A Biostimulant Seed Treatment Improved Heat Stress Tolerance During Cucumber Seed Germination by Acting on the Antioxidant System and Glyoxylate Cycle.

Cristina Campobenedetto,Giuseppe Mannino,Valeria Contartese,Jeroen Van Arkel,Christian Garabello,Jules Beekwilder,Eric Grange,Rumyana Karlova,Cinzia M Bertea

doi:10.3389/fpls.2020.00836

Cristina Campobenedetto, Giuseppe Mannino + Show 7 more

Open Access

https://doi.org/10.3389/fpls.2020.00836

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Abstract

Seed enhancement technologies have the potential to improve germination and seedling growth under environmental stress. The effects of KIEM®, an innovative biostimulant based on lignin derivatives and containing plant-derived amino acids and molybdenum, were investigated on cucumber (Cucumis sativus L.) seed germination. To determine the metabolic targets of this product, biometric, transcriptional and biochemical analyses were carried out on both non-treated and KIEM®-treated seeds incubated for 24 and 48 h under standard (28°C) and heat stress (35°C) conditions. The application of the biostimulant as a seed treatment increased the percent germination (+6.54%) and fresh biomass (+13%) at 48 h, and decreased the content of H2O2 in treated seeds at 28°C (−70%) and at 35°C (−80%). These changes in biometric and biochemical properties were accompanied by changes in expression levels of the genes coding for ROS-producing (RBOH) and scavenging (SOD, CAT, GST) enzymes and their specific activity. In general, the treatment with KIEM® in heat-stress condition appeared to stimulate a higher accumulation of three scavenger gene transcripts: CuZnSOD (+1.78), MnSOD (+1.75), and CAT (+3.39), while the FeSOD isoform was dramatically downregulated (0.24). Moreover, the amount of non-protein thiols, important antioxidant molecules, was increased by the biostimulant after 48 h (+20%). Taken together these results suggest that KIEM® acts through mitigation of the effects of the oxidative stress. Moreover, after 48 h, the pre-sowing treatment with KIEM® increased the transcription levels (+1.5) and the activity of isocitrate lyase (+37%), a key enzyme of the glyoxylate cycle, suggesting a potential effect of this product in speeding up the germination process. Finally, the chemical characterization of KIEM® identified five essential and three non-essential amino acids, and others bioactive compounds, including five organic and inorganic acids that might be potentially involved in its activity. Based on these data, insights on the potential mechanism of action of the biostimulant, suggested that there are broader applications as a product able to increase seed tolerance to different abiotic stress typical of adverse environmental conditions.

Highlights

Plants may encounter a variety of abiotic stresses during their life cycle and these factors may have a significant impact on plant growth and final productivity
We evaluated the potential effects of KIEM R, an innovative biostimulant based on lignin derivatives and containing plant-derived amino acids and the nutrient molybdenum (Mo) on cucumber seed germination under heat stress conditions
The biostimulant treatment was investigated on cucumber seeds at the early germination phase under heat stress conditions, the percent germination and fresh weight were measured on control and KIEM R -treated seeds at 48 h after incubation at 28◦C and 35◦C

Summary

Introduction

Plants may encounter a variety of abiotic stresses during their life cycle and these factors may have a significant impact on plant growth and final productivity. Different approaches have been employed to enhance plant stress tolerance. Seed priming could represent an alternative tool to prepare plants to counteract more successfully abiotic stress conditions (Filippou et al, 2013). The application of amino acids, hormones, reactive oxygen– nitrogen–sulfur species or just water can be effective in enhancing plant tolerance to different abiotic stresses (Savvides et al, 2016). In the past decades attention has been focused on seed enhancements to alleviate environmental stress on germination and early seedling growth (Taylor et al, 1998). Seed treatment technologies (Taylor, 2003) provide methods to apply synthetic or natural compounds, aimed to increase the uniformity and vigor of seedlings and to enhance the tolerance of plants to different abiotic stresses. Biostimulant pretreatments generally cause a faster germination and a faster field emergence, which have practical agronomic implications, notably under adverse conditions (Yildirim et al, 2000)

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