Evidence for Mitochondrial Regulation of Photosynthesis by a Starchless Mutant of Nicotiana sylvestris

Mutant NS458 of Nicotiana sylvestris (Speg. et Comes) contains a defective plastid phosphoglucomutase and accumulates only trace amounts of starch. Determinations of carbon partitioning using tracer d-[3-¹⁴C]glyceric acid showed that the maximal CO₂ assimilation by mature leaves of the mutant at saturating [CO₂] and light and low [O₂] was close to the flux for sucrose formation in the wild type. The mutant is characterized by exceptionally slow oscillations in maximal CO₂ assimilation. The postulate that these slow oscillations follow changes in the cytosolic rate of sucrose phosphate synthesis has been investigated. Studies with wild-type and mutant leaf discs subjected to various treatments failed to indicate that any significant activation-inactivation cycle in sucrose-P synthase activity can occur. The rate of sucrose phosphate synthesis, however, might be altered by variations in the supply of uridine UDP-glucose which is controlled by the rate of ATP regeneration (via UTP regeneration). Treating mutant leaf protoplasts and young leaves with oligomycin, an inhibitor of mitochondrial ATP regeneration, reduced photosynthesis by as much as 25 and 40%, respectively. The wild type failed to show inhibition by oligomycin, i.e. its effect is masked when starch and sucrose synthesis can interact. It is concluded that maximal CO₂ assimilation in the mutant is fine tuned by mitochondrial metabolism such that interactions between sucrose synthesis and mitochondrial processes may generate the observed oscillations.     

Carbon Partitioning and Growth of a Starchless Mutant of Nicotiana sylvestris

We have further characterized the photosynthetic carbohydrate metabolism and growth of a starchless mutant (NS 458) of Nicotiana sylvestris that is deficient in plastid phosphoglucomutase (Hanson KR, McHale NA [1988] Plant Physiol 88: 838-844). In general, the mutant had only slightly lower rates of photosynthesis under ambient conditions than the wild type. However, accumulation of soluble sugars (primarily hexose sugars) in source leaves of the mutant compensated for only about half of the carbon stored as starch in the wild type. Therefore, the export rate was slightly higher in the mutant relative to the wild type. Starch in the wild type and soluble sugars in the mutant were used to support plant growth at night. Growth of the mutant was progressively restricted, relative to wild type, when plants were grown under shortened photoperiods. When grown under short days, leaf expansion of the mutant was greater during the day, but was restricted at night relative to wild-type leaves, which expanded primarily at night. We postulate that restricted growth of the mutant on short days is the result of several factors, including slightly lower net photosynthesis and inability to synthesize starch in both source and sink tissues for use at night. In short-term experiments, increased “sink demand” on a source leaf (by shading all other source leaves) had no immediate effect on starch accumulation during the photoperiod in the wild type or on soluble sugar accumulation in the mutant. These results would be consistent with a transport limitation in N. sylvestris such that not all of the additional carbon flux into sucrose in the mutant can be exported from the leaf. Consequently, the mutant accumulates hexose sugars during the photoperiod, apparently as the result of sucrose hydrolysis within the vacuole by acid invertase.     

Steady-State and Oscillating Photosynthesis by a Starchless Mutant of Nicotiana sylvestris

The photosynthetic characteristics of wild type Nicotiana sylvestris (Speg. et Comes) were compared with those of a `starch-less' mutant NS458 that contains a defective plastid phosphoglucomutase (EC 2.1.5.1) (KR Hanson, NA McHale [1988] Plant Physiol 88: 838-844). The steady-state rate of net CO₂ assimilation (A) was studied as a function of [CO₂], [O₂], irradiance, and temperature. At 30°C with saturating light and [CO₂] and low [O₂], A for the mutant was half that for the wild type, whereas in normal air it was 90%. The irradiance and [CO₂] at low [O₂] required for saturation were lower than the values for the wild type. At 2000 microbars CO₂, 30°C, and saturating irradiance A for both the mutant and wild type was stimulated on going from 4 to 25% O₂ by at least 13%. Slow oscillations in A were readily induced with the mutant but not the wild type, provided irradiance and [CO₂] were saturating and [O₂] was low. The period, which was about 5 minutes at 30°C and decreased by about 0.67 minutes per degree, was an order of magnitude slower than periods reported for other plants at corresponding temperatures. To achieve the full oscillation amplitude both irradiance and [CO₂] had to exceed the minimal levels for steady-state saturation. The slowness and duration of the oscillations and the metabolic simplification introduced by deleting starch synthesis makes the mutant especially suitable for investigating the regulatory processes that generate such oscillations.     

