PhDThe 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.BBSR
