Histological Observations of Arbuscular Mycorrhizal Fungus Infection to Root Tissue of Asparagus officinalis L. Seedlings

Abstract

The infection process of arbuscular mycorrhizal (AM) fungus, Gigaspora margarita, in asparagus (Asparagus officinalis L.) seedling roots was histologically investigated to clarify the mechanism as to how the organism enhances asparagus plant growth. Such information may lead to a better understanding of growth through symbiosis. The sequential infection process was classified into four main stages.
Stage I: a hypha penetrated into the host roots via the intercellular spaces of the epidermal cells to the cortex. Stage II: the hypha initially elongated longitudinally in the outer cortex and then in the inner cortex. Stage III: the hypha invaginated to the surface layer of the cortical cell; at the invaginating point, the primary cell wall became thin and indistinguishable; the secondary cell wall also became thin but remained visible. After invaginating, the hypha formed a ramified arbuscule which pushed the host cell plasmalemma inwardly but did not crush it. No hypha penetrated the endodermis. Stage IV: the arbuscule collapsed into a mass.
This study clarified the histological characteristics of host cell wall and middle lamella during an infection by the AM fungus (Gigaspora margarita) in asparagus seedling roots.