arbuscules

Arbuscules are specialized, highly branched hyphal structures formed by arbuscular mycorrhizal fungi within the cortical cells of plant roots. Each arbuscule develops when fungal hyphae penetrate a root cortical cell, becoming enveloped by a plant-derived periarbuscular membrane that creates the periarbuscular space. This interface concentrates the exchange of nutrients between partners.

The arbuscule serves as the principal site of nutrient exchange in arbuscular mycorrhizal symbiosis. Phosphorus and certain micronutrients absorbed by the fungus are transferred to the plant, while carbon compounds such as sugars—and in some systems lipids—are supplied by the plant to the fungus. The result is a bidirectional transfer that enhances nutrient uptake for the plant and carbohydrate provisioning for the fungus.

Arbuscules are most commonly formed by fungi in the phylum Glomeromycota and are characteristic of arbuscular mycorrhizal associations, which are widespread among land plants and ecologically important. The structures are dynamic and generally short-lived, maintained while the symbiosis is active, and degraded and renewed as needed when carbon supply or demand changes.

Key features include their highly branched architecture, which maximizes surface area for exchange, and their intimate intracellular location within plant root cells, coordinated by signaling between plant and fungus. Arbuscules are often used as a histological indicator of active AM symbiosis.