温度变化下银白杨叶片中线粒体呼吸对光合作用和异戊二烯释放的影响

温度的升高增加了银白杨叶片异戊二烯的释放水平;随着温度的升高,线粒体呼吸速率则有所下降。用线粒体呼吸途径的抑制剂处理叶片能够增加叶片异戊二烯的释放水平;然而,同样的处理对光系统II叶绿素荧光参数并没有显著性的影响,并降低了叶片的光合速率。基于以上结果,本文认为在温度上升时,异戊二烯的释放可能并不依赖于光合作用,而线粒体呼吸的上游底物流向异戊二烯的合成路径可能促进了温度上升时异戊二烯释放的增加。     

关于光合作用和呼吸作用的比较实验

光合作用和呼吸作用是植物生命活动的两个重要的生理过程,它们既有区别又有联系。那么如何用实验说明光合作用和呼吸作用的区别呢?在这里介绍一种方法。     

烟草叶片中呼吸电子传递途径在缓解叶绿体PSⅡ光抑制中的作用

前期研究发现线粒体交替氧化酶(AOX)呼吸途径对叶绿体光系统II(PSII)的光抑制有明显的缓解作用。线粒体内另一条呼吸途径——细胞色素氧化酶(COX)呼吸途径是否也具有光保护作用尚不清楚。该文通过荧光快速诱导动力学和荧光淬灭分析,解析了烟草(Nicotiana tabacum)叶片中COX途径对PSII光保护的贡献及其与AOX途径的关系。结果表明,强光处理后PSII活性在所有叶片中均下降。AOX途径受抑明显加速了叶片PSII活性的下降。而当COX途径受抑后,叶片PSII活性的下降与水处理的对照叶片无明显差异。当AOX途径与COX途径同时受抑时,叶片PSII活性的下降比单独抑制AOX途径时更严重。此外,呼吸电子传递受抑均导致叶片非光化学淬灭(NPQ)增加,AOX途径受抑导致的NPQ上调比COX途径受抑时更明显,AOX和COX途径同时受抑时NPQ的增幅最大。上述结果表明,烟草叶片中COX途径和AOX途径均参与PSⅡ的光保护。当COX途径受抑时,其光保护功能可以被AOX途径和NPQ补偿,而AOX途径的光保护作用不能被COX途径和NPQ完全补偿。     

成熟和褐变荔枝果实呼吸作用和脂氧合酶活性

荔枝果实完全成熟和果皮变鮮红时,呼吸速率降低,仅相当于果皮带绿时的39.4％。此时果皮和果肉的脂氧合酶活性亦明显降低,分别相当于后者的60.2％和49.1％。成熟荔枝果实果皮呼吸作用对KCN抑制敏感。2mM KCN抑制果皮总呼吸的91.8％,而仅抑制果肉的56.9％。荔枝果皮呼吸的电了传递主要是通过细胞色素氧化酶途径,而果肉則可能一半是通过其它氧化酶途径。2mKCN和1.5mM SHAM抑制成熟果皮总呼吸97.9％,为SHAM抑制的交替途径呼吸占总呼吸5.28％。相同浓度KCN和SHAM抑制褐变果皮总呼吸79.7％,则SHAM抑制的交替途径呼吸占27.1％。果实褐变时,果成交替途径呼吸比例增高。这一变化可能促进H_2O_2积累、乙烯产生和果皮褐变深化。     

人参叶片的叶龄对光合作用和呼吸作用的影响

叶片光合作用效率受叶龄的影响。在叶片发育期间光合作用发生明显变化。人参为多年生草本阴生植物,在整个生长季节只形成一次叶片。前人对其光合作用特征的研究已有报道,但关于人参叶片发育过程中光合作用的变化尚未见到报道。研究人参植株不同     

叶片水势降低对荔枝光合作用的影响

荔枝(Litchi chinensis)是岭南佳果。但它生长的地区范围狭小,植株生长缓慢,故不易扩大种植和增加果实产量。除了研究荔枝开花习性的工作外,关于荔枝对环境适应性所知甚少。在华南,植物仍遭受季节性干旱。在自然田间情况下,荔枝也常受到土壤缺水和低的空气相对湿度的影响。研究叶片水势降低和空气相对湿度变化对荔枝叶片光合作用的影响,将有助于阐明荔枝对环境因素的适应性和生理反应。本文报道叶片水势降低、叶片/空气水蒸汽压陡度和细胞间 CO_2浓度变化对荔枝光合作用的影响。     

