【作者】 姚广；

【导师】 高辉远；

【作者基本信息】 山东农业大学 ， 植物学， 2008， 硕士

【摘要】 本文以鲁玉9号玉米(Zea mays cv.Luyu9)和津春4号黄瓜(Cucumis sativus L.JInchun4)为材料,通过对叶片气体交换、叶绿素荧光、快速叶绿素荧光诱导动力学曲线以及820nm的光吸收、色素含量、抗氧化酶活性、离子含量等分析,着重研究了Pb胁迫对叶片光合机构的影响,探讨了Pb对光合机构的伤害机理,主要结果如下:1.分别以0.25和0.5mmol·L-1Pb处理玉米,以1和2mmol·L-1Pb处理黄瓜幼苗20天后,与对照相比,其生长受到抑制,叶片面积减小,叶绿素含量降低,地上、地下部分生物量都下降,并且随着Pb胁迫浓度的增大,其伤害程度增大。2. Pb胁迫后玉米、黄瓜叶片叶绿素含量显著降低,而叶片中可能影响色素含量的Mg、N、P、S、K、Fe、Mn等离子含量反而有升高的趋势,因此叶绿素含量的降低不是由于Pb影响了离子吸收引起的。3. Pb胁迫后,玉米、黄瓜的净光合速率(Pn)、表观量子效率(AQY)、羧化效率(CE)、气孔导度(Gs)降低,而细胞间隙CO2浓度(Ci)升高。气孔导度不是Pn下降的主要原因。羧化效率的下降可能是其光合作用下降的一个重要因素。4.与对照相比,Pb胁迫下,玉米、黄瓜叶片光系统II的实际光化学效率(ФPSII)、PSII的天线转化效率(Fv’/Fm’)、PSII反应中心的开放程度(qP)降低;非光化学猝灭(NPQ)升高。5.在PSII中,随着Pb处理浓度的增大,综合反应PSII的性能指数PIABS、φEo和ψO逐渐降低;Wk升高。通过叶绿素荧光诱导动力学曲线我们可知PSII的供体侧和受体侧都受到伤害。单位面积吸收的光量子(ABS/CSm)、用于电子传递的光量子(ETo/CSm)以及单位面积有活性的反应中心数目(RC/CSm)也随着Pb胁迫浓度的增大而逐渐下降,相反,单位面积所耗散的光量子(DIo/CSm)逐渐增加。随着Pb浓度的增大,虽然PSII的光化学活性降低,然而单位反应中心捕获的光量子(TR/RCm)和用于电子传递的光量子(ETo/RC)增加了,这可能是叶片捕获的激发能更多地传给有活性的反应中心并导致电荷分离所致。6.随着Pb处理浓度的增大,玉米、黄瓜叶片的PSI的活性逐渐降低。而PSII和PSI究竟谁先受到伤害还是同时受到伤害?还需要进一步研究。7. Pb处理玉米、黄瓜幼苗20天后其抗氧化酶SOD、APX活性下降。Pb胁迫后Cu离子含量降低,Cu离子会影响SOD、APX等酶的活性。抗氧化酶活性的下降从而使过剩的激发能产生的活性氧分子会进一步对生物大分子以及生物膜产生伤害。8. Pb胁迫后MDA含量升高,表明膜系统受到伤害,而与光合作用相关的色素蛋白复合体都定位在膜上,Pb胁迫对膜伤害后必然会影响光合活性。Pb处理后硝酸还原酶活性显著降低。硝酸还原酶活性降低,会影响植株的铵态氮供应,从而进一步影响生长。总之,Pb胁迫通过影响玉米、黄瓜叶片的色素含量、羧化效率、PSII和PSI的活性来最终影响其光合作用,而对生物膜、抗氧化酶和硝酸还原酶活性的影响进一步影响作物的生理状态而影响光合作用,并最终降低作物产量。更多还原

【Abstract】 By measurement of gas exchange, chlorophyll fluorescence, chlorophyll a fluorescence transient and light absorbance at 820 nm, etc., effects of Pb-stress on photosynthetic apparent in cucumber and maize seedling leaves were investigated in this paper. The main results are as follows:1. After treated with different Pb concentration for 20days, the growth of cucumber and maize seedlings was significantly inhibited; leaf area, chlorophyll content and biomass were decreased in Pb treated seedlings leaves and the damage accelerated with the increase of the Pb concentration.2. Chlorophyll content significant decreased in Pb treated cucumber and maize leaves. There was no significant decrease in the concentration of Mg, N, P, K, Fe and Mn irons Pb treated leaves, which showed that the decreased content of chlorophyll was not caused by the change in the content of the above irons.3. Pb treatment resulted in a big decrease in net photosynthetic rate, stomatal conductance, apparent quanta yield, as well as carboxylation efficiency, whereas a considerably increase in intercellular CO₂ concentration was observed in Pb treated leaves. The decrease of photosynthesis was not due to stomatal limiting under Pb stress. The decrease in carboxylation efficiency indicated that the inhibition of dark reaction was the limiting factor of photosynthesis decrease in Pb treated leaves.4. Pb treatment decreased the actual efficiency of PSII （ФPSII）, photochemical quenching （qP） and the efficiency of light energy capture by open PSII reaction centers （Fv’/Fm’） in leaves of cucumber and maize . However, non- photochemical quenching was increased in these leaves .5. The parameters obtained from the chlorophyll a transient such as PIABS,φEo andψO decreased and WK increased with the increase of the Pb concentration. The changes of these parameters showed that donor and acceptor sides of PSII were damaged in Pb treated leaves. Photons absorbed by per excited cross-section （ABS/CSm）, photons used to move electron transport beyond QA-per excited cross-section （ETo/CSm） and the density of active reaction center per excited cross-section （RC/CSm） decreased and the dissipated flux per excited cross-section （DIo/CSm） increased in Pb treated leaves. It was observed that the fraction of photons used to move electron transport beyond QA-per reaction center （ETo/RC） and trapped photons per reaction center （TR/RCm） increased markedly in the Pb treated leaves, which was attributed to that more absorbed photons by leaves was transported to active reaction centers and resulted in charge separation.6. The activity of PSI decreased with the increase of the Pb concentration. Hower further studies are needed to clarify which system btween PSII and PSI was damaged first under the Pb treatement.7. The activity of active oxygen scavenging enzymes SOD and APX were declined in Pb treated leaves. Pb stress decreased the content of Cu in cucumber and maize leaves, which might affect the activity of SOD and APX. The decrease in the activity of active oxygen scavenging enzymes may result in more active oxygen species which would damage the large biomolecule and membrane.8. The content of MDA increased in Pb treated leaves, indicating the damage of membrane. The damage of membrane affected the activity of membrane bonding protein associated with photosynthesis, which might result in the decrease of photosynthesis. The activity of nitrate reductase （NR） was damaged in Pb treated leaves, which decreased NH₄⁺ application.In conclusion, Pb stress decreased the content of chlorophyll, the efficiency of carboxylation, the activities of PSII and PSI, oxygen scavenging enzyme and nitrate reductase, which decreased the Pn in cucumber and maize seedling leaves. The decrease of Pn resulted in the decrease of biomass.更多还原