The goal of this dissertation is to provide information critical for understanding the function of the major chloroplast LMW HSP. The results of this research show that the production of a nuclear-encoded, chloroplast LMW HSP is a highly conserved event in the plant HS response, and that the HSP itself is highly homologous in divergent plant species. Three major conserved regions were identified in the chloroplast LMW HSP. The carboxyl-terminal HS domain of the chloroplast LMW HSP is also found in cytoplasmic LMW HSPs and identifies it as a member of the superfamily of eukaryotic LMW HSPs. The amino-terminal region is unique to the chloroplast LMW HSP and is capable of forming a Met-rich amphipathic α-helix. The chloroplast LMW HSP cannot be detected at normal growth temperatures, but accumulates dramatically in both leaves and roots during HS. The chloroplast LMW HSP is a stable protein with a half-life of approximately 52 h. In the chloroplast, the majority of PsHSP21 is localized in the soluble protein fraction. In its native state, PsHSP21 exists in a 200 kDa particle as is observed for cytoplasmic LMW HSPs. However, unlike the cytoplasmic LMW HSPs, the PsHSP21-containing particles do not aggregate into heat shock granules even under severe, abrupt HS conditions. The formation of the PsHPS21-containing particle can be replicated in isolated chloroplasts, but the chloroplasts must be from heat stressed plants. The protein sequence homology and the similar native structure of the LMW cytoplasmic and chloroplast HSPs suggests they perform similar functions in different cellular compartments. I propose that the 200 kDa particle is the functional form of PsHSP21. Furthermore, the chloroplast LMW HSP performs functions in all types of plastids similar to those of the cytoplasmic LMW HSPs, but with unique substrates within the special environment of plastids. This study provides the first information regarding the expression and structure of the chloroplast LMW HSP. Since the chloroplast contains only a single major LMW HSP, this study also provides the basis for developing a simple model system for studies of the function of all members of the ubiquitous LMW HSP family.

No description available.

Members of the genus Packera (Asteraceae) are widespread in North America, but most are found in western regions of the continent where extensive morphological integradation is common. Previous molecular systematic studies found that four species in southwestern Alberta, a region proposed to be at the interface of the Cordilleran and Laurentide ice sheets during the last advance of Pleistocene glaciation, showed unusually high levels of inter- and intrapopulational chloroplast DNA variation. The present study analyzed chloroplast haplotype phylogeny, frequency variation, and geographic distribution patterns in Packera contermina and closely related species P. pseudaurea, P. cana, and P. cymbalarioides from southwestern Alberta, nothern Montana, and northwestern Wyoming. Restriction site analyses of chloroplast DNA from 730 individuals across 34 populations of the four species revealed fifteen haplotypes, of which seven are commonly found in other North American Packera species. Three haplotypes were detected in P. cymbalarioides, seven in P. cana, eight in P. pseudaura, and twelve in P. contermina. The level of ahplotype frequency variation among populations was high in P. cymbalarioides (0=I) moderate to low in P. contermina (0=0.333) and P.cana (0=0.261), and very low in P.pseudaurea (0=0.085), possibly reflecting differences in the species' history. Phylogenetic analyses revealed 2 groups of haplotypes, one of which is found mainly in populations from the Great Basin of North America and the second in populations of more coastal and northern regions. The presence of haplotypes from both groups of Packera species suggests that the cpDNA diversity in southern Alberta arisen through hybridization/introgression events that have involved a number of species from outside of the region. / x, 81 leaves : ill., maps ; 28 cm.