Arbuscular Mycorrhizal Fungi Increase Pb Uptake of Colonized and Non-Colonized Medicago truncatula Root and Deliver Extra Pb to Colonized Root Segment

Abstract

Arbuscular mycorrhizal (AM) fungi establish symbiosis and improve the lead (Pb) tolerance of host plants. The AM plants accumulate more Pb in roots than their non-mycorrhizal counterparts. However, the direct and long-term impact of AM fungi on plant Pb uptake has been rarely reported. In this study, AM fungus (Rhizophagus irregularis) colonized and non-colonized roots of Medicago truncatula were separated by a split-root system, and their differences in responding to Pb application were compared. The shoot biomass accumulation and transpiration were increased after R. irregularis inoculation, whereas the biomass of both colonized and non-colonized roots was decreased. Lead application in the non-colonized root compartment increased the R. irregularis colonization rate and up-regulated the relative expressions of MtPT4 and MtBCP1 in the colonized root compartments. Rhizophagus irregularis inoculation increased Pb uptake in both colonized and non-colonized roots, and R. irregularis transferred Pb to the colonized root segment. The Pb transferred through the colonized root segment had low mobility and might be sequestrated and compartmented in the root by R. irregularis. The Pb uptake of roots might follow water flow, which is facilitated by MtPIP2. The quantification of Pb transfer via the mycorrhizal pathway and the involvement of MtPIP2 deserve further study.

The bianchetto truffle (Tuber borchii) a lead‐resistant ectomycorrhizal fungus increases Quercus cerris phytoremediation potential

“…Another hypothesis to explain the increasing Pb uptake in mycorrhizal plants is that the Pb uptake of roots follows water flow, which is facilitated by the aquaporins as suggested by Zhang et al (2021) P concentration in the leaf was remarkably reduced in the plants treated with Pb. This could be attributed to Pb phytotoxicity on major metabolic processes such as reducing water and nutrients uptake and transport, chlorophyll formation with induced oxidative stress via production of reactive oxygen species (Zulfiqar et al, 2019).…”

“…Another hypothesis to explain the increasing Pb uptake in mycorrhizal plants is that the Pb uptake of roots follows water flow, which is facilitated by the aquaporins as suggested by Zhang et al (2021) in plants of Medicago truncatula Gaertn. colonized with the arbuscular mycorrhizal fungus Rhizophagus irregularis (Błaszk., Wubet, Renker & Buscot) C. Walker & A. Schüßler.…”

Pb Transfer Preference of Arbuscular Mycorrhizal Fungus Rhizophagus irregularis in Morus alba under Different Light Intensities

“…The mulberries in different compartments were labeled according to their positions (L: left; R: right) and shading status (as in Figure 1A,B). To assess the transfer capacity of Pb by the hyphae, 10 g AM inoculum was applied underneath the root of the mulberry for all treatments [27]. Each treatment contained three biological replications following a completely randomized design.…”

“…Plant C investment in this mutualistic symbiosis stimulates the enhancement of the photosynthetic rates, transpiration flow, and water uptake of mycorrhizal plants [23][24][25]. Under Pb stress, the increment of plant growth can dilute the contaminant concentration within the plant, which leads to an improved Pb tolerance of the host plants and a decrease in the Pb concentrations in soils [26,27]. In addition, AM fungi can reduce Pb toxicity to their host plant by modulating the plant antioxidant enzyme system to protect the host plant [26,28,29].…”

“…Several studies have demonstrated that the transpiration of host plants is the driving force for the transport of nutrients (e.g., P, K, and N) from AM fungi to host plant roots [39][40][41] and the suppression of host plant transpiration can decelerate nutrient translocation in proportion to the level of suppression [42]. A previous study has proposed that AM fungi are capable of transferring Pb to the host plant by stimulating transpiration flow [27]. However, a detailed understanding of how Pb is transferred to mycorrhizal roots remains unknown.…”