| In this study, we assessed the effects of heavy metal nickel (Ni2+) on physiological metabolism of ubiquitous submerged plant Potamogeton crispus L. In details, it was consist of three parts:a. the response of anti-oxidative system and proline (Pro) metabolism pathway under Ni2+stress (0,0.05,0.10,0.15,0.20mmol/L) in P. crispus aseptic seedlings; b. the change of Ni2+distributes in the sub-cellular and various mineral element absorption of P. crispus leaves growing in the wild; c. the determination of reactive oxygen speicies (ROS) levels and polyamine metabolism under exposure to rare earth element yttrium (Y3+) and Ni2+. All results are shown below:(1) The response of anti-oxidative system and proline (Pro) metabolism pathway under Ni2+stress in P. crispus aseptic seedlings. We found that, due to elevated Ni2+levels exposure, the enzymatic activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), reduced glutathione (GSH), and non-protein sulfhydryl (NP-SH) was significantly induced and then declined backward, respectively; no significant difference was detected in ascorbic acid (AsA); phytochelatins (PCs) was significantly induced. In Pro metabolism section, ornithine aminotransferase (OAT) was significantly induced at0.05-0.10mmol/L Ni2+, compared to the control;1-pryrroline-5-carboxylate synthestase (P5CS) was significantly induced over0.10mmol/L Ni2+; there was no significant fluctuation in proline dehydrogenase (ProDH) under Ni2+stress; furthermore, Pro was significantly induced by Ni2+stress. The results abovementioned illustrate that Ni2+stress is toxic to anti-oxidative system in P. crispus aseptic seedlings as Ni2+could contribute to increase ROS, enhance membrane lipid peroxidation. In addition, accumulation of Pro heavily relies on ornithine pathway when exposure to low Ni2+levels, whereas on glutamic acid when exposure to high levels.(2) The effect of waterborne Ni2+stress on chlorophyll, soluble protein level, and anti-oxidative system, as well as the change of Ni2+distributes in the sub-cellular and various mineral element absorption of P. crispus leaves growing in the wild. Results showed that:with the elevated Ni2+levels, chlorophyll (Chi.) and the ratio of Chi. a:Chi. b significantly declined compared to the control; total anti-oxidative capacity (T-AOC) significantly increased and had the peak at0.15mmol/L Ni2+, then reduced backward; SOD activity was significantly induced over0.05mmol/L Ni2+; POD and CAT shared the similar response pattern:first increase then reduction; while soluble protein was significantly declined with increasing Ni2+levels. Furthermore, we analyzed Ni2+distributes in the sub-cellular and found that most Ni2+existed in the soluble components in the control. The sub-cellular components had more Ni2+contents under exposure to Ni2+, and distribution ratio was different from the control:cell wall> soluble components> cell organelle. Furthermore, due to Ni2+stress, absorption of Ca, P, K, Mg was significantly inhibited under exposure to Ni2+; Fe and Mn accumulation share the similar response pattern:first increase then reduction backward; while Cu, Zn and B had different distribution in the sub-cellular components, respectively. As results abovementioned, we can conclude that Ni2+is harmful to P. crispus as it causes chlorophyll and soluble protein reduction, mineral element absorption damage, ion dynamics disbalance. What is more, anti-oxidative enzymes such as SOD, POD and CAT, eliminate low Ni2+stress at a certain extent, but cannot relieve high Ni2+stress disruption.(3) The determination of reactive oxygen speicies (ROS) levels and polyamine metabolism under exposure to rare earth element yttrium (Y3+) and Ni2+. Results showed that under the absence of Y3+, Ni2+significantly increased the generating rate of O2·-, the level of H2O2and malondialdehyde (MDA), respectively; under exposure to Y3+, the generating rate of O2·-and H2O2accumulation was significantly lowered than Ni2+treatments at the absence of Y3+, respectively; and there was no significant difference in MDA accumulation. Under the absence of Y3+, spermidine (Spd) was significantly reduced, whereas spermine (Spm) was significantly induced and then inhibited backward. In details, ornithine decarboxylase (ODC), polyamine oxidase (PAO) and diamine oxidase (DAO) shared the similar response pattern:first increase then reduction backward; under exposure to Y3+, putrescine (Put) was significantly increased at the low levels of Ni2+(0.05mmol/L-0.10mmol/L), while Put was significantly declined at the high levels of Ni2+(0.15mmol/L-0.20mmol/L). In addition, Y3+significantly elevated conjugated PAs and bound Spd and Spm, and reduced bound PAs, inhibited PAO and DAO activities. To sum up, it is clearly that Ni2+stress induced the ROS and enhance membrane lipid peroxidation in P. crispus; moreover Y3+is able to relieve Ni2+stress toxicity on P. crispus as it could regulate polyamine metabolic enzymes activities, partly recovery polyamine metabolic balance. |
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