Ectomycorrhizal fungi and exogenous auxins influence root and mycorrhiza formation of Scots pine hypocotyl cuttings in vitro

Abstract

We studied the ability of the ectomycorrhizal (ECM) fungi, Pisolithus tinctorius (Pers.) Coker and Couch and Paxillus involutus (Batsch) Fr. (Strain H), to produce indole-3-acetic acid (IAA) and to affect the formation and growth of roots on Scots pine (Pinus sylvestris L.) hypocotyl cuttings in vitro. Effects of indole-3-butyric acid (IBA) and the auxin transport inhibitor, 2,3,5-triiodobenzoic acid (TIBA), on rooting and the cutting-fungus interaction were also studied. Both fungi produced IAA in the absence of exogenous tryptophan, but the mycelium and culture filtrate of Pisolithus tinctorius contained higher concentrations of free and conjugated IAA than the mycelium and culture filtrate of Paxillus involutus. Inoculation with either fungus or short-term application of culture filtrate of either fungus to the base of hypocotyl cuttings enhanced root formation. Inoculation with either fungus was even more effective in enhancing root formation than treatment of the hypocotyl bases with IBA. Fungal IAA production was not directly correlated with root formation, because rooting was enhanced more by Paxillus involutus than by Pisolithus tinctorius. This suggests that, in addition to IAA, other fungal components play an important role in root formation. Treatment with 5 microM TIBA increased the rooting percentage of non-inoculated cuttings, as well as of cuttings inoculated with Pisolithus tinctorius, perhaps as a result of accumulation of IAA at the cutting base. However, the marked reduction in growth of Pisolithus tinctorius in the presence of TIBA suggests that the effects of TIBA on rooting are complicated and not solely related to IAA metabolism. The high IAA-producer, Pisolithus tinctorius, formed mycorrhizas, and the IBA treatment increased mycorrhizal frequency in this species, whereas TIBA decreased it. Paxillus involutus did not form mycorrhizas, indicating that a low concentration of IAA together with other fungal components were sufficient to stimulate formation and growth of the roots, but not the formation of ECM symbiosis.

New Approaches for Bioaugmentation as a Remediation Technology

“…147,175 Other agricultural applications of bioaugmentation include inoculation of plant seeds with plantgrowth-promoting microorganisms or with plant-protecting microorganisms that are antagonistic to plant pathogens. 15,88,157 Inoculation is also used to transform agricultural products into more useful forms such as the generation of silage from forages. 227 More recently, bioaugmentation has been applied in attempts to remediate numerous environmental problems.…”

Biosynthesis and Secretion of Indole-3-Acetic Acid and Its Morphological Effects on Tricholoma vaccinum-Spruce Ectomycorrhiza

“…Some studies have supported the role for IAA in mycorrhiza (6,8,9), whereas others have refuted it (10)(11)(12). This controversy remains unresolved, and explanations of the mechanisms involved remain elusive.…”

Development of the Poplar-Laccaria bicolor Ectomycorrhiza Modifies Root Auxin Metabolism, Signaling, and Response

“…Some ECM root tips have a recognizable phenotype made of (1) an extensive extramatrical hyphae network prospecting the soil, (2) a mantle of aggregated hyphae that form a sheath-like storage compartment around rootlets, and (3) the Hartig net, a network of hyphae growing intercellularly between epidermal and cortical cells, where nutrients and carbohydrates are exchanged (Massicotte et al, 1987). The formation of ECM roots involves a chain of complex and overlapping developmental processes in the plant host, including the formation of new LRs (Burgess et al, 1996;Tranvan et al, 2000;Niemi et al, 2002;Rincón et al, 2003;Felten et al, 2009;Splivallo et al, 2009), radial expansion of epidermal cells in angiosperm hosts, root hair decay (Horan et al, 1988;Ditengou et al, 2000), and a reduction in the size of the root cap (Massicotte et al, 1987). Together, these morphological changes lead to the characteristic short-root phenotype of ECM roots.…”