Starch Formed in Plastids

Starch is formed in chloroplasts of moss, fern and green algae.18 Chlorophyceae (green algae) starch is similar to that of higher plants, and several species have been used in studies of starch biosynthesis.19,22,29 In a recent set of studies, Ball et al.22 used Chlamydomonas reinhardtii to study starch biosynthesis. They produced several Chlamydomonas mutants which produce starch with characteristics similar to starches produced by maize endosperm mutants.31-34 The various starch mutations of Chlamydomonas will be discussed in Section 3.7. Other classes of algae which produce starch are Prasinophyceae19,35 and Cryptophyceae.35,36 

Reserve starch is usually formed in amyloplasts, although it is occasionally formed in chloroamyloplasts. These are chloroplasts that have lost their lamellar structure and subsequently start producing fairly large reserve starch granules.17 Chloroamyloplasts form starch independent of photosynthesis. They have been described in tobacco (Nicotiana tabacum L.) leaves, Aloe leaves and flowers, central pith of potato (Solanum tuberosum L.) fruit, Pellionia and Dieffenbachia stems, and other tissues.17,18 Such sources of reserve starch are insignificant, however, when compared to the reserve starch formed in roots, tubers and seeds. 

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