Pinwheel inclusions in morphogenesis: a possible alternative to induction by viruses

Area of Science:

• Plant biology
• Cell biology
• Plant pathology

Background:

• Pinwheel inclusions (PWs) are cytoplasmic inclusions observed in plant cells.
• Their association with viral infections is a common hypothesis.
• Carrot (Daucus carota) storage root callus tissue provides a model system for studying cellular changes.

Purpose of the Study:

• To investigate the origin of pinwheel inclusions (PWs) in Daucus carota callus tissue.
• To determine if PWs are indicative of viral infection or a result of specific culture conditions.

Main Methods:

• Culturing carrot explants from secondary phloem parenchyma on various media formulations.
• Observing cells for cytoplasmic inclusions using light microscopy.
• Comparing inclusion types (PWs, multifibrillar bundles - MFBs) under different hormonal and nutrient conditions.

Main Results:

• PWs were observed in callus grown on media supplemented with plant growth regulators (zeatin, indoleacetic acid, naphthalene acetic acid) or coconut milk.
• No PWs were found in callus grown on basal medium alone.
• Multifibrillar bundles (MFBs) were observed on a differentiation-inducing medium, but not PWs.
• Callus initially forming MFBs, when transferred to a supplemented medium, subsequently developed both PWs and MFBs.

Conclusions:

• The presence of PWs in Daucus carota callus is strongly correlated with specific culture media compositions, particularly those containing plant growth regulators.
• Evidence suggests PWs are a manifestation of culture conditions rather than a definitive marker of viral infection.
• Further studies are warranted to elucidate the precise biochemical pathways leading to PW formation under these conditions.