Regulation of Catalase Activity in Leaves of Nicotiana sylvestris by High CO(2)

The effect of high CO₂ (1% CO₂/21% O₂) on the activity of specific forms of catalase (CAT-1, -2, and -3) (EA Havir, NA McHale [1987] Plant Physiol 84: 450-455) in seedling leaves of tobacco (Nicotiana sylvestris, Nicotlana tabacum) was examined. In high CO₂, total catalase activity decreased by 50% in the first 2 days, followed by a more gradual decline in the next 4 days. The loss of total activity resulted primarily from a decrease in CAT-1 catalase. In contrast, the activity of CAT-3 catalase, a form with enhanced peroxidatic activity, increased 3-fold in high CO₂ relative to air controls after 4 days. Short-term exposure to high CO₂ indicated that the 50% loss of total activity occurs in the first 12 hours. Catalase levels increased to normal within 12 hours after seedlings were returned to air. When seedlings were transferred to air after prolonged exposure to high CO₂ (13 days), the levels of CAT-1 catalase were partially restored while CAT-3 remained at its elevated level. Levels of superoxide dismutase activity and those of several peroxisomal enzymes were not affected by high CO₂. Total catalase levels did not decline when seedlings were exposed to atmospheres of 0.04% CO₂/5% O₂ or 0.04% CO₂/1% O₂, indicating that regulation of catalase in high CO₂ is not related directly to suppression of photorespiration. Antibodies prepared against CAT-1 catalase from N. tabacum reacted strongly against CAT-1 catalase from both N. sylvestris and N. tabacum but not against CAT-3 catalase from either species. This observation, along with the rapid changes in CAT-1 and the much slower changes in CAT-3 suggest that one form is not directly derived from the other.     

Reduced Inorganic Carbon Transport in a CO(2)-Requiring Mutant of Chlamydomonas reinhardii

A mendelian mutant of the unicellular green alga Chlamydomonas reinhardii has been isolated that is deficient in inorganic carbon transport. This mutant strain, designated pmp-1-16-5K (gene locus pmp-1), was selected on the basis of a requirement of elevated CO₂ concentration for photoautrophic growth. Inorganic carbon accumulation in the mutant was considerably reduced in comparison to wild type, and the CO₂ response of photosynthesis indicated a reduced affinity for CO₂ in the mutant. At air levels of CO₂ (0.03-0.04%), O₂ inhibited photosynthesis and stimulated the synthesis of photorespiratory intermediates in the mutant but not in wild type. Neither strain was significantly affected by O₂ at saturating CO₂ concentration. Thus, the primary consequence of inorganic carbon transport deficiency in the mutant was a much lower internal CO₂ concentration compared to wild type. From these observations, we conclude that enzyme-mediated transport of inorganic carbon is an essential component of the CO₂ concentrating system in C. reinhardii photosynthesis.     

Limitation of Photosynthesis by Carbon Metabolism : I. Evidence for Excess Electron Transport Capacity in Leaves Carrying Out Photosynthesis in Saturating Light and CO(2)

It has been investigated how far electron transport or carbon metabolism limit the maximal rates of photosynthesis achieved by spinach leaves in saturating light and CO₂. Leaf discs were illuminated with high light until a steady state rate of O₂ evolution was attained, and then subjected to a 30 second interruption in low light, to generate an increased demand for the products of electron transport. Upon returning to high light there is a temporary enhancement of photosynthesis which lasts 15 to 30 seconds, and can be up to 50% above the steady state rate of O₂ evolution. This temporary enhancement is only found when saturating light intensities are used for the steady state illumination, is increased when low light rather than darkness is used during the interruption, and is maximal following a 30 to 60 seconds interruption in low light. Decreasing the temperature over the 10 to 30°C range led to the transient enhancement becoming larger. The temporary enhancement is associated with an increased ATP/ADP ratio, a decreased level of 3-phosphoglycerate, and increased levels of triose phosphate and ribulose 1,5-bisphosphate. Since electron transport can occur at higher rates than in steady state conditions, and generate a higher energy status, it is concluded that leaves have a surplus electron transport capacity in saturating light and CO₂. From the alterations of metabolites, it can be calculated that the enhanced O₂ evolution must be accompanied by an increased rate of ribulose 1,5-bisphosphate regeneration and carboxylation. It is suggested that the capacity for sucrose synthesis ultimately limits the maximal rates of photosynthesis, by restricting the rate at which inorganic phosphate can be recycled to support electron transport and carbon fixation in the chloroplast.     

