with symbiotic fungi. Symbiotic fungi and root hairs produce mycorrhizal symbioses like arbuscular mycorrhiza, formed by AM fungi, and ectomycorrhiza, formed by EM fungi. These are very common, occurring in 90% of terrestrial plant species, because of the benefits it brings to both the fungus and plant. Formation of this relationship for EM fungi begins with the colonization of the root hairs. This process begins when the EM fungus adheres to the root hair from the soil. The fungus then secretes diffusible factors, to which root hairs are highly sensitive, allowing the hyphae to penetrate into the epidermal cells and create a Hartig net in the first layers of the root cortex. This highly branched structure serves as an interface between the two organisms as fungal cells adapt to the exchanges that occur between the plant and fungus. This process is similar to how AM fungi colonize root hairs, but instead of diffusible factors, they secrete hydrolases to relax the cell wall, which allows hyphae to enter, and there is no Hartig net. Various effects of fungal colonization in root hairs show that this relationship is beneficial to both plant and fungal species, but the main effect is on root hair growth. Fungi actually affect the growth of root hairs if there is water or nutrient deficiency. Since both of these organisms require nutrients and water, their cooperation is essential to their mutual survival. Upon detection of deficiency, the drought stress response of the plant is triggered, causing growth of the root hairs. The mycorrhizae of the fungus then uses its extended system to help the plant find the correct area of nutrition, signaling the direction in which the roots should grow. This makes root growth more efficient, preserving energy for other metabolic processes, which in turn benefits the fungus that feeds off those metabolic products. Survival When a new root hair cell grows, it excretes a hormone that inhibits the growth of root hairs in nearby cells. This ensures equal and efficient distribution of the actual hairs on these cells. Repotting or transplanting a plant can result in root hair cells being pulled off, perhaps to a significant extent, which can cause wilting. See also Trichome References Plant anatomy Plant roots Soil biology