Roland R. Dute

TORUS LIGNIFICATION IN HARDWOODS

Tori in wood of Osmanthus americanus, Daphne odora, Celtis occidentalis and Ulmus alata were tested for lignins using KMnO4 staining in conjunction with TEM, and acriflavine staining in concert with CLSM. It was hypothesized that impregnation with lignin could explain torus survival during cytoplasmic apoptosis. KMnO4 staining indicated torus lignification in all four woods, whereas only Osmanthus and Daphne tested positive for lignin with acriflavine. Tori in Celtis and Ulmus showed some evidence of partial breakdown during cell maturation, which might expose non-lignin sites for KMnO4 binding and thus produce spurious results. The acriflavine data correlate with developmental studies in which torus ontogeny occurs by one method in Osmanthus and Daphne and by another method in Celtis and Ulmus.

EFFECTS OF AMBROSIA BEETLE ATTACK ON CERCIS CANADENSIS

Damage caused to Cercis canadensis by the Asian ambrosia beetle and its associated micro-organisms was investigated as was host response to infestation. Various micro-organisms were connected with beetle infestation but only filamentous fungi exhibited extensive growth. In particular, species of Ambrosiella were associated with beetle tunnels. Fungal hyphae infected all cell types by growing directly through cell walls, by penetrating pit membranes, and by traversing perforations. Colonization of parenchyma was intensive and these cells probably provided the nutrients for continued hyphal growth. Host cell response to damage included breakdown of the protective layer of some parenchyma cells and accumulation of polysaccharide gels within vessel members. Measurements showed no significant difference in ethylene production by wood samples from infected versus uninfected trees. However, established literature indicates that damage-induced ethylene production was responsible for initiating events that caused vascular blockage by carbohydrate gel.

Torus structure and development in the woods of Ulmus alata Michx., Celtis laevigata Willd., and Celtis occidentalis L.

Pit membranes between tracheary elements of Ulmus alata, Celtis laevigata, and Celtis occidentalis often contained tori. The degree of development of tori varied and was greatest in those membranes connecting elements of small diameter. Complete tori consisted of two wall thickenings adjoined by a central layer. In three dimensions the shape of the torus often approximated a grooved wheel. Initiation of thickening in the pit membrane occurred first on the side of the older cell and was well underway prior to the beginning of secondary wall synthesis. Torus formation resulted from the thickening of the primary walls of the pit membrane. Development of the torus was associated with membranous vesicles and cisternae but not with microtubule complexes as was reported in Osmanthus. The pit membranes in this study are capable of aspiration, and the tori may prevent rupture of the pit membrane during this process.

Tyloses in Abscission Scars of Loblolly Pinel

During a study of fascicle abscission in Pinus taeda L., tyloses were observed to occlude tracheids of both proximal and distal abscission scars. The tyloses represent the protrusion of ray parenchyma cells into tracheid lumens. Multiple tyloses often arise from a given parenchyma cell and can enter multiple tracheids. Tyloses occur as part of an abscission process that also includes the presence of Type II cells (programmed to enlarge during abscission in the presence of ethylene) and rupture of tracheids-features common to abscission in angiosperms.

Pit Membrane Structure and Development in Ginkgo Biloba

Pit membrane ontogeny in radial walls of Ginkgo biloba tracheids was followed using transmission electron microscopy. Torus initiation occurs prior to initiation of the pit border and without benefit of a microtubule plexus. The developing pit membrane is associated with masses of wall material located within plasmalemma invaginations. Wall material is added in such a manner as to form a torus with highly irregular surfaces. Margo and torus are traversed by plasmodesmata, whose channels are connected by extcnsive median cavities. Matrix material is removed from both margo and torus shortly after hydrolysis of the adjacent cytoplasms. Matrix removal begins at the pit membrane surface and is not preferentially associated with the plasmodesmata. Tori in aspirated pit membranes have compacted fibrils, and their fibrillar compaction might reduce permeability to air embolisms.

