Root Silicon Addition Induces Fe Deficiency in Cucumber Plants, but Facilitates Their Recovery After Fe Resupply. A Comparison With Si Foliar Sprays

Abstract

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.