An Orchid, Two Fungi

An Orchid, Two Fungi - Small Things Considered Skip to content by Roberto What do you do when you have a headache? Per­haps you ob­tain re­lief by tak­ing a pill, maybe ac­eta­minophen, maybe ibupro­fen. Thanks to the won­ders of mod­ern med­i­cine, we can tend to nu­mer­ous ail­ments with a panoply of syn­thetic com­pounds, i.e., phar­ma­ceu­ti­cals. But, if you fol­low Tra­di­tional Chi­nese Med­i­cine, your treat­ment of headaches, as well as other mal­adies like ver­tigo and dizzi­ness, would no doubt in­clude the widely used "Tian ma." The use of this med­i­c­i­nal herb goes back more than 2000 years; it is doc­u­mented in the Shen­nong Ben­cao­jing , the clas­sic com­pi­la­tion of Chi­nese med­i­c­i­nal plants writ­ten around the first cen­tury. Tian ma is the com­mon name for the tu­ber of the or­chid Gas­tro­dia elata. Be­fore div­ing deeper into the fas­ci­nat­ing life cy­cle of G. elata , here's a very brief primer on or­chids. The or­chid fam­ily of plants (Or­chi­daceae) is very large. It is thought to rep­re­sent about 10% of all seed plants and con­tains in the or­der of 30,000 species. Within the stun­ning di­ver­sity of this fam­ily, there are sev­eral shared char­ac­ter­is­tics among its mem­bers. Quite no­tably, their seeds are ex­tremely small. Thus, the em­bryo has vir­tu­ally no nu­tri­ents to grow on. In­stead, to ini­ti­ate growth, or­chids of­ten need the help of other or­gan­isms. This is where the mi­cro­bi­ol­ogy of or­chids gets in­ter­est­ing. To ger­mi­nate, most or­chid seeds must land on or very near fungi and then es­tab­lish an in­ti­mate re­la­tion­ship where the fun­gus pro­vides most nu­tri­ents. This de­pen­dency of the plant on a fun­gus is known as my­co­heterotro­phy. Most or­chids are fac­ul­ta­tive my­co­heterotrophs. They even­tu­ally turn on pho­to­syn­the­sis and be­come au­totrophs. But not G. elata. Gas­tro­dia elata . Source As plants go, G. elata has some un­ex­pected fea­tures. Above ground, it con­sists of a sin­gle stem with flow­ers at its tip. But it does not de­velop any branches or leaves. Most strik­ingly, there is noth­ing green about this plant. It never makes any chloro­phyll, no pho­to­syn­the­sis. What? Is this re­ally a plant? No leaves, no branches, no pho­to­syn­the­sis? What kind of a plant is this? G. elata takes my­co­heterotro­phy to the ex­treme, it is an ob­lig­ate my­co­heterotroph. The bulk of this plant's mass is un­der­ground. But, com­ple­ment­ing its above-ground odd­ity, it has no ma­jor root sys­tem. Rather, the or­chid forms a sin­gle large tu­ber, the source of Tian ma. The life cy­cle of Gas­tro­dia elata . Mycena is es­sen­tial for the stage de­noted by the red ar­rows, Armil­laria is nec­es­sary for the stage de­picted by the green ar­rows, no fungi are re­quired for the stages in­di­cated by the blue ar­rows. Source It takes around three years for G. elata to com­plete its life cy­cle. I sug­gest this re­view as an ex­cel­lent read to get at the nitty gritty de­tails of how this cy­cle is de­pen­dent on the es­tab­lish­ment of in­ti­mate as­so­ci­a­tions with two dif­fer­ent fungi. Here I will sum­ma­rize some of this orchid's de­vel­op­ment that I find most fas­ci­nat­ing. First, to ger­mi­nate, the seeds must en­counter a fun­gus of the genus Mycena . This is a rare event in nat­ural set­tings; it is no won­der that a sin­gle G. elata plant will pro­duce sev­eral mil­lion of these tini­est of seeds. The Mycena fungi pro­vide the sig­nals needed for seed ger­mi­na­tion and the nu­tri­ents for the ini­tial veg­e­ta­tive growth of the plant. But de­vel­op­ment stops there. The plant en­ters an ini­tial dor­mancy that lasts some four months. Then, a