Tracheid
Atracheidis a long and taperedlignifiedcell in thexylemofvascular plants.It is a type of conductive cell called a tracheary element.Angiospermsuse another type of conductive cell, calledvessel elements,to transport water through the xylem. The main functions of tracheid cells are totransport water and inorganic salts,and to provide structural support for trees. There are oftenpitson thecell wallsof tracheids, which allows for water flow between cells. Tracheids are dead at functional maturity and do not have aprotoplast.Thewood(softwood) ofgymnospermssuch as pines and otherconifersis mainly composed of tracheids.[1]Tracheids are also the main conductive cells in the primary xylem offerns.[2]
The tracheid was first named by the German botanist Carl Gustav Sanio in 1863, from the GermanTracheide.[3]
Evolution
[edit]Tracheids were the main conductive cells found in early vascular plants.
In the first 140-150 million years of vascular plant evolution, tracheids were the only type of conductive cells found in fossils of plant xylem tissues.[4]Ancestral tracheids did not contribute significantly to structural support, as can be seen in extant ferns.[5]
Thefossilrecord shows three different types of tracheid cells found in early plants, which were classified as S-type, G-type and P-type. The first two of them were lignified and had pores to facilitate the transportation of water between cells. The P-type tracheid cells had pits similar to extant plant tracheids. Later, more complex pits appeared, such as bordered pits on many tracheids, which allowed plants to transport water between cells while reducing the risk of cavitation and embolisms in the xylem.
As tracheids evolved along with secondary xylem tissues, specialized inter-tracheid pits appeared.[2]Tracheid length and diameter also increased, with tracheid diameter increasing to an average length of 80 μm by the end of theDevonianperiod.[6]
Tracheids then evolved into the vessel elements and structural fibers that make up angiosperm wood.[2]
References
[edit]- ^Cuny, Henri E.; Rathgeber, Cyrille B. K.; Frank, David; Fonti, Patrick; Fournier, Meriem (2014)."Kinetics of tracheid development explain conifer tree-ring structure".New Phytologist.203(4): 1231–1241.doi:10.1111/nph.12871.ISSN1469-8137.PMID24890661.S2CID22862428.
- ^abcPittermann, Jarmila; Limm, Emily; Rico, Christopher; Christman, Mairgareth A. (2011)."Structure–function constraints of tracheid-based xylem: a comparison of conifers and ferns".New Phytologist.192(2): 449–461.doi:10.1111/j.1469-8137.2011.03817.x.ISSN1469-8137.PMID21749396.
- ^Sanio, C. (1863). "Vergleichende Untersuchungen über die Elementarorgane des Holzkörpers".Bot. Zeitung.21:85–91, 93–98, 101–111.ISSN2509-5420.
- ^Sperry, John S. (2003-05-01)."Evolution of Water Transport and Xylem Structure".International Journal of Plant Sciences.164(S3): S115–S127.doi:10.1086/368398.ISSN1058-5893.S2CID15314720.
- ^Sperry, John S.; Hacke, Uwe G.; Pittermann, Jarmila (2006)."Size and function in conifer tracheids and angiosperm vessels".American Journal of Botany.93(10): 1490–1500.doi:10.3732/ajb.93.10.1490.ISSN1537-2197.PMID21642096.
- ^Niklas, Karl J. (September 1985)."The Evolution of Tracheid Diameter in Early Vascular Plants and ITS Implications on the Hydraulic Conductance of the Primary Xylem Strand".Evolution; International Journal of Organic Evolution.39(5): 1110–1122.doi:10.1111/j.1558-5646.1985.tb00451.x.ISSN1558-5646.PMID28561493.S2CID13045808.
Further reading
[edit]- Wilson, K.; White, D. J. B. (1986).The Anatomy of Wood: Its Diversity and Variability.London: Stobart & Son Ltd.ISBN0-85442-033-9.
External links
[edit]
- Pictures of softwood tracheidsin cross sectionandin maceration;both in pine.
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