Figure 4.

Bacterial VOC‐mediated induction of iron‐uptake responses in Arabidopsis roots requires shoot‐derived signals.

(a) Quantitative RT‐PCR analysis of FRO2 and IRT1 transcript levels in the roots of intact and decapitated 15‐day‐old Col‐0 seedlings that were grown under standard conditions (+Fe) or subjected to iron deficiency for 3 days (−Fe, 300 μm Ferrozine). Shoot decapitation was performed immediately prior to the start of the iron‐deficiency treatment.

(b) Quantitative RT‐PCR analysis of FRO2 and IRT1 transcript levels in the roots of intact and decapitated Col‐0 seedlings that were grown under standard conditions (+Fe) and treated or not with P. simiae WCS417 VOCs. Seedlings were treated with VOCs in a two‐compartment plate assay when 12 days old, and samples were collected 2 days later. Shoot decapitation was performed immediately prior to the VOC treatment.

(c) Quantitative RT‐PCR analysis of MYB72,FRO2 and IRT1 transcript levels in the roots of control and WCS417 VOC‐treated Col‐0 seedlings that were grown with sufficient iron (50 μm Fe(III)EDTA) under the indicated conditions. Decapitation and darkness treatments were started just prior to application of VOCs. Root samples were harvested 2 days after VOC application.

(d) Representative images of segments of the late maturation zone of GUS‐stained roots of pMYB72:GFP‐GUS seedlings exposed to WCS417 VOCs under the indicated conditions (+Fe). Carbon dioxide (CO ₂) was trapped by adding a 1 m KOH solution in the three‐compartment plate assay, just prior to VOC treatment. Chemical inhibition of photosynthesis was achieved by transferring 11‐day‐old seedlings to norflurazon‐supplemented plates 24 h before VOC treatment. Images were taken 2 days after VOC application. Scale bars = 50 μm.

Values in (a–c) are means ± SD of three replicates. Gene expression was normalized to that of ACTIN7. Asterisks indicate statistically significant differences compared with mock‐treated roots (Student's t test; P < 0.05).