Inflorescence stem grafting made easy in Arabidopsis
© Nisar et al.; licensee BioMed Central Ltd. 2012
Received: 17 September 2012
Accepted: 17 December 2012
Published: 19 December 2012
Plant grafting techniques have deepened our understanding of the signals facilitating communication between the root and shoot, as well as between shoot and reproductive organs. Transmissible signalling molecules can include hormones, peptides, proteins and metabolites: some of which travel long distances to communicate stress, nutrient status, disease and developmental events. While hypocotyl micrografting techniques have been successfully established for Arabidopsis to explore root to shoot communications, inflorescence grafting in Arabidopsis has not been exploited to the same extent. Two different strategies (horizontal and wedge-style inflorescence grafting) have been developed to explore long distance signalling between the shoot and reproductive organs. We developed a robust wedge-cleft grafting method, with success rates greater than 87%, by developing better tissue contact between the stems from the inflorescence scion and rootstock. We describe how to perform a successful inflorescence stem graft that allows for reproducible translocation experiments into the physiological, developmental and molecular aspects of long distance signalling events that promote reproduction.
Wedge grafts of the Arabidopsis inflorescence stem were supported with silicone tubing and further sealed with parafilm to maintain the vascular flow of nutrients to the shoot and reproductive tissues. Nearly all (87%) grafted plants formed a strong union between the scion and rootstock. The success of grafting was scored using an inflorescence growth assay based upon the growth of primary stem. Repeated pruning produced new cauline tissues, healthy flowers and reproductive siliques, which indicates a healthy flow of nutrients from the rootstock. Removal of the silicone tubing showed a tightly fused wedge graft junction with callus proliferation. Histological staining of sections through the graft junction demonstrated the differentiation of newly formed vascular connections, parenchyma tissue and lignin accumulation, supporting the presumed success of the graft union between two sections of the primary inflorescence stem.
We describe a simple and reliable method for grafting sections of an Arabidopsis inflorescence stem. This step-by-step protocol facilitates laboratories without grafting experience to further explore the molecular and chemical signalling which coordinates communications between the shoot and reproductive tissues.
KeywordsGrafting Wedge Plant development Inflorescence stem Systemic Signal Molecule Transmission Arabidopsis Scion
Grafting is a traditional method for uniting one part (scion) of a plant (e.g. shoot or bud) with the root system of another. It has become a fundamental method for studying physiological, genetic and molecular aspects of long distance signalling events. There are many grafting techniques described, of which some are widely used in agriculture as a mean to facilitate asexual propagation. Advantages are to induce dwarfing and fruitfulness, avoid juvenility, promote sturdiness[1, 2] as well as facilitate domestication of both woody and non woody plant species[3, 4]. In the laboratory, grafting for most dicot species is now a well-established practice widely used to study plant nutrition, disease resistance against phloem associated pathogens[6, 7], apical dominance and shoot branching[8, 9].
Grafting has provided a powerful approach to combine diverse genotypes and investigate the transport of various long-distance signalling molecules. The technique of grafting has demonstrated that 1) the transfer of tuberigen stimulates tuberization in potato[10–12], 2) autoregulation of nodulation is regulated via long-distance shoot and root derived signals,[13–16], 3) allocation of nutrients by the Arabidopsis Na+ transporter AtHKT1 functions in the root to control Na+ accumulation in the shoot[17–20] and that the phloem mobile miRNA that acts as long-distance signal regulating phosphate homeostasis in Arabidopsis[18, 19], 4) transport of phytohormone growth molecules such as the movement of cytokinin from roots to shoots and translocation of strigolactone from root to shoot which inhibits shoot branching[22, 23], 5) the movement of secondary metabolites such as alkaloids and 6) mobile flowering signals synthesized in the leaves can stimulate flowering within the shoot apical meristem[25–28].
Hypocotyl micrografting techniques have been successfully used to study developmental and physiological processes between the root and shoot[2, 8, 29–31], while the inflorescence meristem grafting methods have generally been used to investigate the nature of signals coordinating floral reproductive growth[32–36]. Indeed small RNAs have been shown to move across the junctions from hypocotyl and inflorescence grafts, most likely via the plasmodesmata rather than the phloem[37–39]. Experiments investigating the movement of mobile signals that control apical dominance (cytokinins and auxin), nutrient uptake (phosphorus) and cellular differentiation (small RNAs) are key research areas that can benefit from the inflorescence grafting technique. Given that this technique investigates a post-floral transition, it provides a unique system to discover signals mediating reproductive development.”
