Photosynthesis in Cell Suspension Culture of a C4 Plant, Gisekia pharnaceoides L.

Photomixotrophic cell suspension culture was established fromthe leaf derived callus cells of Gisekia pharnaceoides L., aC₄ dicotyledonous weed. The late log phase cells possessed shade-typecharacters such as low chlorophyll a/b ratio, less pronouncedO₂ evolution and CO₂ fixation, saturation of photosyntheticCO₂ fixation at low intensity. The chloroplasts from these cellscontained granal stacking with high degree of a very few granawhich are characterized by their wide and high degree of stackings. The predominant labelling of 3-phosphoglyceric acid and sugarphosphates (40% of the total ¹⁴C incorporated) during 5 s exposureto ¹⁴CO₂ in light and subsequent decrease in percentage of ¹⁴Cin these compounds with increase in exposure time indicatedthe operation of the C₃ pathway in these cells. The simultaneoussynthesis of malate (23% of the total ¹⁴C incorporated) is relatedto the much pronounced glycolytic and tricarboxylic acid cycleactivities in these cells. The initial proliferation of callimainly from the zones of vascular supplies in the leaf, highstarch content of the cells, presence of large starch grainsin all the chloroplasts, activities of Calvin cycle enzymes,heavy labelling of C₃ type intermediates and less labellingof aspartate as early photosynthates and rapid accumulationof radioactivity into starch during ¹⁴CO₂ assimilation indicatedthat most of the cells in photomixotrophic culture were derivedfrom bundle sheath cells or the leaf cells of Gisekia changetheir function under culture conditions. ¹Present address: Tropical Botanic Garden and Research Institute,Navaranga Road, Trivandrum 695 011, India. (Received January 29, 1982; Accepted June 4, 1983)     

Photosynthesis by developing embryos of oilseed rape (Brassica napus L.)

The aim of this study was to assess the photosynthetic potentialof developing seeds of oilseed rape (Brassica napus L.) andto compare photosynthetic properties of embryo plastids withthose of leaf chloroplasts from the same species. Measurementsof CO₂-dependent O₂ evolution show that developing seeds ofB. napus are photosynthetically active in vitro. Essentially,all of the photosynthetic activity of the developing seed isaccounted for by the embryo. The rate of photosynthesis by developingembryos increased until the onset of desiccation, after whichit declined, so that by maturity embryos were no longer photosyntheticallyactive. Photosynthetic activity was positively correlated withchlorophyll content throughout development. Comparison of thephotosynthetic characteristics of leaf and embryo chloroplastsrevealed that rates of uncoupled electron transport were 2.5-foldgreater in those from the embryo. Light-saturated rates of CO₂-dependentO₂ evolution, per unit chlorophyll, and CO₂ saturation pointswere similar for chloroplasts from both tissues. However, light-saturationpoints and chlorophyll a/b ratios were lower for embryo thanfor leaf choroplasts. Embryos and embryo chloroplasts also containedconsiderably less ribulose 1,5-bisphosphate carboxylase/oxygenaseprotein per unit total protein, than leaves. Although excisedembryos were capable of high rates of CO₂-dependent O₂ evolution(90–100 mol mg^–1 chlorophyll h^–1) under asaturating photosynthetic photon flux density (PPFD), low transmittanceof light through the silique wall (30%), together with the highPPFD required to achieve light compensation points in developingseeds (500 mol m^–2 s^–1), suggests that photosynthesisin vivo is unlikely to make a net contribution to carbon economyunder normal environmental conditions. Key words: Embryo, development, photosynthesis, chloroplast, Brassica napus L.     