sec­ond fun­gus comes into the scene that pro­vides the nu­tri­ents re­quired for the for­ma­tion of im­ma­ture tu­bers. Af­ter a sec­ond dor­mancy pe­riod, this sec­ond fun­gus again pro­vides the nu­tri­ents for the de­vel­op­ment of ma­ture tu­bers. Af­ter yet a third dor­mancy, and us­ing the nu­tri­ents from the tu­ber, the sin­gle stem emerges. The life cy­cle is com­pleted with the for­ma­tion of flow­ers, pol­li­na­tion, and seed de­vel­op­ment. I must ad­mit that it was the na­ture of the sec­ond fun­gal sym­biont that drew my at­ten­tion to this or­chid. It was none other that Armil­laria gal­lica ! Why does this ex­cite me so? Well, A. gal­lica and closely re­lated species are well-known for an­other rea­son. In­di­vid­u­als can get very old and very large. These fea­tures were pop­u­lar­ized by the gifted writer and evo­lu­tion­ary bi­ol­o­gist Stephen Jay Gould in his de­light­ful 1992 es­say "A Hu­mungous Fun­gus Among Us," pub­lished in Nat­ural His­tory Mag­a­zine. (The whole of the 1992 vol­ume is down­load­able from the AMNH Dig­i­tal Li­brary . Within that vol­ume, search for is­sue 7, page 10 and en­joy the read!) Some Armil­laria in­di­vid­u­als com­pete for be­ing among the biggest, heav­i­est, and old­est in­di­vid­u­als on Earth. One found in east­ern Ore­gon is thought to cover ten square kilo­me­ters, weigh some­where be­tween 7,000 and 35,000 tons, and may be up­wards of 8,000 years old. Armil­laria achieve fast growth and ef­fec­tive pre­da­tion by bundling many in­di­vid­ual hy­pha into root-like threads, rhi­zomorphs. Long-time STC fans might re­mem­ber Elio's post on Armil­laria de­scrib­ing its gar­gan­tuan di­men­sions. Armil­laria in­vades the veg­e­ta­tive prop­a­ga­tion corm of G . elata. Epi­der­mal cells (A) . Pelo­ton cells (B) . Sus­cep­ti­ble fun­gal cell © . Di­ges­tive cells (D) . Rhi­zomorph (E) . Outer sheath (F) . Mem­brane (G) . Hy­phae (H) . The hy­phal chan­nel (I) . Hy­phal flow (J) . Pap­il­lary pro­tru­sion (K) . Pelo­ton (L) . Hy­phal frag­ments (M) . Source Back to G. elata . What is the Hu­mungous Fun­gus do­ing on this de­vel­op­ing or­chid. This is yet an­other ex­am­ple of an in­tri­cate two-way chem­i­cal ex­change process be­tween dif­fer­ent species. The or­chid se­cretes phy­to­hor­mones such as strigo­lac­tones that are sensed by the fun­gus as an at­trac­tant. Us­ing the strength pro­vided by its large rhi­zomorphs, along with di­ges­tive en­zymes, the fun­gus bores into the de­vel­op­ing or­chid by break­ing through the epi­der­mis (out­er­most layer). Once in the cor­tex, the rhi­zomorph dis­so­ci­ates and hy­phae pen­e­trate in­di­vid­ual "fun­gal-sus­cep­ti­ble" cells. From here on­wards the en­dosym­bio­sis reaches a fas­ci­nat­ing equi­lib­rium. In­side some of the cor­ti­cal cells the hy­phae grow as coils (called pelo­tons, prob­a­bly be­cause of the sim­i­lar­ity to groups of cy­clists...). If such growth were to con­tinue un­abated, the or­chid would suf­fer. In­stead, the or­chid con­trols the fun­gal in­fec­tion. First, through the ac­tion of gas­tro­di­an­ins, small an­ti­fun­gal pro­teins. Sec­ond and more im­por­tantly, some of the plant's cor­ti­cal cells turn into di­ges­tive cells, where the fun­gal pelo­tons are com­pletely de­graded, pro­vid­ing the plant all the nu­tri­ents it needs for tu­ber growth. Of course, there's a lot more to these in­ter­ac­tions than these two part­ners. Where does the fun­gus ob­tain its nu­tri­ents? As any self-re­spect­ing sapro­phyte, from de­cay­ing leaf mat­ter and dead trees. Armil­laria rhi­zomorphs can also in­vade liv­ing trees and slowly kill them. So, the hu­mungous fun­gus can be killing a tree in one place while, at