SEM studies on vessels in ferns. 17. Psilotaceae

Area of Science:

• Plant anatomy
• Vascular plant evolution
• Pteridophyte biology

Background:

• Perforation plates are key features in the xylem of vascular plants, facilitating efficient water transport.
• Psilotaceae, including Psilotum nudum and Tmesipteris obliqua, represent early diverging lineages of vascular plants, making their xylem structure evolutionarily significant.

Purpose of the Study:

• To investigate and characterize the perforation plates in the tracheary elements of Psilotum nudum and Tmesipteris obliqua.
• To compare the perforation plate morphology between aerial and subaerial axes within these species.
• To determine the suitability of light microscopy versus scanning electron microscopy for observing these structures.

Main Methods:

• Specimens of Psilotum nudum and Tmesipteris obliqua were examined using scanning electron microscopy (SEM).
• Light microscopy was also employed for comparative analysis.
• Detailed morphological observations of perforation plates and associated pit structures were conducted.

Main Results:

• Perforation plates were identified in both aerial and subaerial axes of Psilotum nudum and aerial axes of Tmesipteris obliqua.
• Observed perforations in Psilotum included those lacking pit membranes and those with remnants, varying in type within species.
• Tmesipteris exhibited perforations with threadlike or porose pit membranes. Wide perforations alternating with narrow pits were noted in Psilotum subaerial axes.
• Perforations were more prevalent in metaxylem than protoxylem in Psilotum.
• SEM was essential for visualizing porose walls and perforations, as light microscopy revealed no distinguishing secondary wall modifications.

Conclusions:

• The tracheary elements of Psilotaceae share features with other ferns when examined by SEM.
• SEM is indispensable for the detailed study of perforation plates in Psilotum and Tmesipteris.
• The observed variations in perforation plates contribute to understanding water transport mechanisms and xylem evolution in early vascular plants.