Adaptation and tolerance mechanisms developed by mycorrhizal Bipinnula fimbriata plantlets (Orchidaceae) in a heavy metal-polluted ecosystem

Abstract

The adaptation and performance of orchid mycorrhizae in heavy metal-polluted soils have been poorly explored. In the present study, proteomic and metabolic approaches were used to detect physiological changes in orchid roots established in a heavy metal-polluted soil and to ascertain whether mycorrhizal fungi affect the metabolic responses of roots. Young Bipinnula fimbriata plantlets were established in control and heavy metal-polluted soils in a greenhouse. After 14 months, exudation of root organic acids, phenolics, percentage of mycorrhization, mineral content, and differential protein accumulation were measured. More root biomass, higher root colonization, and higher exudation rates of citrate, succinate, and malate were detected in roots growing in heavy metal-polluted soils. Higher accumulation of phosphorus and heavy metals was found inside mycorrhizal roots under metal stress. Under non-contaminated conditions, non-mycorrhizal root segments showed enhanced accumulation of proteins related to carbon metabolism and stress, whereas mycorrhizal root segments stimulated protein synthesis related to pathogen control, cytoskeleton modification, and sucrose metabolism. Under heavy metal stress, the proteome profile of non-mycorrhizal root segments indicates a lower induction of defense mechanisms, which, together with the stimulation of enzymes related to carotenoid biosynthesis and cell wall organization, may positively influence mycorrhizal fungi colonization. The results point to different metabolic strategies in mycorrhizal and non-mycorrhizal root segments that are exposed to heavy metal stress. The results indicate that root colonization by mycorrhizal fungi is stimulated to alleviate the negative effects of heavy metals in the orchids.

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“…Endomycorrhizal also have defense strategy to heavy metal stress, the strategy is likely to involve one of the mechanisms, including: (i) new expression of fungus gene (Cicatelli et al, 2010;Ferrol et al, 2016), (ii) metal of quarantined and deposited at extracellular (Koohi, 2014;, (iii) produce of metal binding protein (Singh, 2012;Hrynkiewicz et al, 2012), (iv) reduce of metal absorption (Karimi et al, 2011;Emamverdian et al, 2015), (v) increase efflux (Hildebrandt et al, 2007;Tiwari and Lata, 2018), (vi) formation of complexes outside the cell (Violante et al, 2010;Singh et al, 2016), (vii) release of organic acids (Adeleke et al, 2017;Mishra et al, 2017), and (viii) ligand synthesis such as polyphosphates and metallothionein (Ferrol et al, 2016;Zhan et al, 2019). Indigenous endomycorrhiza spores identified in various plant rhizosphere, obtained spores from two genera that are able to adapt in areas that have high concentrations of Fe and Mn, namely Acaulospora sp.…”

Mycorrhizal Fungi Isolated from Native Terrestrial Orchids from Region of La Araucanía, Southern Chile

“…Despite the fact that asymbiotic seed germination has been tested in Andean terrestrial orchids with positive results, such processes are far from what occurs under natural conditions and the plants lack mycorrhizal benefits, such as nutrition, stress tolerance and defense against plant pathogens [44][45][46][47]. Our results agree with resent studies into mycorrhizal fungi associated with native orchids from Chile, which have shown contrasting abilities to induce seed germination under laboratory conditions, which denotes the crucial role of the OMF in providing the initial C to start germination and promote embryo growth and differentiation [19,22].…”

Root Endophytic Fungal Community and Carbon and Nitrogen Stable Isotope Patterns Differ among Bletilla Species (Orchidaceae)

“…Symbiosis mycorrhizae are a widespread association between fungi and orchid, and play a vital role throughout the whole life cycle of orchid [1]. Root endophytic fungi can not only provide nutrients and hormones for plant growth, but also enhance plant disease resistance and stress tolerance [9,13]. Using the FunGuild database, there were 122, 77, and 62 OTUs could be assigned to the putative life strategies for B. striata, B. ochracea and B. formosana, respectively.…”

“…However, the external hyphae of orchid mycorrhizae can offset these deficiencies in absorbing ability [7]. Researchers have found that root endophytic fungi can not only transport carbohydrates and break down cellulose in the matrix, but can also directly provide nutrients and hormones (e.g., amino acids, gibberellins and jasmonate) for plant growth [5,8,9]. In addition, root endophytic fungi were found to promote the absorption ability of macroelements and microelements by orchids [10][11][12].…”