SULTR1;3 , SULTR2;1 and SULTR3;4 mRNA accumulation in response to Pi and sulfate availability. For Pi treatments, WT and phr1 mutant plants were grown on medium containing 1 mM Pi for 7 days, followed by an additional 4 days in media containing 1 mM Pi (+Pi), no Pi (-Pi) or 1 mM phosphite (+Phi). For sulfate treatments, plants were grown on medium containing 1 mM sulfate for 7 d, followed by an additional 4 days on sulfate-free medium (-S). The pho1 mutant was grown on complete medium containing 1 mM Pi and 1 mM sulfate for 11 days. Shoots and roots were separately harvested and mRNA accumulation was quantified by Q-RT-PCR. mRNA abundance of SULTR1;3 (a, b), SULTR2;1 (c, d), SULTR3;4 (e, f) and SQD1 (g, h) for all genotypes and treatments was normalized to the level of the control gene ubiquitin mRNA (UBQ10: At4g05320) and expressed as relative values against WT plants grown in complete (+Pi and +sulfate) medium. Expression level is expressed as log2 values. Black and gray histograms represent values for roots and shoots, respectively. Individual measurements were obtained from the analysis of shoots or roots collected from a pool of 'n' plants (n ≥ 12). Error bars indicate SD; biological repeats (n ≥ 3).