Abstract
During nodule development on pea roots, apoplast undergoes changes in activity of plant cell wall proteins such as expansins (EXPs). Because the accumulation of EXP protein has been correlated with the growth of various plant organs, we investigated using Western Blot and immunolocalization studies with antibody against PsEXP1, whether this protein was accumulated in the expanding cells of nodule. Immunoblot results indicated the presence of a 30-kDa band specific for pea root nodules. The EXP proteins content rose during growth of pea root nodules. Expansin(s) protein was localized in nodule apoplast as well as in the infection thread walls. The enhanced amount of expansin-like proteins in meristematic part of nodule, root and shoot was shown. The localization of this protein in the meristematic cell walls can be related to the loosening of plant cell wall before cell enlargement. Both, plant cell enlargement and infection thread growth require activity of expansin(s). Possible involvement of EXPs in the process of pea root nodule development is also discussed.
Highlights
Symbiotic interaction between plants and rhizobia is almost completely restricted to leguminous plants and results in the formation of a new organ, the root nodule
Once we determined that the antibody directed against the pea native expansin cross-reacted with pea root nodule, we have applied the histochemical methods to localize
Gold granules were observed in the cell walls of nodule cortex cells (Fig. 2E), on walls of infection threads localized in cortex cells (Fig. 2F), in the cell walls of meristematic cells (Fig. 2G)
Summary
Symbiotic interaction between plants and rhizobia is almost completely restricted to leguminous plants and results in the formation of a new organ, the root nodule. Colonization of plant cells by rhizobium bacteria involves the progressive remodelling of plant-microbial interface. As a result of local modification of the extracellular matrix an endosymbiont such as rhizobium, creates a subcellular point of entry throught the plant cell wall with minimum damage to host cell and with minimum elicitation of defence responses (Parniske 2000). The synthesis and composition of ITs are thought to be similar to that of the host cell wall, and inside them bacteria become embedded in plant cell wall-like matrix (Newcomb and McIntyre 1981; Rae et al 1992). Growth of infection threads involves remodelling of plant cell walls. It is believed that extension growth of the IT probably depends on secretion of matrix glycoproteins into the lumen and on multiplication of rhizobia at the growing tip (Gage 2002)
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