A brief comparative survey of aerophore structure within the Filicopsida

DAVIES, K. L., 1991. A brief comparative survey of aerophore structure within the Filicopsida. A comparative account of the structure of petiolar aerophores and aerating systems within certain fern families is presented. Approximately 100 species were examined and the results suggest that the petiolar aerophore structure and its relationship to internal petiolar anatomy could prove a useful taxonomic character at the generic level.     

Ultrastructure of the hypodermis during cuticle formation in the third molt of the nematode Nippostrongylus brasiliensis

Summary The fine structure of the hypodermis of Nippostrongylus brasiliensis, a parasitic nematode of the rat, was studied in free-living third-stage filariform (infective) larvae, and in parasitic forms undergoing the third molt. In filariform larvae the hypodermis displayed a comparatively poorly developed RER, and few Golgi complexes, mitochondria, and vesicles. Nuclei contained large amounts of heterochromatin and no nucleoli. After worms reached the lungs and the third molt began, the RER, Golgi complexes, mitochondria, multivesicular bodies, and coated vesicles greatly increased in amounts. Nuclei displayed less heterochromatin and contained prominent nucleoli. These morphological changes were associated with transition from the free-living to the parasitic mode in life. The results were correlated with the fact that the hypodermis in N. brasiliensis is actively synthesizing culticular collagen during the third molt.This investigation was supported, in part, by awards 1-F02-AI3750-02 and AI-09625 from the National Institutes of Health, United States Public Health Service.We are grateful to Lida Petruniak and Dora Lou for technical assistance.     

Comparative anatomy of the vegetative organs in Pleiochiton A. Gray (Melastomataceae), with emphasis on adaptations to epiphytism

We present a comparative analysis on the anatomy of roots, shoots, and leaves of three epiphytic Pleiochiton species and a species of the closely related Clidemia. The four species share similar anatomical characters, suggesting adaptations toward water storage in all the structures and, consequently, to the water-limited epiphytic habitat. All four species present succulent roots with up to 75% of its volume with cells that store water. The leaves have about 50% of the volume formed by a hypodermis that also stores water. They are very similar to leaves of epiphytic Peperomia and Gesneriaceae, suggesting evolutionary convergence. Leaf cells in all species have large vacuoles and compact mesophyll, with little intercellular spaces; all these traits are usually related to CAM photosynthesis. The anatomical features found in all four species agree with previous phylogenetic analyses that show Clidemia blepharodes, Pleiochiton ebracteatum and Pleiochiton micranthum as members of a same clade.     

Chemical analysis and immunolocalisation of lignin and suberin in endodermal and hypodermal/rhizodermal cell walls of developing maize (Zea mays L.) primary roots

The composition of suberin and lignin in endodermal cell walls (ECWs) and in rhizodermal/hypodermal cell walls (RHCWs) of developing primary maize (Zea mays L.) roots was analysed after depolymerisation of enzymatically isolated cell wall material. Absolute suberin amounts related to root length significantly increased from primary ECWs (Casparian strips) to secondary ECWs (suberin lamella). During further maturation of the endodermis, reaching the final tertiary developmental state characterised by the deposition of lignified secondary cell walls (u-shaped cell wall deposits), suberin amounts remained constant. Absolute amounts of lignin related to root length constantly increased throughout the change from primary to tertiary ECWs. The suberin of Casparian strips contained high amounts of carboxylic and 2-hydroxy acids, and differed substantially from the suberin of secondary and tertiary ECWs, which was dominated by high contents of ω-hydroxycarboxylic and 1,ω-dicarboxylic acids. Furthermore, the chain-length distribution of suberin monomers in primary ECWs ranged from C₁₆ to C₂₄, whereas in secondary and tertiary ECWs a shift towards higher chain lengths (C₁₆ to C₂₈) was observed. The lignin composition of Casparian strips (primary ECWs) showed a high syringyl content and was similar to lignin in secondary cell walls of the tertiary ECWs, whereas lignin in secondary ECWs contained higher amounts of p-hydroxyphenyl units. The suberin and lignin compositions of RHCWs rarely changed with increasing root age. However, compared to the suberin in ECWs, where C₁₆ and C₁₈ were the most prominent chain lengths, the suberin of RHCWs was dominated by the higher chain lengths (C₂₄ and C₂₆). The composition of RHCW lignin was similar to that of secondary-ECW lignin. Using lignin-specific antibodies, lignin epitopes were indeed found to be located in the Casparian strip. Surprisingly, the mature suberin layers of tertiary ECWs contained comparable amounts of lignin-like epitopes. Received: 19 August 1998 / Accepted: 3 February 1999     

Some Neuron-Hypodermis Relationships in the Parasitic Nematode Trichurus myocastoris Enigk

The association of neurons and hypodermal cells in longitudinal nerve chords and in interchordal positions (perhaps dorso-ventral commissures) in the body wall of Trichuris myocastoris Enigk has been examined with the electron microscope. Nerve chords are composed of several groups of neurons separated by processes of hypodermal cells; such groups may be functionally separate. Nerve cell bodies occur within the chords, and appear to be at least bipolar. Neurons emerge from the median chords and enter the interchordal regions, showing progressive invagination in hypodermal tissue with increased distance from the median line. Such invagination results in formation of mesaxons and may be significant in the nutrition of the neuron. Mesaxons may branch and may enclose single or groups of neurons; no spiralling of the mesaxon was seen. Occasionally more than one mesaxon was traced to a single neuron.     

Studies on the ultrastructure of the integument of the rotifer Habrotrocha rosa Donner (Aschelminthes)

Summary The integument of the rotifer Habrotrocha rosa Donner is provided with pores and formed by an extrasyncytial cuticle and a syncytial hypodermis. The hypodermis peripherally contains 3 layers of dense cytoplasm and borders the cuticle by an asymmetric cell membrane. The wall of the pores is stiffened proximally like an annulus. The pores lead into cytoplasmic invaginations which are surrounded by vesicles. Close to and also beneath the condensed cytoplasmic layers microbodies are found, which are interpreted as microperoxisomes. Subhypodermal layers of muscles are connected with the cytoplasm of the hypodermis by desmosome-like structures.I am indebted to Dr. H. Breucker, Anatomisches Institut Hamburg, and Prof. Dr. W. Becker, Zoologisches Institut Hamburg, under whose direction this work was carried out. Supported by the Deutsche Forschungsgemeinschaft (Be 464/10)