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

Abstract

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 (δ 30 Si Lsi1 and δ 30 Si Lsi2 ) were −2.95 and −2.61‰, respectively, in 2016 and −1.35 and −1.67‰, respectively, in 2017, indicating that transporter Lsi1 and Lsi2 preferentially absorbed 28 Si rather than 30 Si. Moreover, there was net 28 Si 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 30 Si 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. INTRODUCTIONSilicon is abundant in the environment and silicon dioxide comprises 50-70% of the soil mass on Earth . All soil-grown plants accumulate Si to a concentration of 0.1 to 10.0% of their total dry mass (Epstein,

Silicon isotope fractionation with a low‐silica rice mutant reflects plant uptake strategy in response to different silicon supply levels

“…Two Chinese national reference materials for Si isotopes, GBW04421 and GBW04422, were analyzed together with the samples. GBW04421 resulted in δ 30 Si = −0.05 ± 0.12‰ (2s, n = 18) and GBW04422 in δ 30 Si = −1.99 ± 0.12‰ (2s, n = 18), in line with values in previous studies (Wan et al, 1997;Zhou et al, 2021). All results were reported as δ 30 Si (‰) against NBS-28 silica sand standard (National Institute of Standards and Technology RM 8546) and were calculated using Equation 1.…”

“…Thus, the diffusional effects through simple diffusion cannot account for the differences between isotope compositions of Oochikara and lsi1, which revealed a biologically mediated isotope discrimination during Si uptake. For a better application of isotope fractionation in Si uptake mechanisms, in our previous 2-yr field study on the relationship between isotope fractionation and Si transport pathways, we proposed that transporters Lsi1 and Lsi2 both prefer 28 Si transport rather than 30 Si (Zhou et al, 2021). However, the soil-plant system is rather complicated, so we verified this hypothesis with isotope fractionation in a simplified hydroponic system.…”

“…However, the soil-plant system is rather complicated, so we verified this hypothesis with isotope fractionation in a simplified hydroponic system. Based on Si isotope mass balance and Si accumulation in Oochikara and lsi1 cultured in nutrient solution, we adapted the following relationships in our previous study (Zhou et al, 2021):…”

“…In our previous 2-yr field study, we observed isotope differences of 0.29-0.57‰ between low-silica mutants (lsi1, lsi2) and their corresponding wild-type varieties ('Oochikara' and 'Taichung-65'), which indicated that different transport pathways may result in different Si isotope compositions in the plants. Moreover, in combination with Si isotope mass balance, we proposed that transporter Lsi1 and Lsi2 prefer 28 Si transport rather than 30 Si (Zhou et al, 2021), which helps to apply isotope fractionation to investigate Si uptake. However, the soil-plant system is rather complicated, and soil-plant interactions may influence isotope fractionation during uptake.…”

Impact of Silicon on Plant Nutrition and Significance of Silicon Mobilizing Bacteria in Agronomic Practices

“…R 2 SiO (R = any organic component) is used as a wetting agent in rice fields [144] and it is also considered an agricultural adjuvant due to its qualities as a good transporter of organic molecules [29,95]. Silicic acid is transported in major parts of the plant biomass and is transported in the xylem which is mediated by Lsi6 in the shoot while in roots by the Lsi1 and Lsi2 [145,146].…”