The Research On Hormetic Effects Of Ce On Arabidopsis Thaliana And Its Relationship To Ca Signal Transduction

In the present study, Arabidopsis thaliana var. Columbia, a model plant was used as experimental material. Cerous nitrate, one of the main ingredients in REEs-based fertilizersas was selected as regulatory factor. The relationship between the hormetic effects of Cerium (Ce) on A. thaliana and Ca2+signal transduction were investigated systemically from cellular, subcellular and molecular levels. The results showed that:(1) Ce had obvious hormetic effects on the growth and development of A. thaliana. Lower concentration of Ce promoted the elongation of primary roots, stimulated the synthesis of chlorophyll, and increased markedly root hair density and rosette diameter, however, higher concentration of Ce had evident depression effects that primary root elongation, root hair density, fresh weight, rosette diameter, leaf number, chlorophyll content decreased with the increase of Ce concentration.(2) Scanning electron microscope (SEM) analysis showed that lower level of Ce could promote the expansion of leaf cells, but higher level of Ce leaded to leaf cell crimple, and even badly distortion.(3) Transmission electron microscopy (TEM) analysis showed that most of Ce was deposited on the cell wall; some could also enter the cell when treated with higher concentration of Ce. Lower concentration of Ce had no obvious effects on cell ultrastructure, however, at higher concentration, mitochondria with distinct tubular cristae were found adjacent to the plasma membrane, the chloroplasts became more rounded instead of an ellipsoidal shape, many large starch grains were observed in chloroplasts.(4) Inductively coupled plasma-mass spectrometry (ICP-MS) analysis showed that Ce had evident effects on the uptake and translocation of Ca and other nutrient element. Lower level of Ce promoted Ca uptake, but higher level of Ce intensely inhibited the uptake and translocation of Ca, and the uptake and translocation of Mg, Na, Mn, Fe, Cu, Zn were accelerated by lower level of Ce, but higher level Ce inhibited the uptake of Fe, Cu, K and the translocation of Mg, K, Fe, Cu, Zn.(5) Laser ccanning confocal microscope (LSCM) analysis showed that Ca mainly distributed in the cell walls, which was similar to rare earth elements. Lower level of Ce had no visible effect on Ca2+concentration in the root cells of A. thaliana; higher level of Ce decreased Ca2+concentration; with excessively high Ce treatment, Ca2+concentration increased at first and then decreased. EGTA (a Ca2+chelator), TFP (a calmodulin antagonist), RR (a calcium channel blockers in cell), VP (a calcium channel blocker in cell membrane), all of them could interfere the changes of Ca2+concentration in the cell under Ce stress, it suggested that Ce affected the calcium signal by CaM, calcium channel in cell membrane and inracellar calcium channel.(6) The different gene expression of CaM and calcium pump under lower level Ce or higher level Ce might be one of the significant regulatory mechanisms in hormetic effects of Ce.(7) The lower level Ce increased the content of CaM in shorter time, but higher level Ce inhibited the synthesis of CaM in longer time. It was possible to affect Ca2+-CaM singal by different expression of CaM protein in lower level or higher level Ce.(8) Lower level Ce had no obvious effects on antioxidant system and reactive oxygen species (ROS), but higher level Ce disturbed the dynamic balance of antioxidant system, leaded to ROS accumulation, membrane lipid peroxidation aggravation with increasing Ce concentrations.In conclusion, the hormetic effects of Ce on A.thaliana might be related to different response of Ca2+signal under different levels of Ce.