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We studied the distribution of wall ingrowth (WI) polymers by probing thin sections of companion cells specialized as transfer cells in minor veins of Medicago sativa cv Gabès blade with affinity probes and antibodies specific to polysaccharides and glycoproteins. The wall polymers in the controls were similar in WIs and in the primary wall but differently distributed. The extent of labeling in these papillate WIs differed for JIM5 and JIM7 homogalacturonans but was in the same range for LM5 and LM6 rhamnogalacturonans and xyloglucans. These data show that WI enhancement probably requires arabinogalactan proteins (JIM8) mainly localized on the outer part of the primary wall and WIs. By comparison, NaCl-treated plants exhibited cell wall polysaccharide modifications indicating (1) an increase in unesterified homogalacturonans (JIM5), probably implicated in Na(+) binding and/or polysaccharide network interaction for limiting turgor variations in mesophyll cells; (2) enhancement of the xyloglucan network with an accumulation of fucosylated xyloglucans (CCRC-M1) known to increase the capacity of cellulose binding; and (3) specific recognition of JIM8 arabinogalactan proteins that could participate in both wall enlargement and cohesion by increasing the number of molecular interactions with the other polymers. In conclusion, the cell wall polysaccharide distribution in enlarged WIs might (1) participate in wall resistance to sequestration of Na(+), allowing a better control of hydric homeostasis in mesophyll cells to maintain metabolic activity in source leaves, and (2) maintain tolerance of M. sativa to NaCl.

The study used Actinidia deliciosa endosperm-derived callus to investigate aspects of the morphology, histology and chemistry of extracellular matrix (ECM) structures in morphogenically stable tissue from long-term culture. SEM showed ECM as a membranous layer or reticulated fibrillar and granular structure linking the peripheral cells of callus domains. TEM confirmed that ECM is a distinct heterogeneous layer, up to 4 mum thick and consisting of amorphous dark-staining material, osmiophilic granules and reticulated fibres present outside the outer callus cell wall. ECM covered the surface of cells forming morphogenic domains and was reduced during organ growth. This structure may be linked to acquisition of morphogenic competence and thus may serve as a structural marker of it in endosperm-derived callus. ECM was also observed on senescent cells in contact with the morphogenic area. Treatment of living calluses with chloroform and washing with ether-methanol led to partial destruction of the extracellular layer. Digestion with pectinase removed the membranous layer almost completely and exposed thick fibrillar strands and granular remnants. Digestion with protease did not visibly affect the surface layer. Indirect immunofluorescence showed low-methylesterified pectic epitopes labelled by JIM5 monoclonal antibody. Immunolabelling, histochemistry, and solvent and enzyme treatments suggested pectins and lipids as components of the surface layer. These compounds may indicate protective, water retention and/or cell communication functions for this external layer.

This study aims to clarify the short- and long-term effects of the iron concentration in the medium on androgenesis induced in barley by isolated microspore culture. The ultrastructural features and pectin composition of the intine wall were studied in the initial stages of androgenesis. The evolution of electron-dense iron deposits on the intine was analysed in multicellular pollen grains obtained by isolated microspore culture performed for 3, 6, and 9 days using various concentrations of FeNa(2) EDTA. Finally, the number of embryo-like structures and green plants obtained by microspore culture using different Fe concentrations was evaluated in order to estimate the optimum concentration for isolated microspore culture.