Long Term Effects of High CO2 Concentration on Photosynthesis of Water Hyacinth (Eichhornia crassipes (Mart.) Solms)

The photosynthetic response to CO₂ concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO₂ or at10000 µmol(CO₂) mol^–1 and in winter at 6000 µmol(CO₂)mol^–1 Plants grown and measured at ambient CO₂ had highphotosynthetic rate (35 µmo1(CO₂) m^–2 s^–1),high saturating photon flux density (1500–2000) µmolm^–2 s^–1 and low sensitivity to temperature in therange 20–40 °C. Maximum photosynthetic rate (63 µmol(CO₂)m^–2 s^–1) was reached at an internal CO₂ concentrationof 800 µmol mol^–1. Plants grown at high CO₂ in summerhad photosynthetic capacities at ambient CO₂ which were 15%less than for plants grown at ambient CO₂, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO₂and high light intensity had typical response curves to internalCO₂ concentration with saturation at high CO₂, but for plantsgrown under high CO₂ and low light and plants grown under lowCO₂ and high light intensity photosynthetic rates decreasedsharply at internal CO₂ concentrations above 1000 µmol^–1. Key words: Photosynthesis, CO₂, enrichment, Eichhornia crassipes     

Gas Exchange and Carbohydrate and Nitrogen Concentrations in Leaves of Pascopyrum smithii (C3) and Bouteloua gracilis (C4) at Different Carbon Dioxide Concentrations and Temperatures

Pascopyrum smithii (C₃) andBouteloua gracilis (C₄) are importantforage grasses native to the Colorado shortgrass steppe. Thisstudy investigated photosynthetic responses of these grassesto long-term CO₂enrichment and temperature in relation to leafnonstructural carbohydrate (TNC) and [N]. Glasshouse-grown seedlingswere transferred to growth chambers and grown for 49 d at twoCO₂concentrations (380 and 750 µmol mol^-1) at 20 and 35°C, and two additional temperatures (25 and 30 °C) at750 µmol mol^-1CO₂. Leaf CO₂exchange rate (CER) was measuredat a plant's respective growth temperature and at two CO₂concentrationsof approx. 380 and 700 µmol mol^-1. Long-term CO₂enrichmentstimulated CER in both species, although the response was greaterin the C₃,P. smithii . Doubling the [CO₂] from 380 to 750 µmolmol^-1stimulated CER ofP. smithii slightly more in plants grownand measured at 30 °C compared to plants grown at 20, 25or 35 °C. CO₂-enriched plants sometimes exhibited lowerCER when compared to ambient-grown controls measured at thesame [CO₂], indicating photosynthetic acclimation to CO₂growthregime. InP. smithii , such reductions in CER were associatedwith increases in TNC and specific leaf mass, reductions inleaf [N] and, in one instance, a reduction in leaf conductancecompared to controls. InB. gracilis , photosynthetic acclimationwas observed more often, but significant changes in leaf metabolitelevels from growth at different [CO₂] were generally less evident.Temperatures considered optimal for growth (C₃: 20 °C; C₄:35 °C) sometimes led to CO₂-induced accumulations of TNCin both species, with starch accumulating in the leaves of bothspecies, and fructans accumulating only inP. smithii. Photosynthesisof both species is likely to be enhanced in future CO₂-enrichedand warmer environments, although responses will sometimes beattenuated by acclimation. Acclimation; blue grama (Bouteloua gracilis (H.B.K.) Lag ex Steud.); leaf nitrogen concentration; nonstructural carbohydrates; photosynthesis; western wheatgrass (Pascopyrum smithii (Rydb.) Love)     

Preparation of Radioactive Starch, Glucose and Fructose from C14O2

Radioactive starch, glucose and fructose have been preparedfrom tobacco leaves after assimilation of C¹⁴O₂. The apparatusused for photosynthesis consisted of a shallow Perspex leafchamber connected to a closed gas system, in which C¹⁴O₂ wasgenerated from BaC¹⁴O₂. Six leaves, area 14 to 18 sq. dm. whenexposed to bright sunlight with an initial CO₂ concentrationof 8 to 10 per cent., assimilated 3.35 g. of C¹⁴O₂ in 8 to 10hours. At least 80 per cent. of the C¹⁴O₂ supplied appearedin the leaves as starch and sugar and over 80 per cent. of theradioactivity was accounted for in these carbohydrates. Thespecific activity per m. atom of carbon of the isolated productswas 85 to 90 per cent. of that of the C¹⁴O₂. Small amounts ofradioactive carbon were also incorporated in the leaf proteinand in the celluose, hemicellulose and polyuronides.     

