Regulation of 2,4-epibrassinolide on mineral nutrient uptake and ion distribution in Ca(NO3)2 stressed cucumber plants

2,4-Epibrassinolide (EBL) is a plant hormone that plays a pivotal role in regulation of plants growth and development processes under abiotic stress. The investigation was carried out to study the effect of EBL on mineral nutrients uptake and distribution with ion element analysis and X-ray microanalysis in cucumber seedlings (Cucumis sativus L. cv. Jinyou No.4) under 80 mM Ca(NO3)2 stress. Our study found EBL significantly alleviated the inhibitory of P, K, Na, Mg, Fe, Mn, or Cl uptake in shoot or root by Ca(NO3)2 stress. Under Ca(NO3)2 stress, X-ray microanalysis showed that high levels of Ca by EBL treatment accumulated in the epidermal cells of root and gradually decreased from epidermal cells to stellar parenchyma. K+ levels were restored in different cross section of roots and high K+ level mostly accumulated in stellar parenchyma. The results of Ca2+ ultra-structural localization showed Ca2+ particles of antimonite precipitate by EBL were partly decreased in mesophyll and root cells, and Ca2+ precipitate distributed in intercellular spaces again. Increased Ca2+-ATPase activity and ATP content by EBL were also contributed to extrude excess Ca2+ from the cytoplasm. These results suggested that EBL could alleviate the ion damage from excess Ca2+ through regulating mineral nutrients uptake and distribution.