Distinctive Responses of Ribulose-1,5-Bisphosphate Carboxylase and Carbonic Anhydrase in Wheat Leaves to Nitrogen Nutrition and their Possible Relationships to CO(2)-Transfer Resistance

The amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), total chlorophyll (Chl), and total leaf nitrogen were measured in fully expanded, young leaves of wheat (Triticum aestivum L.), rice (Oryza sativa L.), spinach (Spinacia oleracea L.), bean (Phaseolus vulgaris L.), and pea (Pisum sativum L.). In addition, the activities of whole-chain electron transport and carbonic anhydrase were measured. All plants were grown hydroponically at different nitrogen concentrations. Although a greater than proportional increase in Rubisco content relative to leaf nitrogen content and Chl was found with increasing nitrogen supply for rice, spinach, bean, and pea, the ratio of Rubisco to total leaf nitrogen or Chl in wheat was essentially independent of nitrogen treatment. In addition, the ratio of Rubisco to electron transport activities remained constant only in wheat. Nevertheless, gas-exchange analysis showed that the in vivo balance between the capacities of Rubisco and electron transport in wheat, rice, and spinach remained almost constant, irrespective of nitrogen treatment. The in vitro carbonic anhydrase activity in wheat was very low and strongly responsive to increasing nitrogen content. Such a response was not found for the other C₃ plants examined, which had 10- to 30-fold higher carbonic anhydrase activity than wheat at any leaf-nitrogen content. These distinctive responses of carbonic anhydrase activity in wheat were discussed in relation to CO₂-transfer resistance and the in vivo balance between the capacities of Rubisco and electron transport.     

Effects of temperature pretreatment in the dark on photosynthesis of the intact spinach chloroplast

Isolated, intact spinach (Spinacia oleracea L. var. “Long Standing Bloomsdale”) chloroplasts were heated in the dark and the effect of this treatment on photosynthetic activities was determined at 25°C. Dark incubation of the chloroplasts for 10 minutes at 35°C and pH 8.1 resulted in a 50% decline in CO₂ photoassimilation. This decline in photosynthetic performance was dependent upon time, temperature, and medium pH with the optimum effect at acidic pH values. Photosynthetic decline was not observed if MgATP, MgADP, or a mixture of fructose 1,6-bisphosphate, aldolase, and oxaloacetate or ribose 5-phosphate and oxaloacetate was added prior to but not after the temperature pretreatment. A chloroplast preparation reconstituted with thylakoids and stroma from pretreated (35°C, 10 minutes, pH 8.1) intact chloroplasts and supplemented with ferredoxin, ADP, and NADP was photosynthetically competent, indicating that ATP-coupled electron flow and the enzymes comprising the Benson-Calvin cycle remained stable during the dark treatment. In contrast, exposure of isolated thylakoids to 35°C for 10 minutes uncoupled photophosphorylation from NADP and ferricyanide reduction. We propose that the decline of intact chloroplast photosynthesis is the result of a decrease in the content of or a change in the ratios of the adenine nucleotides. Maintenance of an adequate supply of adenine nucleotide is the effect of the externally added MgATP or of chloroplastic respiration of a sugar phosphate.     

Further characterization of ribosome binding to thylakoid membranes

Previous work indicated more polysomes bound to pea (Pisum sativum cv Progress No. 9) thylakoids in light than in the dark, in vivo (LE Fish, AT Jagendorf 1982 Plant Physiol 69: 814-825). With isolated intact chloroplasts incubated in darkness, addition of MgATP had no effect but 24 to 74% more RNA was thylakoid-bound at pH 8.3 than at pH 7. Thus, the major effect of light on ribosome-binding in vivo may be due to higher stroma pH. In isolated pea chloroplasts, initiation inhibitors (pactamycin and kanamycin) decreased the extent of RNA binding, and elongation inhibitors (lincomycin and streptomycin) increased it. Thus, cycling of ribosomes is controlled by translation, initiation, and termination. Bound RNA accounted for 19 to 24% of the total chloroplast RNA and the incorporation of [³H]leucine into thylakoids was proportional to the amount of this bound RNA. These data support the concept that stroma ribosomes are recruited into thylakoid polysomes, which are active in synthesizing thylakoid proteins.     

