Mode of pollen tube growth in pistils ofTicodendron incognitum(Ticodendraceae, Fagales) and the evolution of chalazogamy

Abstract

Ticodendron incognitum is the sole species of the Ticodendraceae, which was established as a new family in the Fagales less than 20 years ago. Considering the diverse modes of pollen tube growth observed in other Fagales, we investigated the growth of pollen tubes in the pistil of Ticodendron. At the time of pollination, T. incognitum had four immature ovules in a bilocular ovary, thus exhibiting delayed fertilization, as in other Fagales. During the period when fertilization was delayed, pollen tube growth in the pistil was intermittent, consisting of five steps associated with development of the ovules and embryo sacs. Four cessation sites occurred: in the style, in the tissue of the upper part of the ovary, inside and outside of the funicle and at the chalaza. A single pollen tube eventually reaches a mature embryo sac through the chalaza in one of the four ovules. While both delayed fertilization and intermittent pollen tube growth play a role in male and female gametophyte selection, as in other Fagales, the five‐step process of pollen tube growth through the chalaza (i.e. chalazogamy) is characteristic of lineages of the Casuarinaceae, Ticodendraceae and Betulaceae (the latter with the loss of one step). © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157, 621–631.

First Come, First Served: Delayed Fertilization Does Not Enhance Pollen Competition in a Wind-Pollinated Tree,Fraxinus excelsiorL. (Oleaceae)

“…In addition, the number of pollen tubes that can enter the transmitting tract is limited and the growth of consecutive tubes slows down, possibly because of a chemical interaction or as a result of depleted maternal resources. Several authors noticed that starch grains vanish in the cells of the style as pollen tubes pass by (Herrero and Arbeloa 1989; Sogo and Tobe 2005). The loss of directional growth at the base of the style and in the funiculus is most likely caused by the lack of guidance signals from the immature ovules (see, e.g., Wang et al 2008).…”

“…It has been proposed that by delaying fertilization females increase male gametophyte competition, thereby providing an opportunity for pollen from distant sources to arrive. This gives a ''fair start'' for pollen tubes growing from late-coming pollen (Willson and Burley 1983;Dahl and Fredrikson 1996;Sogo andTobe 2006, 2008). In many species ovules are not mature at the moment of pollination, having no or only partly differentiated integuments.…”

“…In these species fertilization does not take place immediately but occurs 4 d to as much as 1 yr after pollination (reviewed by Sogo and Tobe 2006). It has been proposed that by delaying fertilization females increase male gametophyte competition, thereby providing an opportunity for pollen from distant sources to arrive.…”

“…The pollen tubes proceed to grow through the style, but their growth is soon arrested or obstructed, causing thickening or branching of the tube tips. In species with long-term delays, alternate periods of growth cessation and resumption can occur in association with megagametophyte development (Sogo and Tobe 2006).…”

Self-sterility in the mutant ‘Zigui shatian’ pummelo (Citrus grandis Osbeck) is due to abnormal post-zygotic embryo development and not self-incompatibility

“…Samples were immersed in fixing solution of 1:3:1 of chloroform: 95% ethanol: glacial acetic acid (v/v/v) for 24 h, then transferred into 70% ethanol, and stored at 4°C until use. The styles were first washed thoroughly under running tap water, and then incubated in 8 N NaOH for 24 h to soften the tissues, and finally soaked in 0.1% aniline blue solution for 5 h. The fixed ovaries were embedded in wax and sectioned at 10 lm with a rotary microtome, and the sections were stained with aniline blue solution (Sogo and Tobe 2008). Pollen tubes were observed by an ultraviolet fluorescence microscope (BX UCB; Olympus, Tokyo, Japan).…”