Iron is an indispensable factor for the dimorphic insect pathogenic Nomuraea rileyi to form persistent microsclerotia which can replace conidia or blastospores for commercial mass production. There are two high affinity iron acquisition pathways in N. rileyi, siderophore-assisted iron mobilization and reductive iron assimilation systems. Transcription of the two iron uptake pathways related genes is induced under iron-limiting conditions. Stage-specific iron uptake-related genes expression during microsclerotia development shows siderophore-mediated iron acquisition genes are rigorously upregulated specifically during the formation and mature period while reductive iron assimilation related genes just display a higher expression at the late maturation period. Abrogation of reductive iron assimilation, by the deletion of the high affinity iron permease (NrFtrA), has no visible effect on microsclerotia biogenesis in N. rileyi. In sharp contrast, N. rileyi L-ornithine-N5-monooxygenase (NrSidA), required for synthesis of all siderophores, is absolutely necessary for the development of pigmented microsclerotia. In agreement with the lower intracellular iron contents of microsclerotia in ΔNrSidA strains, not only the pigments, but both the number and the biomass are also noticeably reduced. Certain concentration of ROS is required for promoting microsclerotia biogenesis. Combined with expression pattern analysis of related genes and quantitative of intracellular iron or extracellular siderophore in WT and mutants, these data demonstrate the lack of adequate intracellular iron caused by the loss of the siderophore results in the deficiency of ROS detoxication. Furthermore, ΔNrSidA strains show significantly increased sensitivity to hydrogen peroxide. Besides, NrSidA, but not NrFtrA, play a crucial role in vegetative growth under iron-limiting conditions, conidiation, and dimorphic switching. Remarkably, the slower growth of the ΔNrSidA strains in vivo due to a reduced capacity for iron acquisition leads to the loss of virulence in Spodoptera litura while the ΔNrFtrA mutants behaved as WT during infection. Together, these results prove siderophore-assisted iron mobilization is the major pathway of cellular iron uptake and essential for conidiation, dimorphism transition, oxidative stress resistance, pigmented microsclerotium formation and full virulence.
Rare‐earth ion‐doped semiconducting phosphor has attracted extensive attention due to the ability to achieve efficient luminescence through the host sensitization. Here, we present a new type red‐emitting Eu3+ ‐doped BiOCl phosphors possessing a broad excitation band in the near‐ultraviolet (NUV) region. Experimental measurements and theoretical calculations confirm that Eu3+ ion dopants result in forming impurity energy level near valence band, and the excellent broadband NUV‐exciting ability of Eu3+ ion is due to the electronic transitions of BiOCl band gap. Moreover, the highest emission intensity of the phosphors is from the 5D0 → 7F4 transition of Eu3+ around 699 nm (far‐red) through whether host excitation or direct Eu3+ ions excitation, which lie in the particular structure of BiOCl crystals. Our results indicate that the Eu3+ ‐doped BiOCl crystals show great potential as red phosphors for white‐light‐emitting diodes.
In order to investigate the effect of Ce3+ concentration on the emission properties of ErS+/y3+ codoped NaYF4 nanocrystals, Ce3+/Er3+/Yb3+ tri-doped NaYF4 nanocrystals were prepared through a facile EDTA-assisted hydrothermal method. The upconversion .(UC) and the near infrared (NIR) emission properties of Er3+ ions were systematically investigated in the NaYF4:Ce3+/Er3+/Yb3+ nanocrystals. Under 980 nm excitation, with the increasing of Ce3+ concentration, the emission intensity of Er3+ at 1550 nm (4I13/2 --> 4I15/2) band increases initially and then decreases. The increase of the fluorescence intensity of 1550 nm is due to the energy transfer between Er+ and Ce3+ ions: Er3+:4(11/2)+Ce3+:2F5/2 --> Er3+:4I13/2 +Ce3+:2F7/2. But when Ce3+ doping concentration is 2.0%, the cross relaxation:Er3+:4I13/2+ Ce3+:2F5/2 --> Er3+:4I15/2+Ce3+:2F7/2 happens, which depopulates the 4113/2 level of Er3+ and results in the decrease of the emission intensity of Er3+ at 1550 nm band. Meanwhile, incorporation of Ce3+ dramatically decreases the visible UC emission intensity. A possible emission mechanism was proposed.
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