植物叶片氮分配及其影响因子研究进展

氮是植物生长的基本限制性因子,它的有效利用可以增加植物的适应性。叶片氮分配是指氮在植物叶片细胞各细胞结构以及游离化合物中所分配的比例。叶片氮的分配方式决定了叶片光合作用的强弱,影响叶片的坚韧程度以及化学防御强度,因此研究氮在植物叶片内的分配方式具有重要意义。阐述了叶片氮分配的方式,分析了影响叶片氮分配的生物和非生物因子(CO2,光,土壤养分),介绍了常用的叶片氮分配的研究方法,并对未来的研究进行了展望。     

Effects of sulfur on the photosynthesis of intact leaves and isolated chloroplasts of sugar beets

Effects of sulfur on photosynthesis in sugar beets (Beta vulgaris L. cv. F58-554H1) were studied by inducing sulfur deficiency and determining changes in the photosynthesis of whole attached leaves and of isolated chloroplasts. The rates of photosynthetic CO₂ uptake by intact leaves, photoreduction of ferricyanide, cyclic and noncyclic photophosphorylation of isolated chloroplasts, and the rate of CO₂ assimilation by ribulose diphosphate carboxylase, decreased with decrease in total leaf sulfur from 2500 to about 500 μg g⁻¹ dry weight. Sulfur deficiency reduced photosynthesis through an effect on chlorophyll content, which decreased linearly with leaf sulfur, and by decreasing the rate of photosynthesis per unit chlorophyll. There was only a small effect of sulfur deficiency on stomatal diffusion resistance to CO₂ until leaf sulfur decreased below 1000 μg g⁻¹ when stomatal resistance became a more significant proportion of the total diffusion resistance to CO₂. Light respiration rates were positively correlated with photosynthesis rates and dark respiration was unchanged as leaf sulfur concentrations declined.     

CO2 Exchange and Mesophyll Structure in Second-Year Needles of Abies sibirica Ledeb.

Seasonal changes in the net photosynthesis and dark respiration in second-year needles of Siberian fir were investigated. The functional state of needles was shown to determine the structural features of mesophyll cells. Current-year shoot growth is one of the major factors affecting the structure and functional activity of second-year needles during the growing period. The greatest changes occur in the number of mitochondria in mesophyll cells and the respiration rate of second-year needles. The rate of photosynthesis in second-year needles was shown to depend on the number of thylakoids in mesophyll chloroplasts.     

Photosynthesis and nitrogen relationships in leaves of C3 plants

Summary The photosynthetic capacity of leaves is related to the nitrogen content primarily bacause the proteins of the Calvin cycle and thylakoids represent the majority of leaf nitrogen. To a first approximation, thylakoid nitrogen is proportional to the chlorophyll content (50 mol thylakoid N mol^-1 Chl). Within species there are strong linear relationships between nitrogen and both RuBP carboxylase and chlorophyll. With increasing nitrogen per unit leaf area, the proportion of total leaf nitrogen in the thylakoids remains the same while the proportion in soluble protein increases. In many species, growth under lower irradiance greatly increases the partitioning of nitrogen into chlorophyll and the thylakoids, while the electron transport capacity per unit of chlorophyll declines. If growth irradiance influences the relationship between photosynthetic capacity and nitrogen content, predicting nitrogen distribution between leaves in a canopy becomes more complicated. When both photosynthetic capacity and leaf nitrogen content are expressed on the basis of leaf area, considerable variation in the photosynthetic capacity for a given leaf nitrogen content is found between species. The variation reflects different strategies of nitrogen partitioning, the electron transport capacity per unit of chlorophyll and the specific activity of RuBP carboxylase. Survival in certain environments clearly does not require maximising photosynthetic capacity for a given leaf nitrogen content. Species that flourish in the shade partition relatively more nitrogen into the thylakoids, although this is associated with lower photosynthetic capacity per unit of nitrogen.     

Release of Nitrogen From Chloroplasts During Leaf Senescence in Rice (Oryza sativa L.)