铀对菠菜叶片光合作用影响的研究

为了进一步揭示铀对植物光合作用的影响机理,用不同浓度铀[0、20、50、100、150mg·kg-1]土培处理6叶期菠菜(Spinacia oleracea L.),分别于处理7、14、21、28d后分析铀对菠菜叶片光合色素含量、光合气体交换参数、叶绿素荧光参数和生长指标的影响。结果显示:(1)低浓度铀(20、50mg·kg-1)显著促进菠菜叶片的叶绿素含量和净光合速率(Pn)、气孔导度(Gs)以及蒸腾速率(Tr)等光合气体交换参数;高浓度铀(100、150mg·kg-1)则表现出显著抑制作用,且处理浓度越高,处理时间越长,光合气体交换参数的下降幅度就越大,而胞间CO2浓度(Ci)却反而上升,说明导致Pn下降的主要原因是非气孔因素。(2)高浓度铀处理显著影响菠菜叶片的叶绿素荧光动力学参数,其中光系统Ⅱ(PSⅡ)的最大荧光(Fm)、最大光化学效率(Fv/Fm)和PSⅡ潜在活性(Fv/F0)均显著降低,而初始荧光(F0)显著升高。(3)菠菜幼苗的根长、株高、生物量均随着铀浓度的增加表现出先应激性上升后下降的动态变化。研究表明,低浓度铀可以显著增加菠菜叶绿素含量,有效改善叶片光合效率,促进幼苗的生长发育,而高浓度铀则会抑制菠菜叶片的光合作用,导致光合效率显著下降,显著抑制幼苗的生长发育。     

Studies on the CN-resistant Respiration in Callus of Nicotiana rustica,Gansu Yellow Flower

In attempting to examine whether CN-resistant respiratory pathway is present in callus culture, we used tobacco callus cultures grown on different media. The M-1 medium contained tbe mineral and organic elements of MS medium and was supple,nented with 6-BA (0.5 mg/l) and 2,4-D (2 mg/l), and M-2 medium with 6-BA (2mg/l) and IAi (1 mg/l). No differentiation was observed in both of them. The respiration of M-1 callus was partly resistant to CN, and was markedly inhlbited by m-CLAM in the presence or absence of CN. Experiments of m-CLAM titration showed that the averages of relative contribution of alternative and cytochrome pathway in M-1 callus were 31% awl 46%of the total respiration respectively during the euliure period of 25 days. A same experiment was made on the M-2 callus. It was found that the pereeutages of relative contributions of the two electron transport pathways to the total respiration were approximately the same as those of the M-1 callus, although the respiratory rate was higher in M-2 callus. The above results showed that the bulk of respiratory electron flux was mediated by the eytoehrome pathway, although the alternative pathway was operative in callus of tobacco. The change of exogenous hormones added in the medium could not produee significant effects on the degree of relative contribution of two electron transport pathways under non-differentiation conditions.     

Decreased energy synthesis is partially compensated by a switch to sucrose synthase pathway of sucrose degradation in restricted root of tomato plants

Tomato (Solanum lycopersium L.) plants were grown hydroponically to investigate the changes of energy metabolism and adaptive mechanism in response to root restriction. Root restriction resulted in a significant increase in root lipid peroxidation and reduction in leaf net CO₂ assimilation rate, which was accompanied by increase of alcohol dehydrogenase (ADH; EC 1.1.1.1) and lactate dehydrogenase (LDH; EC 1.1.1.27) activities. Total, cytochrome pathway, and alternative pathway respirations were all decreased in the roots after 15 days of root restriction treatment. Accompanied with the decrease of ATP content, ratio of invertase/sucrose synthase activity was increased in the restricted roots together with a decrease in glucose content and an increase in fructose content. We concluded that the decreased energy synthesis under root restriction condition was partially compensated by the energy-conserving sucrose synthase pathway of sucrose metabolism.     

Cyanide-Resistant Respiration in Relation to Fruit Respiratory Climacteric

Changes in respiratory rate and the effects of respiratory inhibitorson respiration were determined in apple (Malus sylvestris cv. Delicious) and red pepper (Capsicum fructescens) fruits dusting different stages of development and ripening.The results showed that there was an abrupt rise in respiration daring ripening inapple fruit, but the respiration of the red pepper declined continuously throughout theripening period. Thus the apple is climacteric and the red pepper is non-climacteric fruit. The respiration of apple fruit was sensitive to KCN (1 mM) during the period ofdevelopment but changed to CLAM-sensitive and CN-resistant during preclimactericand climacteric phases, indicating that a diversion of respiratory pathways from the cy-tochrome path to the alternative path has occurred. The respiration of the red pepperfruit was CN-sensitive thoughout the whole period of fruit ripening, suggesting thatthe operation of the CN-resistant path was insignificant. Slices from climacteric apple fruits developed induced .respiration after aging, bothKCN and CLAM (1 mM) inhibited the induced respiratic considerably. However, slices from red pepper fruits showed no evidence of induced respiration after aging. Slices from climacteric apple fruits infiltrated with 3 mM CLAM before aging, reducedthe peak of the induced respiration by about 30%, indicating that the development ofinduced respiration was suppressed by the presence of CLAM. The above results indicated that the: climacteric fruits were characterized by diversion of traffic from the cytochrome path to the alternative path during ripening andby the development of induced respiration after slicing and aging. While in nonclimacteric fruits no .diversion of electron transport path was observed during ripening andno induced respiration occurred after aging. Although both the eytochrome and alternative pathways were present in the tissue of red pepper fruits, the alternative pathwas not operating except when the cytochrome path was blocked or was saturated by electron flow.     

