Abstract : Arbuscular mycorrhizal (AM) fungi can establish a mutual symbiotic relationship with approximately 70% of terrestrial plants in their roots and supply them with phosphate. Thus, inoculation with AM fungi leads plants to use the phosphate efficiently and improve growth even under phosphate-starvation conditions. We previously demonstrated that secoiridoid glycosides derived from plants belonging to family Gentianaceae can promote hyphal branching and colonization of AM fungi. The present study investigated whether gentian crude drug extract could replace chemical secoiridoid glycoside and be developed as a new agricultural resource at a low cost. The amount of secoiridoid glycoside in a hot water extract of the gentian crude drug (Ryutan) was measured by high-performance liquid chromatography, which was used for the experiments. Bioassay using AM fungus revealed that the crude drug extract promoted hyphal branching equivalent to that promoted by chemical secoiridoid glycoside. Furthermore, treatment with crude drug extract substantially enhanced the colonization rate of AM fungus in chives and tomatoes. Expression analysis of marker genes for symbiosis in tomatoes revealed no significant changes after treatment with crude drug extract. Considering that crude drug extract had no effect on plant growth, our results demonstrate that gentian crude drug extract can be used as secoiridoid glycoside derived from plants belonging to the Gentianaceae family.

Abstract : It is estimated that the annual gross primary production in tropical rainforests is as high as 1/3 of which produced on terrestrial area. Additionally, about 1/3 of the assimilated products by photosynthesis is allocated to fine root. However, because fine root growth, mortality, and decomposition occur simultaneously in a relatively short period of time in underground, it is difficult to observe them throughout the year to elucidate the factors that affect them. In this mini-review, I present our case study that investigated the spatial and temporal patterns of root dynamics in a Bornean tropical rainforest, Malaysia, using a scanner method. Scanner images were taken at five locations in the forest of Lambir Hills national park. Roots were extracted from scanner images using software, and root lengths were measured for each root diameter. The results showed that there was no clear seasonal pattern in the monthly average amount of fine root growth and mortality. In addition, there was little correlation with climatic factors with peak fine root growth and/or mortality for each location. These results may be due to the lack of clear seasonality in tropical rainforests and high diversity of tree species. Furthermore, very fine roots (<0.5 mm diameter) dominated substantial proportion of fine root growth and mortality. I also stated the challenges and perspectives of research on fine root dynamics using the scanner method.