Overexpression of C(4)-cycle enzymes in transgenic C(3) plants: a biotechnological approach to improve C(3)-photosynthesis

The process of photorespiration diminishes the efficiency of CO(2) assimilation and yield of C(3)-crops such as wheat, rice, soybean or potato, which are important for feeding the growing world population. Photorespiration starts with the competitive inhibition of CO(2) fixation by O(2) at the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and can result in a loss of up to 50% of the CO(2) fixed in ambient air. By contrast, C(4) plants, such as maize, sugar cane and Sorghum, possess a CO(2) concentrating mechanism, by which atmospheric CO(2) is bound to C(4)-carbon compounds and shuttled from the mesophyll cells where the prefixation of bicarbonate occurs via phosphoenolpyruvate carboxylase (PEPC) into the gas-tight bundle-sheath cells, where the bound carbon is released again as CO(2) and enters the Calvin cycle. However, the anatomical division into mesophyll and bundle-sheaths cells ("Kranz"-anatomy) appears not to be a prerequisite for the operation of a CO(2) concentrating mechanism. Submerged aquatic macrophytes, for instance, can induce a C(4)-like CO(2) concentrating mechanism in only one cell type when CO(2) becomes limiting. A single cell C(4)-mechanism has also been reported recently for a terrestrial chenopod. For over 10 years researchers in laboratories around the world have attempted to improve photosynthesis and crop yield by introducing a single cell C(4)-cycle in C(3) plants by a transgenic approach. In the meantime, there has been substantial progress in overexpressing the key enzymes of the C(4) cycle in rice, potato, and tobacco. In this review there will be a focus on biochemical and physiological consequences of the overexpression of C(4)-cycle genes in C(3) plants. Bearing in mind that C(4)-cycle enzymes are also present in C(3) plants, the pitfalls encountered when C(3) metabolism is perturbed by the overexpression of individual C(4) genes will also be discussed.     

High light-induced switch from C(3)-photosynthesis to Crassulacean acid metabolism is mediated by UV-A/blue light

The high light-induced switch in Clusia minor from C(3)-photosynthesis to Crassulacean acid metabolism (CAM) is fast (within a few days) and reversible. Although this C(3)/CAM transition has been studied intensively, the nature of the photoreceptor at the beginning of the CAM-induction signal chain is still unknown. Using optical filters that only transmit selected wavelengths, the CAM light induction of single leaves was tested. As controls the opposite leaf of the same leaf pair was studied in which CAM was induced by high unfiltered radiation (c. 2100 micromol m(-2) s(-1)). To evaluate the C(3)-photosynthesis/CAM transition, nocturnal CO(2) uptake, daytime stomatal closure and organic acid levels were monitored. Light at wavelengths longer than 530 nm was not effective for the induction of the C(3)/CAM switch in C. minor. In this case CAM was present in the control leaf while the opposite leaf continued performing C(3)-photosynthesis, indicating that CAM induction triggered by high light conditions is wavelength-dependent and a leaf internal process. Leaves subjected to wavelengths in the range of 345-530 nm performed nocturnal CO(2) uptake, (partial) stomatal closure during the day (CAM-phase III), and decarboxylation of citric acid within the first 2 d after the switch to high light conditions. Based on these experiments and evidence from the literature, it is suggested that a UV-A/blue light receptor mediates the light-induced C(3)-photosynthesis/CAM switch in C. minor.     

