The Symbiotic and Parasitic Relationship Between Orchids and Fungi
A Science Enthusiast
We’ve discussed symbiotic relationships before, from the endosymbiosis that bacteria have with plants and fungi to the mutualistic relationships between plants and fungi directly. But those occasional dalliances are nowhere on the scale of what happens with orchids in the family Orchidaceae.
The Deadly Life of Orchids
Practically all orchids currently known, 28,000 and counting, have a mycorrhizal relationship with fungi. Though not all of it is beneficial for both parties. Due to the heavy reliance that orchids have on fungi, there are often times when this connection is referred to as myco-heterotrophy, where the orchids parasitize the fungi for the nutrients they need without giving much back.
Not all orchids act like this, but the ones that do rely exclusively on the fungi even for photosynthesis during some part of their life cycle, while being more beneficial in other stages. Regardless, for orchids to germinate and grow, they require this fungus relationship. Organic carbon and nitrogen are the two primary commodities that they glean from their fungal partners.
New research from the University of Turin in Italy has focused on the cellular mechanisms and genetics involved in this molecular transfer. Orchids require high amounts of nitrogen to enrich and sustain their plant tissues, but the form of the nitrogen being transferred has been unknown until now. The specific fungus being looked at was Tulasnella calospora.
Their study sequenced the RNA involved in protein creation and found that the nitrogen transfer system had ammonium (NH3) and amino acid transporter pumps, but no mechanisms for assimilating nitrate, showing that that wasn’t the form of nitrogen being used.
Instead, the genes in both the fungi and the orchid implied that it is direct organic nitrogen being transferred and that the ammonium is instead taken by the fungi itself. This better showcases the molecular relationship between the two and how necessary nutrients like nitrogen are given to orchids during their growth cycle.
The Pulse of Plants
This is the first study of its kind to identify the particular genes involved in nitrogen transport for orchids and their symbiotic fungi. Understanding this system allows it to be modeled for various plants and also how fungal interactions with other plants may function.
Figuring out the relationships plants have to their soil environment is critical to sussing out how to grow them better and in wider environmental ranges.
Photo CCs: Blume Gewaechshaus Mainau from Wikimedia Commons