Cell wall matrix polysaccharides and mesophyll cell morphogenesis

The acquisition of the photosynthetic mesophyll cell shape in the dicotyledonous species Vigna sinensis and the fern Asplenium nidus is the result of the coordination of (a) the cortical microtubule alignment that controls cellulose microfibril orientation and (b) the local differentiation of the cell wall matrix polysaccharides, a rather general phenomenon, also described in monocotyledonous species.

Vigna sinensis
Vigna Sinensis. Photo by 영철 이 / Flickr.

Sotiriou et al. showed that cell wall matrix differentiation leads to establishment of two distinct types of alternating cell wall subdomains. The first type defines the contact sites between mesophyll cells and is marked by the presence of callose and certain homogalacturonan epitopes. The second type defines the sites of intercellular space formation and is characterized by the absence of callose and the presence of different homogalacturonan epitopes from mesophyll cell contacts.