Simultaneous Measurements of Steady State Chlorophyll a Fluorescence and CO(2) Assimilation in Leaves: The Relationship between Fluorescence and Photosynthesis in C(3) and C(4) Plants

Rates of CO₂ assimilation and steady state chlorophyll a fluorescence were measured simultaneously at different intercellular partial pressures of CO₂ in attached cotton (Gossypium hirsutum L. cv Deltapine 16) leaves at 25°C. Electron transport activity for CO₂ assimilation plus photorespiration was calculated for these experiments. Under light saturating (1750 microeinsteins per square meter per second) and light limiting (700 microeinsteins per square meter per second) conditions there was a good correlation between fluorescence and the calculated electron transport activity at 19 and 200 millibars O₂, and between fluorescence and rates of CO₂ assimilation at 19 millibars but not 200 millibars O₂. The values of fluorescence measured at about 220 microbars intercellular CO₂ were not greatly affected by increasing O₂ from 19 to 800 millibars. Fluorescence increased with light intensity at any one intercellular CO₂ partial pressure. But the values obtained for fluorescence, expressed as a ratio of the maximum fluorescence obtained in DCMU-treated tissue, over the same range of CO₂ partial pressure at 500 microeinsteins per square meter per second were similar to those obtained at 1000 and 2000 microeinsteins per square meter per second. There were two phases in the observed correlation between fluorescence and calculated electron transport activity: an initial inverse relationship at low CO₂ partial pressures which reversed to a positive correlation at higher values of CO₂ partial pressures. Similar results were observed in the C₃ species Helianthus annuus L., Phaseolus vulgaris L., and Brassica chinensis. In all C₄ species (Zea mays L., Sorghum bicolor L., Panicum maximum Jacq., Amaranthus edulis Speg., and Echinochloa frumentacea [Roxb.] Link) examined changes in fluorescence were directly correlated with changes in CO₂ assimilation rates. The nature and the extent to which Q (primary quencher) and high-energy state (q_E) quenching function in determining the steady state fluorescence obtained during photosynthesis in leaves is discussed.     

The stoichiometry of photorespiration during C3-photosynthesis is not fixed: evidence from combined physical and stereochemical methods

The stoichiometry of photorespiration, S, is defined as the fraction of glycolate carbon photorespired. It is postulated that under steady-state conditions there are two determinants of the ratio of photorespiration to net photosynthesis: the partitioning of ribulose bisphosphate between oxidation and carboxylation, and the partitioning of glycolate between reactions leading to complete oxidation to CO2 (S = 100%) and those yielding CO2 plus serine (S = 25%). S may be calculated using two independent probes of the system. The physical probe, using an infrared gas analyzer, measured photorespiration and net photosynthesis, and hence their ratio PR/NPS = pn(phys). The metabolic probe employed tracer (3R)-D-[3-3H1,3-14C]glyceric acid to determine r, the fraction of 3H retained in the triose phosphates leaving the chloroplasts. It is deduced from the postulated model that S = pn(phys) . r/(1 - r). Experiments have been performed with illuminated tobacco leaf discs (inverted) under varying concentrations of O2 and CO2. Increasing O2 at constant CO2 increased pn(phys) and decreased r, whereas increasing CO2 at constant O2 had the opposite effect. S more than doubled at 32 degrees C on going from 16 to 40% O2 (340 microliters CO2/liter) and decreased 40% on going from 200 to 700 microliters CO2/liter (21% O2). For discs in normal air S was somewhat greater than 27%. It is suggested that net photosynthesis, and therefore crop yields, could be increased by selecting for crop plants with reduced photorespiration stoichiometry.     

培养基对不同性别水蕨配子体叶绿素荧光特性的影响

研究了MS和改良knop’s培养基条件下水蕨(Ceratopteris thalictroides)两性配子体和雄配子体叶绿素荧光参数的差异,结果表明:MS培养基中两性配子体PSⅡ线性电子传递的量子效率ФPSⅡ和PSⅡ驱动的电子传递速率ETRPSⅡ值显著高于MS培养基中的雄配子体以及改良knop’s培养基中的配子体;各组配子体光化学效率Fv/Fm值无显著差异;外源营养对各组配子体光化学荧光猝灭系数qP和非光化学荧光猝灭系数qN的影响不具明显规律性。综上所述,MS培养基中外源糖类的添加使水蕨配子体PSⅡ的光合活性增强,有利于大量快速生长的两性配子体的形成。     

