Xanthone and flavonol constituents of Swertia hookeri

The whole plant of Swertia hookeri, collected at flowering has been shown to contain two tri- and nine tetraoxygenated free, glucosyloxy, and stearyl ester xanthones and one flavonol stearyl ester. Among these, three are previously unreported in nature and one was known previously only as a synthetic compound. The xanthones are based on 1,3,5,-, 1,3,5,8- and 1,3,7,8-oxygenated systems with the middle oxygenation pattern predominating. The two ester compounds appeared only at the flowering stage. Plants collected at the pre-flowering stage gave the corresponding free compounds. The biochemical and biological significance of these findings are appraised.     

Flavonoids and xanthones from the leaves of Amorphophallus titanum (Araceae)

The flavonoids and xanthones in the leaves of Amorphophallus titanum, which has the largest inflorescence among all Araceous species, were surveyed. Eight C-glycosylflavones, five flavonols, one flavone O-glycoside and two xanthones were isolated and characterized as vitexin, isovitexin, orientin, isoorientin, schaftoside, isoschaftoside, vicenin-2 and lucenin-2 (C-glycosylflavones), kaempferol 3-O-robinobioside, 3-O-rutinoside and 3-O-rhamnosylarabinoside, and quercetin 3-O-robinobioside and 3-O-rutinoside (flavonols), luteolin 7-O-glucoside (flavone), and mangiferin and isomangiferin (xanthones). Although the inflorescence of this species has been surveyed for flavonoids, those of the leaves were reported for the first time.     

Differences in the chemical constituents of Mangifera indica, infected with Aspergillus niger and Fusarium moniliformae

The isolation and characterization of the chemical constituents of different parts of Mangifera indica, sound and infected with two pathogenic fungi, viz. Aspergillus niger and Fusarium moniliformae, are described. Natural occurrence of two polyketideshikimate-derived depsides is reported for the first time. Additionally, a number of xanthones, flavonoids, triterpenes and amino acids, not encountered before in this species, are reported. The co-occurrence of mangiferin, 1,3,6,7-tetra- and 1,3,5,6,7-pentaoxygenated xanthones and the quantitative variation of the latter two compounds with the growing of the plant and during the fungal infection are biochemically significant. The protector role of the flavonoids and other C₁₅ metabolites to M. indica from the ingress of the fungal hyphae is indicated. The two pathogenic fungi secreted a number of mycotoxins in different parts of the host species during its vegetation and flowering periods. During the elaboration of these toxic metabolites, the host-pathogen interaction played an important role. Evidence is presented for A. niger as a mycotoxin producing fungus.     

The structures of garcinones a,b and c: Three new xanthones from Garcinia mangostana

Three new tetraoxygenated xanthones (garcinones A, B and C), each disubstituted with C₅-units, have been isolated from the chloroform extract of the fruit-hulls of Garcinia mangostana. Their structures were established by a combination of spectral interpretation and chemical correlation.     

Minor xanthones of Garcinia mangostana

Two new trioxygenated xanthones with a 3,3-dimethyl allyl side chain have been isolated from the fruit hulls of Garcinia mangostana. The structures were established from spectral and chemical data.     

Xanthones from formosan Gentianaceous plants

A reinvestigation of the whole plants ofTripterospermum lanceolatum gave, in addition to compounds isolated previously, two new xanthones, named lanceolin and methyllanceolin, respectively. The compound previously reported to be oleanolic acid was re-examined and identified as ursolic acid by a¹³C NMR study. An isomeric mixture, oleanolic acid and ursolic acid, and sweroside were isolated from the whole plants ofSwertia arisanensis.     

Diversity in forms of C4 in the genus Cleome (Cleomaceae)

Background and Aims

Cleomaceae is one of 19 angiosperm families in which C₄ photosynthesis has been reported. The aim of the study was to determine the type, and diversity, of structural and functional forms of C₄ in genus Cleome.

Methods

Plants of Cleome species were grown from seeds, and leaves were subjected to carbon isotope analysis, light and scanning electron microscopy, western blot analysis of proteins, and in situ immunolocalization for ribulose bisphosphate carboxylase oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC).

