Plant virus spread between adjacent cells: which channels mediate direct virion transfer? Identify the primary intercellular structures responsible for cell-to-cell transfer of plant viruses.

Introduction / Context:
After a plant virus gains entry into a cell, it must move to neighboring cells to establish a local infection and, eventually, systemic spread. Plant cells are connected by specialized channels that enable this movement, often assisted by viral movement proteins.

Given Data / Assumptions:

• Rigid cell walls prevent direct budding or endocytosis-based spread typical of animal viruses.
• Intercellular connectivity exists via microscopic channels.
• Some terms in the options are nonstandard or incorrect in modern plant biology.

Concept / Approach:
Plasmodesmata are cytoplasmic channels crossing plant cell walls, connecting adjacent cells. Plant viruses encode movement proteins that modify plasmodesmatal size exclusion limits to allow passage of viral ribonucleoprotein complexes or even whole virions, depending on the virus family.

Step-by-Step Solution:
Recall that plasmodesmata provide symplastic continuity.Recognize viral movement proteins target plasmodesmata to increase permeability.Select “Plasmodesmata” as the correct choice for direct intercellular transfer.

Verification / Alternative check:
Classic studies on Tobacco mosaic virus and many potyviruses demonstrate movement through plasmodesmata via dedicated movement proteins and tubule formation in some cases.

Why Other Options Are Wrong:
“Cytodesmata” and “protodesmata” are not standard modern terms for these channels; “None” is wrong because plasmodesmata are well-established structures; “Tight junctions” occur in animal epithelia, not plants.

Common Pitfalls:
Confusing initial entry structures with intercellular movement routes. Entry may be via wounding or vectors; spread is mainly via plasmodesmata.

Final Answer:
Plasmodesmata.