Arbuscular mycorrhizal fungi and endophytic fungi differentially modulate polyamines or proline of peach in response to soil flooding

Symbiotic fungi are involved in plant flooding tolerance, while the underlying mechanism is not yet known. Since polyamines and proline are also associated with stress tolerance, it is hypothesized that the enhancement of stress resistance by symbiotic fungi is associated with changes in polyamines (PAs) and/or proline. The aim of this study was to analyze the effect of inoculation with Funneliformis mosseae and Serendipita indica on growth, polyamine and its metabolism, and proline and its metabolism in peach (Prunus persica) under flooded conditions. Two-week flooding did not affect root colonization frequence of F. mosseae, while it promoted root colonization frequence of S. indica. Inoculated plants with F. mosseae and S. indica maintained relatively higher growth rates of peach under flooding than those of uninoculated plants. F. mosseae promoted root ornithine levels and arginine decarboxylase and ornithine decarboxylase activities under flooding, which promoted putrescine (Put), cadaverine (Cad) and spermidine (Spd) levels. Conversely, S. indica inhibited levels of arginine, ornithine, and agmatine and arginine decarboxylase activities, thus decreasing PAs under flooding. PAs were negatively correlated with expressions of polyamine uptake transporter 1 (PUT1) and PUT4 in peach. Transporters of polyamine (TPO) of F. mosseae and S. indica were regulated by flooding, of which FmTPO1 was positively correlated with Put, Cad, and Spd, along with a positive correlation of Spd with SiTPO1, SiTPO2, and SiTPO4. Under flooding, F. mosseae inhibited proline, while S. indica increased proline, correlated with Δ1-pyrroline-5-carboxylate synthetase 2 expressions. It thus was concluded that F. mosseae modulated polyamine accumulation while S. indica induced proline accumulation to tolerate flooding.