| dc.description.abstract | Photosynthetic machinery in higher plants is localised in the thylakoids enclosed in
a chloroplast. To optimise and regulate the photosynthetic efficiency under different,
rapidly changeable environmental conditions the dynamics of the thylakoid
membrane components is required. It has been invoked in several contexts, for
example during assembly and turnover of the photosynthetic apparatus, regulation of
light-harvesting and photosynthetic electron transport. In this study, by employing
a confocal FRAP technique combined with freeze-fracture electron microscopy,
I addressed a fundamental problem of visualising the mobility and distribution of
photosynthetic complexes in a direct way close to the situation in vivo - the
thylakoids of intact chloroplasts isolated from green plants. Firstly, I provided direct
evidence that the dynamic changes in the distribution of photosynthetic complexes
are involved in two high-light related physiological phenomena, namely
photoinhibition and non-photochemical quenching. My study indicates that the
photoinhibited membranes exhibit an elevated level of protein mobility accompanied
by a decreased spacing between the complexes with the opposite effect observed in
the photoprotective state. Secondly, my work allowed the identification of some key
elements that are responsible for controlling the mobility under different
physiological conditions such as: (1) phosphorylation of PSII core complexes after
photoinhibition, (2) PsbS protein enhancing the membrane fluidity in a dark-adapted
state and decreasing it after light treatment, (3) different xanthophyll composition of
light-harvesting antenna with particular attention being paid to zeaxanthin which
decreases the size of mobile fraction, (4) the degree of macromolecular crowding and
the organisation of PSII-LHCII supercomplexes in the grana membranes which is
dependent strongly on individual light-harvesting proteins, the minor antenna
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complexes in particular. Lastly, a completely new approach of visualising the
mobility of photosynthetic machinery in intact leaves has been introduced as a useful
tool to study different aspects of plant acclimation and physiology under natural
conditions. | |