This paper describes a protocol for efficient wedge-style grafting of the primary inflorescence scion to the rootstock. We define the location, timing and preparation of the floral stems for grafting. An inflorescence growth assay was developed to determine the healthiest of grafts. Histological studies confirmed the differentiation of vascular connections as well as a successful graft union.
Results and discussion
A robust and highly efficient grafting method for arabidopsis
Preliminary homografting experiments were carried out using young primary inflorescence stems of uniform age, length, and diameter using the model plant, Arabidopsis thaliana. Both horizontal and wedge-style grafting techniques proved less successful then previously reported. Difficulties were encountered in maintaining hydraulic turgor as well as providing structural support to the grafted stem sections. For the horizontal grafts we found that by sliding silicone tubing over the graft junction and sealing with either parafilm or Petroleum Jelly (Vaseline) provided structural support as well as minimise scion transpiration allowing reproductive tissues to survive until the graft union re-establishes xylem and phloem continuity. However, within one week of growth the grafted scions began to wilt showing signs of necrosis, most likely due to poor contact between the grafted stem sections. It is essential that sufficient contact between the stem of the scion and root stock is maintained in order to promote the development of vascular connections, which allow the flow of nutrients through the stem to the reproductive organs.
A non-destructive inflorescence growth assay for identifying healthy grafts
The success of grafting was determined by monitoring scion growth and development: processes that require the transport of water, nutrients and signalling molecules. Previously, grafting had been considered successful when scions remained alive on top of the rootstock. Here we further redefine that a successful floral stem graft should 1) be able to maintain shoot apical dominance as evidenced by a taller primary stem (Figure2C; 7 DAGr), 2) grow healthy cauline shoot branches which continue to develop (Figure2D; 14 DAGr) and 3) produce fertile reproductive siliques (Figure2E; 22 DAGr). The most definitive measure of success of a grafted plant is by pruning (i.e. remove cauline shoot branches and reproductive siliques), which promotes the growth of new cauline leaf and shoot tissues eventually leading to the formation of new reproductive siliques (Figure2F; 60 DAGr).
Anatomy of graft union formation at the wedge junction
Technical tricks for successful wedge-style inflorescence grafting in Arabidopsis
Description of method
Tips and tricks
Plant Growth Before Grafting
Vernalise seedlings to synchronise the initiation of floral meristem development.
Use young inflorescence stems of uniform age, length (<10 cm), and diameter (1.5 to 3 mm).
Horizontal Excision of Stem
Use flexible razor blade to cut the floral stem below the cauline node (2 cm above the shoot meristem) and immediately place scion in sterile water.
Preparation of Root Stock Stem
Slide 1 cm of soft and flexible silicone tubing (sizes range from 1–3 mm ID) over the root stock stem.
Cut vertical incision into the root stock stem.
Preparation of Scion Stem
Trim the scion stem using flexible razor blade into a wedge.
Join and Support Grafted Stems
Place scion wedge into root stock stem incision.
Slide the silicone tubing over the graft junction.
Inject sterile water on top of silicone tube to maintain turgor.
Pre-stretch parafilm and wrap over the graft junction supported by silicone tube so as to avoid desiccation.
Plant Growth After Grafting
Maintain high humidity (70%) for 1–2 weeks.
Slowly acclimate grafted plants to normal growth conditions.
Clip new rosette shoot growth to promote further development of the primary grafted floral stem.
Remove meristems showing reproductive siliques to promote new cauline shoot growth of new tissues.
Evaluation of Grafting Success
Grafting was considered successful when scions remained green and health on top of the rootstock as evident by the maintenance of apical dominance, development of new cauline leaves and branches, as well as production of reproductive siliques.
Use the inflorescence growth assay to select the best and most successful grafted plants for further analysis.
Planting and growth conditions
Dried seeds were sown onto DEBCO seed raising mixture, fertilized with 3 g/L of mini Osmocote and cold-stratified at 4°C in the dark for three days to synchronise germination. Seeds were germinated in the light (16 hrs, 21°C, 55% humidity, 150 μmol m-2 s-1 irradiance), irrigated twice a week with water and grown under these conditions unless otherwise stated. In order to synchronise inflorescence meristem initiation, germinated seedlings (7 DAG) were vernalised for four weeks at 4°C before returning seedlings to the growth conditions described above. Vernalization may not need to be performed if all plant genotypes flower simultaneously. Reducing the day length will slow growth and produce larger rosettes with thicker inflorescence meristems, thereby facilitating preparation of the scion and root stock for wedge style grafting.
