Fig. 5. Tracer loading and movement in wild-type embryos. Mid-torpedo embryos were incubated with HPTS for a shorter amount of time (1-3 minutes versus 5 minutes in other experiments) to allow observation of partially loaded embryos. (A) A detached cotyledon reveals the movement of HPTS only in a small number of cells at the base. Arrow indicates the direction of probe movement. (B) A detached cotyledon partially loaded in the center (c), and the tracer has subsequently spread into ground tissues (g). (C) A detached cotyledon showing complete loading with HPTS. (D) The same cotyledon as in C viewed with a different filter set allowing visualization of combined chlorophyll and FITC fluorescence. Loaded region with HPTS appears yellowish green owing to the additive effect between red autofluorescence from chlorophyll and green emission from HPTS. (E) A whole embryo, fully loaded with HPTS in its radicle (ra) and hypocotyl (hy), but partially loaded at the base (*) of cotyledons (co). (F) The same embryo as in E monitored with a different filter set allowing visualization of combined chlorophyll and FITC fluorescence. Images were obtained by using Chroma FITC (HPTS fluorescence; A,B,C,E) and Zeiss FITC (chlorophyll plus HPTS fluorescence; D,F) filter sets on a compound epifluorescence microscope (see Materials and Methods). Scale bars, 50 µm.