Nematode-induced syncytium - A multinucleate transfer cell

The formation and structure of a syncytium induced by the potato cyst-nematode (Heterodera rostochiensis Woll.) in potato roots is described. At the permanent feeding site of the nematode larva, usually in the root cortex, the larva pierces a cell with its mouth stylet and injects saliva. Cell wall dissolution occurs to incorporate neighbouring cells into a syncytium. A column of cells is incorporated towards the vascular tissue. Centripetal advance is limited by the lignifled xylem, then syncytial spread continues laterally along xylem parenchyma and pericycle cells. Wall protuberances form on syncytial walls adjacent to conducting elements. This indicates the syncytium is a multinucleate transfer cell, and by ingesting syncytial contents the larva is the nutrient sink. As syncytial expansion occurs, sieve elements are crushed and probably cease to function, hence protuberance development continues only against xylem elements. Cell alterations on incorporation into the syncytium involve expansion, loss of cell vacuole, nuclear hypertrophy and a proliferation of cytoplasmic organelles free to move through wall gaps into the communal cytoplasm. ‘Boundary formations’ and microtubules are associated with the growing ends of protuber ances, and appear to be involved in their synthesis. Fibrillar material, possibly cellulose microfibrils, occurs between the plasrnalemma and the membrane of the ‘boundary formation’, and the forming protuberance. To induce the formation of the syncytium, the larva controls the differentiation of unspecialized cells to cells with a specific physiological function. The occurrence of wall protuberances suggests that transfer cells form as a response to solute flow

Multinucleate transfer cells induced in coleus roots by the root-knot nematode, Meloidogyne arenaria

The occurrence and position of wall protuberances in giant cells induced in coleus roots by the root-knot nematodeMeloidogyne arenaria is described, and the structure and function of giant cells is compared with that of syncytia induced by cyst-nematodes. Extensive protuberance development occurs on walls of giant cells adjacent to xylem vessels. Protuberances are less well developed next to sieve elements, and almost absent next to parenchyma cells. On walls between giant cells they occur on both sides or only one side. The formation of protuberances indicates that giant cells are multinucleate transfer cells. The position of protuberances marks the wall area where solutes enter the cell. Solutes are obtained from xylem and phloem elements, and the position of protuberances at the junction between giant cells and vascular elements indicates an extensive flow of solutes along cell walls. The observations support the hypothesis that wall protuberances form as a result of selective solute flow across the plasmalemma. No cell wall dissolution was observed, although wall gaps may occur between giant cells as a result of breakage during rapid cell expansion

A membrane-bound enzyme complex synthesizing glucan and glucomannan in pine tissue

Particulate membrane preparations isolated from cambial cells and differentiating and differentiated xylem cells of pine (Pinus sylvestris L.) trees synthesised [14C]glucans using either guanosine 5prime-diphosphate (GDP)-D-[U-14C]glucose or uridine 5prime-diphosphate (UDP)-D-[U-14C]glucose as glycosyl donors. Although these glucans had beta-(1rarr3) and beta-(1rarr4) linkages in an approximate ratio 1:1, the distribution of the linkages in the glucan synthesised from GDP-D-glucose was different from that synthesised from UDP-D-glucose. The synthesis of the mixed beta-(1rarr3) and beta-(1rarr4) glucan from GDP-D-[U-14C]glucose was changed to that of beta-(1rarr4) glucomannan in the presence of increasing concentrations of GDP-D-mannose. The glucan formed from UDP-D-[U-14C]glucose was not affected by any concentration of GDP-D-mannose. The membrane preparations epimerized GDP-D-glucose to GDP-D-mannose; however, the low amount of GDP-D-mannose formed was not incorporated into the polymer becaus the affinity of the synthase for GDP-D-glucose was much greater than that for GDP-D-mannose. The glucan formed from GDP-D-glucose and the glucomannan formed from GDP-D-glucose together with GDP-D-mannose were characterized. The apparent K m and V max of the glucan synthase for GDP-D-glucose were 6.38 mgrM and 5.08 mgrM·min-1, respectively. No lipid intermediates were detected during the synthesis of either glucan or glucomannan. The results indicated that an enzyme complex for the formation of the glucomannan was bound to the membrane

Glucomannan synthesis in pea epicotyls - the mannose and glucose transferases

Membrane fractions and digitonin-solubilized enzymes prepared from stem segments isolated from the third internode of etiolated pea seedlings (Pisum sativum L. cv. Alaska) catalyzed the synthesis of a beta-1,4-[su14C]mannan from GDP-d-[U-14C]-mannose, a mixed beta-1,3- and beta-1,4-[14C]glucan from GDP-d-[U-14C]-glucose and a beta-1,4-[14C]-glucomannan from both GDP-d-[U-14C]mannose and GDP-d-[U-14C]glucose. The kinetics of the membrane-bound and soluble mannan and glucan synthases were determined. The effects of ions, chelators, inhibitors of lipid-linked saccharides, polyamines, polyols, nucleotides, nucleoside-diphosphate sugars, acetyl-CoA, group-specific chemical probes, phospholipases and detergents on the membrane-bound mannan and glucan synthases were investigated. The beta-glucan synthase had different properties from other preparations which bring about the synthesis of beta-1,3-glucans (callose) and mixed beta-1,3- and beta-1,4-glucans and which use UDP-d-glucose as substrate. It also differed from xyloglucan synthase because in the presence of several concentrations of UDP-d-xylose in addition to GDP-d-glucose no xyloglucan was formed. Using either the membrane-bound or the soluble mannan synthase, GDP-d-glucose acted competitively in the presence of GDP-d-mannose to inhibit the incorporation of mannose into the polymer. This was not due to an inhibition of the transferase activity but was a result of the incorporation of glucose residues from GDP-d-glucose into a glucomannan. The kinetics and the composition of the synthesized glucomannan depended on the ratio of the concentrations of GDP-d-glucose and GDP-d-mannose that were available. Our data indicated that a single enzyme has an active centre that can use both GDP-d-mannose and GDP-d-glucose to bring about the synthesis of the heteropolysaccharide