The root barrier to radial oxygen loss (ROL) is a key root trait that prevents oxygen loss from roots to the anoxic soil thereby enabling root elongation into anoxic, waterlogged soils. The ROL barrier was shown to restrict radial intrusion of reduced Fe and H2.
We hypothesized that the ROL barrier can also prevent radial intrusion of hydrogen sulphide (H2S), a potent phytotoxin produced by anaerobic bacteria. Using H2S and O2 sensitive microsensors, we measured the apparent permeance to H2S in rice roots and tested if resistance to H2S intrusion reduced its toxic effect on root respiration. Finally, we assessed whether low H2S concentrations could induce the formation of an ROL barrier.
The study showed that the ROL barrier reduced apparent permeance to H2S by almost 99%, greatly restricting H2S intrusion. The barrier also protected from the toxic effect of H2S; oxygen consumption in roots with an ROL barrier remained unaffected even at high H2S concentration (500 μM), compared to a 67% decline in roots without a barrier. Importantly, low H2S concentrations induced the formation of an ROL barrier.
We demonstrated that the ROL barrier has a strong protective role against H2S intrusion and toxicity, besides preventing O2 loss to the soil. In addition, H2S can act as an environmental signalling molecule for the induction of the ROL barrier. The study demonstrates the functionally versatile nature of the suberized exodermis beyond that of restricted ROL.