Polarity, aperture condition and germination in pollen grains ofEphedra (Gnetales)

El‐Ghazaly, Gamal; Rowley, John R.; Hesse, Michael

doi:10.1007/bf00985202

Cited by 33 publications

(40 citation statements)

References 27 publications

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“…Maceration of the seeds revealed shed, upcurled exines inside the integument (Fig. 1E), matching completely the unusual shed exines of extant Ephedra (16). The shed exines indicate that the pollen grains had germinated in the ovule, leaving the male gametophyte naked in the same peculiar way described for extant Ephedra (16).…”

Section: Resultssupporting

confidence: 62%

“…Pollen grains are distinct, with longitudinal ridges and valleys (polyplicate), due to alternation of thicker and thinner exine regions. During germination, the exine is shed, leaving the male gametophyte naked (16), and the shed exine curls up in a characteristic way, resulting in transverse striations (16). Dispersed polyplicate pollen, similar to that of Ephedra and Welwitschia, occurs in sediments ranging back to the Permian, Ͼ250 Myr (17), and is particularly common in the Early Cretaceous (18), but their presumed affinity to the Gnetales has rarely been confirmed.…”

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confidence: 99%

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On the evolutionary history of Ephedra: Cretaceous fossils and extant molecules

Rydin

Pedersen

Friis

2004

Proc. Natl. Acad. Sci. U.S.A.

156

153

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Gnetales comprise three unusual genera of seed plants, Ephedra, Gnetum, and Welwitschia. Their extraordinary morphological diversity suggests that they are survivors of an ancient, more diverse group. Gnetalean antiquity is also supported by fossil data. Dispersed ''ephedroid'' (polyplicate) pollen first appeared in the Permian >250 million years ago (Myr), and a few megafossils document the presence of gnetalean features in the early Cretaceous. The Cretaceous welwitschioid seedling Cratonia cotyledon dates the split between Gnetum and Welwitschia to before 110 Myr. Ages and character evolution of modern diversity are, however, controversial, and, based on molecular data, it has recently been suggested that Ephedra is very young, only 8 -32 Myr. Here, we present data on the evolutionary history of Ephedra. Fossil seeds from Buarcos, Portugal, unequivocally link one type of Cretaceous polyplicate pollen to Ephedra and document that plants with unique characters, including the peculiar naked male gametophyte, were established already in the Early Cretaceous. Clades in our molecular phylogeny of extant species correspond to geographical regions, with African species in a basal grade͞clade. The study demonstrates extremely low divergence in both molecular and morphological characters in Ephedra. Features observed in the fossils are present in all major extant clades, showing that modern species have retained unique reproductive characters for >110 million years. A recent origin of modern species of Ephedra would imply that the Cretaceous Ephedra fossils discussed here were members of widespread, now extinct sister lineage(s), and that no morphological innovations characterized the second diversification. molecular phylogeny ͉ fossil record ͉ Gnetales ͉ molecular dating

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Section: Resultssupporting

confidence: 62%

mentioning

confidence: 99%

On the evolutionary history of Ephedra: Cretaceous fossils and extant molecules

Rydin

Pedersen

Friis

2004

Proc. Natl. Acad. Sci. U.S.A.

156

153

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“…But Ephedra pollen tube growth rates are similar to other gymnosperms. I calculated in vivo rates of 14 m/h in E. distachya and 6-19 m/h in E. trifurca (Table S2); in vitro rates of 4 m/h are reported for other Ephedra species (22). Ephedra pollen germinates directly on the surface of the female gametophyte and a narrow pollen tube must grow only a short distance (60-230 m) to the egg within a pathway entirely composed of archegonial neck cells of the female gametophyte (14,15).…”

Section: Developmental Origins Of Rapid Fertilization Syndromes In Sementioning

confidence: 99%

Novelties of the flowering plant pollen tube underlie diversification of a key life history stage

Williams

2008

Proc. Natl. Acad. Sci. U.S.A.

131

155

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The origin and rapid diversification of flowering plants has puzzled evolutionary biologists, dating back to Charles Darwin. Since that time a number of key life history and morphological traits have been proposed as developmental correlates of the extraordinary diversity and ecological success of angiosperms. Here, I identify several innovations that were fundamental to the evolutionary lability of angiosperm reproduction, and hence to their diversification. In gymnosperms pollen reception must be near the egg largely because sperm swim or are transported by pollen tubes that grow at very slow rates (< Ϸ20 m/h). In contrast, pollen tube growth rates of taxa in ancient angiosperm lineages (Amborella, Nuphar, and Austrobaileya) range from Ϸ80 to 600 m/h. Comparative analyses point to accelerated pollen tube growth rate as a critical innovation that preceded the origin of the true closed carpel, long styles, multiseeded ovaries, and, in monocots and eudicots, much faster pollen tube growth rates. Ancient angiosperm pollen tubes all have callosic walls and callose plugs (in contrast, no gymnosperms have these features). The early association of the callose-walled growth pattern with accelerated pollen tube growth rate underlies a striking repeated pattern of faster and longer-distance pollen tube growth often within solid pathways in phylogenetically derived angiosperms. Pollen tube innovations are a key component of the spectacular diversification of carpel (flower and fruit) form and reproductive cycles in flowering plants.heterochrony ͉ key innovation ͉ modularity ͉ origin of angiosperms ͉ evo-devo

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“…Isolation and cytological studies of viable de-exined pollen have been performed in angiosperms, including Nicotiana tabacum (Xia et al, 1996), Brassica (Xu et al, 1996(Xu et al, , 1997, and Lilium longiflorum (Loewus et al, 1985). In gymnosperms, exine detaches from the intine of some genera including Taxus (Duhoux, 1982) and Ephedra (El-Ghazaly et al, 1998) when pollen is hydrated and the protoplasts and intine swell, as it occurs in the pollination drop. However, this does not happen to the exine of Pinus and Picea taxa, like Pinus bungeana and Picea wilsonii.…”

Section: Introductionmentioning

confidence: 98%