The physiology of alien chloroplasts: light adaptation mechanisms in cytoplasmic hybrids of the Solanaceae family.
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The investigation presented here is of a new plant model for photosynthesis research. The plant's novelty is a hybrid cytoplasm which was engineered to contain the nuclear genome of Nicotiana tabacum (tobacco) and the chloroplast genome of Hyoscyamus niger (henbane). For photosynthesis research the implications of cytoplasmic hybridisation centre on the nuclear and chloroplast encoded pigment protein complexes of the photosynthetic machinery in the thylakoid membrane of the chloroplast. We investigate how the energy input from nuclear-encoded light harvesting complexes to the chloroplast-encoded core complexes is regulated in the cybrid plants, when light limits or exceeds photochemical capacity. When light limited, the phenomenon of state transitions (ST) serves to redress the imbalance of light input at PSI and PSII. In excess light, non-photochemical quenching (NPQ) mechanisms are activated in order to safely dissipate potentially harmful energy that has been absorbed by the system. Our investigation at first indicated that the cybrid plants had a greater capacity for NPQ compared to wildtype N. tabacum and H. niger. LHCII aggregation, xanthopyll cycle activity and PsbS were investigated for a possible reasons for the increase. However no difference or contradictory evidence was found. NPQ measurements were repeated and showed large variability and no significant difference in NPQ capacity compared to the wildtype parent species. The reason for the variability in the cybrid results could not be resolved but is suggested to be due to heightened environmental sensitivity. STs were found to be consistently inhibited in cybrids. Investigation of cybrid LHC isoelectric points and molecular weight revealed novelties. LHCs were then subjected to proteomic analysis that indicated possible truncation at the N-terminus, and thus the possible removal of a phosphorylation site that crucial for the initiation of ST. We also investigate the ability of the Nt(Hn) cybrid to adjust to high and low intensity light environments in terms of acclimation at the level of the whole plant, leaf, tissue, cell, chloroplast, thylakoid membrane, pigment, and electron transport rates.
AuthorsYeates, Anna M.
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