Quantitative evaluation of protocorm growth and fungal colonization in Bletilla striata (Orchidaceae) reveals less-productive symbiosis with a non-native symbiotic fungus

BMC Plant Biology

Methodology Article

Masako Fuji¹  Chihiro Miura¹  Hironori Kaminaka¹  Masahide Yamato²  Shotaro Nagata³  Yuria Otani³  Tatsuki Yamamoto³  Takahiro Yagame⁴ 

[1]Faculty of Agriculture, Tottori University, Tottori, Japan

[2]Faculty of Education, Chiba University, Chiba, Japan

[3]Graduate School of Agriculture, Tottori University, Tottori, Japan

[4]Tsukuba Botanical Garden, National Museum of Nature and Science, Tsukuba, Japan

关键词: Bletilla striata;    Germination;    Mycorrhizal symbiosis;    Orchid;    Quantitative evaluation;   

DOI  :  10.1186/s12870-017-1002-x

 received in 2016-11-18, accepted in 2017-02-13,  发布年份 2017

来源: Springer

【 摘 要 】

BackgroundIn nature, orchid plants depend completely on symbiotic fungi for their nutrition at the germination and the subsequent seedling (protocorm) stages. However, only limited quantitative methods for evaluating the orchid–fungus interactions at the protocorm stage are currently available, which greatly constrains our understanding of the symbiosis. Here, we aimed to improve and integrate quantitative evaluations of the growth and fungal colonization in the protocorms of a terrestrial orchid, Blettila striata, growing on a plate medium.ResultsWe achieved both symbiotic and asymbiotic germinations for the terrestrial orchid B. striata. The protocorms produced by the two germination methods grew almost synchronously for the first three weeks. At week four, however, the length was significantly lower in the symbiotic protocorms. Interestingly, the dry weight of symbiotic protocorms did not significantly change during the growth period, which implies that there was only limited transfer of carbon compounds from the fungus to the protocorms in this relationship. Next, to evaluate the orchid–fungus interactions, we developed an ink-staining method to observe the hyphal coils in protocorms without preparing thin sections. Crushing the protocorm under the coverglass enables us to observe all hyphal coils in the protocorms with high resolution. For this observation, we established a criterion to categorize the stages of hyphal coils, depending on development and degradation. By counting the symbiotic cells within each stage, it was possible to quantitatively evaluate the orchid-fungus symbiosis.ConclusionsWe describe a method for quantitative evaluation of orchid-fungus symbiosis by integrating the measurements of plant growth and fungal colonization. The current study revealed that although fungal colonization was observed in the symbiotic protocorms, the weight of the protocorm did not significantly increase, which is probably due to the incompatibility of the fungus in this symbiosis. These results suggest that fungal colonization and nutrition transfer can be differentially regulated in the symbiosis. The evaluation methods developed in this study can be used to study various quantitative aspects of the orchid-fungus symbiosis.

【 授权许可】

CC BY   
© The Author(s). 2017