Juvenile leucoplasts (proplastids) of cottonwood

Leucoplasts lack pigmentation

Pleomorphic, small size

Numerous plastid ribosomes, few thylakoids and little starch

Two juvenile leucoplasts (proplastids) from a shoot apical meristem cell of cottonwood (Populus deltoides) are shown.

The main function of juvenile leucoplasts is their replication in dividing cells thus ensuring the continuity of plastids from cell to cell, and from generation to generation. They are capable of developing into various types of plastids. Note the lack of thylakoid stacking and the variable overall profile appearance of the plastid (said to be pleomorphic). The stroma is rich in plastid ribosomes which synthesize constitutive proteins for these replicating plastids. There are a few single irregular thylakoids, some profiles of peripheral reticulum, a small starch grain, and very tiny plastoglobuli. Overall, the plastid is not pigmented.