Characteristics of C4 photosynthesis in stems and petioles of C3 flowering plants.

Most plants are known as C3 plants because the first product of photosynthetic CO2 fixation is a three-carbon compound. C4 plants, which use an alternative pathway in which the first product is a four-carbon compound, have evolved independently many times and are found in at least 18 families. In addition to differences in their biochemistry, photosynthetic organs of C4 plants show alterations in their anatomy and ultrastructure. Little is known about whether the biochemical or anatomical characteristics of C4 photosynthesis evolved first. Here we report that tobacco, a typical C3 plant, shows characteristics of C4 photosynthesis in cells of stems and petioles that surround the xylem and phloem, and that these cells are supplied with carbon for photosynthesis from the vascular system and not from stomata. These photosynthetic cells possess high activities of enzymes characteristic of C4 photosynthesis, which allow the decarboxylation of four-carbon organic acids from the xylem and phloem, thus releasing CO2 for photosynthesis. These biochemical characteristics of C4 photosynthesis in cells around the vascular bundles of stems of C3 plants might explain why C4 photosynthesis has evolved independently many times.     

Unicellular C4 photosynthesis in a marine diatom

Nearly 50 years ago, inorganic carbon was shown to be fixed in microalgae as the C3 compound phosphoglyceric acid. The enzyme responsible for C3 carbon fixation, ribulose-1,5-bisphosphate carboxylase (Rubisco), however, requires inorganic carbon in the form of CO2 (ref. 2), and Rubisco enzymes from diatoms have half-saturation constants for CO2 of 30-60 microM (ref. 3). As a result, diatoms growing in seawater that contains about 10 microM CO2 may be CO2 limited. Kinetic and growth studies have shown that diatoms can avoid CO2 limitation, but the biochemistry of the underlying mechanisms remains unknown. Here we present evidence that C4 photosynthesis supports carbon assimilation in the marine diatom Thalassiosira weissflogii, thus providing a biochemical explanation for CO2-insensitive photosynthesis in marine diatoms. If C4 photosynthesis is common among marine diatoms, it may account for a significant portion of carbon fixation and export in the ocean, and would explain the greater enrichment of 13C in diatoms compared with other classes of phytoplankton. Unicellular C4 carbon assimilation may have predated the appearance of multicellular C4 plants.     

束花石斛和黄花石斛光合特性研究

以大花组的束花石斛（Dendrobium chrysanthum）和黄花石斛（D. dixanthum）为材料,对它们的光合生理等进行了系统研究.2种石斛叶片的解剖结构为异面叶,气孔仅分布在下表面,具气孔盖,叶脉维管束鞘不含叶绿体,无花环型结.2种石斛的光强、CO2浓度和温度的响应研究表明,它们的光补偿点（LCP）和光饱和点（LSP）分别为5～10μmol/(m2?s) 和850～900μmol/(m2?s),最大光合速率（Pn）在～6μmol/(m2?s);CO2补偿点和饱和点分别为80～90 μmol/mol和800 μmol/mol;光合作用的最适温度在26～30℃.2种石斛兰的Pn日变化为双峰型曲线,首峰出现在12:00左右,最大光合速率在5～6μmol/(m2?s),次峰出现在15:00左右,夜间不吸收CO2.2种石斛的PEPCase活性极低,具有较高的RuBPCase和GO酶活性.以上的研究结果表明,束花石斛和黄花石斛光合作用碳同化途径属C3植物类型,具有半阴生植物的特点.     

An inducible CO2 concentrating mechanism in cyanobacteriumAnabaena sp. strain PCC7120

In order to define its characteristics of the photosynthetic utilization of CO2 and HCO3-when the ambient inorganic carbon changed, HCG (High-CO2-Growing Cells) of cyanobacteri-um Anabaena sp. strain PCC7120 were prepared. The growth rate of HCG was higher than that of LCG (low-CO2-growing cells, i.e. air-growing cells). When the HCG cells were transferred from 5% CO2 to air levels of CO2 ,a series of changes took place: its carbonic anhydrase activity as well as its photosynthetic affinity to the external inorganic carbon significantly increased; the number of the carboxysomes, which is one of the most important components of CCM in cyanobacteria also increased. These facts indicated that the CCM activity of Anabaena PCC 7120 was induced. When the pH in the medium increased from 6 to 9, the photosynthetic affinity to external inorganic carbon of both HCG and LCG declined, while the apparent photo-synthetic affinity to external CO2 increased. In the light of these findings, this inducible CCM in cyanobacteria provided a good model for the study of the photosynthetic Ci utilization in the pho-totrophic microoganisms.     

