Photosynthetic microorganisms must acclimate to environmental conditions that may lead to photo-oxidative stress, such as low CO₂ environments or high light intensities. Chlamydomonas reinhardtii, a unicellular, green alga with a Carbon Concentrating Mechanism (CCM), effectively accumulates inorganic carbon (C_i) to levels higher than external concentrations. The CCM concentrates inorganic carbon around Rubisco to increase the CO₂ fixation efficiency of C. reinhardtii. Photorespiration, the water-water cycle, the xanthophyll cycle, and the CCM are adaptations that also prevent the over-reduction of photosystems and thus photoinhibition by dissipating the energy from the absorption of excess photons. In an effort to dissect elements of the CCM, insertional mutants of C. reinhardtii were transformed using the Ble^R cassette, selected for Zeocin resistance, and then screened for a "sick on low CO₂" phenotype. One insertional mutant selected was slc-230. This dissertation describes the molecular and the physiological characterization of slc-230. slc-230 was shown to have a Ble^R insert in the first exon of Hdh1, a novel, single copy gene that seems to be slightly upregulated under low CO₂ and whose predicted gene product has homology with open reading frames in archaebacteria. The Hdh1 gene product has similarity to general phosphatases. Proteins in this family include phosphatases and epoxide hydrolases. In addition, Hdh1 is predicted to be localized to the chloroplast or mitochondria in C. reinhardtii. It was found that a genomic copy of Hdh1 can complement slc-230. Physiological studies were conducted to determine the effects of the altered expression of Hdh1 in slc-230. slc-230 exhibits a lower affinity for inorganic carbon (slightly elevated K_0.5), a decreasing photosynthetic rate (V_max) over time, and a lower content of chlorophylls and quenching xanthophylls than wild-type. Some possible roles of Hdh1 are discussed.

Anacardiaceae Lindl., the cashew family, is an economically important, primarily pantropically distributed family of 82 genera and over 700 species. This family is well known for its cultivated edible fruits and seeds (mangos, pistachios, and cashews), dermatitis causing taxa (e.g., Comocladia, Metopium, Semecarpus, Toxicodendron, etc.), and lacquer plants (Toxicodendron and Gluta spp.). The taxonomy of Anacardiaceae has not been thoroughly investigated since Engler established the currently used five tribal classification system over 100 years ago. This study evaluated evolutionary relationships of the family using nrDNA and cpDNA sequences. The first part of the study investigated the evolutionary position of Anacardiaceae in relation to closely allied families within the order Sapindales. DNA sequence data for the chloroplast trnL intron and 3 exon, and the intergenic spacer between trnL and trnF (trnLF) of Anacardiaceae, Burseraceae, Julianiaceae, Pistaciaceae, Podoaceae, Rutaceae, and Sapindaceae were generated to reconstruct phylogenetic relationships of these families. Julianiaceae, Pistaciaceae, and Podoaceae were all nested within Anacardiaceae. The sister group of Anacardiaceae is Burseraceae. To understand intergeneric relationships within Anacardiaceae, phylogenies were constructed from sequences of three chloroplast loci (matK, trnLF, and rps16), using maximum parsimony and maximum likelihood as the optimality criteria. Based on these reconstructions and current knowledge of morphological and anatomical attributes of the Anacardiaceae, the subfamilies of Takhtajan, Anacardioideae (including tribes Anacardieae, Dobineae, Rhoeae, and Semecarpeae) and Spondioideae (including tribe Spondiadeae), were reinstated. Taxon distributions were mapped onto the phylogeny and the resulting biogeographic patterns were presented as evidence for the complex biogeographical history of the cashew family. Chloroplast (trnLF) and SSU nrDNA (ITS and ETS) loci were sequenced to delimit the generic boundaries and biogeographical history of the Madagascan/African genus Protorhus. These findings resulted in the recognition of a new Madagascan endemic genus, Abrahamia Randrianasolo ined., segregated from Protorhus. From age estimates of the Sapindales, the isolation of Madagascar, and the phylogeny of the African/Madagascan clade of Anacardiaceae, it is unlikely that vicariance played a role in the evolution of Madagascan Anacardiaceae. One possible scenario based on phylogenetic reconstruction is that Anacardiaceae was dispersed over water between Africa and Madagascar a minimum of three times.