Histology and microscopy
Plant samples were stained with aqueous 0.01% Toluidine Blue-O for 1 minute and rinsed in water. Fresh tissue specimens were placed on glass slides, covered with a glass coverslip and water used to fill the airspaces and maintain cell turgor. Slides were examined under a Leica MZ16FA Fluorescence Stereomicroscope and representative sections photographed.
Reagents and consumables
Double edge safety razor blades (fine stainless steel, platinum coated to enhance sharpness)
1 cc/mL Plastic syringe
Silicone Tubing 1.5 mm ID × 2.3 mm OD
Silicone Tubing 2.0 mm ID × 2.8 mm OD
Silicone Tubing 2.5 mm ID × 3.3 mm OD
Silicone Tubing 3.0 mm ID × 3.8 mm OD
Clear plastic humidity chamber
Plastic paraffin film (Parafilm)
Arabidopsis wedge style grafting
Remove the floral bolt from the rootstock (leave 3-5 cm of the inflorescence stem on the root stock) by making a horizontal cut (with a two edge razor blade) and immediately place the scion in a petri dish containing water to prevent air entering the vascular stream. If performing many grafts simultaneously, place a small droplet of water on the rootstock stem to prevent any desiccation.
Place a 1.5 cm long section of silicone tubing (1–4 mm internal diameter depending upon thickness of floral bolt) over the shoot stump on the root stock. The tubing should have a slightly larger internal diameter than the stem to be grafted allowing the tubing to slip up over the graft junction.
Make a 1 cm long median incision along the length of the shoot stump on the root stock and immediately add a drop of water inside the incision using a syringe, creating a v-shape wedge. This will keep the incision moist and promote an efficient union between the scion and rootstock.
Cut the horizontally-severed floral stem into a long v-shape wedge under water and position inside the incision of the root stock stem. The wedge graft will provide greater contact between vascular as well as improve surface tension.
Slide the silicone tubing over the wedge graft to secure contact between the scion and root stock. The silicone tubing will provide vertical support to the upper floral scion. Use a syringe to inject water above the silicone tubing and onto the floral stem stump in order to prevent desiccation.
The graft junction was further sealed by wrapping with parafilm (1 cm above and below the silicone tubing) to maintain hydraulic turgor and prevent desiccation. The parafilm needs to be stretched before application to generate a slightly adhesive surface making it easier to seal around the graft junction.
Cover the grafted plants with a clear plastic humidity chamber in order to maintain a humid environment. If you have a growth chamber, adjust to 70% humidity.
Water the grafted plants regularly to help maintain a humid environment and begin to acclimate to normal growing conditions within two weeks of performing the grafts.
Days after germination
Days after grafting
The research was supported by the Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology (CE0561495).
- Mudge K: A history of grafting. Horticultural Rev. 2009, 35: 437-493.Google Scholar
- Yin H, Yan B, Sun J, Jia P, Zhang Z, Yan X, Chai J, Ren Z, Zheng G, Liu H: Graft-union development: a delicate process that involves cell to cell communication between scion and stock for local auxin accumulation. J Exp Bot. 2012, 63: 4219-4232. 10.1093/jxb/ers109.PubMed CentralView ArticlePubMedGoogle Scholar
- Toogood A, Anderson P: American horticultural society plant propagation: the fully illustrated plant-by-plant manual of practical techniques. 1999, Alexandria, VA: American Horticultural SocietyGoogle Scholar
- Turnbull CG: Grafting as a research tool. Methods Mol Biol. 2010, 655: 11-26. 10.1007/978-1-60761-765-5_2.View ArticlePubMedGoogle Scholar
- Jayawickrama KJS, McKeand SE, Jett JB, Young E: Rootstock and scion effects on carbohydrates and mineral nutrients in loblolly pine. Can J Forest Res. 1992, 22: 1966-1973. 10.1139/x92-256.View ArticleGoogle Scholar
