Elda Castro-Mercado

Avocado roots treated with salicylic acid produce phenol-2,4-bis (1,1-dimethylethyl), a compound with antifungal activity.

We demonstrated the ability of salicylic acid (SA) to induce a compound in avocado roots that strengthens their defense against Phytophthora cinnamomi. The SA content of avocado roots, before and after the application of exogenous SA, was determined by High-Performance Liquid Chromatography (HPLC). After 4h of SA feeding, the endogenous level in the roots increased to 223 μg g(-1) FW, which was 15 times the amount found in control roots. The methanolic extract obtained from SA-treated avocado roots inhibited the radial growth of P. cinnamomi. A thin layer chromatographic bioassay with the methanolic extract and spores of Aspergillus showed a distinct inhibition zone. The compound responsible for the inhibition was identified as phenol-2,4-bis (1,1-dimethylethyl) by gas chromatography and mass spectrometry. At a concentration of 100 μg/mL, the substance reduced germinative tube length in Aspergillus and radial growth of P. cinnamomi. A commercial preparation of phenol-2,4-bis (1,1-dimethylethyl) caused the same effects on mycelium morphology and radial growth as our isolate, confirming the presence of this compound in the root extracts. This is the first report of the induction of this compound in plants by SA, and the results suggest that it plays an important role in the defense response of avocado.

Interaction of Extracellular Proteinases of Phytophthora cinnamomi withProteinase Inhibitors Produced by Avocado Root

The interaction avocado plant/Phytophtora cinnamomi has not been explored at the level of defense responses induced by this pathogen. Here, we show that the infection of avocado plants by Phytophthora cinnamomi induced proteinase inhibitor, which had inhibitor activity against extracellular proteases of P. cinnamomi. Extracellular proteinase activity was not increased with the addition of the avocado root cell wall to liquid culture but decreased in the presence of root of healthy avocado plants. The pretreatment of avocado roots with the avocado inhibitor before the infection by P. cinnamomi inhibited root colonization by the pathogen. Avocado inhibitor had no effect on in vitro growth of the oomycete, suggesting that the inhibition of root colonization could be due to its interaction with pathogen proteinases.

Superoxide anion production in the interaction of wheat roots and rhizobacteria Azospirillum brasilense Sp245

Background and aimsThe aim of this study was to test the effect of Azospirillum brasilense on the superoxide anion production (O2•−) and enzymes related with redox metabolism in roots of wheat (Triticum aestivum).MethodsA. brasilense Sp245 and T. aestivum seeds cv Nana F2007 were used in this study. Wheat roots were stained with nitro blue tetrazolium (NBT) to visualize and localize O2•− production. Superoxide dismutase (SOD) and peroxidase (POX) activities were assayed in native PAGE.ResultsWe found that A. brasilense application resulted in a decrease in meristem length and cell size, and in a reduction in the O2•− level in roots. The bacteria stimulated SOD and soluble POX isoenzymes, particularly in the zone of the root tip. Qualitative O2•− production in roots treated with LaCl3, a Ca2+ channel blocker, in combination with A. brasilense was comparable to inoculated roots. Similar results were observed with the Ca2+ ionophore A23187.ConclusionsOur results suggest that O2•− metabolism is important during the interaction of wheat and A. brasilense, and that the antioxidative enzymes such as SOD and POX are involved in its regulation.