JXB Advance Access originally published online on May 24, 2007
Journal of Experimental Botany 2007 58(8):2225-2236; doi:10.1093/jxb/erm083
RESEARCH PAPER |
Conformation of cytoskeletal elements during the division of infected Lupinus albus L. nodule cells
1Instituto de Recursos Naturales, Centro de Ciencias Medioambientales, CSIC, Serrano 115-bis, E-28006 Madrid, Spain
2K. A. Timiryazev Institute of Plant Physiology RAS, Botanicheskaya 35, Moscow 127276, Russia
* To whom correspondence should be addressed: E-mail: mlucas{at}ccma.csic.es
Lupin nodule cells maintain their ability to divide for several cycles after being infected by endosymbiotic rhizobia. The conformation of the cytoskeletal elements of nodule cells was studied by fluorescence labelling, immunocytochemistry, and laser confocal and transmission electron microscopy. The dividing infected cells showed the normal microtubule and actin patterns of dividing plant cells. The clustered symbiosomes were tethered to the spindle-pole regions and moved to the cell poles during spindle elongation. In metaphase, anaphase, and early telophase, the symbiosomes were found at opposite cell poles where they did not interfere with the spindle filaments or phragmoplast. This symbiosome positioning was comparable with that of the organelles (which ensures organelle inheritance during plant cell mitosis). Tubulin microtubules and actin microfilaments appeared to be in contact with the symbiosomes. The possible presence of actin molecular motor myosin in nodules was analysed using a monoclonal antibody against the myosin light chain. The antigen was detected in protein extracts of nodule and root cytosol as bands of approximately 20 kDa (the size expected). In the nodules, an additional polypeptide of 65 kDa was found. Immunogold techniques revealed the antigen to be localized over thin microfilaments linked to the cell wall, as well as over the thicker microfilament bundles and surrounding the symbiosomes. The pattern of cytoskeleton rearrangement in dividing infected cells, along with the presence of myosin antigen, suggests that the positioning of symbiosomes in lupin nodule cells might depend on the same mechanisms used to partition genuine plant cell organelles during mitosis.
Key words: Actin, bacteroid, Bradyrhizobium, lupin, myosin, organelle, Rhizobium, symbiosome, tubulin
Received 20 December 2006; Revised 5 March 2007 Accepted 20 March 2007