Photosynthesis of White Clover Leaves as Influenced by Canopy Position, Leaf Age, and Temperature

Microswards of white clover (Trifolium repens L.) were grownin controlled environments at 10/7, 18/13 and 26/21 °C day/nighttemperatures. The vertical distribution of leaves of differentages and their rates of ¹⁴CO₂-uptake in situ were studied. Extending petioles carried the laminae of young leaves throughthe existing foliage. A final position was reached within 1/4to 1/3 of the time between unfolding and death. Newly unfoldedleaves had higher rates of ¹⁴CO₂-uptake per leaf area than olderones at the same height in the canopy. At higher temperatures,the decrease with age was faster. However, the light-photosynthesisresponse of leaves which were removed from different heightsin the canopy varied much less with leaf age than did the ratesof ¹⁴CO₂-uptake in situ. The comparison of the rates of ¹⁴CO₂-uptake in situ with thelight-photosynthesis response curves suggests that young leavesreceive more light than older ones at the same height in thecanopy. This would imply that young white clover leaves havethe ability to reach canopy positions having a favourable lightenvironment. This ability may improve the chances of survivalof white clover in competition with other species. Trifolium repens L., white clover, photosynthesis, canopy, leaf age, ¹⁴CO₂-uptake, ecotypes, temperature     

Effects of Anoxia on Phloem Loading in C3 and C4 Species

Changes in phloem loading rate were inferred from observationsof ¹¹C export from attached leaves of C₃ and C₄ monocots anddicots. Loading decreased under anoxia in C₃ leaves, but notin general in the leaves of either C₄ monocots or dicots inthe light. However, loading rate in the C₄ leaves did reduceif the leaf was also darkened or received no CO₂. We suggestthat insensitivity to anoxia in C₄ leaves is due to oxygen fromphotosynthesis which is retained in the bundle sheath at a concentrationsufficient to energize a phloem loading system. There may alsobe another system which is insensitive to anoxia since the effectsof shade and CO₂ deprivation were not always seen, and loadingwas not completely stopped by these treatments. Key words: Phloem loading, C₃, C₄     

Oxygen Exchange in Relation to Carbon Assimilation in Water-stressed Leaves During Photosynthesis

In a study on metabolic consumption of photosynthetic electronsand dissipation of excess light energy under water stress, O₂and CO₂ gas exchange was measured by mass spectrometry in tomatoplants using ¹⁸O₂ and ¹³CO₂. Under water stress, gross O₂ evolution(E_O), gross O₂ uptake (U_O), net CO₂ uptake (P_N), gross CO₂ uptake(TPS), and gross CO₂ evolution (E_C) declined. The ratio P_N/E_Ofell during stress, while the ratios U_O/E_O and E_C/TPS rose.Mitochondrial respiration in the light, which can be measureddirectly by ¹²CO₂ evolution during ¹³CO₂ uptake at 3000 µll^{–1 13}CO₂, is small in relation to gross CO₂ evolutionand CO₂ release from the glycolate pathway. It is concludedthat PSII, the Calvin cycle and mitochondrial respiration aredown-regulated under water stress. The percentages of photosyntheticelectrons dissipated by CO₂ assimilation, photorespiration andthe Mehler reaction were calculated: in control leaves morethan 50 % of the electrons were consumed in CO₂ assimilation,23 % in photorespiration and 13 % in the Mehler reaction. Undersevere stress the percentages of electrons dissipated by CO₂assimilation and the Mehler reaction declined while the percentageof electrons used in photorespiration doubled. The consumptionof electrons in photorespiration may reduce the likelihood ofdamage during water deficit.     

