Silicon uptake and translocation in low-silica rice mutants investigated by isotope fractionation

Silicon (Si) alleviates biotic and abiotic stress in plants and many studies have been conducted in Si uptake by the roots. However, there is limited information about Si translocation during grain filling and the Si transport pathways regulating plant Si uptake. In the present study, we performed a 2-yr field trial on the wild-type rice (Oryza sativa L.) varieties Oochikara and Taichung-65 and their corresponding mutants lsi1 and lsi2. We used multi-collector, inductively coupled plasma mass spectrometry to evaluate Si isotope fractionation by the Lsi1 and Lsi2 transporters. The qualitative isotope fractionation caused by Lsi1 and Lsi2 (delta Si-30(Lsi1) and delta Si-30(Lsi2)) were -2.95 and -2.61 parts per thousand, respectively, in 2016 and -1.35 and -1.67 parts per thousand, respectively, in 2017, indicating that transporter Lsi1 and Lsi2 preferentially absorbed Si-28 rather than Si-30. Moreover, there was net Si-28 enrichment in the mutants, indicating that except for Lsi1 and Lsi2, other Si transport pathways belong to ion channels and electrogenic pumps occur in rice. The unexpected observed decrease in Si-30 from the husk to the grain suggests xylem-to-phloem Si transfer during grain filling. Hence, Si isotope fractionation is a useful tool to investigate plant Si uptake and translocation.

Automated summary

This study investigated the uptake and translocation of silicon in rice, finding that the transporters Lsi1 and Lsi2 play key roles in silicon absorption, with other silicon transport pathways likely belonging to ion channels and electrogenic pumps. The fractionation of silicon isotopes proved to be a useful tool in studying plant silicon uptake and translocation.