OBSERVACIONES SOBRE HISTOLOGIA CAULINAR EN DIOSCOREA MULTIFLORA (DIOSCOREACEAE)

• Published in: Darwiniana 1990-01, Vol.30 (1/4), p.11-19
• Main Author: XIFREDA, CECILIA CARMEN
• Format: Article
• Language: Spanish
• ISSN: 0011-6793; 1850-1699

Observations on the caulinar histology in Dioscorea multiflora (Dioscoreaceae). Dioscorea multiflora Griseb. is a shrubby dioecious vine with vigorous multiannual monopodial shoots. A SEM and optic microscopic study on certain aspects of the caulinar histology and the cellular composition of the xylem is presented. Epidermal glandular trichomes, actinocytic stomata and endodermis in the form of a cristalliferous sheath, are the most important anatomical characters in the cortex. Note-worthy cellular elements in the vascular system are: long and wide metaxylematic vessels, with simple circular pits, scalariform-reticulate perforation plates with 24-64 bars and lignified tertiary helical wall sculpture - cited for the first time in Dioscorea - vasicentric tracheids in axial series around the vessels, with thickening bands interconnected by strands or second order framework; fiber-tracheids in the intervessel tissue and libriform fibers, commonly septate, in the nodal sourroundings. At the nodes, xylem glomeruli consist of tracheary tortuous elements: the vessels are composed of whether simple or irregular, dichotomized branched and anastomosed elements, with terminal or intercalary simple perforation plates; also multiperforated, foraminate plates occur. Nevertheless the bulk of the tissue is formed by irregularly interwoven tracheids with circular bordered pits located in the tracheid walls outside an inner reticulate layer, with the inner circular pit aperture between the bars of this reticulum. Also are present immature tracheid elements in cellular series, with the characteristically lignified walls of biphasic deposition. The present data on the structure of certain xylem elements might suggest a phylogenetical relation with ferns. A functional interpretation of several sylem features could be performed: starch rich parenchyma of the medullary rays, parenchyma distribution in the sourroundings of tracheid-sheathed vessels (mechanical flexibility), unusually wide vessels (efficiency), vascular and vasicentric tracheids (safety), helical sculpture in vessels (mechanic support) and phloem disposition in separated strands (tissue regeneration); all of them suggest similar functional features already reviewed in woody dicotyledoneous vines and lianas. The caulinar histology of Dioscorea, clasically referred as unique in monocotyledons, could be interpreted as an adaptative shift related to the biological form.