The placenta of : transfer cell wall polymers compared across the three bryophyte groups.

Following similar studies of cell wall constituents in the placenta of and , we conducted immunogold labeling TEM studies of to determine the composition of cell wall polymers in transfer cells on both sides of the placenta. 16 monoclonal antibodies were used to localize cell wall epitopes in the basal walls and wall ingrowths in this moss. In general, placental transfer cell walls of contain fewer pectins and far fewer AGPs than those of the hornwort and liverwort. also lacks the differential labeling that is pronounced between generations in the other bryophytes. In contrast, transfer cell walls on either side of the placenta of are relatively similar in composition with slight variation in HG pectins. Compositional similarities between wall ingrowths and primary cell walls in suggest that wall ingrowths may simply be extensions of the primary cell wall. Considerable variability in occurrence, abundance, and types of polymers among the three bryophytes and between the two generations suggests that similarity in function and morphology of cell walls does not require a common cell wall composition. We propose that the specific developmental and life history traits of these plants may provide even more important clues in understanding the basis for these differences. This study significantly builds on our knowledge of cell wall composition in bryophytes in general and transfer cells across plants.