Chlorophyll a Fluorescence Analysis in Response to Excitation Irradiance in Bean Plants (Phaseolus vulgaris L. and Vigna unguiculata L. Walp) Submitted to High Temperature Stress

Bean plants Phaseolus vulgaris L. (cv. Carioca and Negro Huasteco) and Vigna unguiculata L. Walp (cv. Epace-10) were grown in a growth chamber with a photosynthetic photon flux density of 200 mol m^–2 s^–1 at leaf level and air temperature of 25+1 °C. Fully expanded, first pair leaves of 12-d-old plants were submitted for 90 min to high temperature (25, 30, 35, 40, 45, and 48 °C). Chlorophyll a fluorescence parameters (ETR, q_P, q_N, and F₀) were investigated using a modulated fluorimeter at 25 °C during recovery considered here as 48 h after stress induction period. An accentuated decrease in q_P and an increase in q_N at 48 °C in Carioca and Negro Huasteco was not observed in Epace-10. In response to excitation irradiance a great potential for ETR was found in Negro Huasteco at 25 °C, also demonstrated by net photosynthetic rate. At 48 °C ETR was high for Epace-10 while it was equal to zero for Carioca and Negro Huasteco. Tolerance to high temperature observed in Epace-10 provided important information about the adaptative characteristics of Vigna cultivars to warm climates.     

Effects of Simulated Acid Precipitation on Photosynthesis,Chlorophyll Fluorescence,and Antioxidative Enzymes in Cucumis sativus L.

The effects of simulated acid rain on gas exchange, chlorophyll fluorescence, and anti-oxidative enzyme activity in cucumber seedlings (Cucumis sativus L. cv. Jingchun No. 4) were investigated. Acid rain significantly reduced net photosynthetic rate and mainly non-stomatal factors contributed to the decrease of photosynthesis during the experimental period. The reduced photosynthesis was associated with a decreased maximal photochemical efficiency (F_v/F_m) and the average quantum yield of the photosystem 2 (PS2) reaction centres (_PS2). Meanwhile, acid rain significantly increased the activities of guaiacol peroxidase (GPX) and superoxide dismutase (SOD), but decreased the activity of catalase (CAT) together with an increased content of malonyldialdehyde (MDA), Hence the changes in photosynthesis in acid rain treatment might be a secondary effect of acidity damage probably due to lipid peroxidation of lipids and proteins in thylakoid membrane rather than direct effect on PS2 reaction centre.     

Photorespiratory Enzyme Activities in C3 and CAM Forms of the Facultative CAM Plant, Mesembryanthemum crystallimum L.

The extent to which photorespiration occurs in CrassulaceanAcid Metabolism (CAM) plants has received limited attention.No comparative studies of C₃ and CAM development have been made.To address this problem, activities of several photorespiratoryenzymes were measured in a facultative CAM plant—Mesembryanthemumcrystallinum L.—during induction of CAM by water stress(NaCl-treatment). Salt-treatment over a 22 d period produceda progressive change in metabolism from C₃ to CAM. This wasconfirmed by (I) changes in gas exchange from C₃ fixation tothe characteristic CAM pattern of nocturnal CO2 uptake; (2)increases in did acid fluctuation and (3) a 30-fold increasein phosphoenol pyruvate (PEP) carboxylase activity. In contrast,no significant changes were observed in the activities of glycollateoxidase (GO), NAD-dependent-hydroxypyruvate reductase (HPR),glutamine synthetase (GS) or glutamate dehydrogenase (GDH) whenplants were induced into CAM. Ion exchange chromatography onDEAE Sephacel detected only one GS isoenzyme (GS2, chloroplastic)at all stages of CAM induction, Western blot analysis, however,detected an additional, although minor, band of GS1 (cytosolic),in C₃ plants, which disappeared following CAM induction. Ourresults show that, after development of CAM, these plants stillretain the capacity to photorespire. This may be an essentialrequirement of CAM plants growing in habitats with variablerainfall. When water availability is high, stomata may openin the light allowing ribulose bisphosphate carboxylase oxygenase(Rubisco) activity and photorespiration to occur. The inherentcapacity to photorespire would allow plants to survive variableperiods of rainfall. Key words: Mesembryanthemum, C₃, CAM, photorespiration     

