Silicon has not been cataloged as an essential element for higher plants. However,
it has shown beneficial effects on many crops, especially under abiotic and biotic
stresses. Silicon fertilization was evaluated for the first time on plants exposed to
fluctuations in an Fe regime (Fe sufficiency followed by Fe deficiency and, in turn, by
Fe resupply). Root and foliar Si applications were compared using cucumber plants that
were hydroponically grown in a growth chamber under different Fe nutritional statuses
and Si applied either to the roots or to the shoots. The SPAD index, Fe, and Mn
concentration, ROS, total phenolic compounds, MDA concentration, phytohormone
balance, and cell cycle were determined. The results obtained showed that the addition
of Si to the roots induced an Fe shortage in plants grown under optimal or deficient
Fe nutritional conditions, but this was not observed when Si was applied to the leaves.
Plant recovery following Fe resupply was more effective in the Si-treated plants than in
the untreated plants. A relationship between the ROS concentration, hormonal balance,
and cell cycle under different Fe regimes and in the presence or absence of Si was
also studied. The contribution of Si to this signaling pathway appears to be related
more to the induction of Fe deficiency, than to any direct biochemical or metabolic
processes. However, these roles could not be completely ruled out because several
hormone differences could only be explained by the addition of Si