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Australian Journal of Botany Australian Journal of Botany Society
Southern hemisphere botanical ecosystems
RESEARCH ARTICLE

Ultrastructure of symbiotic germination of the orchid Dendrobium officinale with its mycobiont, Sebacina sp.

J. Chen A C , H. Wang A C , S. S. Liu A , Y. Y. Li A and S. X. Guo A B
+ Author Affiliations
- Author Affiliations

A Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100193, P.R. China.

B Corresponding author. Email: sxguo1986@163.com

C These authors contributed equally to this work.

Australian Journal of Botany 62(3) 229-234 https://doi.org/10.1071/BT14017
Submitted: 30 January 2014  Accepted: 8 June 2014   Published: 2 July 2014

Abstract

Dendrobium officinale is an endangered epiphytic orchidaceous medicinal plant. Similar to other orchid plants, the seed germination of D. officinale under natural conditions depends nutritionally upon mycorrhizal fungi. The compatible fungi have been isolated from D. officinale protocorms using in situ seed baiting technique in our previous studies. However, the interaction between seed germination of D. officinale and its mycobiont is still unclear. In the present study, we investigated the morphological changes of seed and fungus during the symbiotic germination using a light microscope and transmission electron microscope. Seeds of D. officinale have no conspicuous suspensor cells. The fungus enters into the embryo cell through the posterior end of the embryo and colonises the cortical cell in the first stage of germination (Stage 1). Then, the hyphae form pelotons with the protocorm development (Stages 1–3). After protocorm formation, the reinvaded fungal hyphae conspicuously decrease. Invaded hyphae lose bioactivity, form clumps and start degeneration at Stage 4 or 5 (seedling development). When penetrating the neighbouring cortical cell, the fungal hyphae constrict to collar shape at the contacted site and follow by swelling in the apex. Our study suggested that fungi trigger protocorm development and concomitant reserve utilisation during the symbiotic germination.

Additional keywords: mycorrhizal association, orchidaceae, seed germination.


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