Acclimation to High CO(2) in Monoecious Cucumbers : II. Carbon Exchange Rates, Enzyme Activities, and Starch and Nutrient Concentrations

Carbon exchange capacity of cucumber (Cucumis sativus L.) germinated and grown in controlled environment chambers at 1000 microliters per liter CO₂ decreased from the vegetative growth stage to the fruiting stage, during which time capacity of plants grown at 350 microliters per liter increased. Carbon exchange rates (CERs) measured under growth conditions during the fruiting period were, in fact, lower in plants grown at 1000 microliters per liter CO₂ than those grown at 350. Progressive decreases in CERs in 1000 microliters per liter plants were associated with decreasing stomatal conductances and activities of ribulose bisphosphate carboxylase and carbonic anhydrase. Leaf starch concentrations were higher in 1000 microliters per liter CO₂ grown-plants than in 350 microliters per liter grown plants but calcium and nitrogen concentrations were lower, the greatest difference occurring at flowering. Sucrose synthase and sucrose-P-synthase activities were similar in 1000 microliters per liter compared to 350 microliters per liter plants during vegetative growth and flowering but higher in 350 microliters per liter plants at fruiting. The decreased carbon exchange rates observed in this cultivar at 1000 microliters per liter CO₂ could explain the lack of any yield increase (MM Peet 1986 Plant Physiol 80: 59-62) when compared with plants grown at 350 microliters per liter.     

Photosynthetic Net CO2 Uptake and Leaf Phosphate Concentrations in CO2 Enriched Clover (Trifolium subterraneum L.) at Three Levels of Phosphate Nutrition

Net CO₂-uptake of sets of clover plants (Trifolium subterraneumL.) was measured over 3 weeks in ambient air and in a highlyCO₂-enriched atmosphere (400 Pa CO₂). Phosphate (P) in the nutrientsolution was varied between 0·05 mol m^–3 P (reducedP) and 2·0 mol m^–3 P (high P). In ambient air,the daily increments of the daily rate of net CO₂-uptake (DICU;a parameter related to relative growth) were higher at reducedP than at high P. Stimulation by high CO₂ of net CO₂-uptakein the first day was less at reduced P than at high P. In thefollowing days, high CO₂ markedly inhibited DICU at reducedP, and thus growthstimulation by high CO₂ ceased after between4 and 12 d. By contrast, at high P, DICU increased more than2-fold upon CO₂-enrichment, and thus growth stimulation by highCO₂ was maintained. Intermediate results were obtained withhalf-strength Hoagland's solution (0·5 mol m^–3P). Leaf pools of inorganic ortho P, soluble esterified P, and totalP declined markedly in high CO₂ when P-nutrition had been reduced.Considerable decline also occurred in high CO₂ when P-nutritionhad been increased suggesting that P-uptake was not well tunedwith net CO₂-uptake (growth). It is proposed that high CO₂ can perturb the P-metabolism ofclover, the impairment being less at high levels of P-nutrition.With regard to high CO₂ as a growth stimulus, these resultsdemonstrate that increasing P-nutrition to a level supraoptimalin ambient air can considerably improve the growth of a C₃-plantin high CO₂. Key words: Atmospheric CO₂-enrichment, phosphate nutrition, photosynthesis, clover     

Influence of Varying CO(2) and Orthophosphate Concentrations on Rates of Photosynthesis, and Synthesis of Glycolate and Dihydroxyacetone Phosphate by Wheat Chloroplasts

Intact chloroplasts of wheat (Triticum aestivum) were isolated from mesophyll protoplasts. With decreasing concentrations of bicarbonate from 10 to 0.3 millimolar (pH 8.0), the optimal concentration of orthophosphate (Pi) for photosynthetic O₂ evolution decreased from a value of 0.1 to 0.2 millimolar to 0 to 0.025 millimolar. The extremely low Pi optimum for photosynthesis at the low bicarbonate levels of 0.3 millimolar was increased by lowering the O₂ concentration from 253 (21% gas phase) to 72 micromolar (6% gas phase). The relative amount of glycolate and dihydroxyacetone phosphate (DHAP) synthesized under high and low levels of bicarbonate and varying levels of Pi was determined. At low levels of bicarbonate, glycolate was the main product, whereas at high bicarbonate levels, DHAP was the main product. Most of the DHAP and glycolate was found in the extrachloroplastic fraction.     

