Pilostyles species (Apodanthaceae) are endoparasites in stems of the plant family Fabaceae. The body comprises masses of parenchyma in the host bark and cortex, with sinkers, comprising groups of twisted tracheal elements surrounded by parenchyma that enter the secondary xylem of the host plant. Here we report for the first time the effects of Pilostyles parasitism on host secondary xylem. We obtained healthy and parasitized stems from Mimosa foliolosa, M. maguirei and M. setosa and compared vessel element length, fiber length, vessel diameter and vessel frequency, measured through digital imaging. Also, tree height and girth were compared between healthy and parasitized M. setosa. When parasitized, plant size, vessel diameter, vessel element length and fiber length are all less than in healthy plants. Also, vessel frequency is greater and vessels are narrower in parasitized stems. These responses to parasitism are similar to those observed in stressed plants. Thus, hosts respond to the parasite by changing its wood micromorphology in favour of increased hydraulic safety.
We analysed how variation in microenvironmental conditions and stem size affects the wood anatomy of Roupala rhombifolia in three contrasting habitats in the same study area: open field, hilltop forest and riparian forest. The wood anatomy features analysed were: vessel area and density, vessel element length, fibre length, and ray width and height. Vegetation cover and soil attributes were also quantified and integrated into the analyses. Separate analyses were performed on i) raw anatomical data and ii) residuals from linear fits between wood anatomical features and plant height and stem diameter. Raw data showed a clear difference between specimens from riparian forest and open fields, which represented the most mesic and xeric anatomical features respectively. After residual extraction to correct size-related variation, only fibre length and vessel area differed between habitats. Vessel areas in riparian forest differed from those in hilltop forest, but were similar to those in open fields. This result can be explained when vegetation cover and soil are considered together. While open field and hilltop forest have similar soils and lower moisture availability when compared to riparian forest, water demand in open fields is lower, presumably resulting in higher water availability.
This paper describes the morphology and size of perforated ray cells in Bathysa meridionalis Smith & Downs and compares its features with the adjacent ray cells and vessel elements. The perforated ray cells are much bigger and more voluminous than normal ray cells. Their shapes vary from ellipsoid to polygonal. The perforation plates may be solitary to tree per wall, round to reniform. The dimensions of perforated ray cells suggest that they are at least as effective for water flow as axial vessel elements.
This paper describes a simple technique borrowed from paleopalynology to produce increased concentrations of perforated ray cells and to isolate them from fibers and vessel elements. The technique provides very clear slides with only parenchyma cells and perforated ray cells. The perforated ray cells are easily distinguished and occur in frequencies of up to 10 perforated cells per square centimeter. The methods described includes the maceration of wood material, separation of cells with granulometrical sieves and measurements of cell dimensions. After separation of parenchyma cells from vessels and fibers the suspension is concentrated by centrifugation. With these methods, perforated ray cells may be more easily compared among plant groups.
Parasitic plants are capable of causing a variety of effects to their hosts, including alterations in the process of wood formation. However, the majority of studies dealing with parasitic plant anatomy have focused on the host–parasite interface and the direct action of the haustorium, which is the organ responsible for attaching the parasite to the host. Considering this gap, we studied the anatomical and functional effects caused by a mistletoe species, Phoradendron crassifolium (Santalaceae), on the wood anatomy of the host tree Tapirira guianensis (Anacardiaceae). Both parasitized and non-parasitized branches were collected from host trees. Traditional wood anatomy procedures were employed, along with functionality experiments using the ascent of safranin solution through the xylem. Prior to the analysis, all sampled branches were divided in “upstream” and “downstream” portions, considering the direction of xylem sap flow inside the plant body. This design was chosen in order to avoid biased results derived from normal ontogeny-related wood anatomical and functional changes. Our results showed that infested wood expressed a higher density of embolized vessels, narrower vessel lumen diameter, higher vessel density, taller and wider rays, and fibers with thinner cell walls. All these responses were most conspicuous in the downstream sections of the parasitized branches. We propose that the wood anatomical and functional alterations were induced by the combination of water stress caused by water use by the parasite and consequent low turgor in differentiating cambial derivates; by unbalanced auxin/cytokinin concentrations originating at the infestation region due to phloem disruptions caused by the parasite’s penetration and action; and by higher than usual ethylene levels. Further analysis of hydraulic conductivity and hormonal changes in host branches are necessary to test this hypothesis.