Development and Structure of Pit Membranes in the Rhizome of the Woody Fern Botrychium Dissectum

Botrychium dissectum Sprengel rhizomes were examined at monthly intervals from February 1993 through December 1994. Sampies taken ranged from those with an inactive cambium and only mature tracheids to those having an active cambium and immature tracheids. The vascular cambium became activated in the early fall prior to maturation of the leaf and fertile spike complex. Intertracheid pit membranes with tori were present in all sampies, although the morphology of the torus varied. The presence of tori was first observed in a tracheid that had just initiated its secondary wall formation. As the pit membrane matured, matrix material was hydrolyzed first from the margo area, then from the torus, and eventually the pit membrane was represented only by a very thin network of microfibrils. In addition, studies confirmed that tracheids bordering parenchyma cells developed a torus thickening, aIthough no thickening of the parenchyma cell wall occurred. Torus ontogeny in B. dissectum combined features previously described for angiosperms and gymnosperms.

Torus structure and development in species of Daphne.

A torus is present in intervascular pit membranes in the wood of Daphne odora and D. cneorum, but not in D. mezereum. In the two former species, each torus is surrounded by a margo consisting of fibrillar material in a tightly woven pattern. Tori are of greater diameter than pit apertures and completely occlude the apertures during aspiration. Evidence from D. odora indicates that torus deposition is spatially associated with vesicles and a plexus of microtubules, and does not begin until pit border formation is complete. The material deposited during torus synthesis also impregnates the wall of the pre-existing pit membrane. The plasmalemma often is closely appressed to the pit membrane at the site of the developing torus. In half-bordered pit pairs between tracheary elements and parenchyma cells, a torus thickening is deposited only on the side of the tracheary element. As in Osmanthus americanus, it is hypothesised that the presence of tori in species of Daphne prevents rupture of the pit membrane during aspiration.

Electron Microscopic Investigation of the Coating Found on Torus-Bearing Pit Membranes of Botrychium Dissectum, the Common Grape Fern

TEM investigation of the torus-bearing pit membranes in tracheids of Botrychium dissectum wood has revealed in some specimens a coating that covers the pit membrane and torus, and sometimes lines the lumen-side of the tracheary wall. Such coatings have been associated with wound response in dicot woods, but have not previously been reported in the wood of Botrychium. In response to wounding, rhizome sampIes incubated on water-saturated filter paper produced the coating material within 4 days. Rhizome sampIes that were incubated with an ethylene inhibitor for a maximum incubation time of 20 days did not develop the wound-response coating. Therefore, based on experimental evidence the wound response appeared to be ethylene mediated. Field sampIes which were artificially grazed by removing the leaf/spike complex exhibited a displaced wound-response coating in the rhizome. Histochemical studies indicate that the coating material has both pectin and phenolic components.

Survey of Intervessel Pit Membrane Structure in Daphne Species

Of 22 species of Daphne surveyed, 19 possessed tori in their intervessel pit membranes. The torus has a circular shape and is centrally-located on the pit membrane. The fibrils of the surrounding margo show a random arrangement. In some specimens, the fibrils are obscured by material that impregnates the margo, coats the torus, and lines the cell lumens. The margo has small pores. In those species without tori, the intervessel pit membranes, when intact, show randomlywoven fibrils and small pores. Air-dried membranes of these speeies tend to separate into two layers along the line of the middle lamella The presence of a torus is not correlated with evergreen or deciduous habit, but absence of a torus seems to be limited to species of the section Mezereum within the genus Daphne.

Intervascular Pit Membrane Structure in Daphne and Wikstroemia - Systematic Implications

Intervascular pit membranes were investigated in species of Daphne, Wikstroemia, and other allied genera of the Thymelaeaceae. Results confirmed a previous study showing that, except for section Mezereum, all sections of Daphne had pit membranes with tori. Taxonomically isolated species D. aurantiaca and D. genkwa had tori, but lacked a G-layer. Tori similar in structure to those of D. aurantiaca and D. genkwa were observed in three species from the subgenus Diplomorpha of Wikstroemia. Tori of a slightly different morphology were noted in W. kudoi (subg. Daphnimorpha). Tori appeared absent from species of the subgenus Wikstroemia (= Euwikstroemia of Domke), and from the genera Drapetes, Edgeworthia, and Eriosolena. These results suggest a close relationship between Daphne and Wikstroemia. The degree of torus development and the distinctiveness of helical thickenings suggest that smaller tracheary elements serve as a backup water-conducting system to larger vessel elements.