Seasonal Pattern of Isoprene Synthase Activity in Quercus robur Leaves and its Significance for Modeling Isoprene Emission Rates

Biogenic emission of hydrocarbons plays an important role in the interactions between plants, especially trees, and the atmosphere. Among these volatile organic compounds isoprene (2-methyl-1,3-butadiene) is the predominant component emitted by many photosynthesizing leaves. Its rapid atmospheric breakdown substantially affects the oxidation potential of the atmosphere. An enzyme, isoprene synthase, extracted from leaves of European oak (Quercus robur L.) was previously found to catalyse the Mg ^2+–dependent elimination of diphosphate from dimethylallyldiphosphate to form isoprene. The present paper describes the seasonal variation of this enzyme acitivity in Quercus robur (L.) leaves in 1995. The enzymatic data obtained were used to create an additional term for the isoprene emission algorithm (ISOC93). The addition of this correction term for the seasonality of isoprene synthase to the emission model improved considerably the simulation of seasonal isoprene emission rates in oaks, avoiding over- and underestimations in the current modeling approach.     

Relationships among Isoprene Emission Rate, Photosynthesis, and Isoprene Synthase Activity as Influenced by Temperature

Isoprene emissions from the leaves of velvet bean (Mucuna pruriens L. var utilis) plants exhibited temperature response patterns that were dependent on the plant's growth temperature. Plants grown in a warm regimen (34/28°C, day/night) exhibited a temperature optimum for emissions of 45°C, whereas those grown in a cooler regimen (26/20°C, day/night) exhibited an optimum of 40°C. Several previous studies have provided evidence of a linkage between isoprene emissions and photosynthesis, and more recent studies have demonstrated that isoprene emissions are linked to the activity of isoprene synthase in plant leaves. To further explore this linkage within the context of the temperature dependence of isoprene emissions, we determined the relative temperature dependencies of photosynthetic electron transport, CO₂ assimilation, and isoprene synthase activity. When measured over a broad range of temperatures, the temperature dependence of isoprene emission rate was not closely correlated with either the electron transport rate or the CO₂ assimilation rate. The temperature optima for electron transport rate and CO₂ assimilation rate were 5 to 10°C lower than that for the isoprene emission rate. The dependence of isoprene emissions on photon flux density was also affected by measurement temperature in a pattern independent of those exhibited for electron transport rate and CO₂ assimilation rate. Thus, despite no change in the electron transport rate or CO₂ assimilation rate at 26 and 34°C, the isoprene emission rate changed markedly. The quantum yield of isoprene emissions was stimulated by a temperature increase from 26 to 34°C, whereas the quantum yield for CO₂ assimilation was inhibited. In greenhouse-grown aspen leaves (Populus tremuloides Michaux.), the high temperature threshold for inhibition of isoprene emissions was closely correlated with the high temperature-induced decrease in the in vitro activity of isoprene synthase. When taken together, the results indicate that although there may be a linkage between isoprene emission rate and photosynthesis, the temperature dependence of isoprene emission is not determined solely by the rates of CO₂ assimilation or electron transport. Rather, we propose that regulation is accomplished primarily through the enzyme isoprene synthase.     

