Phi thickenings, lignified thickenings found on the radial and tangential walls of root cortical cells, are present in a restricted number of angiosperms and gymnosperms. To test whether their occurrence is constitutive or environmentally induced, seedlings of Cryptomeria japonica (L.f.) D. Don (Cupressaceae, phi thickenings present), and Pinus aristata Engel. and Pinus rigida Mill. (Pinaceae, phi thickenings absent) were grown under conditions of waterlogging and soil compaction. After 4 months, five morphological characters and the presence and cross-sectional area of phi thickenings were measured. All measured aspects of seedling morphology were affected by the treatments, and the two treatment factors (waterlogging and compaction) interacted significantly with one another. Taproots were significantly shorter, lateral roots were shorter and fewer in number, and root:shoot ratios were smaller in waterlogged and compacted soil in all three species. Despite these morphological effects, phi thickening presence or absence did not vary: phi thickenings were always found in C. japonica and never in the two Pinus species. However, the phi ratio (the area occupied by phi thickenings relative to the total root area) decreased significantly with both waterlogging and compaction even though it remained unchanged with root maturity. Thus, although root morphology and phi thickening anatomy were significantly affected by the environment, the presence of phi thickenings was not, and is evidently a constitutive anatomical feature in the species examined.Key words: phi thickenings, root anatomy, Cryptomeria, Pinus, waterlogging, soil compaction.
Various categories of mycorrhizas are recognized primarily by the structural changes that occur between fungi and roots. In all mycorrhiza categories, cytological modifications of root cells accompany the establishment of the functional symbiosis, and among these are alterations in the organization of the cytoskeleton. Using immuno labelling combined with confocal scanning laser microscopy, this study documents changes in microtubules (MTs) in root cells of ectendomycorrhizas and monotropoid mycorrhizas; in addition, ectomycorrhizas were reinvestigated to determine the effect of fungal colonization on host root cells. In Pinus banksiana L. Laccaria bicolor (Maire) Orton ectomycorrhizas, MTs were present in epidermal and cortical cells adjacent to the Hartig net. The remaining cortical MTs had a different organization when compared with those of cortical cells of control roots. MTs were present in Hartig net hyphae. In ectendomycorrhizas formed when roots of P. banksiana were colonized by the ascomycete, Wilcoxina mikolae var. mikolae Yang & Korf, MTs were present adjacent to intracellular hyphae and host nuclei, but few cortical MTs were present. MTs were present within Hartig net and intracellular hyphae. In field-collected roots of Monotropa uniflora L., MTs were associated with fungal pegs, intracellular extensions of inner mantle hyphae within epidermal cells. The close association between MTs and fungal pegs may be related to the formation of the highly branched host-derived wall that envelops each fungal peg. The development of exchange interfaces in the three systems studied involve changes in the organization of microtubules.Key words: cytoskeleton, microtubules, Hartig net, mycorrhizas, immunolocalization, confocal microscopy.
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