Abstract:
Thylakoid membrane fractions were prepared from specific regions of thylakoid membranes
of spinach (Spinacia oleracea). These fractions, which include grana (83), stroma (T3), grana core
(8S), margins (Ma) and purified stroma (Y100) were prepared using a non-detergent method
including a mild sonication and aqueous two-phase partitioning.
The significance of PSlla and PSII~ centres have been described extensively in the
literature. Previous work has characterized two types of PSII centres which are proposed to exist
in different regions of the thylakoid membrane. a-centres are suggested to aggregate in stacked
regions of grana whereas ~-centres are located in unstacked regions of stroma lamellae.
The goal of this study is to characterize photosystem II from the isolated membrane vesicles
representing different regions of the higher plant thylakoid membrane. The low temperature
absorption spectra have been deconvoluted via Gaussian decomposition to estimate the relative
sub-components that contribute to each fractions signature absorption spectrum. The relative sizes
of the functional PSII antenna and the fluorescence induction kinetics were measured and used
to determine the relative contributions of PSlla and PSII~ to each fraction. Picosecond chlorophyll
fluorescence decay kinetics were collected for each fraction to characterize and gain insight into
excitation energy transfer and primary electron transport in PSlla and PSII~ centres.
The results presented here clearly illustrate the widely held notions of PSII/PS·I and
PSlIa/PSII~ spatial separation. This study suggests that chlorophyll fluorescence decay lifetimes
of PSII~ centres are shorter than those of PSlIa centres and, at FM, the longer lived of the two PSII
components renders a larger yield in PSlIa-rich fractions, but smaller in PSIlr3-rich fractions.
