Polyphosphate has a central role in the rapid and massive accumulation of phosphorus in extraradical mycelium of an arbuscular mycorrhizal fungus

摘要

This study evaluated the dynamics of polyP, total P and Pi in an arbuscular mycorrhizal (AM) fungus grown under P-starvation conditions to clarify the significance of polyP in P storage/translocation in AM fungal associations. Lotus japonicus cv Miyakojima MG-20 were sown on moistened filter paper in a Petri dish and germinated at 25 degrees C for 2 days in the dark. Three seedlings were transplanted to the mycorrhizal compartment (MC) of a dual mesh bag culture system in a 230 ml plastic pot (7.6 cm diameter) and inoculated with Glomus sp. HR1 (MAFF 520076) at 500 spores per pot. The time course analysis (from 0 to 9 h after Pi application) of total P and that of polyP in the HC were conducted separately using different batches of plant/fungal material. For these analyses, 22 pots were prepared as one batch, and mycelial samples collected from two pots grown in the same batch were combined as one sample (5-30 mg FW per sample). One set of time course experiments (from 0 to 9 h after Pi application) was conducted using one batch (without replication) and triplicated using three independent batches. The total P content of extraradical mycelium in the HC was 3.6 micro mol mg-1 protein at time zero, which increased to 8.2 micro mol mg-1 protein 5 h after Pi application and then decreased to 5.2 micro mol mg-1 protein 9 h after Pi application. Results showed that the polyP content of extraradical mycelium in the HC increased from 0.5 to 7.1 micro mol mg-1 protein from 0 to 6 h after Pi application and decreased to 2.8 micro mol mg-1 protein by 9 h after Pi application. The apparent accumulation rates of total P and polyP from 0 to 5 h after Pi application were 1.03 and 1.14 micro mol mg-1 protein h-1, respectively, and were not significantly different (P<0.05). Total P and polyP content increased synchronously from 2.9 to 6.7 micro mol mg-1 protein and from 0.2 to 4.3 micro mol mg-1 protein, respectively, from 0 to 5 h after Pi application. This study demonstrated the significance of polyP as the largest P storage and a mediator of long-distance P translocation in AM fungi.