Land Plant Evolution: Phylogenetics and Beyond
Oliver, Melvin J. , Mishler, Brent D. .
Desiccation-tolerance: A case study of physiological trends in the evolution of Land Plants.
IT appears clear that the evolution of the ability of a cell to survive air-dryness, where the cytoplasm dries to equilibrium with the surrounding atmosphere, was an important and crucial step in the colonization of the land by primitive plants. The ability to survive air dryness, or desiccation tolerance, is a common feature of at least some cells of all plants, in particular pollen and seeds. Vegetative desiccation tolerance, on the other hand, is an uncommon occurrence in land plants. The majority of desiccation-tolerant plants are found in the less complex clades that constitute the bryophytes. Within the vascular land plants there are 120-130 species that exhibit some degree of vegetative desiccation tolerance. We consider the evidence for the mechanisms of desiccation tolerance in different plants, including differences in cellular protection and repair, and examine this evidence within a phylogenetic-framework. By understanding the trends in the physiological and molecular aspects of desiccation tolerance in different cell types and plants over time we can construct a working hypothesis as to the evolution of desiccation tolerance and its influence on the evolution of land plants in general. Our hypothesis starts with the assumption that desiccation tolerance first evolved in spores of primitive plants as a mechanism of ensuring species survival in ephemeral water sources. Given what we know of tolerance mechanisms it is likely that the mechanism employed by spores was (and is now) based on a developmentally programmed cellular protection mechanism. Physiological and mechanistic studies have enabled us to propose a likely evolutionary path for desiccation tolerance from the establishment of vegetative desiccation tolerance in primitive species, through the loss of vegetative tolerance during tracheophyte evolution, the establishment of tolerance in seeds, and the re-appearance of vegetative tolerance in Selaginella, ferns and the more modern occurrences in the angiosperms.
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1 - University of Missouri, USDA-ARS-MWA, Plant Genetics, 204 Curtis Hall, Columbia, Missouri, 65211, USA
2 - University of California, Berkeley, Department of Integrative Biology, 1001 Valley Life Sciences Bldg. #2465, Berkeley, California, 94720-2465, USA
Presentation Type: Symposium or Colloquium Presentation
Date: Monday, July 31st, 2006
Time: 4:15 PM