- Bertaccini A, Bellardi MG: A rhabdovirus inducing vein yellowing in croton. Plant Path. 1992, 41: 79-82. 10.1111/j.1365-3059.1992.tb02320.x.View ArticleGoogle Scholar
- Cohen R, Horev C, Burger Y, Shriber S, Hershenhorn J, Katan J, Edelstein M: Horticultural and pathological aspects of fusarium wilt management using grafted melons. 2002, Alexandria, VA, ETATS-UNIS: American Society for Horticultural ScienceGoogle Scholar
- Turnbull CGN, Booker JP, Leyser HMO: Micrografting techniques for testing long-distance signalling in arabidopsis. Plant J. 2002, 32: 255-262. 10.1046/j.1365-313X.2002.01419.x.View ArticlePubMedGoogle Scholar
- Mapelli S, Kinet JM: Plant growth regulator and graft control of axillary bud formation and development in the TO-2 mutant tomato. Plant Growth Regul. 1992, 11: 385-390. 10.1007/BF00130646.View ArticleGoogle Scholar
- Ewing EE, Struik PC: Tuber formation in potato: Induction, initiation, and growth. Hort Rev. 1992, 14: 89-197.Google Scholar
- Martinez-Garcia JF, Virgos-Soler A, Prat S: Control of photoperiod-regulated tuberization in potato by the arabidopsis flowering-time gene CONSTANS. P Natl Acad Sci USA. 2002, 99: 15211-15216. 10.1073/pnas.222390599.View ArticleGoogle Scholar
- Navarro C, Abelenda JA, Cruz-Oro E, Cuellar CA, Tamaki S, Silva J, Shimamoto K, Prat S: Control of flowering and storage organ formation in potato by flowering locus T. Nature. 2011, 478: 119-122. 10.1038/nature10431.View ArticlePubMedGoogle Scholar
- Okamoto S, Ohnishi E, Sato S, Takahashi H, Nakazono M, Tabata S, Kawaguchi M: Nod factor/nitrate-induced CLE genes that drive HAR1-mediated systemic regulation of nodulation. Plant Cell Physiol. 2009, 50: 67-77. 10.1093/pcp/pcn194.View ArticlePubMedGoogle Scholar
- Caetano-Anolles G, Gresshoff PM: Plant genetic control of nodulation. Annu Rev Microbiol. 1991, 45: 345-382. 10.1146/annurev.mi.45.100191.002021.View ArticlePubMedGoogle Scholar
- Delves AC, Mathews A, Day DA, Carter AS, Carroll BJ, Gresshoff PM: Regulation of the soybean-rhizobium nodule symbiosis by shoot and root factors. Plant Physiol. 1986, 82: 588-590. 10.1104/pp.82.2.588.PubMed CentralView ArticlePubMedGoogle Scholar
- Searle IR, Men AE, Laniya TS, Buzas DM, Iturbe-Ormaetxe I, Carroll BJ, Gresshoff PM: Long-distance signaling in nodulation directed by a CLAVATA1-like receptor kinase. Science. 2003, 299: 109-112. 10.1126/science.1077937.View ArticlePubMedGoogle Scholar
- Balachandran S, Hull RJ, Vaadia Y, Wolf S, Lucas WJ: Alteration in carbon partitioning induced by the movement protein of tobacco mosaic virus originates in the mesophyll and is independent of change in the plasmodesmal size exclusion limit. Plant Cell Environ. 1995, 18: 1301-1310. 10.1111/j.1365-3040.1995.tb00189.x.View ArticleGoogle Scholar
- Lin S-I, Chiang S-F, Lin W-Y, Chen J-W, Tseng C-Y, Wu P-C, Chiou T-J: Regulatory network of MicroRNA399 and PHO2 by systemic signaling. Plant Physiol. 2008, 147: 732-746. 10.1104/pp.108.116269.PubMed CentralView ArticlePubMedGoogle Scholar
- Pant BD, Buhtz A, Kehr J, Scheible W-R: MicroRNA399 is a long-distance signal for the regulation of plant phosphate homeostasis. Plant J. 2008, 53: 731-738. 10.1111/j.1365-313X.2007.03363.x.PubMed CentralView ArticlePubMedGoogle Scholar
- Rus A, Baxter I, Muthukumar B, Gustin J, Lahner B, Yakubova E, Salt DE: Natural variants of AtHKT1 enhance Na + accumulation in Two wild populations of arabidopsis. PLoS Genet. 2006, 2: e210-10.1371/journal.pgen.0020210.PubMed CentralView ArticlePubMedGoogle Scholar
- Beveridge CA: Axillary bud outgrowth: sending a message. Curr Opin Plant Biol. 2006, 9: 35-40. 10.1016/j.pbi.2005.11.006.View ArticlePubMedGoogle Scholar
- Leyser O: Regulation of shoot branching by auxin. Trends Plant Sci. 2003, 8: 541-545. 10.1016/j.tplants.2003.09.008.View ArticlePubMedGoogle Scholar
