【作者】 刘成；

【导师】 佘小平；

【作者基本信息】 陕西师范大学 ， 植物学， 2004， 硕士

【摘要】 本论文以0.35 w·m^-2剂量的UV-B模拟增强UV-B辐射，研究了增强UV-B辐射对萌发初期绿豆（Phaseolus raditus L．）幼苗生长和光合作用的影响，并对萌发初期绿豆幼苗光合作用的变化机制以及增强UV-B辐射对其影响机制进行了探讨。结果表明，对照和UV-B辐射下绿豆幼苗的鲜重、干重、植株高度、叶面积和叶片厚度均随生长时间延长而逐渐增大。从处理第2天开始，增强UV-B辐射明显降低绿豆幼苗地上部鲜重和干重，显著抑制株高和叶面积，并且增强UV-B辐射的效应随辐射时间延长而增大。与此同时，增强UV-B辐射明显促进叶片厚度增加。 光是光合作用的能量来源，光能的吸收、传递和转换功能是由叶绿体类囊体膜上的色素蛋白复合体完成的。增强UV-B辐射对类囊体膜上色素蛋白复合体含量的影响还未见报道。本文首次证明，增强UV-B辐射有降低色素蛋白复合体含量的效应，其中光系统Ⅱ捕光色素复合体（LHCII）的下降更明显，这从一个侧面反映PSII比PSI对增强UV-B辐射更敏感。 光合电子传递是光合作用中原初光物理和光化学反应与生物化学反应连接的纽带。H₂O->DCPIP的电子传递能够反映PSII电子传递活性。我们发现增强UV-B辐射明显抑制绿豆幼苗叶片离体叶绿体H₂O->DCPIP的电子传递活性。添加人工电子受体后DCPIP光还原活性的恢复情况说明，增强UV-B辐射对PSII电子传递链具有两个抑制位点，其中一个离PSII作用中心较远，位于电子供体间苯二酚（HQ）的供体侧，另一个则靠近PSII作用中心，增强UV-B辐射对前一个位点的伤害较重而对后一个的影响较小。 Rubisco是光合作用C₃途径中的一个关键酶。我们的实验证明，增强UV-B辐射下，Rubisco含量和羧化效率（dPn／dCi）均呈现下降趋势，并且增强UV-B辐射对Rubisco大亚基含量的降低程度小于小亚基。 Ao是气孔限制值（Ls）为零时的光合速率，常用来反映叶肉细胞本身光合活性的大小，故称光合能力。表观量子效率（AQY）可在一定程度上反映PSII光化学效率的大小。本文的结果表明，增强UV-B辐射明显降低幼苗的Ao和AQY，且随辐射时间延长，抑制效应增加。 前述色素蛋白复合体含量、PSII电子传递活性、Rubisco含量、dPn／dCi、Ao和AQY等指标均能反映叶肉细胞本身的光合活性，增强UV-B辐射对幼苗净光合速率（Pn）和上述指标的抑制效应表明，叶肉细胞光合活性降低可能是增强UV-B辐射抑制幼苗净光合速率的原因之一。但我们的实验还发现，增强UV-B辐射在降低幼苗尸n的同时，还使气孔导度（G、）下降。因此，只有进行气孔限制分析，才能正确判断增强UV一B辐射抑制幼苗Pn的主要原因。我们的结果表明，增强UV一B辐射明显降低叶片Pn、GS和气孔限制值（LS），但使胞间隙二氧化碳浓度（Cl）增加。按照Farq。har和Sharkey（1982）的观点，增强UV一B辐射降低幼苗Pn的主要原因是叶肉细胞光合活性的抑制，而非气孔限制。 另外，2一4天中对照和增强Uv一B辐射幼苗的Ci稍有下降，而Pn、Ls上升，光合色素含量、dpn/dCi、Rubjseo含量、Ao、AQY、PSll电子传递活性和类囊体膜色素蛋白复合体含量均提高，表明此时段中两处理幼苗Pn增加的主要原因均是叶肉细胞光合活性增加。由于4一8天期间对照幼苗Pn下降，Ci亦稍有下降，而LS上升，说明此时段中对照幼苗Pn下降的主要原因是GS下降。增强UV一B辐射4一8天期间，幼苗Ci升高而 Pn、LS下降，表明此时段中UV一B辐射幼苗Pn下降的主要原因为叶肉细胞光合活性降低。4一8天期间对照幼苗光合色素含量、dPn/dCi、Rtlbiseo含量、Ao、AQY、psll电子传递活性和类囊体膜色素蛋白复合体含量变化不大以及增强UV一B辐射幼苗相关指标大幅下降，又一次证明了此时段中对照和增强UV一B辐射下幼苗Pn降低的主要原因依次为气孔限制和叶肉细胞光合活性下降。更多还原

