The barrier to radial oxygen loss protects roots against hydrogen sulphide intrusion and its toxic effect
Lucas León Peralta Ogorek, Hirokazu Takahashi, Mikio Nakazono, Ole Pedersen
Abstract
Summary The root barrier to radial O 2 loss (ROL) is a key root trait preventing O 2 loss from roots to anoxic soils, thereby enabling root growth into anoxic, flooded soils. We hypothesized that the ROL barrier can also prevent intrusion of hydrogen sulphide (H 2 S), a potent phytotoxin in flooded soils. Using H 2 S‐ and O 2 ‐sensitive microsensors, we measured the apparent permeance to H 2 S of rice roots, tested whether restricted H 2 S intrusion reduced its adverse effects on root respiration, and whether H 2 S could induce the formation of a ROL barrier. The ROL barrier reduced apparent permeance to H 2 S by almost 99%, greatly restricting H 2 S intrusion. The ROL barrier acted as a shield towards H 2 S; O 2 consumption in roots with a ROL barrier remained unaffected at high H 2 S concentration (500 μM), compared to a 67% decline in roots without a barrier. Importantly, low H 2 S concentrations induced the formation of a ROL barrier. In conclusion, the ROL barrier plays a key role in protecting against H 2 S intrusion, and H 2 S can act as an environmental signalling molecule for the induction of the barrier. This study demonstrates the multiple functions of the suberized/lignified outer part of the rice root beyond that of restricting ROL.