Brassinosteroids are involved in response of cucumber (Cucumis sativus) to iron deficiency.
OBJECTIVE
Brassinosteroids (BR) are a class of plant polyhydroxysteroids with diverse functions in plant growth and development. However, there is little information on the role of BRs played in the response to nutrient deficiency.


METHODS
To evaluate the role of BR in the response of plants to iron (Fe) deficiency, the effect of 24-epibrassinolide (EBR) on ferric reductase (FRO) activity, acidification of the rhizosphere and Fe content in cucumber (Cucumis sativus) seedlings under Fe-deficient (1 µm FeEDTA) and Fe-sufficient (50 µm FeEDTA) conditions were investigated.


RESULTS
There was a significant increase in FRO activity upon exposure of cucumber seedlings to an Fe-deficient medium, and the Fe deficiency-induced increase in FRO activity was substantially suppressed by EBR. In contrast, application of EBR to Fe-sufficient seedlings stimulated FRO activity. Ethylene production evoked by Fe deficiency was suppressed by EBR, while EBR induced ethylene production from Fe-sufficient seedlings. Fe contents in shoots were reduced by treatment with EBR, while Fe contents in roots were markedly increased under both Fe-deficient and Fe-sufficient conditions. The reductions in Fe contents of shoots were independent of chlorophyll (CHL) contents under Fe-sufficient conditions, but they were positively correlated with CHL contents under Fe-deficient conditions. At the transcriptional level, transcripts encoding FRO (CsFRO1) and Fe transporter (CsIRT1) were increased upon exposure to the Fe-deficient medium, and the increases in transcripts were reversed by EBR.


CONCLUSIONS
The results demonstrate that BRs are likely to play a negative role in regulating Fe-deficiency-induced FRO, expressions of CsFRO1 and CsIRT1, as well as Fe translocation from roots to shoots.
State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China.
Baolan
B
Wang
Yansu
Y
Li
Wen-Hao
WH
Zhang
D060406:Brassinosteroids / Q000378:metabolism* / Q000494:pharmacology; D018553:Cucumis sativus / Q000235:genetics / Q000378:metabolism*; D005030:Ethylenes / Q000378:metabolism* / Q000494:pharmacology; D038181:FMN Reductase / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000187:drug effects; D000090463:Iron Deficiencies; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D021381:Protein Transport; D036226:Seedlings / Q000378:metabolism
D060406:Brassinosteroids; D005030:Ethylenes; D010937:Plant Growth Regulators; C036216:ethylene; D038181:FMN Reductase; C023903:ferric citrate iron reductase