Blue-light perception in stage-1 sporangiophores of Phycomyces : a role for apical lipid globules?

Stage-1 sporangiophores (without sporangium) of the zygomycete fungus, Phycomyces blakesleeanus, contain an apical aggregate of some 100 to 200 lipid globules. The approximate diameter of the globules varies between 0.5 and 3.5 μm. Fluorescence microscopy and fluorescence spectroscopy of the globules indicated a green-yellow fluorescence emission near 530 nm after excitation with blue light, which is characteristic for flavins. Microirradiation of the apex of the sporangiophore with microbeams (diameter 16 μm) of monochromatic blue light (460 nm) elicted a transient light-growth response, which subsided in about 20 minutes. When the microbeam hit 2 to 3 lipid globules the ensuing light-growth responses were substantially larger than in cases when areas without globules were hit. The fluence dependence of the light-growth response indicated that the sensitivity was greatest when the globules rather than the globule-free areas were irradiated. The results suggest a possible role for the lipid globules in the blue-light perception of stage-1 sporangiophores.