过量合成ALA转基因烟草叶片光合与叶绿素荧光特性的研究

以转酿酒酵母Hem1基因的转基因烟草和野生型植株为材料,用Li-6400光合测定仪和PAM-2100叶绿素荧光仪检测了2种烟草不同叶位叶片光合和荧光参数,并考察了它们的生长情况.结果表明:过量合成ALA的转基因烟草植株具有更强的光合能力,并伴随着气孔导度(Gs)和蒸腾速率(Tr)提高.暗适应下转基因植株不同叶位叶片的初始荧光(Fo)没有明显差异,而野生型植株下部叶片F0明显升高;转基因植株最大荧光(Fm)、可变荧光(Fv)、PSⅡ最大光化学效率(Fv/Fm)等参数均显著提高,特别是下部叶片表现得更为明显;在光照下,转基因植株PSⅡ有效光化学效率(Fv′/Fm′)和实际光化学效率(ΦPSⅡ)、荧光猝灭系数(qP)、电子传递速率(ETR)、光化学效率(Pc)以及进入PSⅡ反应中心的能量(Pc Ex)普遍高于野生型,而天线热耗散能量(Hd)以及非光化学荧光猝灭系数(NPQ)等明显低于野生型,且这些差异在基部叶片中表现得尤为突出.可见,过量合成ALA有利于延长烟草叶片光合寿命,提高光化学能量转换效应和光合产物积累,从而促进植株生长.     

CAM induction in Clusia minor L. during the transition from wet to dry season in Trinidad: the role of organic acid speciation and decarboxylation

The interrelationships between the induction of CAM and the turnover of malate and citrate in the dicotyledenous tree Clusia minor were compared with seasonal changes in rainfall, leaf water status, PFD and photoinhibitory responses during the transition from wet to dry season in Trinidad. Over a period of 8 weeks, as rainfall declined from a maximum observed around week 3, leaf xylem tensions measured at dusk and dawn reflected the concurrent reduction in day-time carbon gain and an increase in the diel turnover of malate (exposed leaves) and citrate (shaded leaves). Clear seasonal trends were observed in the turnover of malate and citrate during the transition from wet to dry season. In contrast to the declining back-ground concentrations of citrate during the wet-dry season transition, malate accumulation was markedly enhanced and the ratio of malalc:citrate accumulated overnight increased as the dry season advanced. Photo-inhibitory responses, assessed by chlorophyll fluorescence, indicated that photochemistry was largely determined by the diurnal course of PFD incident on leaves, regardless of the magnitude of internal CO₂ release from malate and citrate decarboxylation. In the long term, photochemical efficiency in both shaded and exposed leaves appeared to decline as the dry season progressed. Although there was a clear linear relationship between integrated PFD and overnight accumulation of malate, no such correlation was found for citrate. However, citrate breakdown during the day showed a much closer correlation with PFD as compared to malate, with levels of citrate measured at dusk declining in response to higher daily light intensities. Moreover, enhanced citrate decarboxylation during the day was strongly correlated with increased CAM and overnight accumulation of both malate and citrate.     

