Stress-Induced Silicon Accumulation: Are "Low Accumulators" Really "Inducible Accumulators?".

Silicon (Si) is an abundant element in the lithosphere and is implicated in the tolerance to abiotic as well as biotic stresses across multiple angiosperm taxa.  Plants have classically been characterized based on Si acquisition under favorable environmental conditions into three categories: high-, intermediate-, or low- accumulators.  However, our recent data show induced accumulation of the element in the “low accumulators” Nicotiana tabacum (tobacco) and Antirrhinum majus (snapdragon) in response to stress.  Tobacco plants inoculated with Tobacco ringspot virus (TRSV) and supplemented with Si exhibited significantly higher foliar Si content when compared to control Si-treated/mock-inoculated plants.  The Si-supplemented plants also showed lower TRSV systemic symptom formation.  In contrast to TRSV, Tobacco mosaic virus infection was also tested in N. tabacum, and resulted in no significant changes in foliar Si content or symptoms, indicating that the inducibility is stress-specific.  Si-induced accumulation is not restricted to biotic stress.  Snapdragon plants treated with high levels of copper (Cu) showed significantly higher foliar Si concentrations compared to control plants.  In contrast, the “high” Si accumulator, Zinnia elegans, treated under similar conditions did not show a significant increase in Si content of leaves, suggesting the Cu-induced Si accumulation may be limited to “low” or what we describe as “inducible” accumulators.  We are currently investigating other types of abiotic stress-induced Si accumulation.