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Background and Aims Internal root aeration is essential for root growth in waterlogged conditions. Aerenchyma provides a path for oxygen to diffuse to the roots. In most wetland species, including rice, a barrier to radial oxygen loss (ROL) allows more of the oxygen to diffuse to the root tip, enabling root growth into anoxic soil. Most dryland crops, including barley, do not form a root ROL barrier. We previously found that abscisic acid (ABA) signalling is involved in the induction of ROL barrier formation in rice during waterlogging. Although rice typically does not form a tight ROL barrier in roots in aerated conditions, an ROL barrier with suberized exodermis was induced by application of exogenous ABA. Therefore, we hypothesized that ABA application could also trigger root ROL barrier formation with hypodermal suberization in barley. Methods Formation of an ROL barrier was examined in roots in different exogenous ABA concentrations and at different time points using cylindrical electrodes and Methylene Blue staining. Additionally, we evaluated root porosity and observed suberin and lignin modification. Suberin, lignin and Casparian strips in the cell walls were observed by histochemical staining. We also evaluated the permeability of the apoplast to a tracer. Key Results Application of ABA induced suberization and ROL barrier formation in the adventitious roots of barley. The hypodermis also formed lignin-containing Casparian strips and a barrier to the infiltration of an apoplastic tracer (periodic acid). However, ABA application did not affect root porosity. Conclusions Our results show that in artificial conditions, barley can induce the formation of ROL and apoplastic barriers in the outer part of roots if ABA is applied exogenously. The difference in ROL barrier inducibility between barley (an upland species) and rice (a wetland species) might be attributable to differences in ABA signalling in roots in response to waterlogging conditions. [ABSTRACT FROM AUTHOR]

Using epifluorescent and histochemical techniques, we examined anatomical differences in the shoot organs of Typha latifolia, T. angustifolia and T. glauca. The leaf lamina of T. latifolia and T. glauca had enlarged epidermal cells and a thickened cuticle above the subepidermal vascular bundles; that of T. angustifolia lacked these characteristics. Leaf sheaths were similar among the species and all lacked the epidermal thickenings found in the lamina. The fertile stems had typical scattered vascular bundles with a band of fibres that was most prominent in T. glauca. The sterile stems were only 1 cm in length and contained a multiseriate hypodermis and a uniseriate endodermis over part of their length. The rhizomes were similar except for a pronounced band of fibres surrounding the central core in T. angustifolia. The rhizome was also characterized by an outer cortical region with a large multiseriate hypodermis/exodermis and a uniseriate endodermis with Casparian bands, suberin lamellae and secondarily thickened walls. [ABSTRACT FROM PUBLISHER]

The genusEriosyceas circumscribed by Kattermann (Succulent Plant Research1: 1–176, 1994) comprises six subsections with 33 species and 38 heterotypic infraspecific taxa and is restricted in distribution to Chile and NW Argentina. A total of 19 anatomical and gross morphological characters were studied from stem material of 27 taxa ofEriosyceand six outgroup taxa from the generaAustrocactus,Copiapoa,Corryocactus,EulychniaandNeowerdermannia(all from the tribe Notocacteae of subfamily Cactoideae). Comparisons between field-collected and glasshouse-cultivated plant material, as well as comparisons between samples from different positions on the stem, allowed an assessment of the variability of various characters.A detailed cladistic investigation with different character composition and character coding was conducted to check for combinations of characters that support a number of different clades.Eriosycesubsect.Chileosyce(includingE. napinaandE. odieri, but excludingE. laui) andE.subsect.Neoporteriaare very well characterized by a number of the attributes investigated, such as a papillate or completely flat epidermal relief, a very soft and strongly mucilaginous cortex, or a tuberculate stem with the podaria arranged in helical lines. The usefulness of the anatomical and morphological data was examined further by a cladistic analysis of a subgroup of 21 taxa supplemented with data on flowers, fruits and seeds (data from published sources). The present circumscription ofEriosyce(includingHorridocactus,Neoporteria, andThelocephala) is not seriously questioned by these cladistic analyses, with the possible exception ofIslaya. The position ofE. lauiremains unresolved.Copyright 1997 Annals of Botany Company [ABSTRACT FROM AUTHOR]