Long Term Silicon Exposure Coordinately Downregulates Lipoxygenase Genes, Decreases Reactive Oxygen Species Level and Promotes Growth of Cucumber Plants in a Semi-Hydroponic Cultivation System

Cucumber ( Cucumis sativus L.) F1 cultivar hybrid ‘Dirigent’ was investigated for growth, photosynthetic pigment content and level of reactive oxygen species upon long term silicon Si treatment in a perlite based, semi-hydroponic growth system. Element analysis approved elevated Si content in the shoot of silicate treated plants. Increased shoot growth as well as higher chlorophyll and carotenoid contents of leaves indicated beneficial effects of silicate provision. Increased transcript level of all known silicon transporter genes was revealed in leaves and roots of Si treated plants by RT-PCR and RT-qPCR. Furthermore, decreased level of hydrogen peroxide and lipid peroxidation indicated lower oxidative stress level in silicated shoot tissues. Potentially contributing to decreased lipid peroxidation, coordinately downregulated transcription of all expressed lipoxygenase genes was observed in leaves. Results suggest that downregulation of lipoxygenases may contribute to the antioxidant effect of silicon provision in plants.