A metabolic depletion syndrome was discovered at early vegetative stages in roots of salt sensitive rice cultivars after prolonged exposure to 100mM NaCl. Metabolite profiling analyses demonstrate that this syndrome is part of the terminal stages of the rice salt response. The phenotype encompasses depletion of at least 30 primary metabolites including sucrose, glucose, fructose, glucose-6-P, fructose-6P, organic- and amino-acids. Based on these observations we reason that sucrose allocation to the root may modify the rice response to high salt. This hypothesis was tested using antisense lines of the salt responsive OsSUT1 gene in the salt sensitive Taipei 309 cultivar. Contrary to our expectations of a plant system impaired in one component of sucrose transport, we find improved gas exchange and photosynthetic performance as well as maintenance of sucrose levels in the root under high salinity. Two independent OsSUT1 lines with an antisense inhibition similar to the naturally occurring salt induced reduction of OsSUT1 gene expression showed these phenomena but not a more extreme antisense inhibition line. We investigated the metabolic depletion syndrome by metabolomic and physiological approaches and discuss our results with regard to the potential role of sucrose transporters and sucrose transport for rice salt acclimation.
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