Proteoplasten

Proteoplasten, in English often called proteinoplasts, are non-photosynthetic plastids specialized for the accumulation and storage of proteins. They are considered a form of leucoplasts, a group of plastids lacking pigments, and are found mainly in tissues where protein storage is important, such as seeds and young developing embryos.

Structure and development appearence: Proteinoplasts contain protein storage bodies or protein granules within their stroma, which can vary in appearance from crystalline to more amorphous aggregates. They are bounded by a plastid envelope and lack the chlorophyll-containing thylakoid membranes characteristic of chloroplasts. Proteinoplasts arise during seed development from proplastids or other non-photosynthetic plastids in response to developmental and metabolic cues that promote protein synthesis and storage.

Function and contents: The primary role of proteoplasten is to store seed storage proteins, which serve as a nitrogen and amino acid source during germination and early seedling growth. The stored proteins may include various seed storage proteins such as prolamins, glutenins, globulins, and other protein families depending on the plant species. Mobilization of these proteins during germination provides essential nutrients for the developing seedling.

Occurrence and significance: Proteinoplasts are commonly reported in cereal endosperms and other seed tissues where protein reserves are high. They contribute to the overall nutrient composition of seeds and are of interest in studies of plastid differentiation, protein storage, and seed biology. In germinating seeds, storage proteins are degraded and mobilized, reflecting the dynamic role of proteoplasten in plant development.