JXB Advance Access originally published online on July 7, 2006
Journal of Experimental Botany 2006 57(11):2639-2650; doi:10.1093/jxb/erl027
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RESEARCH PAPER |
The role of arabinogalactan proteins binding to Yariv reagents in the initiation, cell developmental fate, and maintenance of microspore embryogenesis in Brassica napus L. cv. Topas
Key Laboratory of the MOE for the Development Biology, College of Life Science, Wuhan University, Wuhan 430072 China
*To whom correspondence should be addressed. E-mail: mxsun{at}whu.edu.cn
Arabinogalactan proteins (AGPs) are extracellular proteoglycans involved in plant growth and development. The addition of ß-D-glucosyl Yariv reagent (ßGlcY), a synthetic phenylglycoside that specifically reacts with AGPs, to the culture medium notably disturbed microspore embryogenesis in a concentration-dependent manner. The initiation of microspore embryogenesis was clearly inhibited by 30 µM ßGlcY and completely inhibited by 50 µM ßGlcY. The transfer of microspore-derived embryos at different developmental stages into NLN6 medium containing 50 µM ßGlcY prohibited their normal development, as 
21.24, 43.99, and 59.73%, respectively, of the treated globular-, heart-, and torpedo-stage embryos exhibited numerous root hair-like structures. Both heart-stage and torpedo-stage embryos showed a rapid growth of roots with a large number of clustered root hairs. Some root hair-like structures were also observed on the apical portions of embryos. Microscopy of the treated embryos revealed that the basic patterns of cells at both the radial and apical–basal axes were greatly altered, such that the cells lost their ability to carry out programmed embryogenesis. These results show that the ßGlcY–AGP interaction modulates the developmental fate of embryonic cells, especially epidermal cells, and thereby strongly affects root generation and development. Immunofluorescence microscopy revealed that both JIM8 and JIM13 binding to AGP co-localize with ßGlcY-binding sites. Thus, AGPs binding to ßGlcY, co-localized with Jim8- and Jim13-binding protein, appear to play a crucial role in the initiation of Brassica microspore embryogenesis and the maintenance of cell differentiation during embryonic development. In addition, these proteins may also be involved in the regulation of root generation.
Key words: Arabinogalactan protein, Brassica napus L. cv. Topas, cell fate, development expansion, microspore embryogenesis