Light harvesting antenna of plants allow for very quantum efficient capture by high pigment density and long excited-state lifetime design.
“Light harvesting in photosynthetic organisms is largely an efficient
process. The first steps of the light phase of , capture
of light quanta and primary charge separation processes are particularly
well-tuned. In plants, these primary events that take place within the
photosystems possess remarkable quantum efficiency, reaching 80% and
100% in photosystems II and I respectively. This paper presents a view
on the organisation of a natural light harvesting machine—the antenna of
the photosystem II of higher plants. It explains the key principles of
biological antenna design and the strategies of to light
environment which have evolved over millions of years. This article
argues that the high efficiency of the light harvesting antenna and its
control are intimately interconnected owing to the molecular design of
the –s it is built of, enabling high pigment density
combined with the long excited-state lifetime. The protein plays the
role of a programmed solvent, accommodating high quantities of
pigments, while ensuring their orientations and interaction yields are
optimised to efficiently transfer energy to the reaction centres,
simultaneously avoiding energy losses due to concentration quenching.
The minor group of pigments, the xanthophylls, play a central role in
the regulation of light harvesting, defining the antenna efficiency and
thus its abilities to simultaneously provide energy to photosystem II
and protect itself from excess light damage. Xanthophyll hydrophobicity
was found to be a key factor controlling efficiency by
modulating pigment–pigment and pigment–protein interactions.
Xanthophylls also endow the light harvesting antenna with the remarkable
ability to memorise photosystem II light exposure—a light counter principle. Indeed, this type of light harvesting regulation displays hysteretic
behaviour, typically observed during electromagnetic induction of
ferromagnetic materials, the polarization of ferroelectric materials and
the deformation of semi-elastic materials. The photosynthetic antenna
is thus a magnificent example of how nature utilises the principles of
physics to achieve its goal—extremely efficient, robust, autonomic and
yet flexible light harvesting.” (Ruban et al. 2011:1643)