The Influence of Leaf Development on the Expression of C4 Metabolism in Flaveria trinervia, a C4 Dicot

The initial products of ¹⁴CO₂ assimilation were determined understeady state illumination of leaves of Flaveria trinervia, aC₄ dicot of the NADP-mialic enzyme subgroup. Leaf age influencedthe partitioning of ¹⁴CO₂ between the C₄ cycle and the reductivepentose phosphate (RPP) pathway. An estimated 10 to 12%of theCO₂ entered the RPP pathway directly in leaves about 20% fullyexpanded, whereas CO₂ was apparently fixed entirely throughthe C₄ pathway in leaves 75% or more expanded. This partitioningpattern was attributed to the bundle sheath compartment in youngleaves having a relatively high conductance to CO₂ (i.e., beingsomewhat leaky). Of the initially labelled C₄ acids, the proportion that wasmalate, relative to aspartate, increased continuously duringleaf expansion (from 60 : 40 to 87 : 13 at full expansion).Concurrently, there was an increase in the whole leaf activityof NADP malate dehydrogenase and a decrease in the activitiesof aspartate and alanine aminotransferases. Low chlorophylla/b values were observed in young leaves, which may coincidewith an enhanced capacity for non-cyclic electron transportin the bundle sheath chloroplasts of such tissue. Both enhancedaspartate metabolism and direct fixation of CO₂ in the bundlesheath could provide a greater sink for utilization of photochemicallyderived NADPH in the bundle sheath of young leaves. Such metabolicchanges are discussed in relation to a possible decrease inCO₂ conductance of the bundle sheath during leaf development. (Received March 4, 1986; Accepted June 25, 1986)     

Evidence for Predominant Participation of Photosystem II{beta}-Units in Nitrogen Formation by Hydroxylamine-Treated Tobacco Chloroplasts

Relative optical cross sections for flash-induced O₂- and N₂-productionwith water and 1 mM NH₂OH as electron donors to PSII, respectively,as well as that for PSI-mediated O²-uptake have been measuredin tobacco chloroplasts by mass spectrometry. In the wild typetobacco these three reactions are driven by three populationsof photosynthetic units different with respect to the antennasize. The antenna size of O₂-evolving units is twice as largecompared to the N₂-evolving one, but both of these have thesame spectral characteristics in the far red region. In contrastto the wild type, the antenna sizes of O₂- and N₂-evolving unitsin the chlorophyll b-deficient tobacco mutant Su/su var. Aureaare the same as the sizes of the N₂-evolying units in the wildtype chloroplasts. Taking into account the data of Thielen andVan Gorkom [Biochim. Biophys. Acta (1981) 635:111] on a strongdifference in the relative amounts of PSII_ß and PSII_ßin the mutant compared with the wild type (the ratio about 1: 3 and 3 : 1 , respectively) it is concluded that mainly thestroma-exposed PSII_ß units are competent to N₂-evolution. (Received November 11, 1993; Accepted April 25, 1994)     

一个新水稻温敏感叶色突变体的遗传分析及其基因分子定位

在粳稻品种嘉花1号(Oryza sativa L. ssp. japonica ‘Jiahua No.1’)种子经⁶⁰Co γ射线辐照处理的后代中, 发现了1个低温敏感叶色突变体mr21。在较低温度(<25.0°C)条件下, 该突变体幼苗叶色呈黄色; 随着温度逐渐升高, 叶色由黄转绿,其临界温度约为27.5°C; 在低温条件下, 突变体幼苗总叶绿素含量以及叶绿素a、b的含量均较野生型嘉花1号明显下降, 表明该突变体的叶色性状具有明显的温敏感性。遗传分析表明, 该突变体叶色性状受1对隐性核基因控制, 暂将该突变基因命名为thermo-sensitive leaf-color 1(tsl-1)。以该突变体与籼稻9311(Oryza sativa L. ssp. indica ‘9311’)杂交的F₂代分离群体作为定位群体, 利用SSR分子标记将tsl-1基因初步定位在水稻(Oryza sativa)第1号染色体短臂上的MM1799与RM8132分子标记之间, 其遗传距离分别为2.4 cM和3.0 cM; 然后, 进一步利用扩大F₂代群体及新发展的分子标记将tsl-1基因定位在分子标记InDel2与InDel4之间的198 kb内。研究结果为今后对该基因的克隆和功能分析奠定了基础。     

