光暗处理对水稻叶片光合关键酶的效应

稻苗置暗中24h后,Rubisco含量及Rubisco与可溶性蛋白的比值随光强的增加而提高;经2h光照后再置黑暗中,Rubisco含量在最初20min下降迅速,说明苗期Rubisco蛋白在光暗交替下周转较快.Rubisco的初始活力在光照下迅速增加,其上升倍数大大高于量的增加,光强越大达到最大活力所需的时间越短.照光后把稻苗置暗中,Rubisco初始羧化活力很快下降,说明Rubisco的光下活化及暗中失活迅速.Rubisco活化酶的含量随光照增加而逐渐上升,光照处理后再置暗中Rubisco活化酶含量不断下降,但速率不如Rubisco.Rubisco活化酶的活化只依赖低光强,光照处理后再置黑暗中,Rubisco活化酶活力迅速下降.     

小麦叶片内1,5-二磷酸核酮糖羧化酶/加氧酶大亚基由53 000到50 000裂解反应的定位研究

研究了小麦叶片内1，5-二磷酸核酮糖羧化酶／加氧酶（Rubisco，EC 4．1．1．39）大亚基（LSU）由53000裂解为50000的反应。结果显示，成熟叶片的粗提液在pH5．5的条件下反应后能检测到50000的裂解产物，而暗诱导衰老叶片的粗提液在pH7．5的条件下也能发现LSU的这一降解。分别从成熟叶片和衰老叶片中提取叶绿体，以其裂解液为反应体系研究LSU由53000裂解为50000这步反应的细胞器定位。结果显示，衰老叶片中的叶绿体裂解液在pH7．5时反应1h后能检测到50000降解产物，而成熟叶片叶绿体裂解液在pH5．5和pH7．5的条件下反应后均未检测到LSU的50000裂解产物。上述结果表明：衰老叶片中ISU由53000部分裂解为50000的反应定位于叶绿体内，而成熟叶片中LSU由53000裂解为50000的反应可能定位于叶绿体外。     

抽穗期施氮肥对延缓小麦旗叶衰老的机理初探

抽穗期施氮肥可提高小麦旗叶的光合速率、全氮与Rubisco的含量,而蛋白水解酶活力则下降。在小麦旗叶光合功能可逆衰退阶段,叶片全氮、Rubisco的15N丰度均处于高水平,莱州953小麦旗叶全氮、Rubisco的15N丰度分别从0.998降至0.651和1.432降至0.470,扬麦5号旗叶中全氮、Rubisco的15N丰度分别从0.896降至0.485和1.243降至0.511,表明Rubisco仍处于动态的降解、合成这一周转过程中,仍有大量的Rubisco重新合成;而在光合功能不可逆衰退阶段,叶片全氮、Rubisco的15N丰度均处于低水平,全氮、Rubisco的15N丰度分别维持在近对照水平,且基本无变化,表明此时无Rubisco的重新合成;同时也说明小麦植株在生育后期仍有较高的吸收、利用氮素的能力。     

Photosynthetic and stomatal responses of potatoes grown under elevated CO2 and/or O3—results from the European CHIP-programme