中国金丝桃属金丝桃组(藤黄科)新分类群

描述了中国云南北部的金丝桃属Hypericum L.(藤黄科)两个新种,即楚雄金丝桃H. fosteri N. Robson和漾濞金丝桃H. wardianum N. Robson.二者均与短柱金丝桃H. hookerianum Wight & Arn.相近.楚雄金丝桃为一地方特有种,目前仅在模式地点发现;漾濞金丝桃在缅甸东北部还有分布.二者主要以蒴果伸长,非卵状近球形,萼片无中脉而有别于短柱金丝桃.此外,将宽萼金丝桃H. latisepalum (N. Robson) N. Robson从亚种提升为种;将变异较大的纤枝金丝桃H. lagarocladum N. Robson划分为两个亚种,即叶较宽、具有开张习性的原亚种纤枝金丝桃H. lagarocladum ssp. lagarocladum和叶较窄、更为直立的新亚种狭叶金丝桃H. lagarocladum ssp. angustifolium N. Robson.     

Amino Acid Metabolism of Lemna minor L. : II. Responses to Chlorsulfuron

Chlorsulfuron, an inhibitor of acetolactate synthase (EC 4.1.3.18) (TB Ray 1984 Plant Physiol 75: 827-831), markedly inhibited the growth of Lemna minor at concentrations of 10⁻⁸ molar and above, but had no inhibitory effects on growth at 10⁻⁹ molar. At growth inhibitory concentrations, chlorsulfuron caused a pronounced increase in total free amino acid levels within 24 hours. Valine, leucine, and isoleucine, however, became smaller percentages of the total free amino acid pool as the concentration of chlorsulfuron was increased. At concentrations of chlorsulfuron of 10⁻⁸ molar and above, a new amino acid was accumulated in the free pool. This amino acid was identified as α-amino-n-butyrate by chemical ionization and electron impact gas chromatography-mass spectrometry. The amount of α-amino-n-butyrate increased from undetectable levels in untreated plants, to as high as 840 nanomoles per gram fresh weight (2.44% of the total free pool) in plants treated with 10⁻⁴ molar chlorsulfuron for 24 hours. The accumulation of this amino acid was completely inhibited by methionine sulfoximine. Chlorsulfuron did not inhibit the methionine sulfoximine induced accumulations of valine, leucine, and isoleucine, supporting the idea that the accumulation of the branched-chain amino acids in methionine sulfoximine treated plants is the result of protein turnover rather than enhanced synthesis. Protein turnover may be primarily responsible for the failure to achieve complete depletion of valine, leucine, and isoleucine even at concentrations of chlorsulfuron some 10⁴ times greater than that required to inhibit growth. Tracer studies with ¹⁵N demonstrate that chlorsulfuron inhibits the incorporation of ¹⁵N into valine, leucine, and isoleucine. The α-amino-n-butyrate accumulated in the presence of chlorsulfuron and [¹⁵N]H₄⁺ was heavily labeled with ¹⁵N at early time points and appeared to be derived by transamination from a rapidly labeled amino acid such as glutamate or alanine. We propose that chlorsulfuron inhibition of acetolactate synthase may lead to accumulation of 2-oxobutyrate in the isoleucine branch of the pathway, and transamination of 2-oxobutyrate to α-amino-n-butyrate by a constitutive transaminase utilizing either glutamate or alanine as α-amino-N donors.     

Amino Acid Metabolism of Lemna minor L. : III. Responses to Aminooxyacetate

Aminooxyacetate, a known inhibitor of transaminase reactions and glycine decarboxylase, promotes rapid depletion of the free pools of serine and aspartate in nitrate grown Lemna minor L. This compound markedly inhibits the methionine sulfoximine-induced accumulation of free ammonium ions and greatly restricts the methionine sulfoximine-induced depletion of amino acids such as glutamate, alanine, and asparagine. These results suggest that glutamate, alanine, and asparagine are normally catabolized to ammonia by transaminase-dependent pathways rather than via dehydrogenase or amidohydrolase reactions. Aminooxyacetate does not inhibit the methionine sulfoximine-induced irreversible deactivation of glutamine synthetase in vivo, indicating that these effects cannot be simply ascribed to inhibition of methionine sulfoximine uptake by amino-oxyacetate. This transaminase inhibitor promotes extensive accumulation of several amino acids including valine, leucine, isoleucine, alanine, glycine, threonine, proline, phenylalanine, lysine, and tyrosine. Since the aminooxyacetate induced accumulations of valine, leucine, and isoleucine are not inhibited by the branched-chain amino acid biosynthesis inhibitor, chlorsulfuron, these amino acid accumulations most probably involve protein turnover. Depletions of soluble protein bound amino acids are shown to be approximately stoichiometric with the free amino acid pool accumulations induced by aminooxyacetate. Aminooxyacetate is demonstrated to inhibit the chlorsulfuron-induced accumulation of α-amino-n-butyrate in L. minor, supporting the notion that this amino acid is derived from transamination of 2-oxobutyrate.     

