Synchronous versus Asynchronous Mitosis within Permanent Pollen Tetrads of the Winteraceae

Abstract

A survey of pollen mitosis within permanent pollen tetrads of the primitive ranalean family Winteraceae revealed that two types of division, synchronous and asynchronous, are present. In the synchronous type, all four pollen grains are at exactly the same stage of division during formation of generative and vegetative (tube) nuclei and comparatively large cytoplasmic connections link the members of a tetrad. In the asynchronous type, all four pollen grains are not at exactly the same stage of nuclear division and cytoplasmic connections are absent between members of a tetrad. Each type is restricted to a particular taxon, but many species of Winteraceae have yet to be examined for this feature. Asynchronous division occurs in Drimys sect. Drimys and Pseudowintera and synchronous division occurs in Belliolum, Bubbia, Exospermum and Zygogynum and probably in Drimys sect. Tasmannia (syn. Tasmannia) too. There is evidence in Pseudowintera that the asynchronous type has evolved from the synchronous. The adaptive significance of the two types is not obvious.

Key Words:

• pollen tetrads
• Winteraceae
• Belliolum
• Bubbia
• Drimys
• Exospermum
• Pseudowintera
• Zygogynum