Key Results

Three species with C₄-type carbon isotope values occurring in separate lineages in the genus (Cleome angustifolia, C. gynandra and C. oxalidea) were shown to have features of C₄ photosynthesis in leaves and cotyledons. Immunolocalization studies show that PEPC is localized in mesophyll (M) cells and Rubisco is selectively localized in bundle sheath (BS) cells in leaves and cotyledons, characteristic of species with Kranz anatomy. Analyses of leaves for key photosynthetic enzymes show they have high expression of markers for the C₄ cycle (compared with the C₃–C₄ intermediate C. paradoxa and the C₃ species C. africana). All three are biochemically NAD-malic enzyme sub-type, with higher granal development in BS than in M chloroplasts, characteristic of this biochemical sub-type. Cleome gynandra and C. oxalidea have atriplicoid-type Kranz anatomy with multiple simple Kranz units around individual veins. However, C. angustifolia anatomy is represented by a double layer of concentric chlorenchyma forming a single compound Kranz unit by surrounding all the vascular bundles and water storage cells.

Conclusions

NAD-malic enzyme-type C₄ photosynthesis evolved multiple times in the family Cleomaceae, twice with atriplicoid-type anatomy in compound leaves having flat, broad leaflets in the pantropical species C. gynandra and the Australian species C. oxalidea, and once by forming a single Kranz unit in compound leaves with semi-terete leaflets in the African species C. angustifolia. The leaf morphology of C. angustifolia, which is similar to that of the sister, C₃–C₄ intermediate African species C. paradoxa, suggests adaptation of this lineage to arid environments, which is supported by biogeographical information.     

Polyacetylenes in Hawaiian bidens

Leaves and roots of 19 species and six subspecies of Hawaiian Bidens were examined for polyacetylenes. Eleven C₁₃ hydrocarbons, aromatic and thiophenyl derivatives, one C₁₄ tetrahydropyran and three C₁₇ hydrocarbons were isolated all identified. All can be derived from a common precursor, oleic acid. Polyacetylenes were not detected in the leaves of 13 taxa although they are found in the roots of all. The occurrence of 2-[2-phenyl-ethyne-1-yl]-5 acetoxymethyl thiopene in Bidens has not been previously reported. Its ubiquitous presence is consistent with other evidence that the Hawaiian species are all derived from a single ancestral immigrant to the islands. Most taxa could be distinguished by their complement of polyacetylenes in roots and leaves. No variation was found to occur within taxa except in B. torta, in which each population had a unique array of polyacetylenes. Above the species level there appeared to be no taxonomically significant pattern to the distribution of polyacetylenes in this group.     

An investigation for the occurrence of C4 photosynthesis in the Cyperaceae from Australia

Two hundred and twenty species of 38 genera in the Cyperaceae from Australia were examined for the possible occurrence of the C₄ photosynthesis and the anatomical features of leaves and culms. The Kranz type of anatomy and the carbon isotope ratios typical of C₄ plants were found in 84 species in the following six genera of four tribes belonging to subfamily Cyperoideae:Bulbostylis, Crosslandia, andFimbristylis (Fimbristylideae);Lipocarpha (Lipocarpheae);Cyperus (Cypereae);Rhynchospora (Rhynchosporeae). The anatomical observation revealed that the C₄ species possessed any one of the three Kranz anatomical types found by previous investigators. It was suggested that in the Cyperaceae the C₄ syndrome evolved independently within several taxa of the subfamily. The relative distribution of C₃ and C₄ species of the Cyperaceae in Australia was investigated by use of floristic data. It was recognized that the C₄ species dominated in the northern part of the continent which was characterized by tropical and subtropical savannas and hot dry areas with summer rainfall, and the C₃ species in the southern part, which contained temperate areas and mediterranean climatic areas with winter rainfall.     

Photosynthesis research on yellowtops: Macroevolutionn in progress

The vast majority of angiosperms, including most of the agronomically important crop plants (wheat, etc.), assimilate CO₂ through the inefficient C₃ pathway of photosynthesis. Under ambient conditions these organisms loose about 1/3 of fixed carbon via photorespiration, an energetically wasteful process. Plants with C₄ photosynthesis (such as maize) eliminate photorespiration via a biochemical CO₂-pump and thus have a larger rate of carbon gain. The genus Flaveria (yellowtops, Asteraceae) contains not only C₃ and C₄ species, but also many C₃-C₄ intermediates, which have been interpreted as evolving from C₃ to fully expressed C₄ metabolism. However, the evolutionary significance of C₃-C₄Flaveria-intermediates has long been a matter of debate. A well-resolved phylogeny of nearly all Flaveria species has recently been published. Here, we review pertinent background information and combine this novel phylogeny with physiological data. We conclude that the Flaveria species complex provides a robust model system for the study of the transition from C₃ to C₄ photosynthesis, which is arguably a macroevolutionary event. We conclude with comments relevant to the current Intelligent Design debate.     

Xanthones from three Garcinia species

From the stem bark of three previously uninvestigated Garcinia species a number of xanthones have been isolated including three that appear to be novel. The novel compounds are characterized as isocowanin (8-geranyl-4-(3,3-dimethylallyl)-7-methoxy-1,3,6-trihydroxyxanthone), isocowanol (8-geranyl-4-(3-hydroxymethyl-3-methylallyl)-7-methoxy-1,3,6-trihydroxyxanthone) and nervosaxanthone (4,8-di(3,3-dimethylallyl)-2-(1,1-dimethylallyl)-1,3,5,6-tetrahydroxyxanthone). The chemotaxonomic significance of oxygenation patterns in these xanthones is briefly discussed.     

Photosynthetic and photorespiratory characteristics of flaveria species

The genus Flaveria shows evidence of evolution in the mechanism of photosynthesis as its 21 species include C₃, C₃-C₄, C₄-like, and C₄ plants. In this study, several physiological and biochemical parameters of photosynthesis and photorespiration were measured in 18 Flaveria species representing all the photosynthetic types. The 10 species classified as C₃-C₄ intermediates showed an inverse continuum in level of photorespiration and development of the C₄ syndrome. This ranges from F. sonorensis with relatively high apparent photorespiration and lacking C₄ photosynthesis to F. Among the intermediates, the photosynthetic CO₂ compensation points at 30°C and 1150 micromoles quanta per square meter per second varied from 9 to 29 microbars. The values for the three C₄-like species varied from 3 to 6 microbars, similar to those measured for the C₄ species. The activities of the photorespiratory enzymes glycolate oxidase, hydroxypyruvate reductase, and serine hydroxymethyltransferase decreased progressively from C₃ to C₃-C₄ to C₄-like and C₄ species. On the other hand, most intermediates had higher levels of phosphenolpyruvate carboxylase and NADP-malic enzyme than C₃ species, but generally lower activities compared to C₄-like and C₄ species. The levels of these C₄ enzymes are correlated with the degree of C₄ photosynthesis, based on the initial products of photosynthesis. Another indication of development of the C₄ syndrome in C₃-C₄ Flaveria species was their intermediate chlorophyll a/b ratios. The chlorophyll a/b ratios of the various Flaveria species are highly correlated with the degree of C₄ photosynthesis suggesting that the photochemical machinery is progressively altered during evolution in order to meet the specific energy requirements for operating the C₄ pathway. In the progression from C₃ to C₄ species in Flaveria, the CO₂ compensation point decreased more rapidly than did the decrease in O₂ inhibition of photosynthesis or the increase in the degree of C₄ photosynthesis. These results suggest that the reduction in photorespiration during evolution occurred initially by refixation of photorespired CO₂ and prior to substantive reduction in O₂ inhibition and development of the C₄ syndrome. However, further reduction in O₂ inhibition in some intermediates and C₄-like species is considered primarily due to the development of the C₄ syndrome. Thus, the evolution of C₃-C₄ intermediate photosynthesis likely occurred in response to environmental conditions which limit the intercellular CO₂ concentration first via refixation of photorespired CO₂, followed by development of the C₄ syndrome.     

