Selenium activates components of iron acquisition machinery in oilseed rape roots

Abstract

Beneficial elements may stimulate plant growth by favoring the availability of essential nutrients for metabolic processes. This study addresses the still unexplored question whether the beneficial action of selenium (Se) on plants can be due to its interaction with iron (Fe). Oilseed rape (Brassica napus) plants were grown hydroponically without (–Se) or with 10 μM Na2SeO4 (+Se) and exposed to either Fe adequate (+Fe) or starvation (–Fe) treatments. Selenium enhanced leaf chlorophyll concentration, photochemical parameters and CO2 fixation. Although Se did not significantly increase total leaf Fe concentration, the concentration of cytoplasmic FeII pool was enhanced under –Fe + Se conditions. However, the most conspicuous Se effects occurred in Fe-deficient roots. Selenium upregulated both the root expression levels of genes encoding FERRIC-REDUCTION OXIDASE (FRO1) and the activity of FRO and exacerbated the stimulatory effect of –Fe on the exudation rate of organic acids and phenolic compounds. Both –Se and + Se plants used FeIIIEDTA in similar way, while only +Se plants were able to take advantage of the sparingly soluble Fe(OH)3. In order to explore the mechanism of Se action, we recorded higher endogenous level of NO and upregulation of ETHYLENE RESPONSE FACTOR 2 (ERF2) by Se irrespective of Fe conditions. Our results show that Se augments root machinery for Fe acquisition mainly through activation of Fe signaling components.