Fig. 9.

Suggested model for the role of CsiLAC4 in the preferential distribution of boron (B) in Citrus leaves. (a) Schematic diagram of B distribution in B‐intolerant Citrus grandis main veins. B in the xylem vessel is first unloaded into the xylem parenchyma by either equilibration or active transport, followed by further transfer to the phloem and pith parenchyma within the symplast. (b) Schematic diagram of B distribution in B‐tolerant Citrus sinensis main veins. Boric acid treatment triggers cell wall lignification of metaxylem parenchyma expressing CsiLAC4, which restricts B flow between the xylem/apoplast interface and further transfer to the phloem.