Light and electron microscopic investigation of in vitro starch synthesis in chromoplasts.

Chromoplasts having a globular inner structure in the petals of Forsythia suspensa can form starch grains in their stroma when incubated with glucose solution. The same result was obtained with chromoplasts, similar in structure, from Laburnum anagyroides and Ranunculus acer. Fibrillar chromoplasts in tepals of Lilium croceum are able to synthesize starch in vitro, not, however, from glucose but from glucose-1-phosphate. This starch differs from the above mentioned both in respect of electron microscopic structure and digestibility with alpha-amylase, a feature presumably caused by the relatively high activity of the branching (Q) enzyme. The substrate specificity of Lilium-starch synthesis can be explained by blocking of the phosphorylation of glucose in the cytoplasm, rather than by the selective permeability of the plasmalemma.