Plastidák

Plastidák, or plastids, are a family of organelles found in the cells of plants and algae. They are semi-autonomous, containing their own circular DNA and ribosomes, but most of their proteins are encoded in the nuclear genome and imported into the organelle. Plastids arose through endosymbiosis, most likely from ancestral cyanobacteria, and they retain features of their bacterial origin.

Within plant cells plastids differentiate into several forms depending on tissue and developmental stage. Chloroplasts carry out photosynthesis and are equipped with thylakoid membranes and the green pigment chlorophyll. Leucoplasts are non-pigmented and include amyloplasts, which store starch, and elaioplasts, which store lipids; proteinoplasts store storage proteins. Chromoplasts produce and accumulate carotenoid pigments and give color to ripening fruits and flowers. Etioplasts are plastids formed in darkness that can develop into chloroplasts upon illumination.

Plastids have a double membrane and a internal membrane system consisting of thylakoids and a surrounding stroma (in chloroplasts). They contain a small circular genome and 70S-type ribosomes, enabling some gene expression within the organelle. However, most plastid proteins are encoded in the nuclear genome and imported via transit peptides. Plastids can divide and are inherited in various patterns, often maternally in flowering plants.

Functionally, plastids are essential for photosynthesis, synthesis of fatty acids, amino acids, nucleotides, and pigments, as well as the biosynthesis of plant hormones and secondary metabolites. They are critical for plant development, metabolism, and adaptation to environmental changes, and they are widely used in biotechnology for plastid transformation and metabolic engineering.