A. caulinodans to determine whether inoculation of the non-legume wheat with A. caulinodans would result in the endophytic establishment of azorhizobia within wheat roots. Advantage was also taken of the oxygen tolerance of the nitrogenase of free-living azorhizobia to assess the extent to which the endophytic establishment of azorhizobia in wheat roots would provide a niche for nitrogen fixation of benefit to the plant. Wheat was inoculated with A. caulinodans and grown in pots under controlled conditions, without added growth regulators and without addition of fixed nitrogen. Microscopic examination of the short lateral roots of inoculated wheat showed invasion of azorhizobia between cells of the cortex, within the xylem and the root meristem. Acetylene reduction assays combined with analysis of tissue nitrogen levels indicated the likelihood that colonization led to nitrogenase activity. Inoculated wheat showed significant increases in dry weight and nitrogen content as compared with uninoculated controls. We discuss the extent to which this nitrogen fixation is likely to involve symbiotic nitrogen fixation, and we indicate the need for field trials to determine the extent to which inoculation of wheat with A. caulinodans will reduce the requirement for inputs of nitrogenous fertilizers.

The Bi 2 O 3 modified alumino-silicate glasses, when excited at 800 nm exhibited a broadband emission of Cr 4ϩ in the range of 1.2 to ϳ1.6 m at room temperature. The mean lifetime of ( 1 E Ϫ 3 A 2 )→ 3 T 1 transition in Cr 4ϩ -doped glass at RT was as long as ϳ426 s, enabling the realization of both tunable lasers and broadband fiber amplifiers. The Cr 4ϩ emission at RT also showed the dependency on the excitation wavelength and site distribution within the chosen glass host. A photoinduced charge transfer process from the Cr 3ϩ ion into Cr 4ϩ ion appears to be responsible for the excitation of Cr 4ϩ .

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