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

Jason S. Henry,Karen S. Renzaglia

doi:10.3390/d13080378

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. 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 P. patens contain fewer pectins and far fewer AGPs than those of the hornwort and liverwort. P. patens 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 P. patens are relatively similar in composition with slight variation in 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 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.

Highlights

Because the sporophyte of bryophytes is matrotrophic, the placenta is the principal site for nutrient uptake that drives the production and dispersal of spores [1,2]
Transfer cells characterized by localized cell wall ingrowths are common in both generations in bryophytes, but they are not universal, as they may be absent or restricted to either side of the placental junction [1,5]
In addition to bryophyte placentae, transfer cells are common in tracheophytes in areas of high solute transport, such as in phloem, vascular parenchyma [8], angiosperm embryos [7,9,10,11,12], secretory glands [13], and root nodules [14,15]

Summary

Introduction

Because the sporophyte of bryophytes is matrotrophic, the placenta is the principal site for nutrient uptake that drives the production and dispersal of spores [1,2]. In this intergenerational zone, specialized cells facilitate an intensified unidirectional flow of solutes to the sporophyte that is dependent on the persistent gametophyte [3,4]. Wall ingrowths form an elaborate network or labyrinths that vastly increases the surface area of the plasmalemma, which enhances membrane-mediated nutrient transport in strategically located and specialized cell–cell junctions [3,4,6]. The transport pathway at the placental interface of P. patens is beginning to be understood, little is known about the composition of wall polymers in these unique cells in mosses

Objectives

Methods

Results