Submitted to: American Association for the Advancement of Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2001
Publication Date: N/A
Technical Abstract: Vegetative desiccation tolerance is a widespread but uncommon occurrence in the plant kingdom. The majority of desiccation-tolerant plants are found in the less complex clades that constitute the algae, lichens and bryophytes. However, within the larger and more complex groups of vascular land plants there are some 120-130 species that exhibit some degree of vegetative desiccation tolerance. By considering the evidence for the mechanisms of desiccation tolerance in different plants, including differences in cellular protection and repair, and coupling this evidence with a phylogenetic framework, a working hypothesis as to the evolution of desiccation tolerance in land plants can be generated. We hypothesize that the initial evolution of vegetative desiccation tolerance was a crucial step in the colonization of the land by primitive plants from an origin in fresh water. The primitive mechanism of involved constitutive cellular protection coupled with active cellular repair. As plant species evolved, vegetative desiccation tolerance was lost as increased growth rates, morphological complexity, and mechanisms that conserve water and increase the efficiency of photosynthesis were selected. We thus suggest that the mechanism of desiccation tolerance exhibited in seeds, a developmentally induced cellular protection system, evolved from the primitive form of vegetative desiccation tolerance. Once established in seeds, this system became available for induction in vegetative tissues by environmental cues related to drying. Thus the more recent inducible protection mechanisms in desiccation-tolerant angiosperms evolved from that programmed into seeds as species spread into very arid environments.