Palaeontological evidence for membrane fusion between a unit membrane and a half-unit membrane

Abstract

Membrane fusion is of fundamental importance for many biological processes and has been a topic of intensive research in past decades with several models being proposed for it. Fossils had previously not been considered relevant to studies on membrane fusion. But here two different membrane fusion patterns are reported in the same well-preserved fossil plant from the Miocene (15-20 million years old) at Clarkia, Idaho, US. Scanning electron microscope, transmission electron microscope, and traditional studies reveal the vesicles in various states (even transient semi-fusion) of membrane fusion, and thus shed new light on their membrane structure and fusion during exocytoses. The new evidence suggests that vesicles in plant cells may have not only a unit membrane but also a half-unit membrane, and that a previously overlooked membrane fusion pattern exists in plant cells. This unexpected result from an unexpected material not only marks the first evidence of on-going physiological activities in fossil plants, but also raises questions on membrane fusion in recent plants.

A Flower Bud from the Lower Cretaceous of China

“…However, as palaeontology has developed, exceptions to this rule have frequently occurred. For example, reproductive organs of angiosperms (flowers) have been documented in the Yixian Formation [ 3 , 4 , 5 , 6 , 9 , 69 ], cellular ultrastructures and chloroplasts have been seen in Eocene Metasequoia [ 70 ], and even exocytosis snapshots have been observed in a Miocene conifer [ 71 , 72 ]. These exceptions remind us that, theoretically, fragile parts of plants can also be preserved in fossils.…”

Preserved cytoplasm in charred Agathoxylon-type wood from the Permian of Brazilian Paraná Basin

“…Small fragments were sampled with the aid of dissecting needles, mounted on standard stubs with double-sided tape, gold coated, and subsequently examined and photographed with an Inspect F50 FEI field emission gunscanning electron microscope (FEG-SEM). The chemical composition of cell walls and contents was analyzed using energy dispersive spectroscopy (EDS) according to Wang et al (2007). However, since the macroscopic charcoal was included in coal and considering its extremely soft and brittle nature, the samples were not chemically cleansed with acids (HCl, HF).…”