Pollen-wall formation in Arum alpinum

Area of Science:

• Plant reproductive biology
• Palynology
• Cell biology

Background:

• Arum alpinum exhibits an unusual pollen wall lacking a sporopolleninous ektexine.
• The outermost pollen layer consists of endexine covered by polysaccharide ornamentation.
• Pollen wall development, particularly the role of callose, requires clarification.

Purpose of the Study:

• To investigate the ontogeny of the Arum alpinum pollen wall.
• To specifically examine the role of callose during microspore development and release.
• To understand the formation of polysaccharide ornamentation on the pollen surface.

Main Methods:

• Collection of Arum alpinum plants from their natural habitat throughout the vegetative period.
• Processing of plant samples for semi-thin and ultra-thin sectioning.
• Microscopic analysis of pollen development stages.

Main Results:

• Callose was notably absent at all stages of pollen wall formation.
• Microspore separation from the tetrad occurred via invagination of the amoeboid tapetum.
• The tapetum was identified as the source of the polysaccharide wall ornamentations.

Conclusions:

• The dogma that callose is essential for microspore separation and release is refuted.
• Absence of callose does not impair fertility in Arum alpinum.
• The lack of callose is a potential reason for the unique pollen wall structure, including the missing sporopolleninous ektexine.