Further studies on phytoferritin

Crystalline and paracrystalline inclusions found in plastids of willow cambium, grown under dim-light conditions, are considered to be phytoferritin. Phytoferritin is completely unaffected following treatment of cambial cells with deoxyribonuclease or ribonuclease, although other components are, at least in part, denatured. This is considered to exclude the possibility that the inclusions are viral particles. While not normally arranged in crystalline form, phytoferritin from embryonic axes of pea appears identical in structure with the complex found in cambial plastids. It, also, is not affected by treatment with nucleases for periods of up to 18 hours. Phytoferritin has been found only rarely in willow grown under conditions of high illumination.Four, five, or six electron-opaque subunits are most often found in the individual particles of phytoferritin. The most satisfactory explanation of the arrangements seen seems to be that the micellar configuration is in the form of an octahedron with a subunit at each of the six vertices.