Effect of the age of tobacco leaves on photosynthesis and photorespiration

Relationships among the activities of enzymes related to photosynthesisand photorespiration, and ¹⁴CO₂ photosynthetic products wereinvestigated with individual tobacco leaves attached to thestalk from the bottom to the top. P-glycolate phosphatase ofthe chloroplasts and glycolate oxidase of the peroxisomes hadtheir maximum activities in the 25th leaf from the dicotyledons.Maximum photorespiration was similarly distributed. The highestratio of serine-¹⁴C to glycine-¹⁴C in the photosynthesates andmaximum glycolate formation were also observed in the 25th leaf.Glutamateglyoxylate aminotransferase, serine hydroxymethyltransferaseand glycine decarboxylase were more active in the upper leaves.RuDP carboxylase had nearly constant activity in all leaves,except for the youngest in which activity decreased. MaximumCO₂ photosynthesis and enzyme activity for the C₄ dicarboxylicacid cycle occurred in the upper, youngest leaf. Distributionof photosynthetic CO² fixation among the leaves did not coincidewith RuDP carboxylase activity. The photosynthetic capacityappeared to be better related to the distribution pattern forenzymes of the C₄ dicarboxylic acid pathway, i.e. PEP carboxylase,pyruvate Pi dikinase and 3-PGA phosphatase in the upper leaves.The results suggest that the C₄ dicarboxylic acid pathway participates,to some extent, in photosynthesis in young leaves of tobacco,a dicotyledonous plant. ¹This work was reported at the Annual Meeting (1970) of theJapanese Plant Physiologists in Kobe. ²The Central Research Institute, Japan Monopoly Corporation1-28-3, Nishishinagawa, Shinagawaku, Tokyo, 141 Japan. (Received November 2, 1972; )     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). I. Microclimate and Photosynthesis

Measurements of microclimate and photosynthesis of lucerne var.Europe were made in the field during the spring of 1976. Themaximum rate of canopy gross photosynthesis (14.3 g CO₂ m^–2h^–1, I = ) was 2.5 times greater than that of S 24 perennialryegrass at the same LAI. This difference was due to differencesin individual leaf photosynthesis. The photosynthetic rate ofthe youngest fully expanded leaf of lucerne remained constantthroughout the experimental period at 3.6 g CO₂ m^–2 h^–1(300 W m^–2). Measurements of soil water potential profiles indicated thatlucerne extracted water from the soil to a depth of at least800 mm, with a region of maximum uptake between 400 and 600mm. This capability, with a moderate mean leaf resistance of460 s m^–1, conferred a high assimilation efficiency onlucerne, with a mean water use efficiency of 34 g H₂O lost pergram of carbohydrate assimilated, compared with 200 g H₂O pergram of carbohydrate for S 24. Medicago sativa L, lucerne, photosynthesis, assimilation efficiency     

A Comparison of the Growth, Photosynthesis, Stomatal Conductance and Water Use Efficiency of Moricandia and Brassica Species