【Abstract】 The aim of this work was to study the effects of enhanced UV-B radiation (0.35w m-2) on the growth of seedlings and photosynthesis in mung bean’s first pair of true leaves at the initial stage of germination and the involving mechanisms were studied also. It was shown that fresh weight, dry weight, thickness of leaves, height and area of leaves increased during experiment period in both control and UV-B treated seedlings. UV-B radiation remarkable inhibited fresh weight, dry weight, height and area of leaves since 2nd day and the magnitude increased with treatment time. At the same time, the thickness of leaves in UV-B treatment was promoted.The solar light is the energy source of photosynthesis. The chlorophyll-protein complexes on the thylakoid membrane regulate and control the absorption, transportation, distribution and transformation of light energy. There were little report on the effect of enhanced UV-B radiation on the chlorophyll-protein complexes on the thylakoid membrane. Our results showed firstly that enhanced UV-B radiation decreased the contents of different chlorophyll-protein complexes to different extent. Chlorophyll-protein complexes associated with PSII decreased severer than those associated with PSL which suggested that PSII was more sensitive to enhanced UV-B radiation than PSI. LHCII, the main component of chlorophyll - protein complexes on the thylakoid membrane,was remarkably decreased by enhanced UV-B.The photosynthentic electron transfer chain is a bridge between the primary photophysical and photochemical reactions and common reactions. The electron transfer from to DCPIP could reflect the activity of PSII electron chain, which is sensitive to UV-B radiation. We found that enhanced UV-B led remarkable inhibition in it. The differential recovery of DCPIP reduction by the addition of various electron donors indicated that enhanced UV-B radiation probably acts at two sites in PSII: one close to PSII reaction centre and the other near the donor sites of HQ, and the inhibitive effect on the latter site was larger than that on the former one.Ribulose bisphosphate carboxylase/oxygenase or Rubisco is a key enzyme in theC3 pathway. It was indicated that enhanced UV-B radiation led inhibition both in the contents of Rubisco and carboxylation activity of Rubisco. What’s more, enhanced UV-B radiation led smaller inhibition in Rubisco large subunits than small subunits.A0 is the photosynthentic rate when Ls equals to zero, which reflectes the photosynthentic activity of plants, so it is called photosynthentic ability. Apparent quantum yield (AQY) can partly reflect the photochemistry activity of PSII. It was showed that enhanced UV-B led remarkable inhibition in AO and AQY, and the magnitude increased with treatment time.The contents of chlorophyll-protein complexes, dPn/dCi, A0, AQY, PSII electrons transfer activity and the amounts of Rubisco can all reflect photosynthetic activities of mesophyll cell. The results that enhanced UV-B radiation led inhibition in Pn and the parameters above showed that the inhibition of photosynthetic activities of mesophyll cell could probably be one of reasons why Pn decreased. But our results also indicated Gs decreased at the same time. So it is necessary to apply the stomatal analysis in order to judge the main reason why Pn decreased under enhanced UV-B radiation. It was shown that the UV-B treatment limited net photosynthetic rate (Pn), stomatal conduction (Gs) and stomatal limitation (Ls), whereas it promoted intercellular CO2 concentration (Ci). According to the theory of Farquhar and Sharkey (1982), enhanced UV-B radiation reduced Pn mainly by inhibiting photosynthetic activities of mesophyll cell.What’s more, We concluded that main reason of enhancement of Pn in control and UV-B treatment during first 4 days was the promotion of photosynthetic activities of mesophyll cell because of the slight decreased Ci and the enhancements of chlorophyll a ,chlorophyll b ,carotenoid and chlorophyll-protein complexes, dPn/dCi, A0, AQY, PSII electron transfer更多还原