Ephedra pollination and other gnetalean oddities
Little, Stefan , Groot, Edwin , Christianson, Michael , Jernstedt, Judy .
Ephedra monosperma, a potential model organism for studies of development and evolution in Gnetales and gymnosperms.
Our recent research focuses on vegetative development among extant gymnosperms to improve understanding of morphological evolution in seed plants. Model organisms are selected for economic importance or biological traits such as small genomes, annual life cycles, and small stature with weedy growth. Such biological traits are typically lacking in gymnosperms. We suggest that Ephedra monosperma represents a good gymnosperm model organism. Ephedra is the first diverging lineage in Gnetales, and several species are sub-shrubs, with relatively rapid growth compared to other Gnetales and other gymnosperms. We have been propagating E. monosperma for several years in greenhouse conditions. Underground rhizomes produce fine roots at internodes allowing for vegetative propagation. Our greenhouse population of plants produces two flushes of seed cones around the time of each Equinox, although the majority of seed cones are produced in the spring. In this clonal population, a small percentage of pollen cones are produced. This pollen was applied to several pollination droplets in April 2011, and viable seed was produced by July 2011. Further, if the bracteoles and integument are removed to expose the megagametophyte, germination occurs within hours of placement in moist conditions. Over 10 weeks, we measured successive internodes, of both primary (arising from the rhizome) and their secondary shoots, to determine if they meet the assumptions of the plastochron index. Primary shoots produce up to 15 internodes, whereas secondary shoots produce fewer internodes (typically 8-11). The log-linear portions of the growth curves for each internode were tested for uniformity in relative growth rates (RGR, slopes) and plastochron (time between successive curves). Internodes 2-12 of primary shoots and 2-10 of secondary shoots meet the assumptions of the plastochron index: early internode growth is exponential, constant plastochron (4 days), and early RGR for internodes is the same (0.4 d-1). Therefore, we can use simple caliper measurements of internode length to determine high-resolution developmental stages throughout the cycle of leaf initiation in E. monosperma. This allows us to test developmental hypotheses regarding the organization and cell-division dynamics of the shoot apical meristem, incorporating the timing of leaf primordium initiation. Shoot growth in other gymnosperms has not been shown to statistically meet the assumptions of the plastochron. Thus, Ephedra monosperma, being a small, self-fertile, sub-shrub that can be vegetatively propagated and which meets the assumptions of regular plastochron growth, provides a possible model plant to study evolution and development among gymnosperms.
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1 - University Of California, Davis, Mail Stop 1, One Shields Avenue, Davis, CA, 95616, USA
2 - University of Freiburg, Institute of Biology III, Schaenzlestr. 1, Freiburg, 79104, Germany
3 - 1004 SANCHEZ ST, San Francisco, CA, 94114, USA
4 - University Of California Davis, Department Of Plant Sciences, Davis, CA, 95616-8515, USA, 530/752-7166
Presentation Type: Symposium or Colloquium Presentation
Location: Delaware A/Hyatt
Date: Monday, July 9th, 2012
Time: 11:00 AM