Paleozoic seeds with embryos

Organization, anatomy, and fungal endophytes of a Triassic conifer embryo

PREMISE OF THE STUDY

Much is known about the Paleozoic conifers and the conifers assignable to extant families that appear in the Jurassic; however, relatively little is known about the transitional conifers of the early Mesozoic, especially the Voltziales. To better understand the evolution of this group, we aim to increase knowledge of voltzialean anatomy and morphology. A fossil embryo of the group is described in this study. •

METHODS

Several permineralized seeds, one containing a well-preserved embryo, were collected from the early Middle Triassic Fremouw Peak locality in the Central Transantarctic Mountains. Samples were prepared using the standard acetate peel technique and studied in transmitted light. •

KEY RESULTS

The embryo belongs to Parasciadopitys aequata, a member of the Voltziales. The embryo and megagametophyte tissues are exquisitely preserved. The embryo is colonized by two distinct fungi. Sporocarps of the fungi are found in the megagametophyte and in the space between the megagametophyte and nucellus. The additions of embryo and megagametophyte characters to the description of P. aequata have made it one of the most completely known fossil taxa reproductively. •

CONCLUSIONS

Preservation of fossil embryos, although rare, can expand the array of characters available in tracing the evolutionary history of plants. The embryo of P. aequata shares similarities with embryos of other extinct and extant conifer families. The association of the embryo with Combresomyces cornifer and Mycocarpon asterineum increases our understanding of the roles of microorganisms in Triassic ecosystems.

The evolution of embryo size in angiosperms and other seed plants: implications for the evolution of seed dormancy

Seed dormancy plays an important role in germination ecology and seed plant evolution. Morphological seed dormancy is caused by an underdeveloped embryo that must mature prior to germination. It has been suggested that the presence of an underdeveloped embryo is plesiomorphic among seed plants and that parallel directional change in embryo morphology has occurred separately in gymnosperms and in angiosperms. We test these hypotheses using original data on embryo morphology of key basal taxa, a published dataset, and the generalized least squares (GLS) method of ancestral character state reconstruction. Reconstructions for embryo to seed ratio (E:S) using family means for 179 families showed that E:S has increased between the ancestral angiosperm and almost all extant angiosperm taxa. Species in the rosid clade have particularly large embryos relative to the angiosperm ancestor. Results for the gymnosperms show a similar but smaller increase. There were no statistically significant differences in E:S between basal taxa and any derived group due to extremely large standard errors produced by GLS models. However, differences between reconstructed values for the angiosperm ancestor and more highly nested nodes are large and these results are robust to topological and branch-length manipulations. Our analysis supports the idea that the underdeveloped embryo is primitive among seed plants and that there has been a directional change in E:S within both angiosperms and gymnosperms. Our analysis suggests that dormancy enforced by an underdeveloped embryo is plesiomorphic among angiosperms and that nondormancy and other dormancy types probably evolved within the angiosperms. The shift in E:S was likely a heterochronic change, and has important implications for the life history of seed plants.

Morphine-like peptides in mammalian brain: isolation, structure elucidation, and interactions with the opiate receptor

A substance that competes for opiate receptor binding has been isolated from calf brain and identified as two pentapeptides, H-Tyr-Gly-Gly-Phe-Met-OH (methionine enkephalin) and H-Tyr-Gly-Gly-Phe-Leu-OH (leucine enkephalin), with about four times more leucine enkephalin than methionine enkephalin. Sodium and manganese effects on opiate receptor interactions show that both peptides are agonists, whereas leucine enkephalin may be a "purer" agonist than methionine enkephalin.