Developmental Transition from Enzymatic to Acid Hydrolysis of Sucrose in Acid Limes (Citrus aurantifolia)

The sucrose breakdown mechanisms in juice sacs of acid lime (Citrus aurantifolia [Christm.] Swing.) were investigated throughout fruit development. All three enzymes of sucrose catabolism (sucrose synthase, acid, and alkaline invertase) are present during the initial stages. The activities of these enzymes declined rapidly and disappeared by stage 5 (80% development) but not before vacuolar pH had decreased to approximately 2.5. At this stage, sucrose breakdown occurs by acid hydrolysis. By attaining a vacuolar pH of 2.5 prior to enzyme disappearance, the cell maintains a continuous ability to break down sucrose throughout ontogeny. Thus, acid limes possess a unique and coordinated system for sucrose breakdown that involves both enzymatic and nonenzymatic pathways.     

Changes of water-relation characteristics and levels of organic cytoplasmic solutes during salinity induced transition of Mesembryanthemum crystallinum from C3-photosynthesis to crassulacean acid metabolism

Summary NaCl was added to the nutrient solution of 4–6-week old Mesembryanthemum crystallinum plants so that the concentration rose by 50 mM per day. Ten to fifteen days after a concentration of 400 mM was reached, pronounced diurnal oscillations of malate levels indicated that plants had changed from C₃-photosynthesis to crassulacean acid metabolism (CAM). Due to the NaCl-treatment the solute potential (_s) decreased from about -6 bar to -25 bar, and the water potential () changed from about -5 bar to -23 bar on average. showed small diurnal oscillations both in controls and NaCl-treated plants, with an amplitude of 1 to 3 bar, the value at the end of the dark phase being less negative than that at the end of the light phase. Changes of ion levels due to the NaCl-treatment were average increases in Na⁺ and Cl^- from 10–20 to 370–470 mmol kg^-1 FW and from below 10 to 280–325 mmol kg^-1 FW, respectively, and a decrease in K⁺ from 70–80 to 25 mmol kg^-1 FW. These changes of ion levels corresponded very closely to an increase of dry weight in per cent of fresh weight observed during the NaCl-treatment (e.g. a change of 2% in one experiment), and osmotically they matched the measured change in _s (e.g. about 18–20 bar in one experiment).Most of the organic solutes analysed did not show any significant changes as a result of the NaCl-treatment. The following compounds were identified within the respective ranges of concentrations: mannitol (0.2 to 0.5 mmol kg^-1 FW), sum of quaternary ammonium compounds (60 to 140 mg kg^-1 FW), choline (0.1 to 0.4 mmol kg^-1 FW), betaine (0.3 to 0.7 mmol kg^-1 FW), hexoses (2–9 mmol kg^-1 FW), pentoses (1–5 mmol kg^-1 FW) and sucrose (2–4 mmol kg^-1 FW). The levels of proline and of total amino acids minus proline rose during the NaCl-treatment from 0.1–1 mmol kg^-1 FW to 2.5–5 mmol kg^-1 FW and from 2.5–4 mmol kg^-1 FW to 6–8 mmol kg^-1 FW, respectively.The changes of _s and , and of Na⁺- and Cl^--levels were complete, and new steady levels were attained by the time 400 mM NaCl was reached in the nutrient solution, i.e. many days before pronounced diurnal malate oscillations indicated that the change from C₃-photosynthesis to CAM had occurred. The attainment of new steady levels of proline and K⁺, however, was much slower and coincided with the onset of CAM.Dedicated to Professor Dr.Dr.h.c. Michael Evenari on the occasion of his 75th birthday in appreciation of his great achievements in promoting experimental ecology and with gratitude for encouragements and help with the investigation of the adaptation of Mesembryanthemum crystallinum     