Chlamydomonas reinhardtii Dangeard does not have two major phospholipids, PS and PC. This fact renders C. reinhardtii a desirable system for investigations of the PE biosynthetic pathway and its regulation independent of PC and PS biosynthesis. The cDNA coding for ECT protein in C. reinhardtii was cloned from a cDNA library. The ECT cDNA encodes a protein of 443 amino acid residues. The ECT protein in C. reinhardtii has a repetitive internal sequence in its N- and C-terminal halves. Each repeat half of the protein has a HXGH motif, a site considered to be in the catalytic domain. The protein has a RTXGVSTT signature sequence typical of the cytidylyltransferase family. The first 70 amino acid residues appear to be a subcellular targeting signal to mitochondria. The translated product of cloned cDNA was expressed as a fusion protein with maltose-binding protein in E. coli, and was shown to have ECT activity. Northern blot analysis showed mRNA abundance is increased by reflagellation. The enzyme requires Mg2+ and pH 7.5 for maximum activity in vitro, and it appears to have a sequential reaction mechanism. The activity of the enzyme in vivo in C. reinhardtii cells changes during the cell cycle while the mRNA level does not change. A cDNA coding for EPT protein was obtained from a C. reinhardtii cDNA library. The EPT cDNA encodes a protein of 383 amino acid residues. The EPT protein has a signature sequence and a conserved region in the CDP-alcohol phosphatidyltransferase family. Very similar membrane topology was found between the C. reinhardtii EPT and the aminoalcoholphosphotransferases from mammals, yeast and plants. A yeast mutant deficient in both cholinephosphotransferase and ethanolaminephosphotransferase was complemented by the C. reinhardtii EPT gene coding for EPT. Enzymatic assays of C. reinhardtii EPT from the complemented yeast microsomes demonstrated that the C. reinhardtii EPT synthesized PC in the transformed yeast. EPT activity from the transformed yeast or C. reinhardtii cells was inhibited nearly identically by unlabeled CDP-choline, CDP-ethanolamine and CMP. This provides evidence that C. reinhardtii EPT is capable of catalyzing the final step of phosphatidylcholine biosynthesis, as well as that of phosphatidylethanolamine.

Southeastern coastal plain pine savannas lack direct evidence of past fire regimes. As a result, uncertainty exists regarding the range of variation in frequency and seasonal timing of past fire regimes and the relative importance of anthropogenic and lightning-ignited fires. Characterization of past fire regimes is needed for effective restoration and management of these high-biodiversity ecosystems. I used dendrochronologically dated fire scars from stumps of old growth longleaf pines in a large coastal, mainland pine savanna and from dead slash pines on a small, coastal barrier island in north Florida to explore past fire regimes. In the mainland savanna, 71 different fires occurred from 1592-1883, based on a composite record of 109 fire scars from six fire-scarred trees. Almost all (95%) scars occurred during the middle growing season. Only three fires, all in the 1800s after European settlement of the local area, occurred during the dormant season. There was a 2-3 year fire return interval between 1679 and 1868. Variability in fire return intervals was low, with 92% of all fires occurring at < 5 yr intervals. On the barrier island 159 fire scars occurred in 21 separate years from 1864-2000, based on a record of 52 pines scarred during turpentine operations. Two periods of no fire scars corresponded to times of active pine resin extraction on the island (1911-1918, 1948-1958). Mean fire return intervals averaged four years from 1864-1910 and 1919-1947. A longer nine-year fire return interval occurred from 1959-2000. Most (86%) fires recorded in scars occurred during the growing season. The very high frequencies of growing season fires recorded in annual rings of these trees indicate that fire regimes were primarily driven by synoptic climatic conditions rather than by cultural burning practices. Both sites recorded frequent, growing season fires, suggesting that lightning fires were occurring frequently both before and after settlement despite differences in size and landscape context. This direct evidence of fire history in southeastern pine savannas can resolve some outstanding questions regarding ecological fire management. Fire managers now have direct evidence that supports frequent, growing season fires in pine savanna.