Aerial stem and leaf-scale anatomy of Monotropa uniflora L. -- a descriptive study

Abstract

Light microscopic investigation of the aerial stem and leaf-scale anatomy of heterotrophic Monotropa uniflora L. confirmed major clues supportive of a probable photosynthetic ancestor. Observation and measurement of callose plug diameters indicated uniformity in pore size between those found on the lateral cell walls and those located on the end walls. There was evidence for a possible intercellular connection between a sieve tube member and its associated parenchyma cell even though companion cells have not been described for Monotropa uniflora L. by earlier researchers. The presence of sieve tube member nuclei and P-protein were not indicated. These structural features approach those reported earlier for lower vascular plants. Sieve tube member occurrence decreased acropetally culminating in total absence of detectable sieve elements in the leaf-scales. This does not coincide with phloem distributional patterns described for photosynthetic vascular plants. The reduction of sieve element specialization and characteristic distribution were probably brought about by the evolutionary loss of photosynthetic capability.