When grown in pots and well-watered, the relative growth ratesof the above ground parts of two species of Moricandia (M. arvensis,an intermediate C₃–C₄ species, and M. moricandioides,a C₃ species) were inferior to those of two cultivated Brassicaspecies (B. campestris and B. napus). The Moricandia specieshad thicker leaves (greater d.wt per unit leaf area) with morechlorophyll than the Brassica species and had slightly greaterrates of photosynthesis per unit leaf area at an irradiance(400–700 nm) of 2000 µmol quanta m^–2 s ^–1.Leaves of M. arvensis, known to have a CO₂ compensation pointbetween that of C₃ and C₄ species, had a lower ratio of theintercellular to atmospheric partial pressure of CO₂ (C₁/C_a)and a greater instantaneous water use efficiency (WUE) thanthose of M. moricandioides and the Brassica species. Carbon isotope discrimination (     

The Response of the C3-CAM Tree, Clusia rosea, to Light and Water Stress: I. GAS EXCHANGE CHARACTERISTICS

Gas exchange measurements were undertaken on 2-year-old plantsof Clusia rosea. The plants were shown to have the ability toswitch from C₃-photosynthesis to CAM and vice versa regardlessof leaf age and, under some conditions, CO₂ was taken up continuously,throughout the day and night. The light response was saturatedby 120 µmol m^–2 s^–1 typical of a shade plant. Gas exchange patterns in response to light, water and VPD wereexamined. All combinations of daytime and night-time CO₂ uptakewere observed, with rates of CO₂ uptake ranging from 2 to 11µmol m^–2 s^–1 depending upon water status andlight. Categorization of this plant asC₃, CAM or an intermediateis impossible. Differing VPD affected the magnitude of changesfrom CAM to C₃-photosynthesis (0 to 0.5 and 0 to 6.0 µmolm^–2 s^–1 CO₂, respectively) when plants were watered.Under well-watered conditions, but not under water stress, highPPFD elicited changes from CAM to C₃ gas exchange. This is unusualnot only for a shade plant but also for a plant with CAM. Itis of ecological importance for C. rosea, which may spend theearly years of its life as an epiphyte or in the forest understorey,to be able to maximize photosynthesis with minimal water loss. Key words: Clusia rosea, CAM, C₃, stress     

Antenna Sizes of Photosystem I and Photosystem II in Chlorophyll b-Deficient Mutants of Rice. Evidence for an Antenna Function of Photosystem II Centers That are Inactive in Electron Transport

Light-harvesting capacities of photosystem I (PSI) and photosystemII (PSII) in a wild-type and three chlorophyll b-deficient mutantstrains of rice were determined by measuring the initial slopeof light-response curve of PSI and PSII electron transport andkinetics of light-induced redox changes of P-700 and Q_A, respectively.The light-harvesting capacity of PSI determined by the two methodswas only moderately reduced by chlorophyll b-deficiency. Analysisof the fluorescence induction that monitors time course of Q_Aphotoreduction showed that both relative abundance and antennasize of PSII_a decrease with increasing deficiency of chlorophyllb and there is only PSII_rß in chlorina 2 which totallylacks chlorophyll b. The numbers of antenna chlorophyll moleculesassociated with the mutant PSII centers were, therefore, threeto five times smaller than that of PSII_a in the wild type rice.Rates of PSII electron transport determined on the basis ofPSII centers in the three mutants were 60–70% of thatin the normal plant at all photon flux densities examined, indicatingthat substantial portions of the mutant PSII centers are inactivein electron transport. The initial slopes of light-responsecurves of PSII electron transport revealed that the functionalantenna sizes of the active populations of PSII centers in themutants correspond to about half that of PSII in the wild typerice. Thus, the numbers of chlorophyll molecules that serveas antenna of the oxygen-evolving PSII centers in the mutantsare significantly larger than those that are actually associatedwith each PSII center. It is proposed that the inactive PSIIserves as an antenna of the active PSII in the three chlorophyllb-deficient mutants of rice. In spite of the reduced antennasize of PSII, therefore, the total light-harvesting capacityof PSII approximately matches that of PSI in the mutants. (Received July 29, 1994; Accepted February 7, 1996)     

