• Biochemistry of diatom photosynthetic membranes and pigment-protein complexes

      Martinson, Tracey Ann; Plumley, F. Gerald (1996)
      Diatoms are an ecologically important group of algae in both marine and freshwater systems, but in spite of their significance little is known about the structure of their photosynthetic apparatus. This is due in part to the lack of a highly purified, oxygen-evolving thylakoid membrane preparation. Since thylakoid membranes purified from diatoms using methods developed for green plants did not evolve oxygen, a new procedure was developed for use with diatoms. An oxygen-evolving thylakoid membrane preparation is crucial for the study of photosynthetic pigment-protein complexes from these algae because the stability of the Photosystem I (PS I) and Photosystem II reaction centers was shown to be greatly reduced in thylakoid preparations that did not retain electron transport activity. As a result of the instability of PS I in some thylakoid preparations, a novel chlorophyll-binding complex was isolated that contained only the PsaA polypeptide. The isolation of this complex should prove useful in elucidating the structure of the PS I reaction center in all plants. Immunological and N-terminal protein sequencing methods were used to identify several photosynthetic proteins in the purified thylakoid preparation. These results provided evidence for posttranslational modification of two light-harvesting polypeptides (LHCPs) as well as of the PsaB subunit of the PS I reaction center core. Posttranslational modification of LHCPs and/or of PsaB has not been observed in green plants. In contrast to green plants, PS I in diatoms has been shown to be located in the inner thylakoid membranes. It was hypothesized that proteolytic processing of the C-terminus of PsaB in diatoms may be necessary for the PS I holocomplex to be present in the inner membranes, and that this processing may be responsible for the instability of PS I in purified diatom thylakoids. The existence of a functional, highly purified, and extensively characterized thylakoid preparation from diatoms will promote our understanding of the photosynthetic apparatus in these algae.
    • Establishment of native plants on disturbed sites in arctic Alaska

      Cargill, Susan Marjorie; Chapin, F. Stuart III (1988)
      Roads, camps and other structures associated with the Trans-Alaska Pipeline were placed on gravel pads to protect underlying permafrost. Gravel was mined from floodplains, resulting in loss of riparian wildlife habitat. Revegetation of abandoned pads using non-native grasses has been unsuccessful. Native plants might be more persistent and contribute to replacing lost habitat. The naturally-occurring pioneer community on gravel pads consists mainly of willows Salix alaxensis and S. glauca, fireweed Epilobium latifolium, horsetails Equisetum arvense and legumes in the genera Astragalus, Oxytropis and Hedysarum, all species of riparian gravel bars. Ten years after abandonment mean total cover of native species on 16 gravel pads was only 2.7% and mean number of species per site was 4.4. Distance from riparian seed sources explained 25% and 40% of variation in cover and diversity respectively. Legumes were more restricted to sites near the river than were fireweed and willows. In the laboratory, no germination of S. alaxensis occurred at water potentials $< -0.2$ MPa, which probably occur often on gravel pads. In the field, germination was increased by watering or by a rough surface which provided moister microsites. Growth of seedlings was limited by the supply of mineral nutrients. Survival was high and not limited by availability of water or nutrients. In the laboratory, few legume seeds germinated at water potentials $< -0.5$ MPa. In the field, germination was higher on a rough surface which provided moister microsites. Greenhouse experiments indicated that symbiotically-fixed nitrogen contributed significantly to the growth of legume seedlings, especially when availability of mineral N was low. Rhizobia-free legume seedlings transplanted to a gravel pad developed nodules whether or not they were inoculated with rhizobia, but total weight and nodule weight tended to be higher in inoculated seedlings. Some native plants, primarily riparian species, are capable of establishing and growing on abandoned gravel pads. The low cover and diversity of naturally-colonized sites are attributed to (1) limited dispersal from riparian seed sources, (2) lack of water for germination, and (3) lack of nutrients to support growth. Both willows and legumes have promise for use in restoration.
    • Systematics and biogeography of the arctic and boreal species of Primula

      Kelso, Sylvia; Murray, David F. (1987)
      Four sections of the genus Primula are represented in northern North America: Aleuritia, Armerina, Crystallophlomis, and Cuneifolia. In this dissertation I discuss anatomical, morphological, cytological, ecological, and reproductive characters for thirteen species, and demonstrate coherence of sectional groups through cluster analysis and ordination. In Primula, distyly and homostyly play critical roles in systematics and biogeography. It is generally assumed that distylous individuals are almost completely outcrossed, and homostyles are capable of selfing. In the taxa examined here, distyly exists at the diploid and tetraploid levels while homostyly is seen in both diploids and higher polyploids. I suggest that distyly breaks down with selection for reproductive assurance in environments where pollinators are unreliable, or following hybridization in conjunction with polyploidy. While most northern Primula species are homostylous, several examples of distylous taxa demonstrate that this can be a successful breeding system in higher latitudes. In homostyles, self-compatibility and the proximity of reproductive organs assures a high degree of selfing; however, most northern homostylous taxa also exhibit attributes which suggest facultative outcrossing is common. In North America, evolution in Primula has been strongly influenced by Quaternary events leading to isolation, migration, and secondary contact of gene pools, in association with the breakdown of distyly to homostyly. The success of homostylous taxa is at least partially due to their ability to self-fertilize coupled with the availability of areas to colonize when Pleistocene ice retreated. The phytogeographic affinities, cytology, and reproductive shifts of Primula make it a useful model for processes occurring in the Alaskan flora. The steppes and mountains of Asia have been important source areas, and migration has taken place along mountains, rivers, island arcs, and coastlines. Speciation in the genus has been aided by hybridization, polyploidy, and reproductive diversity.