In order to ascertain the possibility that nitrogen associatedwith chloroplasts serves as a major source of nitrogen redistributedfrom senescent leaves, chloroplasts were isolated from riceleaves and changes with leaf age in total leaf nitrogen andchloroplast nitrogen were examined. Results presented here showthat decrease in total leaf nitrogen during leaf senescencewas closely correlated with decrease of chloroplast nitrogenand roughly 85–95 per cent of leaf nitrogen released fromsenescent leaves during the experimental period could be accountedfor by a loss of chloroplast nitrogen. By dividing chloroplastnitrogen into two fractions, i.e. lamellar and stroma fractions,the question of which fraction was more deeply concerned withthe loss of leaf nitrogen was clarified. Results suggested thatin the vegetative stage of plant growth the stroma was mainlyresponsible for the loss of leaf nitrogen. On the other hand,nitrogen was released from lamellar and stromal fractions atalmost the same rate during the reproductive stage. Oryza sativa L., rice, chloroplasts, nitrogen, leaf senescence     

Capacities of pea chloroplasts to catalyse the oxidative pentose phosphate pathway and glycolysis

The aim of this work was to measure the capacities of pea (Pisum sativum) shoot chloroplasts to catalyse the oxidative pentose phosphate pathway and glycolysis. Of the total activities in the unfractionated homogenates, appreciable proportions of those of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and phosphofructokinase, and smaller but significant proportions of those of phosphopyruvate hydratase and pyruvate kinase were recovered in crude preparations of chloroplasts, and co-purified with intact chloroplasts on sucrose gradients. The activities in the chloroplasts showed considerable latency that was closely correlated with chloroplast integrity. Phosphoglyceromutase activity in the above preparations of chloroplasts did not exceed that expected from cytoplasmic contamination. The mass-action ratio for phosphoglyceromutase in illuminated isolated chloroplasts differed markedly from the enzyme's equilibrium constant. Isolated chloroplasts converted 2-phosphoglycerate to pyruvate. The enzyme activities of the chloroplasts were compared with the rates of respiration and starch breakdown in pea leaves in the dark. It is concluded that in the dark chloroplasts could metabolize all the products of starch breakdown and catalyse much of the respiration of pea shoots via the oxidative pentose phosphate pathway and/or glycolysis as far as 3-phosphoglycerate. It is suggested that pea shoot chloroplasts lack phosphoglyceromutase but contain some phosphopyruvate hydratase and pyruvate kinase.     

Changes in Protein Content and in the Structure and Number of Chloroplasts during Leaf Senescence in Rice Seedlings

Two types of experiment were carried out to examine whetheror not the inactivation of photosynthesis is related to lossof chloroplasts during foliar senescence of rice seedlings.Levels of both soluble and insoluble leaf proteins decreasedduring senescence, the loss of the soluble proteins being fasterthan that of the insoluble ones. There was a good positive correlationbetween the rate of oxygen evolution and the level of solubleproteins. The inactivation of photosynthesis was also linearlyrelated to the loss of a major fraction of insoluble proteins.Thus, the loss of photosynthetic ability is ascribable to thedegradation of relevant proteins and enzymes during leaf senescence.Electron microscopy revealed that senescence caused the disorientationof the grana and stroma thylakoids, a decrease in the numberof starch granules, and an increase in the size and number ofplastoglobuli. Large grana consisting 20 to 30 thylakoids appearedin aged leaves. In addition to these changes in ultrastructure,there was a significant decrease in the size of chloroplasts.Furthermore, the number of chloroplasts in mesophyll cells wasalso notably reduced during senescence. Thus, the loss of leafproteins and inactivation of photosynthesis are both relatedto the decrease in the total mass of chloroplasts during senescenceof rice seedlings. ³Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113 Japan. (Received January 4, 1989; Accepted April 19, 1989)     

