铅胁迫对苦草生理生化及氮、磷代谢关键酶的影响

Impact of the Pb-stress on the physio-biochemical features associated with the keymetabolic enzymes of N and P in Vallisneria

通过研究不同时间(1 d、3 d、5 d、7 d)和不同铅浓度(0、5μmol/L、25μmol/L、50μmol/L、100μmol/L、250μmol/L)胁迫下苦草的生理特性及其氮、磷代谢关键酶的变化,探讨了苦草对铅胁迫的响应。结果表明,叶绿素(Chl)质量比和硝酸还原酶(NR)、谷氨酰胺合成酶(GS)和酸性磷酸酶(ACP)活性在低浓度铅胁迫下5 d内均有所提高,而在高浓度铅胁迫下,叶绿素质量比呈下降趋势。在试验第7 d,各浓度下的酶活性均受到抑制,并且低于对照组。丙二醛(MDA)含量和游离脯氨酸(Fpro)质量比随铅浓度增加呈现先增加后降低的趋势。研究表明,苦草对铅胁迫具有一定的抵抗缓解能力,氮磷代谢关键酶对铅胁迫的响应更为敏感,可以考虑将其作为铅胁迫的响应指标。

This paper is aimed to investigate the effects of the lead stress on Vallisneria. Lead （ Pb）, one of the persistent hazardous pollutants in the environment. As a matter of fact, more and more close attention has been being paid to the exploration of the detrimen- tal effects of heavy metals in the aquatic ecosystem in recent years, with the study of Pb stress being one of the key topics, for it has very serious effects on the nutrition uptake of the submerged plants, yet little is known about the risk background and mechanism. For exam- ple, the enzyme activity of nitrogen and phosphorus metabolism tends to change greatly under the effect of Pb stress. The experimental re- suits of this paper prove that the change of physiological and biochem- ical properties has been related with the key enzyme activities of ni- trogen and phosphorus metabolism during the different periods of time （1 d, 3 d, 5 d, and 7 d） under the different Pb concentrations （0, 5 t.tmol/L, 25 ~mol/L, 50 ttmol/L, 100/zmol/L and 250 ~mol/L）, which reveals that it would be possible for the nitrate reductase （NR）, glutamine synthetase （GS） and acid phosphatase （AEP） to accelerate their activities in less than 5 days, if the content rate of chlorophyll were at the low Pb concentrations, though they may de- crease their speed at higher Pb ones. However, on the 7-th day, all the enzyme activities tend to slow down either at low or at high Pb concentrations. In spite of this, in the process of the 7 days, both the content of malondiadehyde （MDA） and that of the free proline （Fpro） tend to keep rising at the low Pb concentrations and decreas- ing at the high Pb concentrations. Thus, it can be summed up that with the increase of Pb concentrations, the activities of NR, GS and ACP tend to increase first but decrease later, with Chl revealing the same changing rate. And, on the fifth day, there would appear a peak of activities of NR, GS and ACP, indicating that the increasing rate can be compared with that of the control group. That is to say, in all the different Pb concentrations, the content rate of Chl at 25 ktmol/L Pb concentrations should be the highest in all the times under study, which tends to be distinctively different from MDA and Fpro. Therefore, it can be concluded that Vallisneria is potentially endowed with some function to alleviate toxic effects under Pb stress in the aquatic ecosystem. And, in turn, the key enzymes of nitrogen and phosphorus metabolism should thus be regarded as an important re- sponsive indicator to the Pb stress.