A Flexible, Low-Cost Hydroponic Co-Cultivation System for Studying Arbuscular Mycorrhiza Symbiosis.

Debatosh Das,Philipp Chapman,Caroline Gutjahr,Salar Torabi

doi:10.3389/fpls.2020.00063

Abstract

Arbuscular mycorrhiza (AM) is a widespread symbiosis between plant roots and fungi of the Glomeromycotina, which improves nutrient uptake by plants. The molecular mechanisms underlying development and function of the symbiosis are subject to increasing research activity. Since AM occurs in the soil, most studies targeting a molecular understanding of AM development and function, use solid substrates for co-cultivating plants and AM fungi. However, for some experiments very clean roots, highly controlled nutrient conditions or applications of defined concentrations of signaling molecules (such as hormones) or other small chemicals (such as synthetic inhibitors or signaling agonists) are needed. To this end, hydroponics has been widely used in research on mechanisms of plant nutrition and some hydroponic systems were developed for AM fungal spore amplification. Here, we present a hydroponics set-up, which can be successfully utilized for experimental root colonization assays. We established a “tip-wick” system based on pipette tips and rock wool wicks for co-cultivation of AM fungi with small model plants such as Lotus japonicus. A larger “Falcon-wick” system using Falcon tubes and rockwool wicks was developed for larger model plants such as rice. The hydroponic system can also be employed for growing L. japonicus hairy roots after transformation by Agrobacterium rhizogenes, thus circumventing the laborious cultivation on agar medium-containing Petri dishes during hairy root development. The tip-wick and Falcon-wick systems are easy to use and can be built with low cost, conventional and reusable lab plastic ware and a simple aquarium pump.

Highlights

The roots of most land plant species including prominent economic crops are colonized by beneficial soil fungi of the Glomeromycotina to form a symbiotic association called arbuscular mycorrhiza (AM) (Smith and Read, 2008)
To understand whether arbuscular mycorrhiza can be studied using a simple hydroponic culture setup we established the tipwick hydroponics with L. japonicus and the Arbuscular mycorrhiza (AM) fungus R. irregularis as described in Materials and Methods
No significant difference in total root colonization was observed between plants grown in tip-wick hydroponics or sand pots (Figure 2A)

Summary

Introduction

The roots of most land plant species including prominent economic crops are colonized by beneficial soil fungi of the Glomeromycotina to form a symbiotic association called arbuscular mycorrhiza (AM) (Smith and Read, 2008). Fungal intraradical hyphae spread longitudinally in the root and form specialized highly branched tree-shaped structures, the arbuscules, inside cortical cells (Gutjahr and Parniske, 2013; MacLean et al, 2017; Choi et al, 2018). These arbuscules are surrounded by a plant derived peri-arbuscular membrane and the pair of arbuscule and arbuscule-containing cortex cell is thought to represent the main entity for nutrient exchange between fungus and plant (Luginbuehl and Oldroyd, 2017; Keymer and Gutjahr, 2018). At later stages of the symbiosis, some AM fungi (of the Glomeraceae family) form vesicles, which are filled with lipids and nuclei and increased vesicle formation is often associated with a decline in the number of intact arbuscules (Kobae et al, 2016)

Methods

Results

Conclusion