Studies on Photosynthesis,Respiration and Morphology of Nostoc flagelliforme

Nostoc flagelliforme Born. et Flah. is one of the terrestrial cyanobacteria naturally distributed in arid and semi-arid areas in the Northern and the North-western parts of China. The cyanobacterium is an edible delicacy with special medical value. However, commercial N. flagelliforme has nov been collected from the field only. For cultivation of this valuable cyanobacterium, it is necessary to understand how it grows and how it adapts to the environment.The experimental material was collected in Siziwangqi of Nei Monggol. The effects of light intensity, temperature, pH, salinity, length of thallus and rewetting on photosynthesis and respiration of N. fiagelli[orme were measured using an oxygen electrode. The results were as follows: The photosynthetic light compensation point was around 40–90μmol photons·m-2·s-1, the light saturation point was 1200μmol photons·m-2·s-1, and no photoinhibition appeared when the light intensity was increased to 1800μmol photons· m-2·s-1. N. fiagelliforme exhibited its photosynthetic and respiratory activities in the temperature range of 5–45℃. The optimum temperature for its photosynthesis was 25℃ and that for respiration was 35--40℃. Between pH range of 4.5–9.5 N. flagelliforme had photosynthetic activity and respiratory activity at pH range of 4-10, with optimum pH for photosynthesis at 7.5 and for respiration at 7.5–8.0. N. flagelliforme exhibited maximum net photosynthesis in 0.15mol/L of NaC1 in BG-11 medium. When the salinity was increased to 0.9 mol/L the net photosynthesis dropped down to zero. Respiration decreased concordantly with the increasing salinity as well. Maxima photosynthesis and respiration was also detected when the thallus of N. flagelliforme reached a length of 0.5cm and aftewords the more the length the less the activities. The recovery time attaining to the maximum photosynthesis and respiration activities after rewetting was dependent on storage time in dryness. The cyanobacterial mats after being reserved for 3 months, attained its maximum photosynthesis by 0.5h after rewetting, and that being reserved for 18 months needed 3.5h after rewetting. For respiration, the mats reserved for 3 months and 18 months required 5 minutes and lh after rewetting, respectively to attain its maximum. Under scanning electron microscope, cells of N. flagelliforme were wrapped up within a gluey sheath, and usually attached closely to each other in pairs and the filaments were uni-trichome with branches in some cases. The surface of thallus tip was rougher than other parts which meant that the tip portion had greater surface area beneficial to water absorption and cell growth.     

Combinational biosynthesis of isoprene by engineering the MEP pathway in Escherichia coli

As an important feedstock in petrochemistry, isoprene is used in a wide range of industrial applications. It is produced almost entirely from petrochemical sources; however, these sources are being progressively depleted. A reliable biological process for isoprene production utilizing renewable feedstocks would be an industry-redefining development. There are two biosynthetic pathways producing isoprene: the mevalonate (MVA) pathway and the methyl erythritol 1-phosphate (MEP) pathway. In this study, the MEP pathway was modified in Escherichia coli BL21 (DE3) to produce isoprene. The isoprene synthase (IspS) gene chemically synthesized from Populus alba after codon optimization for expression in E. coli was heterologously expressed. The endogenous genes of 1-deoxy-d-xylulose-5-phosphate synthase (DXS) and 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR) were over-expressed. The isopentenyl pyrophosphate isomerase (Idi) gene from Streptococcus pneumoniae was exogenously over-expressed, and farnesyl diphosphate synthase (ispA) was weakened to enhance the yield. The control strain harboring empty plasmids did not emit any isoprene. The over-expression of the DXR gene only had little impact on the yield of isoprene. Idi from S. pneumoniae played a significant role in the improvement of isoprene production. The highest yield was achieved by an ispA-weakened DXS-IDI-IspS recombinant with 19.9 mg/l isoprene, which resulted in a 33-fold enhancement of the isoprene yield from the IspS recombinant.     

Respiration in mature leaves of Lolium perenne as affected by nutrient supply, cutting and competition

The rate of oxygen uptake was measured on sections of mature leaf tissue derived from two populations of Lolium perenne L. cv. S23, selected for contrasting rates of mature leaf respiration. Under conditions of sufficient nutrient supply, GL72 had a lower rate of respiration and a greater yield than GL66. The populations were exposed to important management variables to investigate their effect on the selection criterion, the two variables being nutrient supply and defoliation. Conditions of low nutrient supply were characterized by a similarity in respiration rate and a change in the regulation of respiration. Enzyme levels, rather than adenylates, controlled respiration. Weekly cutting induced activity of the otherwise latent alternative pathway.     

Respiration of barley roots: Assessment of activity of the alternative path using SHAM

The activity of the alternative path of O₂ consumption in detached and intact roots of barley [ Hordeum distichum (L.) Lam. cv. Maris Mink] was determined by titration with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. In the absence of cyanide, only high concentrations were inhibititory (> 5 m M ). whilst in its presence low SHAM concentrations (2.5–5.0 m M ) gave maximum inhibition: the resulting ϱ V_alt plots were non-linear. A SHAM-stimulated peroxidase could readily be washed from these roots, but non-linearity cannot be explained in terms of SHAM-stimulation of this peroxidase as it is not active in the absence of an exogenous supply of NADH. In detached roots the degree of inhibition of respiration with 25 m M SHAM was nearly double the capacity of the alternative path (measured as the degree of inhibition by SHAM in the presence of cyanide), suggesting non-specific inhibition. Effects of SHAM on cytochrome path activity in intact roots were examined by reverse titration with cyanide in the presence and absence of SHAM. At 5 m M SHAM had no effect on the cytochrome path, but at 25 m M it inhibited. We conclude that the only factor causing non-linearity of ϱV_alt plots in barley roots is non-specific inhibition of the cytochrome path by high concentrations of SHAM; consequently only low concentrations of SHAM (2.5–5.0 m M ) are suitable for estimating alternative path activity in barley roots.