OLIVER, MELVIN J.1* and BRENT D. MISHLER2. 1USDA-ARS. Plant Stress and Water Conservation Laboratory, 3810 4th St, Lubbock TX 79415; 2University Herbarium, Jepson Herbarium, and Department of Integrative Biology, University of California, Berkeley, CA 94720. - Desiccation-tolerant pteridophytes: A unique position in the evolution of desiccation tolerance in land plants.
Vegetative desiccation tolerance is a widespread but uncommon
occurrence in plants. The majority of desiccation-tolerant plants are
found in the less complex clades that constitute the algae 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. A phylogenetic look at
vegetative desiccation tolerance reveals that this capability was lost
during the time when tracheophytes first evolved and subsequently “re
evolved” at least twelve separate times in various vascular plant
lineages. The primitive mechanism of vegetative desiccation tolerance
in the first land plants probably involved constitutive cellular
protection coupled with active and inducible cellular repair, similar
to that described for modern-day desiccation-tolerant mosses.
Desiccation-tolerant angiosperms utilize an inducible cellular
protection mechanism of tolerance that appears to derive from the
programmed cellular protection mechanism seen in seeds.
Desiccation-tolerant pteridophytes appear to employ a mechanism of
tolerance that appears to have characteristics of both the primitive
and the more recently evolved mechanisms seen in the angiosperms. Much
of our evidence for this comes from the interpretation of a wealth of
physiological data derived from the ecophysiology of Selaginella
lepidophylla and a few desiccation tolerant ferns such as
Polypodium polypodioides. However, detailed mechanistic studies
have only been attempted using the desiccation-tolerant fern
Polypodium virginianum so much still needs to be accomplished.
Pteridophytes are in a unique position for the study of desiccation
tolerance and its role in the evolution of the land plants and that
with the availability of the modern tools of genomics the time is
right for this area to expand.
Key words: desiccation tolerance, environment, evolution, pteridophytes, stress biology