3D Confocal Laser Scanning Microscopy for the Analysis of Chlorophyll Fluorescence Parameters of Chloroplasts in Intact Leaf Tissues

We analyzed the chlorophyll fluorescence parameters in a 3Dcellular arrangement in vivo by using a modified Nipkow disk-typeconfocal laser scanning microscope (CLSM). We first definedthe 3D values of _PSII (photochemical yield of PSII) and NPQ(non-photochemical quenching) in mesophyll, epidermal and guardcell chloroplasts from the leaf surface to several tens of micronsin depth. We also used this CLSM method to analyze the relationshipsbetween actinic light intensity and the chlorophyll fluorescenceparameters for Boston fern and broad bean leaf specimens. Asthe actinic light intensity increased, the mean _PSII valuesdecreased and the NPQ values increased in all chloroplasts ofBoston fern and broad bean leaf. These values differed withcell type and species. The Boston fern chloroplasts had lower_PSII values than the broad bean chloroplasts, and vice versafor the NPQ values. The _PSII values of Boston fern chloroplastsdecreased in the order mesophyll, epidermal and guard cell chloroplasts.The NPQ values decreased in the order guard cell, mesophylland epidermal chloroplasts, except at 12 µmol m^–2s^–1 actinic light, when the mesophyll value was slightlylower than that of the epidermis. The trend in the _PSII andNPQ values of broad bean mesophyll and guard cell chloroplastswas opposite to that of Boston fern chloroplasts. As 3D CLSMcan provide the _PSII and NPQ values of each chloroplast in a3D cellular arrangement, this method has potential for investigatingdifferences in the functions of chloroplasts in vivo.     

Characterization of the Type of Photosynthetic Carbon Dioxide Fixation in Jute (Corchorus olitorius L.)

Activities of photosynthetic and photorespiratory enzymes viz.,ribulose bisphosphate carboxylase, phosphoenol pyruvate carboxylaseand glycolate oxidase from jute (Corchorus olitorius L.; cv.JRO 632) leaves were compared with those from maize (C₄) andsunflower (C₃) leaves. The photosynthetic CO₂ fixation products,the release of ¹⁴CO₂ in light and dark following photosynthesisin ¹⁴CO₂, chlorophyll a: b ratio, gross leaf photosyntheticrate and dry matter production rate were also studied. The resultsshow that jute is a C₃ plant. Key words: Jute, Corchorus olitorius, C₃ photosynthesis     

Panicum milioides, a Gramineae plant having Kranz leaf anatomy without C4-photosynthesis

Light and electron microscopic observations of the leaf tissueof Panicum milioides showed that the bundle sheath cells containeda substantial number of chloroplasts and other organelles. Theradial arrangement of chlorenchymatous bundle sheath cells,designated as Kranz leaf anatomy, has been considered to bespecific to C₄ plants. However, photosynthetic ¹⁴CO₂ fixationand ¹⁴CO₂ pulse-and-chase experiments revealed that the reductivepentosephosphate pathway was the main route operating in leavesof P. milioides. The interveinal distance of the leaves wasintermediate between C₃and C₄Gramineae species. These resultsindicate that P. milioides is a natural plant species havingchracteristics intermediate between C₃ and C₄ types. (Received March 6, 1975; )     

Photosynthesis of Stands of Tomato, Cucumber and Sweet Pepper Measured in Greenhouses under Various CO2-concentrations

The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO₂-concentrations between 200 and 1200 µmolmol^-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO₂ balance, usingnitrous oxide (N₂O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO₂ concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyP_max 5-9 g m^-2 h^-1 CO₂ uptake; ratio P_max/LAI 1·5-3 gm^-2 h^-1; light compensation point 32-86 µmol s^-1 m^-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol^-1 and CO₂ compensation point 18-54 µmolmol^-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO₂, CO₂ balance, CO₂ use efficiency, cucumber, _{Cucumis sativus} L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas