Oligoglucans as Elicitors of an Enzymatic Antioxidant System in Zucchini Squash (Cucurbita pepo L.) Seedlings at Low Temperature

Abstract

Abstract: Problem statement: Non-controlled low temperatures affect physiological and biochemical processes leading to Reactive Oxygen Species (ROS) accumulation in plants, which normally are stabilized by the antioxidant system. Superoxide Dismutase (SOD), Ascorbate Peroxidase (APX) and Catalase (CAT) are the most important ROS-detoxification enzymes in stressed plants. Approach: The activity of these enzymes were examined in response to fungal Oligoglucans (OG) in cold-stressed cotyledons of Cucurbita pepo L. Cold stress condition was settled in zucchini cotyledons using relative Ion Leakage (IL) and H₂O₂ accumulation. Then, OG were obtained from Trichoderma harzianum cellwall by enzymatic and chemical hydrolysis. These elicitors were purified by size-exclusion and anionexchange chromatography and tested in cold-stressed cotyledons. Results: No significant changes on H₂O₂ content and IL were observed between treated and control cold-stressed cotyledons, during the first 7 days of storage at 5°C. Afterwards H₂O₂ values increased greatly after cold-stressed. Then, cold stress conditions were established (7 d, 5°C). The APX and CAT activities remained stable, but not SOD activity, which decreased about 42% in control cotyledons. When a chemical OG mixture (CM) was applied to cold-stressed cotyledons, APX and CAT activity levels increased. The SOD activity was only increased by an enzymatic OG mixture (EM). The APX activity level was increased in coldstressed cotyledons using OG size-exclusion chromatography fractions from both CM and EM; however, changes in CAT activity were only possible using EM fractions and no changes were detected in SOD activity. The highest CAT activity levels were triggered using OG anion-exchange chromatography sub-fractions from both CM and EM fractions (120 and 119 % of enzymatic activity, respectively). Conclusion: The oxidative stress can be counteracted by the triggering of APX and CAT activity in cold-stressed zucchini cotyledons mediated by T. harzianum cell-wall OG.