A Comparison of Dark Respiration between C(3) and C(4) Plants

Lower respiratory costs were hypothesized as providing an additional benefit in C₄ plants compared to C₃ plants due to less investment in proteins in C₄ leaves. Therefore, photosynthesis and dark respiration of mature leaves were compared between a number of C₄ and C₃ species. Although photosynthetic rates were generally greater in C₄ when compared to C₃ species, no differences were found in dark respiration rates of individual leaves at either the beginning or after 16 h of the dark period. The effects of nitrogen on photosynthesis and respiration of individual leaves and whole plants were also investigated in two species that occupy similar habitats, Amaranthus retroflexus (C₄) and Chenopodium album (C₃). For mature leaves of both species, there was no relationship between leaf nitrogen and leaf respiration, with leaves of both species exhibiting a similar rate of decline after 16 h of darkness. In contrast, leaf photosynthesis increased with increasing leaf nitrogen in both species, with the C₄ species displaying a greater photosynthetic response to leaf nitrogen. For whole plants of both species grown at different nitrogen levels, there was a clear linear relationship between net CO₂ uptake and CO₂ efflux in the dark. The dependence of nightly CO₂ efflux on CO₂ uptake was similar for both species, although the response of CO₂ uptake to leaf nitrogen was much steeper in the C₄ species, Amaranthus retroflexus. Rates of growth and maintenance respiration by whole plants of both species were similar, with both species displaying higher rates at higher leaf nitrogen. There were no significant differences in leaf or whole plant maintenance respiration between species at any temperature between 18 and 42°C. The data suggest no obvious differences in respiratory costs in C₄ and C₃ plants.     

Reorganization of chloroplast ultrastructure associated with low-temperature hardening of Arabidopsis plants

When following low-temperature acclimation (5 days at 2°C) of cold-resistant plants of Arabidopsis (Arabidopsis thaliana Heynh. (L.), ecotype Columbia) in relation to the changes in chloroplast ultrastructure, we registered the high efficiency of hardening and the ability of hardened plants to lower a threshold of frost damage by about 3°C. During hardening, the area of grana in the chloroplasts more than doubled, with considerably increased numbers of thylakoids per granum and thylakoids per chloroplast. The rate of apparent photosynthesis decreased to lesser extent than the rate of dark respiration, as a result the content of soluble sugars increased fourfold, ensuring an adaptive reorganization of metabolism, which enabled the hardened plants to survive even at below-zero temperatures (up to ?7°C). The authors conclude that a considerable increase in the number of thylakoids in the chloroplasts helps maintain photosynthesis at low above-zero temperatures and is a prerequisite for the accumulation of soluble sugars in Arabidopsis leaves.     

Carbon Balance of Tall Fescue (Festuca arundinacea Schreb.): Effects of Nitrogen Fertilization and the Growing Season

The C balance of a tall fescue sward grown under different ratesof N fertilization in summer, autumn, and spring was calculatedusing models derived from measurements of shoot growth, canopygross photosynthesis, shoot respiration and of C partitioningto the roots. Under the diverse growing conditions associatedwith the seasons and the N fertilization, C utilization forabove- and below-ground biomass accumulation never exceeded39 and 14% of the canopy gross photosynthesis, respectively.Carbon losses attributed to root respiration and exudation,which were estimated by difference between canopy net photosynthesisand total growth, ranged between 3 and 30% of canopy gross photosynthesis.Seasonal differences in shoot growth could be attributed tothe amount of intercepted radiation, the radiation-use efficiencyand the C partitioning to the roots. The effect of N deficiencyon shoot growth can be attributed to its effects on canopy photosynthesis(principally resulting from changes in intercepted photosyntheticallyactive radiation) and C partitioning. In comparison with theeffect on shoot growth, the effect of the N deficiency on thecanopy gross photosynthesis per unit of light intercepted overthe regrowth cycle was limited. It is concluded that most ofthe effect of N fertilization on shoot growth is due to changesin C partitioning which result in faster leaf area developmentand greater light interception.Copyright 1994, 1999 AcademicPress Tall rescue, Festuca arundinacea Schreb., carbon balance, nitrogen, grass, fertilization     

Redox conditions specify the proteins synthesised by isolated chloroplasts and mitochondria

In chloroplasts and mitochondria isolated from pea leaves, ³⁵S-methionine incorporation reveals that different subsets of proteins are selected for synthesis in the presence of the external redox reagents ferricyanide, ascorbate, duroquinol, dithiothreitol and dithionite, and in the presence of different electron transport inhibitors in the light (in chloroplasts) or with respiratory substrates (in mitochondria). Redox state of specific electron carriers may therefore regulate expression of specific genes in chloroplasts and mitochondria. The results are consistent with the hypothesis that chloroplast and mitochondrial genomes encode proteins whose synthesis must be regulated by electron transport in photosynthesis and respiration.     