The physiological effects of elevated CO₂ and/or O₃ on Solanum tuberosum cv. Bintje were examined in Open-Top Chambers during 1998 and 1999 at experimental sites across Europe as part of the EU ‘Changing Climate and Potential Impacts on Potato Yield and Quality’ programme (CHIP). At tuber initiation (≈20 days after emergence, DAE) elevated CO₂ (680 μl l⁻¹) induced a 40% increase in the light saturated photosynthetic rate (A_sat) of fully expanded leaves in the upper canopy. This was 16% less than expected from short-term exposures of plants grown under ambient CO₂ (360 μl l⁻¹) to elevated CO₂, indicating that photosynthetic acclimation began at an early stage of crop growth. This effect resulted from a combination of a 12% reduction in stomatal conductance (g_s) and a decline in photosynthetic capacity, as indicated by the significant reductions in the maximum carboxylation rate of Rubisco (Vc_max) and light-saturated rate of electron transport (J_max) under elevated CO₂. The seasonal decline in the promotion of photosynthesis by elevated CO₂ reflected the concurrent decrease in g_s. Vc_max and J_max were both reduced in plants grown under elevated CO₂ until shortly after maximum leaf area (MLA) was attained. Although non-photorespiratory mitochondrial respiration in the light (R_d) increased during the later stages of the season, net photosynthesis was consistently increased by elevated CO₂ during the main part of the season. Photosynthetic rate declined more rapidly in response to elevated O₃ under ambient CO₂, and the detrimental impact of O₃ was most obvious after MLA was attained (DAE 40–50). Several exposure indices were compared, with the objective of determining the critical ozone level required to induce physiological effects. The critical O₃ exposure above which a 5% reduction in light saturated photosynthetic rate may be expected (expressed in terms of cumulative exposure above 0 nl l⁻¹ O₃ between emergence and specific dates during the season (AOT0-cum)) was 11 μl l⁻¹ h; however this value should only be extrapolated beyond the CHIP dataset with caution. The interaction between O₃ and stomatal behaviour was more complex, as it was influenced by both long-term and daily exposure levels. Elevated CO₂ counteracted the adverse effect of O₃ on photosynthesis, perhaps because the observed reduction in stomatal conductance decreased O₃ fluxes into the leaves. The results are discussed in the context of nitrogen deficiency, carbohydrate accumulation and yield.     

温室效应与植物光合作用——大气CO_2浓度升高对植物光合机理影响的分析

比较分析了植物光合同化 CO2 速率、Rubisco活性等性状对长期和短期高浓度 CO2 的反应 .结果表明 :所研究的植物在高浓度 CO2 下生长 ,可以长期保持高的 CO2 同化速率 ;长期在高浓度 CO2 下生长植物的光合速率增加有两个来源 ,其一 ,是 CO2 浓度增加而增加的底物浓度效应 (Δ Pc) ,它的大小随外界短期 CO2 浓度改变而改变 ,其二 ,是植物光合系统结构改变而提高光合能量转换或是电子传递效率所产生的光合速率增加 (ΔPs) ,它的大小不随外界短期 CO2 浓度变化而改变。植物光合速率对大气 CO2 浓度升高的增加量是上述两者之和     

放牧干扰对内蒙古草甸草原羊草光合特性的影响

以内蒙古呼伦贝尔草甸草原放牧草地和围封草地为实验样地,通过对两种样地羊草的水分关系、气体交换、渗透调节等生理生态学特性进行测定分析,比较研究放牧干扰对羊草的光合特性的影响。结果表明,在放牧处理下,羊草对水分亏缺更加敏感,通过降低蒸腾速率、提高水分利用效率(WUE)来应对放牧干扰。羊草能够提高叶绿素含量、 改变电子流动方向、提高实际光化学量子产量(Φ_PSⅡ)活性、增强Rubisco酶活性、提高光合氮、磷利用效率(PNUE、PPUE)适应放牧干扰,利于有机物积累。放牧和围封样地羊草净光合速率日变化都呈“双峰型”,出现“午休现象”,受气孔因素和非气孔因素的共同限制。在光合能量分配上,两种样地羊草PSⅡ的最大光化学量子产量(F_v/F_m)均出现光抑制现象,放牧样地羊草在光照较强时增加非光化学猝灭(NPQ),而在光照适宜时增加光化学猝灭(qP),将更多的能量用于光合反应中心,放牧干扰下羊草对能量的分配和利用更加迅速灵敏。因此,适宜放牧能够促进羊草的生长发育,维持草地较高的生产力,为内蒙古草甸草原生产力的恢复提供一定的理论依据。     

Differential influence of herbicide treatments on activity and kinetic parameters of C4 photosynthetic enzymes from Zea mays