Exogenous carbon acquisition of photosynthesis in Porphyra haitanensis (Bangiales, Rhodophyta) under emersed state

The photosynthetic performances of Porphyra haitanensis thalli were investigated in order to understand its mechanisms for exogenous carbon acquisition during emersion at low tide. The emersed photosynthesis was studied by altering the pH value in the water film on the thalli surface, treating them with carbonic anhydarase inhibitors (acetazolamide and 6-ethoxyzolamide), adjusting the CO2 concentrations in the air, and comparing the theoretical maximum CO2 supply rates within the adherent water film with the observed photosynthetic CO2 uptake rates. It was found that the principal exogenous inorganic carbon source for the photosynthesis of P. haitanensis during emersion was atmospheric CO2. The driving force of CO2 flux across the water film was the CO2 concentration gradient within it. Carbonic anhydrase accelerated both extracellular and intracellular CO2 transport. The emersed photosynthesis of P. haitanensis was limited by the present atmospheric CO2 level, and would be enhanced by atmospheric CO2 rise that would trigger global warming.     

辣木在不同CO2体积分数下的光合作用

辣木是一种经济价值高的热带植物,前期已成功在韶关引种.在此基础上,研究了辣木在不同CO2体积分数下的光合速率的变化,结果表明:辣木在不同CO2体积分数（3 250~400 L/L）下的净光合速率不同,当叶室CO2体积分数在700~450 L/L时,净光合速率最大,继续增加CO2体积分数,辣木叶片的净光合速率会降低,体积分数越高降低幅度越大,在高CO2体积分数时净光合速率会下降为负值.胞间CO2体积分数随着叶室CO2体积分数的增加而增加,气孔导度和蒸腾速率随CO2体积分数增加的变化不大.     

Plant biomarkers in aerosols record isotopic discrimination of terrestrial photosynthesis

Carbon uptake by the oceans and by the terrestrial biosphere can be partitioned using changes in the (12)C/(13)C isotopic ratio (delta(13)C) of atmospheric carbon dioxide, because terrestrial photosynthesis strongly discriminates against (13)CO(2), whereas ocean uptake does not. This approach depends on accurate estimates of the carbon isotopic discrimination of terrestrial photosynthesis (Delta; ref. 5) at large regional scales, yet terrestrial ecosystem heterogeneity makes such estimates problematic. Here we show that ablated plant wax compounds in continental air masses can be used to estimate Delta over large spatial scales and at less than monthly temporal resolution. We measured plant waxes in continental air masses advected to Bermuda, which are mainly of North American origin, and used the wax isotopic composition to estimate Delta simply. Our estimates indicate a large (5 6 per thousand) seasonal variation in Delta of the temperate North American biosphere, with maximum discrimination occurring in late spring, coincident with the onset of production. We suggest that the observed seasonality arises from several factors, including seasonal shifts in the proportions of production by C(3) and C(4) plants, and environmentally controlled adjustments in the photosynthetic discrimination of C(3)-plant-dominated ecosystems.     

Photosynthetic bicarbonate utilization inPorphyra haitanensis (Bangiales, Rhodophyta)

The activities of carbonic anhydrase (CA) and photosynthesis of Porphyra haitanensis were investigated in order to see its photosynthetic utilization of inorganic carbon source. Both intra- and extra-cellular CA activities existed in the thallus. CA inhibitors, acetazolamide (AZ) and ethoxyzolamide (EZ), remarkably depressed the photosynthetic oxygen evolution in seawater of pH 8.2 and 10.0, and EZ showed stronger inhibition than AZ. The observed net photosynthetic rate in seawater of pH 8.2 was much higher than that of CO2 supply theoretically derived from spontaneous dehydration of HCO3-. P. haitanensis also showed a rather high pH compensation point (9.9). The results demonstrated that P. haitanensis could utilize bicarbonate as the external inorganic carbon source for photosynthesis. The bicarbonate utilization was closely associated with dehydration catalyzed by extracellular CA activity. The inorganic carbon composition in seawater could well saturate the photosynthesis of P. haitanensis. The low Km value and compensation points for inorganic carbon reflected the existence of CO2- concentrating mechanism in this alga.     

