Making more orchids

Spathoglottis plicata Spathoglottis plicata is a ter­restrial orchid spe­cies that is sold com­mer­cially by many grow­ers. Orchids are slow to pro­pa­gete, and for com­mer­cial suc­cess, many spe­cies rely on micro­p­ropaga­tion. Although this is a com­mon method these days, much of the sci­ence behind regen­er­a­tion of whole plants from tiny specks of plant tis­sue remains uncertain.

This paper describes the impact of auxin dis­tri­bu­tion on the ini­ti­ation of first leaves and the effect of exo­gen­ous auxin applic­a­tion on the form­a­tion of trich­omes and propagat­ive struc­tures in S. plicata seed­lings at three stages of development.


Novak, S.D., & Whitehouse, G.A. (2013) Auxin reg­u­lates first leaf devel­op­ment and pro­motes the form­a­tion of pro­to­corm trich­omes and rhizome-like struc­tures in devel­op­ing seed­lings of Spathoglottis plicata (Orchidaceae). AoB Plants.
Auxin flows in a polar man­ner to tar­get tis­sues and exert its morpho­genic effect. Preventing auxin move­ment, with polar auxin trans­port (PAT) inhib­it­ors, or increas­ing auxin levels in tis­sues through exo­gen­ous applic­a­tion can provide a means for assess­ing the import­ance of appro­pri­ate tis­sue dis­tri­bu­tion and con­cen­tra­tion of this hor­mone dur­ing devel­op­ment. The for­mu­la­tion of cul­ture media for micro­p­ropaga­tion has been the primary focus of most orchid tis­sue cul­ture research, a goal that unveils seed­ling hor­mone responses at a single point in devel­op­ment. This study was unique because it eval­u­ated the auxin response of orch­ids dur­ing three stages of seed­ling devel­op­ment. Seedlings were grown on stand­ard cul­ture media for 10, 35 and 85 days. Each group was sub-cultured onto auxin– and/or PAT inhibitor-containing media for an addi­tional 10, 30 and 60 days, respect­ively. Data were col­lec­ted on first leaf ini­ti­ation, trich­ome form­a­tion and the appear­ance of propagat­ive struc­tures. In the 20-day seed­lings, aux­ins and PAT inhib­it­ors pro­moted pre­co­cious form­a­tion and ran­dom place­ment of pro­to­corm hairs rather than in tufts, as seen in older, con­trol seed­lings. The 65-day seed­lings formed protocorm-like bod­ies, rhizome-like growths from the stem, and fleshy leaves with trich­omes. Seedlings cul­tured for 145 days developed microshoots or cal­lus growth in the axils of older leaves and exhib­ited nec­rosis of ori­ginal seed­ling roots and leaves. In gen­eral, exo­gen­ously applied auxin pro­moted the rever­sion of dif­fer­en­ti­ated Spathoglottis plicata seed­ling tis­sue to a mor­pho­logy that had propagat­ive prop­er­ties. Additionally, aux­ins com­monly induced hair form­a­tion, which sug­gests that pro­to­corm hairs may be root hair-like in nature. This work char­ac­ter­ized three auxin growth responses in S. plicata seed­lings that have not been repor­ted in orch­ids: (i) the inhib­i­tion of first leaf ini­ti­ation and abnor­mal first leaf mor­pho­logy; (ii) the pro­mo­tion of trich­ome form­a­tion; and (iii) the induc­tion of rhizome-like struc­tures and microshoots at a spe­cific stage in seed­ling development.


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