Induction of silicon defences in wheat landraces is local not systemic and driven by mobilisation of soluble silicon to damaged leaves

In response to herbivory, many grasses, including crops such as wheat, accumulate significant levels of silicon (Si) as an antiherbivore defence. Damage-induced increases in Si can be localised in damaged leaves or more systemic, but the mechanisms leading to these differences in Si distribution remain untested.

Ten genetically diverse wheat landraces (Triticum aestivum) were used to assess genotypic variation in Si induction in response to mechanical damage and how this was affected by exogenous Si supply. Total and soluble Si levels were measured in damaged and undamaged leaves, as were Si levels in the phloem, to test how Si was allocated to different parts of the plant after damage.

Localised, but not systemic, induction of Si defences occurred, more pronounced when plants had supplemental Si. Damaged plants had significant increases in Si concentration in their damaged leaves, while the Si concentration in undamaged leaves decreased, such that there was no difference in the average Si concentration of damaged and undamaged plants.

The increased Si in damaged leaves was due to the redirection of soluble Si, present in the phloem, from undamaged to damaged plant parts, potentially a more cost-effective defence mechanism for plants than increased Si uptake.