a very dis­tant lo­ca­tion, it is di­gested by a de­vel­op­ing or­chid, giv­ing the plant nu­tri­ents to grow its tu­ber. A tu­ber which, in turn, may some­day be dug out and in­gested by a hu­man to re­lieve a mal­ady. A hu­man, who, in time, might plant a tree... Mul­ti­par­tite sym­bioses know no end! We'd be de­lighted to hear from you! You can com­ment be­low, send us an email or reach us via Bluesky or Mastodon . Please sub­scribe to get email no­ti­fi­ca­tions of our new posts. Other Posts by Aleks Prochera — Imag­ine you look like some­one dan­ger­ous, a crim­i­nal, an en­emy. De­spite be­ing an ex­em­plary cit­i­zen, you have to deal with the pos­si­bil­ity that, at one point or an­other, you might get in trou­ble with law en­force­ment sim­ply be­cause you ap­pear threat­en­ing. That's a strug­gle that many bac­te­r­ial mem­bers of a plant's mi­cro­biome face. by Elio — This is the ti­tle my friend Fred Nei­d­hardt re­cently used for a talk, and a good ques­tion it is. I sup­pose that most mi­cro­bi­ol­o­gists and the read­ers of this blog would split the an­swer down the mid­dle, the bio­mass of this planet and the chem­i­cal trans­ac­tions therein be­ing about half… by Janie — From a mi­cro­bial per­spec­tive, in­sect me­ta­mor­pho­sis is a trea­cher­ous bu­si­ness. The trans­for­ma­tion from lit­tle earth­bound craw­ler to lapis-blue flier is a fla­shy eye-cat­cher, but the change is more than skin-deep. Deep with­in the lar­va, the con­tents of the gut are emp­tied, in­tes­ti­nal cells wi­ther away by auto­phagy and apo­pto­sis, and the ca­vi­ty is re-up­­hol­ster­ed with di­vi­ding stem cells... by Elio — The di­ges­tive sys­tem of an­i­mals can be won­drously com­plex. Think of our own, which con­sists of such di­verse or­gans as the mouth, the esoph­a­gus, stom­ach, the small and large in­testines, and the anus. Each one is re­spon­si­ble for a par­tic­u­lar set of func­tions. Is such a di­vi­sion of la­bor also seen in "sim­pler" an­i­mals? This ques­tion was asked re­cently of wood-feed­ing bee­tles by a group of no less than 18 in­ves­ti­ga­tors from all over the US. by Elio — Fungi, along with se­lected bac­te­ria and in­ver­te­brates, are in­cluded in the list of bi­o­lu­mi­nes­cent or­gan­isms. These fungi are pretty unique be­cause, un­like the other light-emit­ting or­gan­isms, fungi don't walk, swim, or fly. Thus, the usual ex­pla­na­tions for bi­o­lu­mi­nes­cence... by Elio — We dealt with a mon­ster fos­sil fun­gus be­fore. In the in­ter­est of ex­pe­di­ency, let me reprint part of what I said: "Sev­eral mu­se­ums pos­sess spec­i­mens of a cylin­dri­cal or­gan­ism named Pro­to­tax­ites whose tree-like trunks mea­sure up to 8 me­ters long by 1 me­ter wide. Pro­to­tax­ites dated from ap­prox­i­mately 420 to 350 mil­lion... Subscribe Notify of new follow-up comments new replies to my comments Label {} [+] Name* Email* Website Label {} [+] Name* Email* Website 4 Comments Oldest Newest Most Voted Inline Feedbacks View all comments Andrea Clardy 17 days ago Wow! What a re­mark­able, im­prob­a­ble, com­plex set of sym­bioses! 0 Reply Admin STC 17 days ago Reply to Andrea Clardy Hi An­drea, many thanks for your com­ment! Yes, these sorts of sym­bioses will never cease to amaze us. Won­der­ful to know you are read­ing STC! — Roberto 0 Reply Ole Skovgaard 17 days ago Thanks for this beau­ti­ful piece link­ing these mys­te­ri­ous plants with mi­cro­bi­ol­ogy – well, in this case mac­ro­bi­ol­ogy would hardly be a mis­spelling … 0 Reply Admin STC 16 days ago Reply to Ole Skovgaard Thanks for your kind words Ole! It is all one won­der­ful bi­ol­ogy! — Roberto 0 Reply wpDiscuz Insert Search Search Toggle Menu Close Search for: Search