病虫害侵染对植物光合作用影响研究进展

随着人类商业运输和旅游活动扩大了病虫害的分布范围,气候变化增加了病虫害的爆发频率,造成了巨大的经济损失.光合作用是陆地生态系统吸收大气CO2的重要途径,也影响人类粮食生产.病虫害对植物光合作用的影响主要在两个方面:一方面通过采食植物的光和器官,减少了植物的光合能力.另一方面,病虫害侵染后植物的生理参数发生变化(如影响植物体中的叶绿素含量以及叶绿素a与b的比值、气孔导度和细胞内的CO2浓度),进而影响到植物的光合作用.因此,本文综述了近年来国内外关于病虫害对植物光合生理和光合作用的研究,并在此基础上对未来的研究方向进行了探讨和展望.     

山核桃果皮黄酮提取液对四种作物苗期光合性能的影响

采用6种浓度山核桃果皮黄酮提取液（0.1～2.0mg·L^-1）处理盆栽小麦、玉米、大豆和绿豆幼苗,研究对苗期叶片光合速率、气孔导度、蒸腾速率、细胞间隙CO2等光合性能的影响.结果显示：在试验浓度范围内,黄酮提取液对四种作物苗期的光合性能具有低浓度促进、高浓度抑制影响;0.1、0.5mg·L^-1黄酮提取液提高了叶绿素a、叶绿素b和叶绿素总量,促进光合速率、气孔导度、蒸腾速率,适当增加细胞间隙内部的CO2浓度,以0.1mg·L^-1处理效果最明显,与对照相比,四种作物的叶绿素总量和光合速率最高增加了20.9%和21%,处理的影响达显著或极显著水平（（P〈0.05或P〈0.01）;超过0.5mg·L^-1叶绿素含量、光合速率、气孔导度、蒸腾速率逐渐降低,细胞间隙的CO2浓度快速增加.研究表明,适宜浓度的山核桃黄酮提取液具有提高叶片叶绿素含量,促进气孔开放度,增加对细胞内的CO2供应,改善叶片光合性能的作用.     

辣椒（Onza和Cajamarca）光合特性研究

本文通过研究两种长势一致的不同辣椒品种（Onza和Cajamarca）的光合特性,探讨不同品种辣椒光合特性是否存在差异。通过LI-6400便携式光合作用系统测定两种辣椒的光合特性。结果袁明：Cajamama的光饱和点低于Onza,而光补偿点高于Onza。Onza和Cajamarca净光合速率具有相同的变化趋势,最大净光...     

Climate as the dominant control on C<Subscript>3</Subscript> and C<Subscript>4</Subscript> plant abundance in the Loess Plateau: Organic carbon isotope evidence from the last glacial-interglacial loess-soil sequences

Two modes of photosynthesis predominate in terres-REPORTS trial plants: the C3 and C4 modes[1]. The C3 mode is used by all of trees, bushes, and cold season grasses. The C4 mode is used by the most of tropical and warm season grasses. They are disadvantaged relative to C3 plants at high CO2/O2 ratios because of the additional energy ex-pense needed to concentrate CO2 in the bundle-sheath cells. At low CO2/O2, however, C4 plants can achieve a relatively high quantum yield by suppressin…     

Bacterial photosynthesis in surface waters of the open ocean

The oxidation of the global ocean by cyanobacterial oxygenic photosynthesis, about 2,100 Myr ago, is presumed to have limited anoxygenic bacterial photosynthesis to oceanic regions that are both anoxic and illuminated. The discovery of oxygen-requiring photosynthetic bacteria about 20 years ago changed this notion, indicating that anoxygenic bacterial photosynthesis could persist under oxidizing conditions. However, the distribution of aerobic photosynthetic bacteria in the world oceans, their photosynthetic competence and their relationship to oxygenic photoautotrophs on global scales are unknown. Here we report the first biophysical evidence demonstrating that aerobic bacterial photosynthesis is widespread in tropical surface waters of the eastern Pacific Ocean and in temperate coastal waters of the northwestern Atlantic. Our results indicate that these organisms account for 2-5% of the photosynthetic electron transport in the upper ocean.     

