Ontogeny of pollen grains inZingiber spectabile(Zingiberaceae)

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Abstract
The aim of the present study was to describe the ontogeny of the pollen wall in Zingiber in order to provide a basis for understanding the usefulness of mature pollen in assessing the broader phylogenetic relationship within the Zingiberales. Inflorescences of Zingiber spectabile Griff, were processed for light and transmission electron microscopy. The study revealed that Zingiber microspores developed a thick primexine whereas the mature pollen exhibited an extremely thin and discontinuous exine. The development of a channelled intine was initiated after the disintegration of the callose wall, when the microspores had entered the free stage. It reached its maximum thickness in the late microspore period, after which it decreased in thickness. Furthermore, a thin inner intine was found and an electron dense material appeared in the channels of the outer intine. Thus the general pattern of sporoderm development is similar to that observed in the other members of the Zingiberales. A comparison of Zingiber spectabile with members of other genera of the Zingiberales shows diversity in the development of the primexine. It is suggested that the stratified primexine in Strelitzia and Heliconia is primitive for Zingiberales, while its development has been reduced in Zingiber. In Canna the development of the primexine is further reduced and it is limited to isolated spinules on the microspore surface.