Nitrogen deficiency as well as phosphorus deficiency in sorghum promotes the production and exudation of 5-deoxystrigol, the host recognition signal for arbuscular mycorrhizal fungi and root parasites
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Strigolactones released from plant roots induce hyphal branching of symbiotic arbuscular mycorrhizal (AM) fungi and germination of root parasitic weeds, Striga and Orobanche spp. We already demonstrated that, in red clover plants (Trifolium pratense L.), a host for both AM fungi and the root holoparasitic plant Orobanche minor Sm., reduced supply of phosphorus (P) but not of other elements examined (N, K, Ca, Mg) in the culture medium significantly promoted the secretion of a strigolactone, orobanchol, by the roots of this plant. Here we show that in the case of sorghum [Sorghum bicolor (L.) Moench], a host of both the root hemiparasitic plant Striga hermonthica and AM fungi, N deficiency as well as P deficiency markedly enhanced the secretion of a strigolactone, 5-deoxystrigol. The 5-deoxystrigol content in sorghum root tissues also increased under both N deficiency and P deficiency, comparable to the increase in the root exudates. These results suggest that strigolactones may be rapidly released after their production in the roots. Unlike the situation in the roots, neither N nor P deficiency affected the low content of 5-deoxystrigol in sorghum shoot tissues.
KeywordsArbuscular mycorrhizal fungi 5-Deoxystrigol Nitrogen deficiency Phosphorus deficiency Sorghum Striga
High performance liquid chromatography/tandem mass spectrometry
We acknowledge Dr. Kohki Akiyama (Osaka Prefecture University) for generous gift of synthetic (±)-5-deoxystrigol. We thank Dr. D. M. Joel (Agricultural Research Organization, Ramat Yishay, Israel) for critical reading of the manuscript. A part of this study was supported by the Sasakawa Scientific Research Grant from The Japan Science Society, a Grant-in Aid for Scientific Research (1820810) from Japan Society for the Promotion of Science (JSPS), and a grant for Eminent Research at Utsunomiya University (2006).
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