A carbon isotope record of CO2 levels during the late Quaternary

Analyses of gases trapped in continental ice sheets have shown that the concentration of CO2 in the Earth's early atmosphere increased from 180 to 280 p.p.m. during the most recent glacial-interglacial transition. This change must have been driven by an increase in the concentration of CO2 dissolved in the mixed layer of the ocean. Biochemical and physiological factors associated with photosynthetic carbon fixation in this layer should lead to a relationship between concentrations of dissolved CO2 and the carbon isotopic composition of phytoplanktonic organic material, such that increased atmospheric CO2 should enhance the difference in 13C content between dissolved inorganic carbon and organic products of photosynthesis. Here we show that a signal related to atmospheric CO2 levels can be seen in the isotope record of a hemipelagic sediment core, which we can correlate with the CO2 record of the Vostok ice core. Calibration of the relationship between isotope fractionation and CO2 levels should permit the extrapolation of CO2 records to times earlier than those for which ice-core records are available.     

南京椴和心叶椴苗期光合特性比较

利用Li 6400便携式光合作用测定仪,分别测定南京椴(Tilia miqueliana)和心叶椴(T.cordata)2年生苗木叶片的净光合速率(Pn)、气孔导度(Cond)、蒸腾速率(Tr)和胞间CO2浓度(Ci)等指标的日变化,对两树种光合特性进行对比分析。结果表明：8月中旬天气晴朗时,两种椴树净光合速率、气孔导度和蒸腾速率均呈双峰曲线,胞间CO2浓度变化呈单谷曲线;两树种的光补偿点分别为36.2 μmol/(m2·s)和22.8 μmol/(m2·s),光饱和点分别为1 384.8 μmol/(m2·s)和1 216.5 μmol/(m2·s),CO2补偿点分别为76.4 μmol/mol和80.9 μmol/mol,CO2饱和点则分别为1 872.5 μmol/mol和1 655 μmol/mol。基于对这两个树种净光合作用的分析,笔者发现南京椴净光合速率日均值大于心叶椴。     

The life span of the biosphere revisited

A decade ago, Lovelock and Whitfield raised the question of how much longer the biosphere can survive on Earth. They pointed out that, despite the current fossil-fuel induced increase in the atmospheric CO2 concentration, the long-term trend should be in the opposite direction: as increased solar luminosity warms the Earth, silicate rocks should weather more readily, causing atmospheric CO2 to decrease. In their model, atmospheric CO2 falls below the critical level for C3 photosynthesis, 150 parts per million (p.p.m.), in only 100 Myr, and this is assumed to mark the demise of the biosphere as a whole. Here, we re-examine this problem using a more elaborate model that includes a more accurate treatment of the greenhouse effect of CO2, a biologically mediated weathering parameterization, and the realization that C4 photosynthesis can persist to much lower concentrations of atmospheric CO2(<10 p.p.m.). We find that a C4-plant-based biosphere could survive for at least another 0.9 Gyr to 1.5 Gyr after the present time, depending respectively on whether CO2 or temperature is the limiting factor. Within an additional 1 Gyr, Earth may lose its water to space, thereby following the path of its sister planet, Venus.     

