Biochemical Effect Of Exogenous Rare Earth Eu～(3+) In Lathyrus Sativus L Seedlings Exposed To Drought Stress

Non-hydraulic root-sourced signal was a new concept supposed by scientists to distinguish with hydraulic root-sourced signal. It is mainly about: in the early time of dought stress, plant root system could perceive the signal of dought and synthesize a chemical substance (generally, it is supposed to be ABA), which could depress the conduct of stoma, reduce the transpiration and prevent the water loss of leaf. For this action of root-shoot communication was occured before the leaf water potential change markedly and wasn't caused by the hydraulic signal, so we call it non-hydraulic root-sourced signal. Many experiments proved that: as a thulium, europium has physiological action. Appropriate europium could change development and growth of plant, increased the biomass, especially it had notables effects on enhancing the ability of plant stress resistant.In this consideration, the investigation was conducted (Lathyrus sativus was arranged as our experimental plant) to study the effect of europium ions in double drought stress patterns on the threshold of non-hydraulic root-sourced signal (from non-hydraulic root-sourced signal appeared to the hydraulic signal appeared), ABA, proline and WUE.Six regimes were set as: 1 control (CK), 2 natural drought stress (ND),3 PEG simulative drought stress (PEG), 4 control irrigated with EU~3+ (Eu~3+—CK), 5 natural drought stress irrigated with Eu~3+ (Eu~3+—ND), 6 PEG simulative drought stress irrigated with Eu~3+(Eu~3+—PEG )。The results showed that:1, Non-hydraulic root-sourced signal of Lathyrus sativus (RS of L.S) appeared at when the soil water potential was—0.51MPa, disappeared (hydraulic signal appeared) at—1.12MPa in regime 2; appeared at—0.48MPa, disappeared at—1.07 MPa in regime 3; appeared at—0.47MPa, disappeared at—1.33 MPa in regime 5; appeared at—0.53MPa, disappeared at—1.39 MPa in regime 6. Eu~3+ had no effect on the non-hydraulic root-sourced signal appeared; but it could delay dramatically the appearance of the hydraulic signal.2, with the drought stress, ABA content in leaves increased remarkably when non-hydraulic root-sourced signal appeared and decreased tardily later but is steady in water supply adequately. Eu~3+ promoted ABA content increased early but in a undersized level. Normally, the peak value appeared in the middle of threshold of non-hydraulic root-sourced signal.3, with the drought stress, proline content increased remarkably at the beginning and placidly in the evening. The growth process usually happened in threshold of non-hydraulic root-sourced signal. 4, WUE is steady in water supply adequately. But in drought stress, it increased remarkably at the beginning and decreased in the evening. Eu~3+ would increase water use efficiency (WUE).5, Drought stress depressed aboveground biomass but promoted underground biomass. Eu~3+ promoted the aboveground biomass in drought stress but had no effect in water supply adequately. On the contrary, it depressed underground biomass, in other words, it depressed ratios of root and shoot of Lathyrus safivus.