Respiratory CO2 Fluxes in Photosynthesizing Leaves of C3 Species Varying in Rates of Starch Synthesis1

The rates of CO₂ fixation and respiratory CO₂ fluxes in six C₃ species, namely Solanum tuberosum, Nicotiana tabacum, Arabidopsis thaliana, Hordeum vulgare, Triticum aestivum, and Secale cereale, were determined under steady-state photosynthesis. The plants may be divided into two groups: (a) cereals with a low rate of starch synthesis (7–5% of true photosynthesis); (b) plants with a high rate of starch synthesis (45–35% of true photosynthesis). In the light, primary and stored photosynthates are consumed as substrates for both respiratory and photorespiratory pathways. In leaves of cereals, the total rate of respiratory and photorespiratory decarboxylations of stored photosynthates was higher in the light than in the dark, while, in starch-synthesizing species, stored photosynthates were consumed at a higher rate in the dark. Under normal environmental conditions, respiratory decarboxylation of stored photosynthates was suppressed by light in all species studied. The total rate of respiration as the sum of decarboxylation of stored and primary photosynthates was not affected by light in cereals, but suppressed in starch-accumulating plants. This suppression was not compensated for by the additional supply of respiratory substrates from primary photosynthates in the light.     

Acclimation of Two Tomato Species to High Atmospheric CO(2): I. Sugar and Starch Concentrations

Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO₂ concentrations (330 or 900 microliters per liter) for 10 weeks. Tomato plants grown at 900 microliters per liter contained more starch and more sugars than the control. However, we found no significant accumulation of starch and sugars in the young leaves of L. esculentum exposed to high CO₂. Carbon exchange rates were significantly higher in CO₂-enriched plants for the first few weeks of treatment but thereafter decreased as tomato plants acclimated to high atmospheric CO₂. This indicates that the long-term decline of photosynthetic efficiency of leaf 5 cannot be attributed to an accumulation of sugar and/or starch. The average concentration of starch in leaves 5 and 9 was always higher in L. esculentum than in L. chmielewskii (151.7% higher). A higher proportion of photosynthates was directed into starch for L. esculentum than for L. chmielewskii. However, these characteristics did not improve the long-term photosynthetic efficiency of L. chmielewskii grown at high CO₂ when compared with L. esculentum. The chloroplasts of tomato plants exposed to the higher CO₂ concentration exhibited a marked accumulation of starch. The results reported here suggest that starch and/or sugar accumulation under high CO₂ cannot entirely explain the loss of photosynthetic efficiency of high CO₂-grown plants.     

Adaptation to Low CO(2) Level in a Mutant of Anacystis nidulans R(2) which Requires High CO(2) for Growth

The mutant E₁ of Anacystis nidulans R₂ requires high CO₂ concentration for growth but was able to adapt to low CO₂ concentration. This was exhibited by the increased ability to accumulate inorganic carbon within the cells and the large increase in the amount of a 42-kilodalton polypeptide located in the cytoplasmic membrane. The adaptation occurred in E₁ cells at an extracellular CO₂ concentration as high as 0.3%, which was 8 times the concentration for maximal adaptation in R₂ cells. The ability of E₁ cells to exhibit low CO₂ characteristics at a higher CO₂ concentration was attributed to lower intracellular CO₂ concentration.     

Kinetics of l-Valine Uptake in Suspension-Cultured Cells and Protoplast-Derived Cells of Tobacco: Comparison of Wild-Type and the Val-2 Mutant

A kinetic analysis was made of l-valine uptake in protoplast-derived cells (mesophyll protoplasts cultured for 6 days) and in suspension-cultured cells of tobacco (Nicotiana tabacum L., cv Xanthi). Cells from wild-type and Val^r-2 mutant plants were compared. A low-K_m component was found in protoplast-derived cells (K_m = 45 ± 5 micromolar) as well as in suspension-cultured cells (K_m = 84 ± 21 micromolar). In the mutant cells the V_max of this component was 12- to 14-fold less than in wild-type cells. A second component (K_m = 2.4 ± 0.7 millimolar) was found in suspension-cultured cells but not in protoplast-derived cells; its V_max was the same in wild-type and mutant cells. A third component was apparently unsaturable (linear component). It was present in protoplast-derived cells but not in suspension-cultured cells, and had the same magnitude in wild-type and mutant cells. The results are discussed with reference to the uptake of l-valine in leaf tissue, in which the three kinetic components have been found simultaneously. The reduced V_max of the low-K_m component in the Val^r-2 mutant, and the differential expression of the other two components in suspension-cultured cells and protoplast-derived cells indicate that the kinetically distinguishable components represent physically distinct transport systems.     

