sentence: Under N deficiency , amino acid assimilation is suppressed , thus leading to reduced demand for C skeletons ( amino acid precursors such as malate , citrate , and 2-oxoglutarate ) ( Scheible et al ., 1997 ; Paul and Pellny , 2003 ) , followed by greater C flux into transitory starch for storage rather than into sucrose synthesis ( Supplementary Fig. S2 ) .