Foliar or subirrigational silicon supply modulates salt stress in strawberry during vegetative propagation

Availability of silicon (Si) to the plant as a silicic acid could be a limiting factor for crop productivity. Although the effect of Si has been shown to vary by plant species, Si has been shown to improve photosynthesis, and to remediate nutrient imbalances and abiotic stresses in plants. Plants of two Korean strawberry cultivars 'Seolhyang' and 'Maehyang' at a propagation stage was grown for 58 days with a complete nutrient solution (EC of 0.8 dS m(-1)) and also with supplementation of either 0, 35, or 70 mg L-1 Si from either potassium silicate (K2SiO3), sodium silicate (Na2SiO3), or calcium silicate (CaSiO3). The Si in solution was supplied to the roots through subirrigational nutrient solution or to the leaves by daily foliar applications. The growth and development of the plants were assessed after this period. Then the plants were subjected to one of different salt stress conditions (EC of either 0.0, 0.8, 1.6, or 2.4 dS m(-1)) for 14 days. The high EC (2.4 dS m(-1)) resulted in oxidative stress in the form of H2O2 and O-2(-1) in the leaves of the Si-non-treated plants as compared to Si-treated plants, and no or less stress was observed in the 0.0, and 0.8 or 1.6 dS m(-1), respectively. However, Si, especially supplied from K2SiO3, relieved the stress level. Interestingly, the isozyme activities of three important antioxidant enzymes, superoxide dismutase, catalase and guaiacol peroxidase, were abundantly increased in the Si-treated plants, particularly with K2SiO3, even under the high EC (2.4 dS m(-1)) treatment and decreased in the Si-non-treated plants. The observed responses to Si supply in high salt-stressed plants indicate that Si, particularly supplied from K2SiO3, has a significant role in limiting the negative effects of salt stress by maintaining antioxidative enzymes during the vegetative propagation.