Bioimaging of multiple elements by high-resolution LA-ICP-MS reveals altered distribution of mineral elements in the nodes of rice mutants

Inter-vascular transfer in rice (Oryza sativa) nodes is required for delivering mineral elements to developing tissues, which is mediated by various transporters in the nodes. However, the effect of these transporters on distribution of mineral elements in the nodes at a cellular level is still unknown. Here, we established a protocol for bioimaging of multiple elements at a cellular level in rice node by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and compared the mineral distribution profile between wild-type (WT) rice and mutants. Both relative comparison of mineral distribution normalized by endogenous C-13 and quantitative analysis using spiked standards combined with soft ablation gave valid results. Overall, macro-nutrients such as K and Mg were accumulated more in the phloem region, while micro-nutrients such as Fe and Zn were highly accumulated at the inter-vascular tissues of the node. In mutants of nodal Zn transporter OsHMA2, Zn localization pattern in the node tissues did not differ from that of WT; however, Zn accumulation in the inter-vascular tissues was lower in uppermost node I but higher in the third upper node III compared with the WT. In contrast, Si deposition in the mutants of three nodal Si transporters Lsi2, Lsi3 and Lsi6 showed different patterns, which are consistent with the localization of these transporters. This improved LA-ICP-MS analysis combined with functional characterization of transporters will provide further insight into mineral element distribution mechanisms in rice and other plant species.