The graft framework: Quantitative changes in cell wall matrix polysaccharides throughout the tomato graft union formation.

Plant cell walls provide essential functions in cell recognition, differentiation, adhesion and wound responses. Therefore, it is tempting to hypothesize that cell walls play a key role in grafting, but to date there are no quantitative studies targeting on cell wall changes during grafting. The aim of this work was to investigate the dynamics of pectic and hemicellulosic polysaccharides at the graft junctions in tomato homografts throughout the first 12 days after grafting. Cell wall fractionation, combined with ATR-FTIR spectroscopy and gas-chromatography, evidenced a marked increase in pectin content and a decrease in the degree of methyl-esterification of homogalacturonan in scion and rootstock throughout grafting. Also, recovery of tightly-bound hemicelluloses decreased at late times after grafting suggesting an increase of cross-linked hemicelluloses along grafting. In addition, immuno-dot assays revealed an increase in xyloglucan and arabinogalactan proteins in the first days after grafting, pointing to a presumed role in tissue adhesion-cohesion.

ß-1,3-Glucanases and chitinases participate in the stress-related defence mechanisms that are possibly connected with modulation of arabinogalactan proteins (AGP) required for the androgenesis initiation in rye (Secale cereale L.).

This work presents the biochemical, cytochemical and molecular studies on two groups of PR proteins, ß-1,3-glucanases and chitinases, and the arabinogalactan proteins (AGP) during the early stages of androgenesis induction in two breeding lines of rye (Secale cereale L.) with different androgenic potential. The process of androgenesis was initiated by tillers pre-treatments with low temperature, mannitol and/or reduced glutathione and resulted in microspores reprogramming and formation of androgenic structures what was associated with high activity of ß-1,3-glucanases and chitinases. Some isoforms of ß-1,3-glucanases, namely several acidic isoforms of about 26 kDa; appeared to be anther specific. Chitinases were well represented but were less variable. RT-qPCR revealed that the cold-responsive chitinase genes Chit1 and Chit2 were expressed at a lower level in the microspores and whole anthers while the cold-responsive Glu2 and Glu3 were not active. The stress pre-treatments modifications promoted the AGP accumulation. An apparent dominance of some AGP epitopes (LM2, JIM4 and JIM14) was detected in the androgenesis-responsive rye line. An abundant JIM13 epitopes in the vesicles and inner cell walls of the microspores and in the cell walls of the anther cell layers appeared to be the most specific for embryogenesis.

A Cellular Networking Model Involving Interactions Among Glycosyl-Phosphatidylinositol (GPI)-Anchored Plasma Membrane Arabinogalactan Proteins (AGPs), Microtubules and F-actin in Tobacco BY-2 Cells.

Arabinogalactan-proteins (AGPs) are perhaps the most abundantly expressed set of proteins at the plant cell surface and play probable roles in cellular architecture and signaling. Although considerable progress has been made to understand the role of AGPs in plant growth and development, their exact functional roles and the molecular mechanisms underlying their interactions with either intra- or extra-cellular molecules are unknown. These unknown interactions were addressed in a recent research article in Plant Physiology. This study reported molecular interactions between AGPs and the cytoskeleton [microtubules, (MTs) and F-actin] in tobacco BY-2 cells. Here in this addendum, a summary of this recent publication and additional perspectives are presented. As reported, perturbation studies were conducted in tobacco BY-2 cells to analyze the effects of an AGP inhibitor (beta-Yariv reagent) on the organization of microtubules [labeled by GFP-MBD (green fluorescent protein-microtubule binding domain)] and F-actin (labeled by rhodamine-phalloidin) and conversely to analyze the effects of a microtubule inhibitor (amiprophosmethyl) and an F-actin inhibitor (cytochalasin-D) on the localization of GPI-anchored GFP-LeAGP-1. These studies implicate a role for GPI-anchored LeAGP-1 in mediating a cell wall-plasma membrane-cytoskeleton connection.