Asymmetric wall ingrowth deposition in Arabidopsis phloem parenchyma transfer cells is tightly associated with sieve elements

In Arabidopsis, polarized deposition of wall ingrowths in phloem parenchyma (PP) transfer cells (TCs) occurs adjacent to cells of the sieve element/companion cell (SE/CC) complex. However, the spatial relationships between these different cell types in minor veins, where phloem loading occurs, are poorly understood. PP TC development and wall ingrowth localization were compared to other phloem cells in leaves of Col-0 and the transgenic lines AtSUC2::AtSTP9-GFP and AtSWEET11::AtSWEET11-GFP that identify CCs and PP respectively. The development of PP TCs in minor veins, indicated by deposition of wall ingrowths, proceeded basipetally in leaves. However, not all PP develop ingrowths and higher levels of wall ingrowth deposition occur in abaxial- compared to adaxial-positioned PP TCs. Furthermore, the deposition of wall ingrowths was exclusively initiated on and preferentially covered the PP TC/SE interface, rather than the PP TC/CC interface, and only occurred in PP cells that were adjacent to SEs. Collectively, these results demonstrate the dominant impact of SEs on wall ingrowth deposition in PP TCs and suggest the existence of two sub-types of PP cells in leaf minor veins. Compared to PP cells, PP TCs showed more abundant accumulation of AtSWEET11-GFP, indicating functional differences in phloem loading between PP and PP TCs.

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

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.

Ultrastructure of fertilization in Plumbago zeylanica

The synergidless female gametophyte of <em>Plumbago zeylanica</em> receives the pollen tube through specialized cell wall ingrowths at the base of the egg; tube growth continues between egg and central cells. Pollen tube discharge occurs between egg and central cell and results in release of two male gametes, vegetative nucleus, and some pollen cytoplasm. Except for the location of gamete discharge, details of transmission and fusion of gametic nuclei appear to conform to reports of these processes in taxa possessing conventional embryo sacs.

Structure of syncytia induced by Heterodera schachtii Schmidt in roots of susceptible and resistant radish (Raphanus sativus L., var. oleiformis)

The structure of syncytia induced by <i>Heterodera schachtii</i> Schmidt in roots of susceptible <i>Raphanus sativus</i> L. cv. "Siletina" and resistant radish cv. "Pegletta" was investigated. In the radish cultivar "Siletina" the syncytia most often appeared in the elongation zone of lateral roots. They were initiated in the procambium and pericycle but also included the parenchyma cells of vascular cylinder. In the susceptible cultivar "Siletina" the cells forming the female's syncytia were subject to hypertrophy. Their cytoplasmic density increased. The cytoplasm contained numerous organella. The proliferation of the smooth endoplasmic reticulum took place. Branched cell wall ingrowths were formed next to the vessels. In the male's syncytia the cells were only slightly increased. Their protoplasts contained few organelles. The cell wall ingrowths were poorly developed. In the syncytia of the resistant cultivar "Pegletta" there was only a slight increase of the cell volume. A well developed system of rough endoplasmic reticulum was observed in the protoplast. Distended ER cisterns contained fine fibrillar material. Material of similar structure also appeared in numerous small vacuoles. In resistant plants only some, not numerous, syncytia spreading in procambium fully developed and functioned long enough for the parasite females to mature. At an advanced stage of infection a well developed system of a rough ER was observed also in those syncytia and numerous vacuoles appeared.

Structural character of sorghum endosperm transfer cells and their relationship with embryo and endosperm

Endosperm transfer cells mainly occur in the epithelial layer of the endosperm and transport the nutrient unloaded by the maternal vascular tissue. They have wall ingrowths that can facilitate solute transportation. Here we report our further investigation of endosperm transfer cells in sorghum (Sorghum bicolor L. Moench). We observed endosperm transfer cells, embryo, and endosperm with different kinds of microscopes. Our experimental results showed that the distribution and configuration of endosperm transfer cells were fit for solute transportation, and they had a tight relationship with the embryo and endosperm.