- Foo E, Turnbull CG, Beveridge CA: Long-distance signaling and the control of branching in the rms1 mutant of pea. Plant Physiol. 2001, 126: 203-209. 10.1104/pp.126.1.203.PubMed CentralView ArticlePubMedGoogle Scholar
- Wilson PMW: Distribution of ‘Solanaceous’ alkaloids in some new graft combinations. New Phytol. 1952, 51: 260-262. 10.1111/j.1469-8137.1952.tb06134.x.View ArticleGoogle Scholar
- Zeevaart JAD: Florigen coming of age after 70 years. Plant Cell. 2006, 18: 1783-1789. 10.1105/tpc.106.043513.PubMed CentralView ArticlePubMedGoogle Scholar
- Mylne JS, Wigge PA: Plant chemical biology: florigen takes two to tango. Nat Chem Biol. 2011, 7: 665-666. 10.1038/nchembio.666.View ArticlePubMedGoogle Scholar
- An H, Roussot C, Suarez-Lopez P, Corbesier L, Vincent C, Piñeiro M, Hepworth S, Mouradov A, Justin S, Turnbull C, Coupland G: CONSTANS acts in the phloem to regulate a systemic signal that induces photoperiodic flowering of arabidopsis. Development. 2004, 131: 3615-3626. 10.1242/dev.01231.View ArticlePubMedGoogle Scholar
- Corbesier L, Vincent C, Jang S, Fornara F, Fan Q, Searle I, Giakountis A, Farrona S, Gissot L, Turnbull C, Coupland G: FT protein movement contributes to long-distance signaling in floral induction of arabidopsis. Science. 2007, 316: 1030-1033. 10.1126/science.1141752.View ArticlePubMedGoogle Scholar
- Bainbridge K, Bennett K, Turnbull C, Leyser O: Grafting. Methods Mol Biol. 2006, 323: 39-44.PubMedGoogle Scholar
- Cazzonelli C, Cuttriss A, Cossetto S, Pye W, Crisp P, Whelan J, Finnegan E, Turnbull C, Pogson B: Regulation of carotenoid composition and shoot branching in arabidopsis by a chromatin modifying histone methyltransferase, SDG8. Plant Cell. 2009, 21: 39-53. 10.1105/tpc.108.063131.PubMed CentralView ArticlePubMedGoogle Scholar
- Hirsch J, Misson J, Crisp PA, David P, Bayle V, Estavillo GM, Javot H, Chiarenza S, Mallory AC, Maizel A: A novel fry1 allele reveals the existence of a mutant phenotype unrelated to 5’- > 3’ exoribonuclease (XRN) activities in arabidopsis thaliana roots. PLoS One. 2011, 6: e16724-10.1371/journal.pone.0016724.PubMed CentralView ArticlePubMedGoogle Scholar
- Ayre B, Turgeon R: Graft transmission of a floral stimulant derived from CONSTANS1. Plant Physiol. 2004, 135: 2271-2278. 10.1104/pp.104.040592.PubMed CentralView ArticlePubMedGoogle Scholar
- Chen A, Komives EA, Schroeder JI: An improved grafting technique for mature arabidopsis plants demonstrates long-distance shoot-to-root transport of phytochelatins in arabidopsis. Plant Physiol. 2006, 141: 108-120. 10.1104/pp.105.072637.PubMed CentralView ArticlePubMedGoogle Scholar
- Flaishman M, Loginovsky K, Golobowich S, Lev-Yadun S: Arabidopsis thaliana as a model system for graft union development in homografts and heterografts. J Plant Growth Regul. 2008, 27: 231-239. 10.1007/s00344-008-9050-y.View ArticleGoogle Scholar
- Rhee S, Somerville C: Flat-surface grafting in arabidopsis thaliana. Plant Molec Biol Rep. 1995, 13: 118-123. 10.1007/BF02668781.View ArticleGoogle Scholar
- Tsukaya H, Naito S, Rédei G, Komeda Y: A new class of mutations in arabidopsis thaliana, acaulis1, affecting the development of both inflorescences and leaves. Development. 1993, 118: 751-764.Google Scholar
- Molnar A, Melnyk CW, Bassett A, Hardcastle TJ, Dunn R, Baulcombe DC: Small silencing RNAs in plants are mobile and direct epigenetic modification in recipient cells. Science. 2010, 328: 872-875. 10.1126/science.1187959.View ArticlePubMedGoogle Scholar
- Liang D, White RG, Waterhouse PM: Gene silencing in arabidopsis spreads from the root to the shoot, through a gating barrier, by template-dependent, nonvascular, cell-to-cell movement. Plant Physiol. 2012, 159: 984-1000. 10.1104/pp.112.197129.PubMed CentralView ArticlePubMedGoogle Scholar
- Haywood V, Yu T-S, Huang N-C, Lucas WJ: Phloem long-distance trafficking of gibberellic acid-insensitive RNA regulates leaf development. Plant J. 2005, 42: 49-68. 10.1111/j.1365-313X.2005.02351.x.View ArticlePubMedGoogle Scholar
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