Uptake of Lysine by Wild-Type and S-(2-Aminoethyl)-L-cysteine-Resistant Suspension-Cultured Cells of Triticum aestivum

The kinetics of uptake of L-lysine in wheat (Triticum aestivumcv. Chinese Spring) were analyzed in wild-type cells and inAEC-1 variant cells that are resistant to S-(2-aminoethyl)-L-cysteine(AEC). Uptake of lysine by AEC-1 cells was considerably slowerthan that by the wild-type cells. In the presence of carbonylcyanidem-chlorophenylhydrazone, the rates of uptake by both types ofcell were reduced to a similar linear component. Fitting theuptake data to one linear (diffusional) component and one Michaelis-Menten(active) system showed that, as compared to wild-type cells,AEC-1 cells have a reduced V_max and an increased K_m with respectto the active component, byt they have a similar diffusionalcomponent. Inhibition experiments with various amino acids indicatedthat the active component represents a carrier specific forbasic amino acids, which was competitively inhibited by AEC.The AEC-1 cells also showed reduced uptake of several neutraland acidic amino acids, but the rate of uptake of 3-O-methylglucosewas somewhat higher than that by wild-type cells. (Received May 16, 1989; Accepted September 4, 1989)     

Partitioning of Noncyclic Photosynthetic Electron Transport to O(2)-Dependent Dissipative Processes as Probed by Fluorescence and CO(2) Exchange

The partitioning of noncyclic photosynthetic electron transport between net fixation of CO₂ and collective O₂-dependent, dissipative processes such as photorespiration has been examined in intact leaf tissue from Nicotiana tabacum. The method involves simultaneous application of CO₂ exchange and pulse modulated fluorescence measurements. As either irradiance or CO₂ concentration is varied at 1% O₂ (i.e. absence of significant O₂-dependent electron flow), the quantum efficiency of PSII electron transport (_se) with CO₂ as the terminal acceptor is a linear function of the ratio of photochemical:nonphotochemical fluorescence quenching coefficients (i.e. q_Q:q_NP). When the ambient O₂ concentration is raised to 20.5% or 42% the q_Q:q_NP is assumed to predict the quantum efficiency of total noncyclic electron transport (′_se). A factor which represents the proportion of electron flow diverted to the aforementioned dissipative processes is calculated as (′_se − _se)/′_se where _se is now the observed quantum efficiency of electron transport in support of net fixation of CO₂. Examination of changes in electron allocation with CO₂ and O₂ concentration and irradiance at 25°C provides a test of the applicability of the Rubisco model to photosynthesis in vivo.     

Variable Chlorophyll a Fluorescence and CO(2) Uptake in Water-Stressed White Spruce Seedlings

Regulation of photosynthetic activity can contribute to the prevention of photodamage in stress resistant plants during exposure to drought or low temperatures. Responses to increasing levels of water stress were examined in seedlings of the stress resistant forest conifer, white spruce (Picea glauca [Moench.] Voss). Some seedlings were grown under aseptic in vitro conditions and others in pots. In relatively resistant in vivo seedlings, photosynthetic activities changed slowly in response to increasing water stress. Highly sensitive in vitro seedlings responded to water deficits similarly to in vivo seedlings but over a much shorter time scale. Fluorescence, CO₂ exchange, and stomatal conductance data reported here suggest possible mechanisms for the regulation of photochemical activity in these plants.     

