Relative expression levels by real-time qRT-PCR of SlST1.1 (A), SlST1.2 (B), SlST2.1 (C), SlST2.2 (D), and SlST4.1 (E) genes in shoots (white bars) and roots (gray bars) of tomato plants subjected to varying nutritional stress. Data are means ± sd of three independent replicates run in triplicate. Significant differences between samples are indicated by different letters: different uppercase letters indicate significant differences in roots (P < 0.05), and different lowercase letters indicate significant differences among in shoots (P < 0.05). C, Control; D, dual deficiency; F, Fe deficiency; S, S deficiency.