Structure And Development Of The Lateral-Line Aerenchyma In Bracken Ferns (Pteridium: Dennstaedtiaceae)

Premise of research. Bracken ferns have a worldwide distribution. Plants consist of aerial fronds with petioles (stipes) that extend underground to specialized subterranean stems (rhizomes). A narrow continuous surface strip of specialized aerenchyma on each side of rhizomes and stipes, referred to as the lateral line, forms a pathway for gases. Developmental changes in the lateral line appear to affect gas exchange and influence water relations, soil exploitation, dormant survival, and disease resistance in these plants. An integrated account of the ontogeny and cytochemistry of the lateral line in the rhizomes and stipes of Pteridium has not been published.Methodology. LM with fluorescence cytochemistry, supported by SEM, was used to compare developmental changes in tissues of the lateral-line aerenchyma in the stipes (petioles) and rhizomes (stems) of representative bracken taxa.Pivotal results. The lateral lines of the rhizome and stipe in Pteridium aquilinum and Pteridium esculentum are a continuous organ. Developmental changes in the lateral lines of stipe and rhizome are similar. Cell walls of the closed lateral line but not the rind of the mature rhizome and the stipe belowground are rich in tannins. Intercellular protuberances extending from the walls of parenchyma cells below the lateral lines are primarily composed of pectin and polyphenols and contain tannin only late in development. Stomata of the lateral lines of the stipe above ground remain functional until frond senescence.Conclusions. The lateral-line aerophores in the stipe and rhizome of bracken ferns are continuous, with similar anatomy, development, and likely roles in aeration and resistance to waterlogging.