Photosynthesis, Dark Respiration, and Growth of Rumex patientia L. Exposed to Ultraviolet Irradiance (288 to 315 Nanometers) Simulating a Reduced Atmospheric Ozone Column

Net photosynthesis, dark respiration, and growth of Rumex patientia L. exposed to a ultraviolet irradiance (288-315 nanometers) simulating a 0.18 atm·cm stratospheric ozone column were determined. The ultraviolet irradiance corresponding to this 38% ozone decrease from normal was shown to be an effective inhibitor of photosynthesis and leaf growth. The repressive action on photosynthesis accumulated through time whereas leaf growth was retarded only during the initial few days of exposure. Small increases in dark respiration rates occurred but did not continue to increase with longer exposure periods. A reduction in total plant dry weight and leaf area of approximately 50% occurred after 22 days of treatment, whereas chlorophyll concentrations remained unaltered.     

A model of the acclimation of photosynthesis in the leaves of C3 plants to sun and shade with respect to nitrogen use

A model of leaf photosynthesis of C₃, plants has been developed to describe their nitrogen economy. In this model, photosynthetic proteins are categorized into five groups depending on their functions. The effects of investment of nitrogen in each of these groups on the maximal rate of photosynthesis and/or the initial slope of the light-response curve are described as simple equations. Using this model, the optimal pattern of nitrogen partitioning which maximizes the daily rate of CO₂ exchange is estimated for various light environments and leaf nitrogen contents. When the leaf nitrogen content is fixed, the amount of nitrogen allocated to Calvin cycle enzymes and electron carriers increases with increasing irradiance, while that allocated to chlorophyll-protein complexes increases with decreasing irradiance. For chlorophyll-proteins of photosystem II, the amount of light-harvesting complex II relative to that of the core complex increases with decreasing irradiance. At any irradiance, partitioning into ribulose bisphosphate carboxylase increases with increasing leaf nitrogen content Taking the total leaf nitrogen content and the daily CO₂ exchange rate as ‘cost’ and ‘benefit’, respectively, the optimal amount and partitioning of nitrogen are examined for various conditions of light environment and nitrogen availability. The leaf nitrogen content that maximizes the rate of daily carbon fixation increases with increasing growth irradiance. It is also predicted that, at low nitrogen availabilities, low leaf nitrogen contents are advantageous in terms, of nitrogen use efficiency. These trends predicted by the present model are largely consistent with those reported for actual plants. The differences in the total amount of leaf nitrogen and in the organization of photosynthetic components that have been reported for plants from different environments would therefore be of adaptive significance, because such differences can contribute to realization of efficient photosynthesis. These results are fürther discussed in an ecological context.     

Carbon and nitrogen economy of 24 wild species differing in relative growth rate

The relation between interspecific variation in relative growth rate and carbon and nitrogen economy was investigated. Twentyfour wild species were grown in a growth chamber with a nonlimiting nutrient supply and growth, whole plant photosynthesis, shoot respiration, and root respiration were determined. No correlation was found between the relative growth rate of these species and their rate of photosynthesis expressed on a leaf area basis. There was a positive correlation, however, with the rate of photosynthesis expressed per unit leaf dry weight. Also the rates of shoot and root respiration per unit dry weight correlated positively with relative growth rate. Due to a higher ratio between leaf area and plant weight (leaf area ratio) fast growing species were able to fix relatively more carbon per unit plant weight and used proportionally less of the total amount of assimilates in respiration. Fast growing species had a higher total organic nitrogen concentration per unit plant weight, allocated more nitrogen to the leaves and had a higher photosynthetic nitrogen-use efficiency, i.e. a higher rate of photosynthesis per unit organic nitrogen in the leaves. Consequently, their nitrogen productivity, the growth rate per unit organic nitrogen in the plant and per day, was higher compared with that of slow growing species.     

