What is chlorophyll used for in plants?


Chlorophyll, Leaf green, Leaf pigments that give the leaves of green plants and the photosynthetically active algae and cyanobacteria their characteristic green color. In these organisms, they occur together with other photosynthetic pigments in the thylakoids of the chloroplasts or, in the case of cyanobacteria, in their thylakoids. Their green color is due to the chemical properties of C., which means that light red and blue parts of sunlight are very strongly absorbed, while green and dark red areas of the spectrum are hardly or not at all absorbed. With the help of C., the light energy of sunlight is absorbed and stored in the light reactions in chemical energy (ATP) that can be used for metabolism and as reduction equivalents (NADPH). C. therefore plays a key role in photosynthesis.

C. is a tetrapyrrole, in which the four pyrrole rings are linked by methine bridges and thus has the basic structure of the porphyrins. The conjugated double bonds of the porphyrin ring structure cause the green coloration already mentioned. C. is structurally closely related to the Hamm (Hemoglobin, cytochrome), except that in C. magnesium takes the place of iron as the central metal atom. The anchoring of the C. molecules in the thylakoid membrane takes place through the lipophilic phytol residue. There are a total of four different chlorophylls, which differ in terms of their different substituents on the ring structure. The Chlorophyll a occurs in all photosynthetically active eukaryotes and cyanobacteria and is of central importance as a photosynthetic pigment. The other three C. are represented differently in different groups. Chlorophyll b was found e.g. in higher plants and green algae and does not occur in diatoms, which, like brown algae, Chlorophyll c have. The Chlorophyll d occurs in red algae. (see table)

In each of the thylakoid membranes there are several hundred C. molecules with C.-binding proteins and other pigments to form what are known as Antenna complexes united, whose function consists in the absorption of light energy and its transmission to the photosynthetically active reaction centers (antenna pigments). In contrast to the other C. molecules, the C. in the reaction centers are associated with one electron acceptor and one electron donor. These complexes are called photo systems.

The C. Synthesis takes place in the chloroplasts and initially always leads to chlorophyll a (see Fig.) which is only converted into the other C. in the thylakoid membrane. Starting with 5-aminolevulinate, which is formed from glutamate in plants, the C. synthesis and the heme synthesis run up to Protoporphyrin IX immediately off. The C.-specific biosynthetic pathway begins with the formation of Mg protoporphyrin IX and ends with a series of further enzymatic steps Chlorophyllide awhich eventually gets the phytol residue. This sequence of reactions, which also applies to Greening by plants (photomorphogenesis) is the enzyme Protochlorophyllide oxidoreductase essentially involved. It is in large quantities in the Prolammellar bodies of the etioplasts included. In contrast to gymnosperms, the reaction of this enzyme in angiosperms is light-dependent. The C. degradation begins with the hydrolysis of the phytol ester group to chlorophyllid a and phytol and is made by the enzyme Chlorophyllase catalyzed (autumn color).

Chlorophyll: Structure of chlorophyll a

Chlorophyll: Occurrence of chlorophylls