Chla

Chla, short for chlorophyll a, is the primary photosynthetic pigment in oxygenic organisms. It is found in plants, algae, and cyanobacteria and is essential for converting light energy into chemical energy during photosynthesis.

Chemically, Chla is a magnesium-porphyrin complex with a long hydrophobic phytol tail. This tail anchors the pigment in the lipid membranes of chloroplasts and, in cyanobacteria, in the thylakoid membranes. The porphyrin ring coordinates the magnesium ion and carries functional groups that participate in light absorption and energy transfer.

Chla absorbs light mainly in the blue and red parts of the spectrum, with peak absorption around blue wavelengths near 430 nm and red wavelengths near 665–670 nm, depending on solvent and environment. Excited Chla molecules transfer energy to the photosynthetic reaction centers, where charge separation initiates electron flow and overall photochemistry.

In plants and algae, Chla is located in the thylakoid membranes within photosystems I and II, functioning in antenna complexes and core reaction centers. It acts as the primary electron donor in the initial photochemical reactions and works in concert with accessory pigments such as chlorophyll a, chlorophyll b, and carotenoids to harvest light.

Chla concentrations are widely used as an index of phytoplankton biomass in aquatic ecosystems. Measuring Chla in water samples provides information about primary production and ecosystem status. Chla should be distinguished from related pigments (chlorophylls b, c, d, f) and from degraded forms that arise during senescence.

Chla is produced by photosynthetic organisms through a conserved biosynthetic pathway that builds the porphyrin ring and inserts magnesium, followed by esterification with the phytol chain.