4. Functions of AGPs in planta

For some AGPs it could be shown, that they influence cell differentiation and play roles in different processes like cell elongation, cell proliferation or programmed cell death. A first step to elucidate possible functions of AGPs is localization of these molecules in the plant. For this purpose, we use antibodies and detect AGPs by immunofluorescence and fluorescence microscopy.

The following antibodies are used in our group:

  • Polyclonal antibodies against AGP from Echinacea (rabbit)
  • Monoclonal antibody (KM = Kiel Monoclonal) against AGP from Echinacea (mouse)
  •  Polyclonal antibodies against β-Glc Yariv reagent (coupled to KLH, rabbit)

Continuously we work on the characterization of the antibody epitops. For KM 1, the epitop has been characterized in detail by affinity tests with several oligosaccharides produced by chemical synthesis (Dr. Fabian Pfrengle, Max Planck Institute of Colloids and Interfaces, Potsdam).

 

Development of water-transporting tissue (xylem)

For roots, stems and leaf stalks of  Echinacea purpurea we could show, that AGPs are present mainly in vessels and tracheids of the xylem. The localization of AGPs changes during differentiation of young vessels (see figures B and C), which supports the hypothesis of other authors that AGPs play a role in xylem development. Furthermore, we detected AGPs in big amounts in the area of the cell walls around pit canals, suggesting that AGPs are also involved in formation of these canals connecting adjacent vessels.

leaf stalk vascular bundles

Immunofluorescence of AGPs in a leaf stalk of Echinacea purpurea.
A Cross section; immunofluorescence of AGPs mainly in the xylem of the vascular bundles.
B Differentiation of the xylem close to the cambium.
1: Young, differentiating vessel, already with secondary wall and AGPs only in the cytoplasm.
2: Fully differentiated vessel of metaxylem without cytoplasm, but with typical secondary wall with pit canals; AGPs now only in the cell wall.
3: Older vessel, probably from protoxylem with huge amounts of AGPs in the area of the secondary wall.
C Cross sections of three differentiating vessels close to the cambium. AGPs are present in the cytoplasm, not in the cell walls.
 

xylem

Immunofluorescence of AGPs in the xylem of E. purpurea.
Left and middle Cross section of the stem.
Immunofluorescence of AGPs mainly in the cell wall close to the cell lumina and in the area of the pit canals.
Right Longitudinal section of a vessel in the leaf stalk.
Immunofluorescence of AGPs in the cell wall around the pit canals.

 

Selected publications:

Göllner EM, Gramann JC, Classen B: Antibodies against Yariv´s reagent for immunolocalization of arabinogalactan-proteins in aerial parts of Echinacea purpurea. Planta Med (2013) 79(2): 175-80.

Bossy A, Blaschek W, Classen B: Characterization and immunolocalization of arabinogalactan-proteins in roots of Echinacea purpurea. Planta Med (2009) 75: 1526-1533.

 

 

Somatic embryogenesis

In plant cell cultures AGPs are able to stimulate somatic embryogenesis. Root extracts of the medicinal plant Pelargonium sidoides, native to South Africa, are used globally for the treatment of common cold and cough. Due to an increasing economic commercialization of P. sidoides remedies, wild collections of root material should be accompanied by effective methods for plant propagation like somatic embryogenesis. We developed a new method to propagate P. sidoides by somatic embryogenesis and investigated the influence of several phytohormones on this process with best results for thidiazuron. Especially the influence of AGPs is interesting. External application of AGPs isolated from P. sidoides (from the native plant or from suspension cultures) to the explants clearly increased the number of somatic embryos. An experiment with over 1000 young plants derived from somatic embryos confirmed this result.

somatic embryogenesisembryo
Development of somatic embryos on explants from  inflorescence shoots of  P. sidoides

 

green house
Development of young plants derived from somatic embryos in the green house

 

Selected publications

Duchow S, Dahlke RI, Geske T, Blaschek W, Classen B: Arabinogalactan-proteins stimulate somatic embryogenesis and plant propagation of Pelargonium sidoides. Carbohydr Pol (2016) 152: 149-155.

Duchow S, Blaschek W, Classen B: Reproduction of the medicinal plant Pelargonium sidoides via somatic embryogenesis. Planta Med (2015) 81: 1169-1174.

 

 

Salt tolerance

In a cooperation (Dr. S. Lutts, University of Louvain, Belgium) we investigate a possible function of AGPs and/or other plant polysaccharides (pectins) in salt tolerance of the mucilage producing plant Kosteletzkya virginica (Malvaceae).

 

Publications

Zhou M, Classen B, Agneessens R, Godin B, Lutts S: Salinity improves Zinc resistance in Kosteletzkya pentacarpos in relation to a modification in mucilage and polysaccharides composition. International Journal of Environmental Research (2020) 14:323–333.

Ghanem ME, Han RM, Classen B, Quetin-Leclerq J, Mahy G, Ruan CJ, Qin P, Perez-Alfocea F, Lutts S: Mucilage and Polysaccharides in the Halophyte Plant Species Kosteletzkya virginica (L.) Presl.: Localization and Composition in relation to salt stress. J Plant Physiol (2010) 167: 382-392.

 

 

Defense against pathogens

In literature, involvement of HPRGs (= hydroxyproline-rich-glycoproteins) in defense against pathogens has been described. In first experiments we could show, that the content of hydroxyproline in cell walls of nematode-infected cereals is higher compared to non-infected plants, possibly due to higher levels of AGPs and/or extensins. In an ongoing project (BMBF-project „NEMARES“, Prof. Dr. C. Jung, Institut für Pflanzenbau und Pflanzenzüchtung, CAU Kiel) this mechanism will be investigated further.