Coordination of the cell-specific distribution of the four subunits of glycine decarboxylase and of serine hydroxymethyltransferase in leaves of C3-C4 intermediate species from different genera

The cell-specific distribution of the four subunit proteins (P, L, T and H) of glycine decarboxylase (GDC) and of serine hydroxymethyltransferase (SHMT) has been studied in the leaves of C₃-C₄ intermediate and C₄ species of three genera (Flaveria, Moricandia and Panicum) using immunogold localization. Antibodies raised against these proteins from pea leaf mitochondria were used to probe Western blots of total leaf proteins of F. linearis Lag., M. arvensis (L.) DC and P. milioides Nees ex Trin. (C₃-C₄), and F. trinervia (Spring.) Mohr and P. miliaceum (L.) (C₄). For all species, each antibody recognised specifically a protein of similar molecular weight to that in pea leaves. In leaves of M. arvensis the P protein was present in the mitochondria of the bundle-sheath cells but was undetectable in those of the mesophyll, whereas the L, T and H proteins and SHMT were present in both cell types. The density of immunogold labelling of SHMT on the mitochondria of mesophyll cells was less than that on those of the bundle-sheath cells, which correlates with the relative activities of SHMT in these cell types. These data reveal that the lack of functional GDC in the mesophyll cells of M. arvensis, which is the principal biochemical reason for reduced photorespiration in this species, is due to the loss of a single subunit protein. This lack of coordinate expression of the subunit proteins of GDC within a photosynthetic cell represents a clear difference between M. arvensis and other C₃ and C₃-C₄ species. None of the GDC proteins was detectable in the mesophyll cells of the C₃-C₄ and C₄ Flaveria and Panicum species but all were present in the bundle-sheath cells. The differences in the distribution of the GDC proteins in leaves of the C₃-C₄ species studied are discussed in relation to the evolution of photosynthetic mechanisms.     

Photosynthesis, Morphology, Leaf Anatomy, and Cytogenetics of Hybrids between C(3) and C(3)/C(4)Panicum Species

The Laxa group of the Panicum genus contains species which have CO₂ exchange and anatomical characteristics intermediate to C₃ and C₄ photosynthetic types (C₃/C₄), and also species characterized as C₃. Hybrids were made between two of the C₃/C₄ species and two C₃ species. Carbon dioxide exchange and morphological, leaf anatomical, and cytogenetic characteristics of F₁ hybrids between Panicum milioides Nees. ex Trin (C₃/C₄) and P. laxum Mez. (C₃), P. spathellosum Doell (C₃/C₄) and P. boliviense Hack. (C₃), and P. spathellosum and P. laxum were studied. There were no consistent differences in apparent photosynthesis, although two of the three hybrids had higher net CO₂ uptake than the C₃ parent. Values of inhibition of apparent photosynthesis by 21% O₂, CO₂ loss in the light, and CO₂ compensation concentration for the hybrids were between those of the parents. All three hybrids showed leaf anatomical traits, especially organelle quantities in the bundle sheath cells, between those of their respective parents. Linear regression of CO₂ compensation concentration on the percentage of mitochondria and chloroplasts in vascular bundle sheaths of the parents and hybrids gave correlation coefficients of −0.94. This suggests that the reduction in CO₂ loss in the C₃/C₄ species, and to a lesser degree in the F₁ hybrids, was due to development of organelles and perhaps a higher proportion of leaf photorespiration in bundle sheaths. The overall morphology of the hybrids was so different from the parents that they could be described as new taxonomic forms. The chromosomes in the hybrids were mainly unpaired or paired as bivalents indicating possible homology between some parental genomes.     