The recommended field dose of rimsulfuron, imazethapyr, alachlor, atrazine or fluometuron differentially reduced shoot fresh and dry weight of 10-day-old maize seedlings as well as leaf protein content during the following 12 days. These reductions seemed consistent during the whole period with fluometuron, atrazine and alachlor but appeared to be nullified by the 5th day of treatment with rimsulfuron and imazethapyr. On the other hand, all herbicides mostly provoked significant inhibitions in specific activities of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), malate dehydrogenase (MDH, EC 1.1.1.82), pyruvate phosphate dikinase (PPDK, EC 2.7.9.1) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in leaves during the first 2 days. Thereafter, the inhibition was recovered in samples treated with rimsulfuron and imazethapyr, leveled off with alachlor but consistently augmented with atrazine and fluometuron. The kinetic characterization showed that rimsulfuron or imazethapyr unchanged V_max of all enzymes in vitro, however, V_max of PEPC, PPDK and Rubisco were decreased in vivo. Nevertheless, atrazine or fluometuron substantially reduced V_max of all enzymes while alachlor showed a reduction in this value of PEPC, MDH and Rubisco. Thus atrazine, fluometuron and, to a lower extent, alachlor reduced concentrations of all enzymes as well as rimsulfuron and imazethapyr for only Rubisco. On the contrary, K_m values of all enzymes were progressively increased by all herbicides indicating that the different herbicides altered the structural integrity of all enzymes. These findings conclude that rimsulfuron or imazethapyr competitively inhibited MDH but revealed mixed inhibition to PEPC, PPDK and Rubisco. Atrazine or fluometuron revealed mixed inhibitions to all enzymes whereas alachlor seemed to be either a competitive inhibitor to PPDK or a mixed inhibitor to PEPC, MDH and Rubisco.     

Correlation of Leaf Nitrogen,Chlorophyll and Rubisco Contents with Photosynthesis in a Supernodulating Soybean Genotype Sakukei 4

Abstract

Soybean requires more nitrogen (N) than gramineous crops because it accumulates a large amount of N in seeds, and its photosynthetic rate per leaf N is low. The supernodulating genotype Sakukei 4 has a superior symbiotic N₂ fixation capability, and thereby is potentially high-yielding. In our previous study, Sakukei 4 was characterized by having a superior ability to maintain high leaf N content and high photosynthetic rate. The objectives of this study were to know photosynthetic characteristics of Sakukei 4 in detail, especially, the responses to CO₂ concentration and light intensity, and to elucidate how the photosynthetic characteristics of Sakukei 4 are associated with the amounts of photosynthesis-related N compounds (chlorophyll and Rubisco). The three genotypes (Sakukei 4 - supernodulating cultivar derived from Enrei, Enrei - normally nodulating cultivar, En1282-non-nodulating line derived from Enrei) were grown at various N levels in this study. The CO₂ exchange rate (CER) in Sakukei 4 was higher than, or equal to that in Enrei at wide ranges of CO₂ concentrations (150-700 μmol mol-¹) and light intensities (200-1,500 μmol m-² s-¹ PPFD). Sakukei 4 had higher leaf N (N_l), chlorophyll (Chl_L) and Rubisco (Rub_L) contents per leaf area, but lower chlorophyll and Rubisco contents per leaf N content (Chl_L/N_l, Rub_L/N_l) than Enrei. The specific leaf weight (SLW) and leaf area trended to be lower in Sakukei 4 than in Enrei. These results indicate that the superior photosynthetic rate in Sakukei 4 is attributed to higher total N, chlorophyll and Rubisco contents per leaf area, but not to high rate of allocation of total N to these N compounds.     

Leafy启动子控制下5-烯醇式丙酮酰-莽草酸-3-磷酸合酶基因(CP4EPSPS)的表达增强芽对草甘膦的抗性

抗草甘膦基因在转基因植物体内持续高效表达,不但增加植物代谢压力,有的甚至改变植物形态造成植物的生长发育畸形。为了减少转基因植株的代谢负担和能源浪费,从拟南芥菜(Arabidopsis thaliana)基因组中克隆了Leafy组织特异性启动子替代CaMV35S启动子,用其驱动改造后加二磷酸核酮糖羧化酶(rubisco)小亚基引导肽的5-烯醇丙酮酰-莽草酸-3-磷酸合酶(CP4EPSPS)基因,同时调控报告基因gus的编码区构建植物表达载体p3300-Leafy-gus和p3300-Leafy-CP4EPSPS,嵌合基因经农杆菌(Agrobacterium)介导转化烟草。稳定表达后经GUS组织染色分析表明,Leafy驱动的gus表达仅局限在植物茎尖和幼叶部分,转基因植株成熟的叶片、茎部和根系均未能检测到GUS活性。草甘膦试验分析表明,Leafy驱动的CP4EPSPS的转基因植株幼芽部位有草甘膦抗性。结果表明,Leafy启动子驱动CP4EPSPS表达增强植株芽端对草甘膦的抗性。