Plastids

The word 'plastid' comes from the Greek Platikas, meaning formed or moulded, and was introduced into biology by A. F. W. Schimper in 1885. Schimper organised plastids into a classification based on their structure, the pigments they contain, and the function they perform, and that basic three-way grouping is still used today. Leucoplasts are colourless plastids whose job is storing food reserves rather than photosynthesis, and they are further split by exactly what they store: amyloplasts store starch, elaioplasts store lipids (oils, typically in the seeds of monocots and dicots), and aleuroplasts (also called proteoplasts) store protein. Chromoplasts are coloured plastids that owe their colour to carotenoid pigments, and are typically what give flowers, fruits and some roots their orange, yellow or red colouring. Chloroplasts are the green, photosynthetic plastids found in green algae and higher plants, coloured by chlorophyll a and b; two further, pigment-specific named types occur in algae - the brownish phaeoplast of brown algae and dinoflagellates (coloured by fucoxanthin), and the red rhodoplast of red algae (coloured by phycoerythrin). Every type of plastid multiplies by simple fission, in much the same way mitochondria do, and, importantly, Schimper also showed that different plastid types are not permanently fixed - a leucoplast can develop into a chloroplast (as happens when a potato tub …