Orchids

aperture in the tissues surrounding the meristems. 'This simple experiment revealed that there were four distinct regions of the embryo with different plasmodesmata apertures. The shoot meristem had the highest aperture enabling movement of single-to-triple sized GFP; the hypocotyl (embryonic stem) allowed single, double and some triple-sized GFP movement; the root allowed single and double-sized GFP movement; and the cotyledons (embryonic leaves) allowed only single-sized GFP movement. Strikingly, these domains of cytoplasmic continuity correspond to the basic layout of the organs of the adult body. Thus, groups of cells with similar developmental fates carry plasmodesmata with similar degrees of aperture. In adult plants, plasmodesmata-mediated cytoplasmic continuity is highest in young organs and minimal in more mature tissues. Thus, plasmodesmata connectivity is critical during organ formation, providing a means whereby groups of cells can exchange factors essential for developmental programming. Where is plasmodesmata research going? Plasmodesmata are established to play dynamic and critical roles during all stages of plant development facilitating transport of micromolecules and macromolecules. The Holy Grail in current plasmodesmata research is to elucidate the intricate mechanisms whereby plasmodesmata function to modify their transport capacities in time and space during development. To do this researchers are hunting for plasmodesmata specific genes. Are there plasmodesmata specific molecular components that define plasmodesmata structure? Are there specific factors that regulate plasmodesmata function? Such analyses will have high impact, as intercellular communication is fundamental to all areas of plant biology and its application. Where can I find out more about plasmodesmata? RNA silencing occurs during early plant embryogenesis and its cell-to-cell spread is dependent on plasmodesmata aperture in different cell types. STM-1XsGFP STM-2XsGFP STM-3XsGFP STM-ERGFP 27 kDa 54 kDa 81 kDa 27.5 kDa Current Biology Figure 2. Movement of single-sized, double-sized and triple-sized GFP during Arabidopsis embryogenesis. GFP expression is under the control of the SHOOTMERISTEMLESS (STM) promoter which drives expression at the shoot and root meristems as revealed when STM drives an endoplas-mic reticulum tethered GFP (ERGFP). The three sizes of GFP are all soluble; following their expression at the shoot and root meristems, they are free to move from cell-to-cell depending on the aperture of plasmodesmata. Single-sized GFP (27 kDa) moves between all cells of the embryo, so that plasmodesmata aperture allows movement of proteins at least 27 kDa in size. Double-sized GFP (54 kDa) moves most readily in the hypocotyl and root, but not in the coty-ledons. Triple-sized GFP (81 …