title: Immunohistochemical investigation of the necrotrophic phase of the fungus Colletotrichum gloeosporioides in the biocontrol of hemp sesbania (Sesbania exaltata; Papilionaceae).
abstract: OBJECTIVE
  Fungal plant pathogens exert much of their effect on plant cells through alterations in the host cell walls. However, obtaining biochemical proof for this change is difficult because of the relatively small number of cells that are affected by the pathogen relative to the bulk of host tissue. In this study, we examined the differences in host wall composition between infected and uninfected areas of seedlings of the weed hemp sesbania (Sesbania exaltata) that were treated with the biocontrol agent Colletotrichum gloeosporioides. •
  
  
  METHODS
  To determine the changes in cell wall composition, we used semi-thin sections and a battery of antibody probes that recognize components of the cell wall and immunogold-silver cytochemistry to visualize the probes. •
  
  
  RESULTS
  A loss of specific plant cell wall polysaccharides in the region surrounding the primary fungal infection and the creation of a defensive layer by the plant to limit the fungal invasion were the two most obvious changes noted in this study. At the invasion site, there was significant loss of rhamnogalacturon-1 (RGI) and esterified and de-esterified homogalacturonan (HG)-reactive epitopes from the cell walls. In contrast, boundary tissue between the vascular tissue and the fungal lesion reacted more strongly with antibodies that recognize arabinogalactan proteins (AGPs) and xyloglucans than in unaffected areas. •
  
  
  CONCLUSIONS
  These data strongly indicate a role of pectinases in the invasion of the biocontrol agent and the importance of extensins, AGPs, and xyloglucans as defense by the host.
authors: Southern Weed Science Research Unit (now Crop Production Systems Research Unit), USDA-ARS, P. O. Box 350, Stoneville, Mississippi 38776 USA.
authors: Andrew J
authors: AJ
authors: Bowling
authors: Kevin C
authors: KC
authors: Vaughn
authors: Robert E
authors: RE
authors: Hoagland
authors: Kenneth
authors: K
authors: Stetina
authors: C Douglas
authors: CD
authors: Boyette