State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China.
Ann Bot. 2012 Aug;110(3):681-8. doi: 10.1093/aob/mcs126. Epub 2012 Jun 8.
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.
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.
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.
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.
油菜素内酯（BR）是一类具有多种功能的植物多羟基甾醇，在植物生长发育中发挥着重要作用。然而，关于 BR 在植物应对养分缺乏中的作用，目前知之甚少。
为了评估 BR 在植物应对缺铁（Fe）中的作用，研究了 24-表油菜素内酯（EBR）对铁还原酶（FRO）活性、根际酸化和黄瓜（Cucumis sativus）幼苗 Fe 含量的影响，实验分别在缺铁（1 µm FeEDTA）和铁充足（50 µm FeEDTA）条件下进行。
在缺铁培养基中培养黄瓜幼苗时，FRO 活性显著增加，EBR 显著抑制 Fe 缺乏诱导的 FRO 活性增加。相比之下，EBR 应用于铁充足的幼苗中会刺激 FRO 活性。EBR 抑制由缺铁引起的乙烯产生，而诱导铁充足的幼苗产生乙烯。EBR 处理降低了地上部的 Fe 含量，而在缺铁和铁充足条件下均显著增加了根中的 Fe 含量。在铁充足的条件下，EBR 处理导致的地上部 Fe 含量降低与叶绿素（CHL）含量无关，但在缺铁条件下与 CHL 含量呈正相关。在转录水平上，CsFRO1 和 CsIRT1 基因的转录本在缺铁培养基中增加，EBR 逆转了这种增加。
结果表明，BR 可能在调节 Fe 缺乏诱导的 FRO 以及 CsFRO1 和 CsIRT1 的表达和从根部向地上部的 Fe 转运中发挥负作用。
