VBA-AMF: A VBA Program Based on the Magnified Intersections Method for Quantitative Recording of Root Colonization by Arbuscular Mycorrhizal Fungi

Role of melatonin in enhancing arbuscular mycorrhizal symbiosis and mitigating cold stress in perennial ryegrass (Lolium perenne L.)

Melatonin is a biomolecule that affects plant development and is involved in protecting plants from environmental stress. However, the mechanisms of melatonin's impact on arbuscular mycorrhizal (AM) symbiosis and cold tolerance in plants are still unclear. In this research, AM fungi inoculation and exogenous melatonin (MT) were applied to perennial ryegrass (Lolium perenne L.) seedlings alone or in combination to investigate their effect on cold tolerance. The study was conducted in two parts. The initial trial examined two variables, AM inoculation, and cold stress, to investigate the involvement of the AM fungus Rhizophagus irregularis in endogenous melatonin accumulation and the transcriptional levels of its synthesis genes in the root system of perennial ryegrass under cold stress. The subsequent trial was designed as a three-factor analysis, encompassing AM inoculation, cold stress, and melatonin application, to explore the effects of exogenous melatonin application on plant growth, AM symbiosis, antioxidant activity, and protective molecules in perennial ryegrass subjected to cold stress. The results of the study showed that compared to non-mycorrhizal (NM) plants, cold stress promoted an increase in the accumulation of melatonin in the AM-colonized counterparts. Acetylserotonin methyltransferase (ASMT) catalyzed the final enzymatic reaction in melatonin production. Melatonin accumulation was associated with the level of expression of the genes, LpASMT1 and LpASMT3. Treatment with melatonin can improve the colonization of AM fungi in plants. Simultaneous utilization of AM inoculation and melatonin treatment enhanced the growth, antioxidant activity, and phenylalanine ammonia-lyase (PAL) activity, while simultaneously reducing polyphenol oxidase (PPO) activity and altering osmotic regulation in the roots. These effects are expected to aid in the mitigation of cold stress in Lolium perenne. Overall, melatonin treatment would help Lolium perenne to improve growth by promoting AM symbiosis, improving the accumulation of protective molecules, and triggering in antioxidant activity under cold stress.

Effects of Arbuscular Mycorrhizal Fungi on the Growth and Root Cell Ultrastructure of Eucalyptus grandis under Cadmium Stress

Eucalyptus grandis (E. grandis) has been reported to form a symbiosis with arbuscular mycorrhizal fungi (AMF), which plays an important role in improving plant tolerance of heavy metal. However, the mechanism of how AMF intercept and transport cadmium (Cd) at the subcellular level in E. grandis still remains to be researched. In this study, a pot experiment was conducted to investigate the growth performance of E. grandis under Cd stress and Cd absorption resistance of AMF and explored the Cd localization in the root by using transmission electron microscopy and energy dispersive X-ray spectroscopy. The results showed that AMF colonization could enhance plant growth and photosynthetic efficiency of E. grandis and reduce the translocation factor of Cd under Cd stress. After being treated with 50, 150, 300, and 500 μM Cd, the translocation factor of Cd in E. grandis with AMF colonization decreased by 56.41%, 62.89%, 66.67%, and 42.79%, respectively. However, the mycorrhizal efficiency was significant only at low Cd concentrations (50, 150, and 300 μM). Under 500 μM Cd concentration condition, the colonization of AMF in roots decreased, and the alleviating effect of AMF was not significant. Ultrastructural observations showed that Cd is abundant in regular lumps and strips in the cross-section of E. grandis root cell. AMF protected plant cells by retaining Cd in the fungal structure. Our results suggested that AMF alleviated Cd toxicity by regulating plant physiology and altering the distribution of Cd in different cell sites.

Endophytism of Fusarium Solani in Meristems of Delonix Regia (Bojer ex Hook.) Raf

A bright yellow pigment-producing endophytic fungus strain GMRS1 was isolated from the meristems of Delonix regia (Bojer ex Hook.) Raf. The fungus was identified as Fusarium solani on grounds of morphological and molecular analysis. The chemical composition of the crude pigments was partially analyzed by Quadrupole Time-of-flight Liquid chromatography/Mass spectrometry/Mass spectrometry and the major compounds were reported. The crude pigments were proved toxic and unsafe by acute oral toxicity study on Wistar rats. The total cholesterol and glucose levels of the rats ingested with crude pigments were significantly elevated than the control rats. The treatment rats were further observed with damaged liver and kidney tissues. The LD₅₀ value of the crude pigments was higher than 1000 mg/kg of body weight.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12088-021-00968-w.

Cultivation of arbuscular mycorrhizal Broussonetia papyrifera seedlings by planting the mycorrhizal nurse plant downwards

Plant mycorrhization can be achieved by transplanting new seedlings with mycorrhizal nurse plants; however, this method inevitably induces plant interactions. Transplanting nurse plants downwards may prevent light competition among new seedlings and nurse plants in the same pot. We hypothesized that seedling mycorrhization via mycorrhizal provision from plants planted downwards would be a feasible and efficient strategy. We used seedlings cultivated for 6 months after inoculation with arbuscular mycorrhizal fungi (AMF) as nurse plants, and seedlings cultivated for 1 month without AMF as recipient plants, transplanting one nurse plant and three recipient plants together in one pot. We compared two approaches for cultivating mycorrhizal Broussonetia papyrifera seedlings: planting mycorrhizal nurse plants upwards (M-NU) and downwards (M-ND). We also planted non-mycorrhizal nurse plants upwards (NM-NU) and downwards (NM-ND) as controls. We analyzed growth parameters and the mycorrhizal colonization status of recipient plants at 45, 60, and 75 days after planting (DAP). As expected, the plant growth, gas exchange, and root morphological parameters of recipient plants with mycorrhizal nurse plants were higher than those of recipient plants with non-mycorrhizal nurse plants at 60 and 75 DAP. Furthermore, the AMF colonization status and physiological growth status of M-ND recipient plants were improved compared with M-NU recipient plants. Our results demonstrate that inducing seedling mycorrhization by planting mycorrhizal nurse plants downwards is a feasible strategy for achieving AMF symbiosis while mitigating negative interactions among plants.

A historical perspective on mycorrhizal mutualism emphasizing arbuscular mycorrhizas and their emerging challenges

Arbuscular mycorrhiza, one of the oldest interactions on earth (~ 450 million years old) and a first-class partner for plants to colonize emerged land, is considered one of the most pervasive ecological relationships on the globe. Despite how important and old this interaction is, its discovery was very recent compared to the long story of land plant evolution. The story of the arbuscular mycorrhiza cannot be addressed apart from the history, controversies, and speculations about mycorrhiza in its broad sense. The chronicle of mycorrhizal research is marked by multiple key milestones such as the initial description of a "persistent epiderm and pellicular wall structure" by Hartig; the introduction of the "Symbiotismus" and "Mycorrhiza" concepts by Frank; the description of diverse root-fungal morphologies; the first description of arbuscules by Gallaud; Mosse's pivotal statement of the beneficial nature of the arbuscular mycorrhizal symbiosis; the impact of molecular tools on the taxonomy of mycorrhizal fungi as well as the development of in vitro root organ cultures for producing axenic arbuscular mycorrhizal fungi (AMF). An appreciation of the story - full of twists and turns - of the arbuscular mycorrhiza, going from the roots of mycorrhiza history, along with the discovery of different mycorrhiza types such as ectomycorrhiza, can improve research to help face our days' challenge of developing sustainable agriculture that integrates the arbuscular mycorrhiza and its ecosystem services.