2018 ASHS Annual Conference

Horseradish (Armoracia rusticana) is a root crop in the Brassicaceae family. Horseradish extract (HRE) contains many bioactive secondary metabolites such as glucosinolates. Sinigrin is the most common glucosinolate accounting for 80% of the HRE glucosinolate content. Sinigrin naturally undergoes hydrolysis to produce isothiocyanates such as allyl isothiocyanate (AITC) as a defense response. AITC can act as an herbicide, insecticide, fungicide, bactericide and more making it valuable for the agricultural industry. Because horseradish is generally utilized for its roots, the glucosinolate rich leaves are often discarded when they could be utilized. The aim of this study is to increase our understanding of the allelopathic effects of HRE for these agriculturally beneficial properties. Lettuce was chosen as an ideal organism for HRE treatment due to its high germination rate and biological reproducibility. Lettuce root length and root hair length were measured after 3 days of treatment with control, 1%, 2%, 4%, and 8% HRE w/v. The average root lengths respectively were 21.9 mm, 22.6 mm, 23.3 mm, 17.0 mm, 11.0 mm. Concentrations of HRE above 2% w/v were significant with all other concentrations. The average root hair lengths respectively were 1.30 mm, 1.27 mm, 0.76 mm, 0.69 mm, and 0.20 mm. All HRE treatments were significant excluding 1% w/v. Lettuce root length increased insignificantly with lower concentrations of HRE and then decreased significantly as the dose increased while root hair length decreased in a dose-dependent manner. H₂O₂ was quantified in lettuce treated with 1% w/v HRE at days 1 through 5 using ABTS and spectrophotometer reading at 414 nm. Control and treatment values at days 1-5 respectively were 2,759, 687.5, 376.2, 575.1, 217.3, and 4,100.8, 835.9, 386.7, 632.3, 239.6 μmol/g fresh weight. There was a significant difference in H₂O₂ concentration at day 1 though after there was no significance and there was a similar trend. Lettuce primary metabolite analysis was done on 36 metabolites using GC-MS and Metaboanalyst. Lettuce were grown for 2 days and then treated with 1% and 2% w/v HRE for 1 day and collected. Proline (Pro), valine (Val), and tryptophan (Trp) all increased significantly in a dose dependent manner with variable importance for projection (VIP) values of 0.46, 0.45, and 0.43 respectively. Trp is a precursor to IAA which can increase root growth via cell elongation at lower concentrations though inhibits growth at higher concentrations which was observed. Pro is the precursor to hydroxyproline which is an important component of extensin in the cell wall which causes mechanical wall stiffening associated with an oxidative burst. This was seen with increased H₂O₂ concentration in HRE treated lettuce at day 1 along with decreased root growth. Valine increases are likely due to feeding electrons to the mitochondria for increased demand and signaling.