不同光照度下水蕨配子体叶绿素荧光特性的研究

以模式植物水蕨的两性配子体和雄配子体为材料,研究了不同光照度下蕨类植物配子体叶绿素荧光参数的差异,探讨水蕨配子体光系统Ⅱ(PSⅡ)对不同光照的响应规律.结果表明:同一光照度条件下,水蕨两性配子体的实际光化学效率(Ф_(PSⅡ))和潜在光化学效率(F_v/F_m)均高于雄配子体,但无显著差异,此时两者间的光化学猝灭系数(q_p)和非光化学猝灭系数(q_N)值也无显著差异;在4 000 lx光照条件下,两性配子体PSⅡ驱动的电子传递速率(ETR_(PSⅡ))显著高于雄配子体.随着光照度的增加,水蕨两性配子体的Ф_(PSⅡ)、ETR_(PSⅡ)和q_p值逐渐增加,且在4 000 lx光照下显著增加,但F_v/F_m和q_N值无显著变化;而雄配子体的Ф_(PSⅡ)、ETR_(PSⅡ)、F_v/F_m、q_p和q_N值均呈先增后减趋势,但各光照处理间无显著差异.研究发现,水蕨两性配子体PSⅡ的活性相对比雄配子体高;两性配子体和雄配子体的光保护能力相似;光照度对水蕨雄配子体的光合能力没有显著影响,而4 000 lx的光照度对水蕨两性配子体的生长最有利.     

Biphenyl and xanthone derivatives from the twigs of a Garcinia sp. (Clusiaceae)

The genus Garcinia is a well known rich source of bioactive xanthones and benzophenones. Some species of this genus also produce flavonoids and biphenyls as minor constituents. In this study, two new biphenyls, doitungbiphenyls A (1) and B (2), along with two biphenyls, schomburgbiphenyl (3) and nigrolineabiphenyl B (4); and four xanthones, 1,3,6-trihydroxy-8-isoprenyl-7-methoxyxanthone (5), morusignin K (6), 1,5-dihydroxyxanthone (7), and 1,7-dihydroxyxanthone (8), were isolated from the acetone extract of the twigs of a Garcinia sp. Their structures were characterized extensively by 1D and 2D NMR spectroscopy and HR-EI-MS. The cytotoxicity of the two new biphenyls against the oral cavity cancer (KB) and the breast cancer (MCF7) cell lines was also evaluated.     

Oxygen and Hydrogen Isotope Ratios of Water from Photosynthetic Tissues of CAM and C(3) Plants

Water samples from photosynthetic tissues of C₃ and Crassulacean acid metabolism (CAM) plants that grew together in the field were extracted and the stable oxygen and hydrogen isotope ratios determined. During the day, ¹⁸O/¹⁶O and deuterium/hydrogen (D/H) ratios of water from CAM plants were lower than those observed in water from C₃ plants. The patterns of diurnal variation (or lack thereof) in isotope ratios of plant water are consistent with the gross anatomical and physiological characteristics of the plants studied here. Our observations support the previously advanced hypothesis that high D/H ratios in cellulose nitrate prepared from CAM plants relative to those for C₃ plants are not caused by greater deuterium enrichment in the water in CAM plants, but rather by isotopic fractionations associated with different biochemical reactions in the two types of plants.