Further studies on phytoferritin

Area of Science:

• Plant Cell Biology
• Biochemistry
• Structural Biology

Background:

• Plastids in willow cambium, under dim light, contain crystalline and paracrystalline inclusions.
• These inclusions were previously unidentified and their nature, potentially viral, was questioned.

Purpose of the Study:

• To identify the nature of crystalline and paracrystalline inclusions in willow cambium plastids.
• To investigate the structural characteristics and composition of these inclusions.
• To differentiate these inclusions from viral particles.

Main Methods:

• Electron microscopy was used to observe the inclusions in willow cambium plastids.
• Nuclease treatments (deoxyribonuclease and ribonuclease) were applied to cambial cells.
• Comparative structural analysis with phytoferritin from pea embryonic axes was performed.

Main Results:

• Inclusions were identified as phytoferritin, unaffected by deoxyribonuclease or ribonuclease treatments.
• Other cellular components were partially denatured by nucleases, supporting the exclusion of viral particles.
• Phytoferritin from pea embryonic axes showed identical structure to the willow cambium inclusions.
• These phytoferritin structures were rarely found in willows grown under high illumination.
• Individual phytoferritin particles often comprised four, five, or six electron-opaque subunits.
• An octahedral configuration with subunits at each vertex best explained the observed micellar arrangement.

Conclusions:

• The nucleases-resistant inclusions in willow cambium plastids are phytoferritin, not viral particles.
• Phytoferritin exhibits a consistent octahedral structure, composed of multiple electron-opaque subunits.
• Environmental factors, such as light intensity, may influence phytoferritin occurrence in willow.