Nitrogen reallocation and photosynthetic acclimation in response to partial shading in soybean plants

The first trifoliate of soybean was shaded when fully expanded, while the plant remained in high light; a situation representative for plants growing in a closed crop. Leaf mass and respiration rate per unit area declined sharply in the first few days upon shading and remained rather constant during the further 12 days of the shading treatment. Leaf nitrogen per unit area decreased gradually until the leaves were shed. Leaf senescence was enhanced by the shading treatment in contrast to control plants growing in low light. Shaded leaves on plants grown at low nutrient availability senesced earlier than shaded leaves on plants grown at high nutrient availability. The light saturated rate of photosynthesis decreased also gradually during the shading treatment, but somewhat faster than leaf N, whereas chlorophyll contents declined somewhat slower than leaf N.
Partitioning of N in the leaf over main photosynthetic functions was estimated from parameters derived from the response of photosynthesis to CO₂. It appeared that the N exported from the leaf was more at the expense of compounds that make up photosynthetic capacity than of those involved in photon absorption, resulting in a change in partitioning of N within the photosynthetic apparatus. Photosynthetic nitrogen use efficiency increased during the shading treatment, which was for the largest part due to the decrease in leaf N content, to some extent to the decrease in respiration rate and only for a small part to change in partitioning of N within the photosynthetic apparatus.     

红松和紫椴叶片暗呼吸及其光抑制性在幼、成树间的差异

叶片暗呼吸是森林碳循环的重要组分,深入分析幼、成树的叶片暗呼吸及其光抑制性的差异,对生态系统总生产力(GPP)的准确估算具有重要意义.本研究以长白山阔叶红松林主要树种(红松和紫椴)的幼树和成树为研究对象,分别测算不同光照下叶片暗呼吸与无光暗呼吸,比较叶片暗呼吸及其光抑制性在幼、成树间的差异,结合幼、成树叶片生理生态参数的对比,对幼、成树叶片暗呼吸及其光抑制性差异的原因进行探讨.结果表明: 两个树种幼树叶片光下暗呼吸的值高于成树,在生长季(6—9月),幼树的值比成树高6.8%～39.6%;两个树种幼树叶片暗呼吸光抑制程度低于成树,幼树叶片暗呼吸光抑制性的值比成树低2.5%～14.1%;红松幼、成树间叶片暗呼吸光抑制性的差异总体高于紫椴幼、成树间叶片暗呼吸光抑制性的差异,差值最高可达18.6%;幼树中较高的光下暗呼吸值和较低的光抑制程度可能与最大净光合速率、比叶面积、气孔导度的变化有关,与叶片氮含量的变化无关.     

Nitrogen allocation and partitioning in invasive and native Eupatorium species

There is a trade-off between nitrogen (N) allocation to photosynthesis and to defence. Invasive species may reduce N allocation to defence because of the absence of natural enemies. Thus, I hypothesised that invasive species may allocate a higher fraction of total leaf N to photosynthesis and have higher light-saturated photosynthetic rate ( P _max) and photosynthetic N-use efficiency (PNUE) than closely related native species. To test these hypotheses, invasive Eupatorium adenophorum and native E.   chinense and E.   heterophyllum were compared in a limestone shrub. Unlike expectation, the invader did not allocate a higher fraction of leaf N to photosynthesis than the natives. However, it was more efficient in photosynthetic N partitioning than the natives. It partitioned a higher fraction of the photosynthetic N to carboxylation and showed higher use efficiency of the photosynthetic N, while the natives partitioned a higher fraction of the photosynthetic N to light-harvesting components. Total leaf N content was not significantly different among the three studied invasive and native species. For the invader, the higher fraction of leaf N allocated to carboxylation resulted in the higher N content in carboxylation and in both carboxylation and bioenergetics, which led to higher P _max, and therefore to higher PNUE, water-use efficiency, respiration efficiency and apparent quantum yield. These physiological advantages of the invader and its higher leaf area ratio may contribute to its invasiveness.