Plants require sunlight to
fuel the conversion of carbon dioxide into sugar. Sunlight however, is not
always the rate-limiting factor in plant growth. During the two
hours before and two hours after solar noon, sunlight
often exceeds the amount of light energy plants can use because other rate limiting factors
come into play, particularly the intake of carbon dioxide. The excess light
energy during this four-hour interval would be damaging to the plant were it
not for the existence of biochemical mechanisms that turn it into harmless
heat. In this study, we have devised two independent strategies aimed at
diverting this otherwise wasted energy into alternative biochemical pathways
that could generate useful chemical compounds. The work involves basic research
into tethering enzymes directly to photosystem I, one of the two protein complexes in
plants that convert light energy into chemical energy. The tether will be
attached to photosystem I entirely within the living cell, either at its
terminal iron-sulfur cluster or at the intermediary quinone. In the former, a
naturally occurring protein that contains iron-sulfur clusters will be used to bind
photosystem I to a catalytic enzyme such as hydrogenase, which generates
hydrogen. In the latter, a molecular wire containing a menaquinone will
displace the naturally occurring plastoquinone-9, thereby providing an
alternative pathway for the extra energy to spill over to an attached catalyst.
If the work is successful, a significant increases into
plant productivity could be achieved. The work addresses the DOE-BES Photosynthetic
Systems Program mission to develop a multidimensional understanding of
photosynthesis to serve as a guide for the development of bioinspired,
biohybrid, and biomimetic energy systems and to inform strategies for the
improvement of biological photosynthesis.
