The Placenta of Physcomitrium patens: Transfer Cell Wall Polymers Compared across the Three Bryophyte Groups

Abstract

Following similar studies of cell wall constituents in the placenta of Phaeoceros and Marchantia, we conducted immunogold labeling TEM studies of Physcomitrium patens to determine the composition of cell wall polymers in transfer cells on both sides of the placenta. Sixteen 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 P. patens contained fewer pectins and far fewer arabinogalactan proteins AGPs than those of the hornwort and liverwort. P. patens also lacked the differential labeling that is pronounced between generations in the other bryophytes. In contrast, transfer cell walls on either side of the placenta of P. patens were relatively similar in composition, with slight variation in homogalacturonan HG pectins. Compositional similarities between wall ingrowths and primary cell walls in P. patens 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 suggested 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 in transfer cells across plants.

Immunocytochemical Analysis of the Wall Ingrowths in the Digestive Gland Transfer Cells in Aldrovanda vesiculosa L. (Droseraceae)

“…This suggests that these AGPs may play an important role in the gland function. AGPs were reported from the wall ingrowths in transfer cells of both angiosperms [ 27 , 41 , 42 , 61 ] and lower plants [ 43 , 44 , 45 ]. Vaughn et al [ 27 ] experimentally proved that AGPs play a role in the development of cell wall ingrowths.…”

“…Due to the positive PAS reaction, we expected HGs to be present in the cell wall ingrowths in the A. vesiculosa gland cells, since methylesterified HGs were found in the wall ingrowths in other plant species [ 27 , 44 , 45 ]. However, we did not detect HGs recognized by JIM5, JIM7, LM19, LM5, and LM6 (using light microscopy) in the cell wall ingrowths of the stalk and head cells.…”

“…Both methylesterified and de-esterified HGs pectins were absent from the wall ingrowths in transfer cells of Elodea canadensis leaves [ 42 ], but occurred in the cell wall ingrowths in transfer cells of Marchantia polymorpha [ 43 ], Phaeoceros carolinianus , P. laevis [ 45 ], and Physcomitrium patens [ 44 ]. HG recognized by JIM7 occurred in the cell wall ingrowths in transfer cells of Vicia faba [ 27 ] and Pisum sativum [ 41 ].…”

“…HG recognized by JIM7 occurred in the cell wall ingrowths in transfer cells of Vicia faba [ 27 ] and Pisum sativum [ 41 ]. Henry and Renzaglia [ 44 ] suggested that, due to their roles in cell wall properties and mechanics, HG may facilitate nutrient uptake by membrane transport proteins, which is important in transfer cell functioning.…”

“…Despite the significant advances in understanding the molecular basis of the formation of wall ingrowths [ 25 ], the knowledge of the chemical composition (studied using immunogold labeling) of the wall labyrinth in transfer cells is still insufficient and based on studies in only a few angiosperm genera: Pisum sativum , Vicia faba , and Elodea canadensis [ 27 , 41 , 42 ]. Recently, nonflowering plants (bryophytes) have also been studied to determine the detailed chemical composition of the wall ingrowths in their placenta [ 43 , 44 , 45 ]. Therefore, there is a need to study the composition of wall ingrowths on various plant models.…”