Strigolactones (SLs) are a new class of carotenoid-derived phytohormones. They act as stimulants for both germination of parasitic weeds in the Orobanchaceae family and for arbuscular mycorrhization initiation, but they also play multiple roles in regulating plant development. In addition, soil nutrient deficiencies, mainly due to low Pi and low nitrate, trigger enhanced SL biosynthesis and exudation, which seems to influence root architecture. In our previous study (Manoli et al., 2016, Frontiers in Plant Science), we showed how a 2 h-nitrate treatment is sufficient to repress the transcription of genes involved in SLs biosynthesis and transport. In the present study, we demonstrated that 24 h of nitrate deficiency are necessary to induce the transcription of the same genes. Moreover, SLs involvement in maize root response to nitrate was investigated by determining their influence on the frequency of sites of lateral root (LR) emergence in maize seedlings. After 24h in a nitrate-depleted solution, an hematoxylin staining assay was carried out to detect the number of LR primordia (LRP) within three treatments groups: 24h in a nitrate-deficient solution, 24h in a nitrate-1mM-supplied solution or 24h in a nitrate-deficient solution with the presence of a SLs biosynthesis inhibitor (TIS108, 2μM). The results from LR density analysis suggest a putative involvement of SLs in the inhibition of LR emergence in nitrate-depleted roots, while nitrate seems to be involved in LR development through inhibition of some SLs pathway. To deepen the SLs involvement in maize root response to nitrate fluctuations, a germination bioassay on Phelipanche ramosa seeds was then performed. P. ramosa belongs to the Orobanchaceae family, namely obligate root-parasitic plants whose seeds can be used to indirectly detect the SLs exudation. A modified bioassay and a neutral red staining were developed to evaluate the germination rate in P. ramosa seeds. Root exudates of maize seedlings grew in nitrate-1mM-supplied solution, or nitrate-deficient solution (-N), or nitrate-deficient solution supplied with TIS108 were tested. On a quality level, a clear induction of germination was shown in those seeds treated with –N root exudates, whereas a very reduced germination was detected in the seeds treated with +NO3-root exudates or with –N+TIS108-root exudates. In conclusion, our preliminary results are consistent with the involvement of strigolactones in the repression of lateral root development in nitrate-deficient media, while the inhibition of SLs action by nitrate supply seems to participate in the complex mechanism leading to regulation of lateral root development by this anion.

Strigolactones involvement in maize root response to nitrate availability

Laura Ravazzolo;Alessandro Manoli;Sara Trevisan;Silvia Quaggiotti
2017

Abstract

Strigolactones (SLs) are a new class of carotenoid-derived phytohormones. They act as stimulants for both germination of parasitic weeds in the Orobanchaceae family and for arbuscular mycorrhization initiation, but they also play multiple roles in regulating plant development. In addition, soil nutrient deficiencies, mainly due to low Pi and low nitrate, trigger enhanced SL biosynthesis and exudation, which seems to influence root architecture. In our previous study (Manoli et al., 2016, Frontiers in Plant Science), we showed how a 2 h-nitrate treatment is sufficient to repress the transcription of genes involved in SLs biosynthesis and transport. In the present study, we demonstrated that 24 h of nitrate deficiency are necessary to induce the transcription of the same genes. Moreover, SLs involvement in maize root response to nitrate was investigated by determining their influence on the frequency of sites of lateral root (LR) emergence in maize seedlings. After 24h in a nitrate-depleted solution, an hematoxylin staining assay was carried out to detect the number of LR primordia (LRP) within three treatments groups: 24h in a nitrate-deficient solution, 24h in a nitrate-1mM-supplied solution or 24h in a nitrate-deficient solution with the presence of a SLs biosynthesis inhibitor (TIS108, 2μM). The results from LR density analysis suggest a putative involvement of SLs in the inhibition of LR emergence in nitrate-depleted roots, while nitrate seems to be involved in LR development through inhibition of some SLs pathway. To deepen the SLs involvement in maize root response to nitrate fluctuations, a germination bioassay on Phelipanche ramosa seeds was then performed. P. ramosa belongs to the Orobanchaceae family, namely obligate root-parasitic plants whose seeds can be used to indirectly detect the SLs exudation. A modified bioassay and a neutral red staining were developed to evaluate the germination rate in P. ramosa seeds. Root exudates of maize seedlings grew in nitrate-1mM-supplied solution, or nitrate-deficient solution (-N), or nitrate-deficient solution supplied with TIS108 were tested. On a quality level, a clear induction of germination was shown in those seeds treated with –N root exudates, whereas a very reduced germination was detected in the seeds treated with +NO3-root exudates or with –N+TIS108-root exudates. In conclusion, our preliminary results are consistent with the involvement of strigolactones in the repression of lateral root development in nitrate-deficient media, while the inhibition of SLs action by nitrate supply seems to participate in the complex mechanism leading to regulation of lateral root development by this anion.
XXXV Convegno Nazionale SICA (Società italiana di Chimica Agraria)
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3324461
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