Pigmentgranulae

Pigmentgranulae are small intracellular inclusions that contain pigments or pigment-protein complexes. The term is used across biology to describe diverse pigment-containing structures in animals, plants, algae, and fungi. Depending on the lineage, pigmentgranulae can be membrane-bound organelles or non-membranous inclusions, and their pigment composition ranges from melanin and carotenoids to chlorophyll derivatives. They commonly contribute to coloration and light interaction with tissues, and they may serve as stores or protective reservoirs for pigment compounds.

In animals, pigmentgranulae most commonly refer to melanosomes, organelles within pigment cells such as melanocytes that synthesize and store melanin and participate in photoprotection and camouflage. In plants and algae, pigment granules include plastoglobuli that reside in chloroplasts and store lipophilic pigments like carotenoids and tocopherols, as well as pigments involved in pigment turnover. In fungi and some bacteria, pigment granules can contain melanin or other pigments, contributing to UV protection, structural reinforcement, or signaling.

Biogenesis varies by type: melanosomes form through endosomal pathways, plastoglobuli arise within thylakoid-associated membranes, and other pigment granules assemble in the cytoplasm or by vesicular trafficking. Functional roles include light absorption for coloration and camouflage, photoprotection against light-induced damage, antioxidant storage, and pigment circulation during development or stress.

Because pigmentgranula is a broad, descriptive term, many well-defined organelles have more specific names in modern literature, such as melanosomes, chromoplasts, or plastoglobuli. The term is most commonly encountered in histological descriptions and comparative physiology.