Kinetic properties of phosphoenolpyruvate carboxylase from c(3), c(4), and c(3)-c(4) intermediate species of flaveria (asteraceae)

Flaveria cronquistii (C₃), F. chloraefolia (C₃-C₄), F. floridana (C₃-C₄), F. pubescens (C₃-C₄), F. anomala (C₃-C₄), F. linearis (C₃-C₄), F. brownii (C₄), F. palmeri (C₄), F. trinervia (C₄) and F. australasica (C₄), comprising 10 out of the 21 known species of the genus Flaveria (Asteraceae), were included in a comparative study of the kinetic and regulatory properties of green leaf phosphoenolpyruvate (PEP) carboxylase. At least three kinetically distinct enzyme-forms were identified on the basis of their affinities for PEP and the degree of allosterism with respect to this substrate. The kinetic properties of PEP carboxylase of most of the species seemingly were modified in vivo depending on the growth conditions of the plants. K_m(PEP_free)-values of the enzyme from the five C₃-C₄ intermediate species ranged from 6 micromolar (F. chloraefolia, low light-grown) to 38 micromolar (F. pubescens, high light-grown). In contrast, the K_m for PEP of PEP carboxylase from the C₃ species F. cronquistii (13 micromolar) apparently was not influenced by growth conditions. The response of the enzyme from the C₃ and C₃-C₄ species was hyperbolic in all cases. A second isoform with a lower affinity for PEP (88-100 micromolar), but also hyperbolic kinetics was found in the C₄ species F. brownii, whereas in the three other C₄ species examined a PEP carboxylase with a still lower affinity for PEP (187-221 micromolar) and sigmoidal kinetics was present. These isozyme-related kinetic data were supported by analyses of the elution behavior of the enzyme during anion-exchange chromatography on DEAE-Trisacryl M. The results are discussed with respect to the evolution of C₄ photosynthesis in the Flaveria genus.     

C-Glycosylflavones and xanthones in leaves of Rigidella,sessilanthera and Fosteria

Four New World genera are included in the tribe tigrideae of the Iridaceae. These genera, which have been the subject of recent systematic treatments [1–4], share many characteristics; e.g. a haploid complement of two large and 12 small chromosomes and bisulcate pollen grains. However, the taxonomic and phyletic relationships within and between these genera have been based strictly on floral morphology and may simply reflect the primary pollinators of these genera [4,5].The flavonoid chemistry of eight species in three of the four genera, Rigidella, Sessilanthera and Fosteria, was investigated as part of a systematic study of Tigrideae. Our results are summarized in Table 1 nad Fig. 1. Although a recurrent pattern of $\text{C-}\text{glycosylflavones}$ and xanthones characterize the leaves of these taxa, each species exhibits a distinctive array of compounds. The same classes of compounds occur in other tribes of the Iridaceae: $\text{C-}\text{glycosylflavones}$ occur in the Irideae [6,7], Cipureae, and Mariceae and xanthones in Irideae [6] and Sisyrinchieae [6].     

Regulation of oxaloacetate, aspartate, and malate formation in mesophyll protoplast extracts of three types of c(4) plants

The use of mesophyll protoplast extracts from various C₄ species has provided an effective method for studying light-and substrate-dependent formation of oxaloacetate, malate, and asparate at rates equivalent to whole leaf C₄ photosynthesis. Conditions regulating the formation of the C₄ acids were studied with protoplast extracts from Digitaria sanguinalis, an NADP-malic enzyme C₄ species, Eleusineindica, an NAD-malic enzyme C₄ species, and Urochloa panicoides, a phosphoenolpyruvate (PEP) carboxykinase C₄ species. Light-dependent induction of CO₂ fixation by the mesophyll extracts of all three species was relatively low without addition of exogenous substrates. Pyruvate, alanine and α-ketoglutarate, or 3-phosphoglycerate induced high rates of CO₂ fixation in the mesophyll extracts with oxaloacetate, malate, and aspartate being the primary products. In all three species, it appears that pyruvate, alanine, or 3-phosphoglycerate may serve as effective precursors to the formation of PEP for carboxylation through PEP-carboxylase in C₄ mesophyll cells. Induction by pyruvate or alanine and α-ketoglutarate was light-dependent, whereas 3-phosphoglycerate-induced CO₂ fixation was not.     

Intracellular localization of certain photosynthetic enzymes in bundle sheath cells of plants possessing the C4 pathway of photosynthesis.

