Effect of silicon addition on soybean (Glycine max) and cucumber (Cucumis sativus) plants grown under iron deficiency.

Silicon is considered an essential element in several crops enhancing growth and alleviating different biotic and abiotic stresses. In this work, the role of Si in the alleviation of iron deficiency symptoms and in the Fe distribution in iron deficient plants has been studied. Thus, soybean and cucumber plants grown in hydroponic culture under iron limiting conditions were treated with different Si doses (0.0, 0.5 and 1.0 mM). The use of a strong chelating agent such as HBED avoided Fe co-precipitation in the nutrient solution and allowed for the first time the analysis of Si effect in iron nutrition without the interference of the iron rhizospheric precipitation. SPAD index, plant growth parameters and mineral content in plant organs were determined. For soybean, the addition of 0.5 mM of Si to the nutrient solution without iron, initially or continuously during the experiment, prevented the chlorophyll degradation, slowed down the growth decrease due to the iron deficiency and maintained the Fe content in leaves. In cucumber, Si addition delayed the decrease of stem dry weight, stem length, node number and iron content in stems and roots independently of the dose, but no-effect was observed in chlorosis symptoms alleviation in leaves. The observed response to Si addition in iron deficiency was plant-specific, probably related with the different Fe efficiency strategies developed by these two species.