| Summary: | <span style="font-variant: small-caps;">d</span>-pinitol is the most commonly accumulated sugar alcohol in the Leguminosae family and has been observed to increase significantly in response to abiotic stress. While previous studies have identified genes involved in <span style="font-variant: small-caps;">d</span>-pinitol synthesis, no study has investigated transcript expression in planta. The present study quantified the expression of several genes involved in <span style="font-variant: small-caps;">d</span>-pinitol synthesis in different plant tissues and investigated the accumulation of <span style="font-variant: small-caps;">d</span>-pinitol, <i>myo</i>-inositol and other metabolites in response to a progressive soil drought in soybean (<i>Glycine max</i>). Expression of <i>myo</i>-inositol 1-phosphate synthase (<i>INPS</i>), the gene responsible for the conversion of glucose-6-phosphate to <i>myo</i>-inositol-1-phosphate, was significantly up regulated in response to a water deficit for the first two sampling weeks. Expression of <i>myo</i>-inositol <i>O</i>-methyl transferase (<i>IMT1</i>), the gene responsible for the conversion of <i>myo</i>-inositol into <span style="font-variant: small-caps;">d</span>-ononitol was only up regulated in stems at sampling week 3. Assessment of metabolites showed significant changes in their concentration in leaves and stems. <span style="font-variant: small-caps;">d</span>-Pinitol concentration was significantly higher in all organs sampled from water deficit plants for all three sampling weeks. In contrast, <i>myo</i>-inositol, had significantly lower concentrations in leaf samples despite up regulation of <i>INPS</i> suggesting the transcriptionally regulated flux of carbon through the <i>myo</i>-inositol pool is important during water deficit.
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