Summary
Plant apoplast represents an essential compartment for the proper function of certain mineral solutes, and vasculature acts as a long-distance system to distribute them between different parts of the continuous apoplast. Guttation occurs at the distal end of the vasculature, but how it adds to ion homeostasis has received scant attention.
Through genomic-scale ionomic profiling of apoplast fluids, guttation fluid, and xylem sap from 184 core accessions of paddy-grown rice, we identified novel ionomic constitution and dynamics. The most unique finding is that boron concentration jumps to a peak level at the distal end of the leaf blade. This phenomenon is conserved in other plants performing guttation. Boron concentration at leaf tips oscillates diurnally depending on guttation.
Tissue-specific gene expression analysis revealed that the boron influx-transporter gene OsNIP3;1 is prominent in leaf tips and oscillates in synchronization with boron. Disruption of OsNIP3;1 decreased amplitudes of boron oscillation and the ratios of [Boron]guttation fluid/xylem sap.
Our findings reveal that OsNIP3;1 mediates boron oscillation at the distal end of the leaf blade during guttation.
