2
J. C. da Silva and A. T. Lombardi
Keywords Photosynthetic pigment · Cyanobacteria · Algae ·
Protochlorophyllide · LPOR · DPOR
1.1 Introduction
The term chlorophyll was first proposed by Pelletier and Caventou (1818) to designate
the green substance (Greek chloros) of leaves (Greek phyllos) for the pigments that
could be extracted from leaves using organic solvent. Chlorophylls are the most
abundant natural pigment that give microalgae their green color and are essential for
the photosynthetic process, whereby microalgae derive their energy for metabolism
and reproduction. The photosynthetic process provides direct and indirect energy
source for all forms of life inhabiting our planet, and chlorophylls support such
important process, therefore chlorophylls are not only the most abundant, but also
the most important pigment. Chlorophyll (Chl) takes part in both light-harvesting
process and energy conversion (Li and Chen 2015). In algae and plants (eukaryotes
organisms) chlorophyll a is present in plastids, the chloroplast. In Cyanobacteria,
Chl a is present in the photosynthetic lamellae distributed in the cell cytoplasm. The
pigment contains four substituted pyrrole rings in addition to a fifth ring that is not a
pyrrole but a porphyrin derivative. Chlorophyll a has a long hydrophobic phytyl side
chain that anchors and orients the pigment molecule in the thylakoid membrane that
is located inside the chloroplast (Lehninger 1987).
Nature has almost exclusively and universally selected chlorophylls (Chl) for the
primary reactions of photosynthesis. The pigment has two main absorption bands,
one near 660–665 nm (red light) and the other near 430 nm (blue light). In vivo
chlorophylls occur as bound chromophores of pigment-protein complexes in the
light-harvesting antennae and photosynthetic reaction centers of photosystems I (PSI)
and II (PSII) in algae. In green algae and plants, Chl a is the most important pigment
in the antenna. The antenna pigments contribute to increase the absorption crosssection of the reaction centers that are assisted by the intense absorptions of most
Chls (Scheer 2006). Even though the individual absorption peaks of the chlorophylls
are narrow, interaction with proteins of in vivo Chls can amplify the absorption bands
and further spread them by combination with other pigments, including other Chls.
In the reaction centers, Chls are indispensable as primary electron donors and
acceptors, transporting the electron within a few picoseconds across half the thylakoid
membrane. They also serve to transport triplet excitation energy to the protective
carotenoids (Angerhofer et al. 1998). In most photosynthetic organisms, Chls also
provide the majority of light-harvesting pigments, which are only supplemented by
linear tetrapyrroles and carotenoids (Sheer 2006). The large aromatic tetrapyrrole
macrocycle is the basis for both the absorption and the redox chemistry of Chls,
and the central metal (Mg) has a decisive influence on the excited state kinetics of
tetrapyrroles, therefore, on their function in photosynthesis. Mg as the central metal
maximizes excited state lifetime as well as the interactions of Chls with their proteins;
in vivo chlorophylls are conjugated with protein (Markwell et al. 1979).
J. C. da Silva and A. T. Lombardi
Keywords Photosynthetic pigment · Cyanobacteria · Algae ·
Protochlorophyllide · LPOR · DPOR
1.1 Introduction
The term chlorophyll was first proposed by Pelletier and Caventou (1818) to designate
the green substance (Greek chloros) of leaves (Greek phyllos) for the pigments that
could be extracted from leaves using organic solvent. Chlorophylls are the most
abundant natural pigment that give microalgae their green color and are essential for
the photosynthetic process, whereby microalgae derive their energy for metabolism
and reproduction. The photosynthetic process provides direct and indirect energy
source for all forms of life inhabiting our planet, and chlorophylls support such
important process, therefore chlorophylls are not only the most abundant, but also
the most important pigment. Chlorophyll (Chl) takes part in both light-harvesting
process and energy conversion (Li and Chen 2015). In algae and plants (eukaryotes
organisms) chlorophyll a is present in plastids, the chloroplast. In Cyanobacteria,
Chl a is present in the photosynthetic lamellae distributed in the cell cytoplasm. The
pigment contains four substituted pyrrole rings in addition to a fifth ring that is not a
pyrrole but a porphyrin derivative. Chlorophyll a has a long hydrophobic phytyl side
chain that anchors and orients the pigment molecule in the thylakoid membrane that
is located inside the chloroplast (Lehninger 1987).
Nature has almost exclusively and universally selected chlorophylls (Chl) for the
primary reactions of photosynthesis. The pigment has two main absorption bands,
one near 660–665 nm (red light) and the other near 430 nm (blue light). In vivo
chlorophylls occur as bound chromophores of pigment-protein complexes in the
light-harvesting antennae and photosynthetic reaction centers of photosystems I (PSI)
and II (PSII) in algae. In green algae and plants, Chl a is the most important pigment
in the antenna. The antenna pigments contribute to increase the absorption crosssection of the reaction centers that are assisted by the intense absorptions of most
Chls (Scheer 2006). Even though the individual absorption peaks of the chlorophylls
are narrow, interaction with proteins of in vivo Chls can amplify the absorption bands
and further spread them by combination with other pigments, including other Chls.
In the reaction centers, Chls are indispensable as primary electron donors and
acceptors, transporting the electron within a few picoseconds across half the thylakoid
membrane. They also serve to transport triplet excitation energy to the protective
carotenoids (Angerhofer et al. 1998). In most photosynthetic organisms, Chls also
provide the majority of light-harvesting pigments, which are only supplemented by
linear tetrapyrroles and carotenoids (Sheer 2006). The large aromatic tetrapyrrole
macrocycle is the basis for both the absorption and the redox chemistry of Chls,
and the central metal (Mg) has a decisive influence on the excited state kinetics of
tetrapyrroles, therefore, on their function in photosynthesis. Mg as the central metal
maximizes excited state lifetime as well as the interactions of Chls with their proteins;
in vivo chlorophylls are conjugated with protein (Markwell et al. 1979).