Strigolactones are transported from roots to shoots, although not through the xylem

Abstract

Strigolactones (SLs) mainly produced in roots move upward to shoots and inhibit axillary bud outgrowth. However, SLs were not detected by LC-MS/MS in xylem saps collected from rice, tomato, cucumber, tobacco, sorghum, and Arabidopsis. d 1 -Orobanchol and d 6 -4-deoxyorobanchol that were fed to roots of rice plants were detected in shoots harvested 20 hr after treatment, although not in the xylem sap. These results imply that both endogenous and exogenous SLs are transported from roots to shoots, although not through the xylem. © Pesticide Science Society of Japan Keywords: xylem sap, strigolactones, transportation. Electronic supplementary materials:The online version of this article contains supplementary materials (analytical conditions and Supplemental Figures S1-S5), which is available at http://www.jstage.jst.go.jp/browse/jpestics/.Strigolactones (SLs) are carotenoid-derived plant secondary metabolites.1-3) SLs released from plant roots into the rhizosphere promote symbiotic interactions with arbuscular mycorrhizal fungi 4) and root nodule bacteria 5,6) ; they also trigger parasitic interactions with the root parasitic weeds witchweeds (Striga spp.) and broomrapes (Orobanche and Phelipanche spp.). 2,3) In plants, SLs as a novel class of plant hormones regulate plant growth and development through crosstalk with other hormones. 2,3,7,8) It is generally accepted that SLs are mainly produced in the roots, move upward to shoots, and inhibit axillary bud outgrowth.

Structure- and stereospecific transport of strigolactones from roots to shoots

“…SLs in the harvested shoot tissues were extracted and analyzed by LC-MS/MS as described previously. 7) These stereoisomers were detected with the same or with very similar sensitivities in the LC-MS/MS analyses conducted in the present study. The separation of SL stereoisomers with chiral LC-MS/ MS was essentially the same as that reported previously.…”

“…In our previous report, we demonstrated that root-applied SLs are transported to shoots, although not through the xylem. 7) In the present study, we examined whether this root-to-shoot transport was dependent on the structure and/or stereochemistry of SLs in rice (orobanchol-type SL producer), sorghum (strigol-type SL producer), and tobacco (producing both types).…”

“…In our previous report, we demonstrated that root-applied SLs are transported to shoots, although not through the xylem. 7) In the present study, we examined whether this root-to-shoot transport was dependent on the structure and/or stereochemistry of SLs in rice (orobanchol-type SL producer), sorghum (strigol-type SL producer), and tobacco (producing both types).A mixture of four stereoisomers of 3a,4,4,5,5,6′[ 2 H] 6 -4DO (or 5DS) (1-4) and four stereoisomers of 6′[2 H]-orobanchol (5-8) was applied to the roots of rice, sorghum, and tobacco plants; shoots were cut at 2 cm above the shoot/root junction 20 hr after treatment. SLs in the harvested shoot tissues were extracted and analyzed by LC-MS/MS as described previously.…”

Structural diversity of strigolactones and their distribution in the plant kingdom

“…The SLs were detected in shoots harvested 20 hr after but not 2 hr after treatment. 53) These results strongly suggest that exogenous and endogenous SLs are transported from roots to shoots not through the xylem but through hypodermal passage cells as in Petunia where polar and asymmetric localization of an ABC transporter (PaPDR1) have been shown to mediate shootward SL transport as well as localized exudation into the rhizosphere. 54,55) Furthermore, aforementioned species-specific phenomena in SL production also occur in the transport of exogenous SLs from the roots to shoots, indicating that the transport is structure-and stereospecific.…”

“…We collected large amounts of xylem sap from various plant species including tomato and Arabidopsis but no signals attributable to known canonical or non-canonical SLs were detected by LC-MS/MS analyses. 53) Then, deuterated SLs, d 1 -orobanchol and d 6 -4DO, were fed to roots of rice plants and the shoots were harvested 2 and 20 hr after SL treatment. The SLs were detected in shoots harvested 20 hr after but not 2 hr after treatment.…”