Statistical Quantification of Detachment Rates and Size Distributions of Cell Clumps from Wild-Type (PAO1) and Cell Signaling Mutant (JP1) Pseudomonas aeruginosa Biofilms

The detachment of cells from bacterial biofilms is an important, yet poorly understood and largely unquantified phenomenon. Detached cell clumps from medical devices may form microemboli and lead to metastasis, especially if they are resistant to host defenses and antibiotics. In manufacturing plants detached clumps entering a process stream decrease product quality. Two strains of Pseudomonas aeruginosa, a wild type (PAO1) and a cell signaling mutant (JP1), were studied to (i) quantify and model detachment patterns and (ii) determine the influence of cell signaling on detachment. We collected effluent from a biofilm flowthrough reactor and determined the size distribution for cell detachment events by microscopic examination and image analysis. The two strains were similar in terms of both biofilm structure and detachment patterns. Most of the detachment events were single-cell events; however, multiple-cell detachment events contributed a large fraction of the total detached cells. The rates at which events containing multiple cells detached from the biofilm were estimated by fitting a statistical model to the size distribution data. For events consisting of at least 1,000 cells, the estimated rates were 4.5 events mm⁻² min⁻¹ for PAO1 and 4.3 events mm⁻² min⁻¹ for JP1. These rates may be significant when they are scaled up to the total area of a real biofilm-contaminated medical device surface and to the hours or days of patient exposure.     

Enhancement of CO(2) Uptake in Avena Coleoptiles by Fusicoccin

When Avena coleoptile segments are immersed in a solution containing H¹⁴CO₃⁻, the appearance of label in the tissue is stimulated approximately 3-fold by fusicoccin application. This effect is rapid (1-2 minutes lag time), dependent upon respiratory energy, inhibited by carbonyl cyanide m-chlorophenylhydrazone, but not appreciably altered by cycloheximide treatment. A large percentage of the cellular radioactivity is found in the form of malate. Preliminary experiments indicate that CO₂, as opposed to HCO₃⁻, is the favored species of “CO₂” taken up by the segments. These results are consistent with the notion that CO₂, presumably by virtue of its fixation and conversion to malic acid, participates in the early events associated with fusicoccin-enhanced acidification of the cell wall region leading to the stimulation of cell extension growth.     

The lack of mitochondrial complex I in a CMSII mutant of Nicotiana sylvestris increases photorespiration through an increased internal resistance to CO2 diffusion

The cytoplasmic male sterile II (CMSII) mutant lacking complex I of the mitochondrial electron transport chain has a lower photosynthetic activity but exhibits higher rates of excess electron transport than the wild type (WT) when grown at high light intensity. In order to examine the cause of the lower photosynthetic activity and to determine whether excess electrons are consumed by photorespiration, light, and intercellular CO(2), molar fraction (c(i)) response curves of carbon assimilation were measured at varying oxygen molar fractions. While oxygen is the major acceptor for excess electrons in CMSII and WT leaves, electron flux to photorespiration is favoured in the mutant as compared with the WT leaves. Isotopic mass spectrometry measurements showed that leaf internal conductance to CO(2) diffusion (g(m)) in mutant leaves was half that of WT leaves, thus decreasing the c(c) and favouring photorespiration in the mutant. The specificity factor of Rubisco did not differ significantly between both types of leaves. Furthermore, carbon assimilation as a function of electrons used for carboxylation processes/electrons used for oxygenation processes (J(C)/J(O)) and as a function of the calculated chloroplastic CO(2) molar fraction (c(c)) values was similar in WT and mutant leaves. Enhanced rates of photorespiration also explain the consumption of excess electrons in CMSII plants and agreed with potential ATP consumption. Furthermore, the lower initial Rubisco activity in CMSII as compared with WT leaves resulted from the lower c(c) in ambient air, since initial Rubisco activity on the basis of equal c(c) values was similar in WT and mutant leaves. The retarded growth and the lower photosynthetic activity of the mutant were largely overcome when plants were grown in high CO(2) concentrations, showing that limiting CO(2) supply for photosynthesis was a major cause of the lower growth rate and photosynthetic activity in CMSII.     

脂蛋白(a)合成的调节

脂蛋白(a) ［ LP(a)］是一种与低密度脂蛋白(LDL)结构极其相似的脂蛋白,它由LDL脂质核心、载脂蛋白B100(apoB100)及特异性的成分载脂蛋白(a)［ apo(a)］组成. 大量的研究表明,高LP(a)是动脉粥样硬化独立的危险因素.而LP(a)在血浆中的水平及致病能力取决于其合成的速率及其颗粒的大小. 因此, 如何抑制LP(a)合成,进而从源头减少LP(a) 的血浆水平,对动脉粥样硬化的防治具有重要的意义.本文就当前关于影响LP(a)合成的环节及相关机制进行综述, 从而为降LP(a)药物的研究提供新的视角.