Effects of anion channel blockers on xylem nitrate transport in barley seedlings

Abstract

The effects of anion channel blockers, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) and anthracene-9-carboxylic acid (A-9-C), on the uptake and xylem transport of nitrate were investigated in intact barley (Hordeum vulgare L.) seedlings using 13NO3 − and 15NO3 − as tracers. The seedling roots were pretreated with either blocker for 1 h and then 13NO3 − or 15NO3 − was supplied to the medium. Real-time images of 13N accumulation in shoots were monitored during the first 30 min using Positron Emitting Tracer Imaging Systems (PETIS). The radioactivity in the shoots of the plants treated with either blocker was about half of that in the shoots of the control plants. Analysis of the distribution of 13N in whole seedlings using a Bioimaging Analyzer System (BAS) showed a 13N-accumulation in both shoots and roots of the control plants but reduced 13N-levels in the shoots of the plants treated with either blocker. Nitrate concentrations in the xylem sap were significantly reduced by the application of either blocker while the net uptake of 15NO3 − was not or slightly influenced by the treatment with blockers. The translocation and uptake of chloride were also significantly reduced by the treatment with A-9-C but not with DIDS. These results suggested that anion channels contributed to xylem loading of nitrate in barley plants.