Silicon-transporters-mediated silicon deposition at root endodermis
decreases bypass flow and consequently alleviates salt toxicity in rice
Abstract
Silicon (Si) can alleviate Na+ toxicity by decreasing
bypass flow in salt-stressed rice (Oryza sativa L.), however, the
underlying mechanisms remain veiled. Here, we demonstrate how Si
decreases bypass flow and alleviates salt toxicity at physiological and
molecular levels by using two rice mutants (lsi1 and lsi2,
defective in OsLsi1 and OsLsi2, respectively) and their wild types
(WTs). Under salt stress, Si promoted plant growth and decreased
Na+ root-to-shoot translocation in WTs, but not in
mutants. Simultaneously, both quantitative estimation and fluorescent
visualization of trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic (PTS, an
apoplastic tracer) show Si blocked bypass flow in WTs, but not in
mutants. Energy-dispersive X-ray microanalysis (EDX) shows Si was
deposited at root endodermis in WTs, but not in mutants. Moreover, root
split experiment using lsi1 WT shows shoot Si accumulation
down-regulated the expression of Si transport genes (OsLsi1 and
OsLsi2) in root and accelerated Si deposition at root endodermis.
In summary, our results reveal that 1) Si deposition at root endodermis
reduces bypass flow, thereby alleviating salt toxicity in rice, and 2)
the deposition of Si, which could be an active and
physiologically-regulated process, is mediated by the cooperation of
OsLsi1 and OsLsi2 and regulated by shoot Si accumulation.