Studies on Pollen Morphology and Exine Ultrastructure in Cephalotaxaceae

Abstract

Abstract:

The pollen morphology of Cephalotaxaceae was examined with LM,

SEM and TEM. Pollen grains in this family are spheroidal or subspheroidal,

rounded in polar view, but usually wrinkled with irregular shape. Pollen size is

22.6- 34.8 μm in diameter. There is a distinct or indistinct tenuity on distal face.

The tenuity occasionally slightly rises above the outline of pollen grains, but often

sukened. Exine rather thin, 1—1.5μm thick, layers obscure, surface of pollen

grains is nearly psilate or weakly granulate. Under SEM exine is covered with

fine and dense granules, and sparse Ubisch bodies are found on the granular lay-

er. The Ubisch bodies are provided with minute gemmate processes on the surface.

Acorrding to our observation under TEM, exine consists of ectexine and lamellate

endexine, with the former divided into outer ectexine of granules densely arranged

and inner ectexine of loosely arranged microgranules. Granules of the outer

ectexine are relatively thick, and connected with each other, forming a structure

just like tectum or separate from each other. Microgranules of the inner ectexine

are distinct or indistinct. Endexine is provided with 5- 7 lamellae.

As far as information of pollen morphology is concerned, Cephalotaxus oliveri

is rather special in the Cephalotaxaceae. First, the tenuity in pollen grains occu-

pies one half of the distal part, much larger than that of the other species in the

family. Second, the ectexine in Cephalotaxus oliveri may be divided into two dis-

tinct layers, outer ectexine and inner ectexine. The former is made of a layer of

sporopollenin masses, which are connected with each other to form tectumlike

structure, while the latter consists of a layer of loosely arranged granules or small

segments of sporopollenin. The inner ectexine is different from that of other species

by having a thicker layer of sporopollenin granules. Based on these two features,

we support the division of Cephalotaxus into two Sections, Sect. Pectinatae and

Sect. Cephalotaxus.

Pollen grains of Cephalotaxaceae are similar to those of the Taxaceae in

having spheroidal shape and the tenuity on its distal face. These characteristics

strengthen the evidence for a close relationship between the Cephalotaxaceae and

Taxaceae. Although pollen grains of the Cephalotaxaceae and Taxaceae are similar

in some characteristics, they have obvious differences in , for example, size of

tenuity, the fine structure of Ulbisch bodies and of the outer and inner ectexine.

On the basis of pollen morphology, the present author considers the

Cephalotaxaceae slightly more primitive than the Taxaceae.

Key words: Cephalotaxaceae, Ultrastructure, Pollen morphology, Cephalotaxus oliveri

Xi Yi-zhen. Studies on Pollen Morphology and Exine Ultrastructure in Cephalotaxaceae[J]. .

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Studies on Pollen Morphology and Exine Ultrastructure in Cephalotaxaceae

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