Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The maize light harvesting system is structurally and functionally perturbed by chilling stress, with alterations in fluorescence parameters and protein processing. The molecular basis for these changes was investigated through biochemical analysis of the photosystem II-associated light-harvesting complexes (LHC II) of maize mesophyll thylakoids.;LHC II complexes from thylakoids were separated into three populations by mildly-denaturing electrophoresis. LHC II-1 contains four polypeptides and is equivalent to the oligomeric LHC IIb complex of Thornber et al. (1988). A less abundant oligomeric band, LHC II-2, contains a subset of the LHC IIb polypeptides, along with the LHC IIa complex (CP 29). The LHC II-3 band contains the LHC IIa and LHC IIc complexes. The LHC IIa and LHC IIb polypeptides were identified by immunoblotting. The LHC II populations separated from PS II-enriched membranes are similar, but isolated LHC II particles generate three chlorophyll-protein bands, all derived from LHC IIb.;Interactions among LHC II complexes were investigated by protein cross-linking with 3,3{dollar}\sp\prime{dollar}-dithio-bis(propionic acid n-hydroxysuccinimide ester) (DSP), a cleavable cross-linker of 1.1 nm length. Cross-linking occurs between appressed thylakoids, as shown by resistance to unstacking following DSP treatments. DSP treatment gave cross-linking between the LHC IIa and LHC IIb complexes, among LHC IIb complexes, between the PS II core and LHC IIa/LHC IIb and between the PS I core and LHC I. Disruption of appression prior to DSP treatment eliminates the LHC IIa/LHC IIb and the LHC IIa/LHC IIb/PS II cross-linked products. Hence, specific linkages occur between the PS II related complexes of adjacent appressed thylakoid membranes. This organization may have functional implications.;The assembly of LHC IIb oligomers is disrupted by low light chilling stress. Three LHC IIb polypeptides are heavily labelled by light-induced phosphorylation of thylakoids. The pattern of LHC IIb phosphorylation is altered by low or high light chilling stress prior to thylakoid isolation; the effect is partially reversed by the presence of high ATP concentrations during phosphorylation. These changes provide biochemical background to disruption of LHC II function following chilling. The timing of chilling stress influences the degree of chill-induced changes.



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