Crystal structure of plant photosystem I

Oxygenic photosynthesis is the principal producer of both oxygen and organic matter on Earth. The conversion of sunlight into chemical energy is driven by two multisubunit membrane protein complexes named photosystem I and II. We determined the crystal structure of the complete photosystem I (PSI) from a higher plant (Pisum sativum var. alaska) to 4.4 A resolution. Its intricate structure shows 12 core subunits, 4 different light-harvesting membrane proteins (LHCI) assembled in a half-moon shape on one side of the core, 45 transmembrane helices, 167 chlorophylls, 3 Fe-S clusters and 2 phylloquinones. About 20 chlorophylls are positioned in strategic locations in the cleft between LHCI and the core. This structure provides a framework for exploration not only of energy and electron transfer but also of the evolutionary forces that shaped the photosynthetic apparatus of terrestrial plants after the divergence of chloroplasts from marine cyanobacteria one billion years ago.     

五种引种栽培的贵州特优观赏山茶光合生理特性研究

本文对引种栽培于贵州省植物园的小黄花茶 (CamellialuteofloraY .K .Li)、美丽红山茶 (C .delicataY .K .Li)、威宁短柱油茶 (C .salenensisStapf.ex .Bean .)、狭叶瘤果茶 (C .neriifoliaChang)和四球茶 (C .tachangensisF .S .Zhang)等贵州特优观赏山茶的光合生理特性进行了研究报道 :(1) ,均为C3植物 ,其CO2补偿点在 6 0 μL/L左右 ,光呼吸速率与总光合的比值为 2 5% ,光补偿点是 80 0～ 2 50 0lx ,光饱和点 16 0 0～4 10 0 0lx ;其中小黄花茶的光补偿点及光饱和点最低 ,威宁短柱油茶的光补偿点及光饱和点最高。 (2 ) ,净光合速率 (Pn) 6 .0 0～ 15.0 0CO2 mg/ (dm2 ·h) ,光呼吸速率 (Pr) 2 .0 0～ 5.0 0CO2 mg/ (dm2 ·h) ,其中威宁短柱油茶的Pn及Pr均较高 ,四球茶的Pn及Pr均较低。暗呼吸速率 (Dr) 0 .70～ 2 .6 0CO2 mg/ (dm2 .h) ,其中威宁短柱油茶的Dr较高 ,小黄花茶的Dr较低。 (3) ,Pn、Pr及Dr相互间呈正相关 ;Chl.(a b) (叶绿素 )含量 7.6 0～ 12 .50mg /dm2 ,其中小黄花茶的含量较高 ,威宁短柱油茶的含量较低。这一结论对研究其观赏植物学特性和扩繁栽培等具有科学价值     

4种苦苣苔科植物光合特性的比较

以苦苣苔科植物半蒴苣苔（Hemiboea henryi Clarke）、温州长蒴苣苔（Didymocarpus cortusifolius（Hance）W．T．Wang）、牛耳朵（Chirita eburnea Hance）和大花旋蒴苣苔（Boea clarkeana Hemsl．）为材料,测定并比较了它们的生理生态因子、光合作用和叶绿素荧光参数．结果表明：4种苦苣苔科植物的净光合速率日变化曲线均为双峰曲线,峰形也相似;4种苦苣苔科植物均有较低的光补偿点和光饱和点,以及较高的CO2补偿点和CO2饱和点,说明低光照（600～750μmol·m-2·s-1）和高CO2浓度（1277—1965mg／m3）可以有效促进植物的生长和发育．叶绿素荧光参数的测定结果显示：随着光合有效辐射从0μmol·m-2·s-1增加到1400μmol·m-2·s-1,4种苦苣苔科植物的光系统Ⅱ实际光化学量子产量和光化学猝灭值逐渐下降,表观电子传递速率和非光化学猝灭值则增加;光化学量子产量、表观电子传递速率和光化学猝灭的大小顺序为温州长蒴苣苔〉牛耳朵〉半蒴苣苔〉大花旋蒴苣苔,非光化学猝灭均值的大小顺序为牛耳朵〉半蒴苣苔〉温州长蒴苣苔〉大花旋蒴苣苔．表明4种苦苣苔科植物中,牛耳朵同时具有较高的光利用能力和光适应能力,是引种开发的优选品种．     

Guard cell abscisic acid signalling and engineering drought hardiness in plants

Guard cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants through transpiration to the atmosphere. Guard cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of guard cell abscisic acid signalling have been discovered. The molecular understanding of the guard cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.