Bundle sheath cells were enzymatically isolated from representatives of three groups of C₄ plants: Zea mays (NADP malic enzyme type), Panicum miliaceum (NAD malic enzyme type), and Panicum maximum (phosphoenolpyruvate (PEP) carboxykinase type). Cellular organelles from bundle sheath homogenates were partially resolved by differential centrifugation and on isopycnic sucrose density gradients in order to study compartmentation of photosynthetic enzymes. A 48-h-dark pretreatment of the leaves allowed the isolation of relatively intact chloroplasts. Enzymes that decarboxylate C₄ acids and furnish CO₂ to the Calvin cycle are localized as follows: NADP malic enzyme, chloroplastic in Z. mays; NAD malic enzyme, mitochondrial in all three species; PEP carboxykinase, chloroplastic in P. maximum. The activity of NAD malic enzyme in the three species was in the order of P. miliaceum > P. maximum > Z. mays. There were high levels of aspartate and alanine aminotransferases in bundle sheath extracts of P. miliaceum and P. maximum and substantial activity in Z. mays. In all three species, aspartate aminotransferase was mitochondrial whereas alanine aminotransferase was cytoplasmic. Based on the activity and localization of certain enzymes, the concept for aspartate and malate as transport metabolites from mesophyll to bundle sheath cells in C₄ species of the three C₄ groups is discussed.     

Photosynthesis of Grass Species Differing in Carbon Dioxide Fixation Pathways : VIII. Ultrastructural Characteristics of Panicum Species in the Laxa Group

Ultrastructural studies of leaves of seven Panicum species in or closely related to the Laxa group and classified as C₃, C₄ or C₃-C₄ intermediate were undertaken to examine features associated with C₃ and C₄ photosynthesis. The C₃ species Panicum rivulare Trin. had few organelles in bundle sheath cell profiles (2 chloroplasts, 1.1 mitochondria, and 0.3 peroxisomes per cell section) compared to an average of 10.6 chloroplasts, 17.7 mitochondria, and 3.2 peroxisomes per bundle sheath cell profile for three C₃-C₄ species, Panicum milioides Nees ex Trin., Panicum decipiens Nees ex Trin. and Panicum schenckii Hack. However, two other C₃ species, Panicum laxum Sw. and Panicum hylaeicum Mez, contained about 0.7, 0.5, and 0.3 as many chloroplasts, mitochondria, and peroxisomes, respectively, as in bundle sheath cell profiles of the C₃-C₄ species. Chloroplasts and mitochondria in bundle sheath cells were larger than those in mesophyll cells for the C₄ species Panicum prionitis Griseb. and the C₃-C₄ species, but in C₃ species the organelles were similar in size or were smaller in the bundle sheath cells. The C₃-C₄ species and P. laxum and P. hylaeicum exhibited an unusually close association of organelles in bundle sheath cells with mitochondria frequently surrounded in profile by chloroplasts. The high concentrations in bundle sheath cells of somewhat larger organelles than in mesophyll cells correlates with the reduced photorespiration of the C₃-C₄ species.     

Differences in drought sensitivities and photosynthetic limitations between co-occurring C3 and C4 (NADP-ME) Panicoid grasses

Background and Aims

The success of C₄ plants lies in their ability to attain greater efficiencies of light, water and nitrogen use under high temperature, providing an advantage in arid, hot environments. However, C₄ grasses are not necessarily less sensitive to drought than C₃ grasses and are proposed to respond with greater metabolic limitations, while the C₃ response is predominantly stomatal. The aims of this study were to compare the drought and recovery responses of co-occurring C₃ and C₄ NADP-ME grasses from the subfamily Panicoideae and to determine stomatal and metabolic contributions to the observed response.

Methods

Six species of locally co-occurring grasses, C₃ species Alloteropsis semialata subsp. eckloniana, Panicum aequinerve and Panicum ecklonii, and C₄ (NADP-ME) species Heteropogon contortus, Themeda triandra and Tristachya leucothrix, were established in pots then subjected to a controlled drought followed by re-watering. Water potentials, leaf gas exchange and the response of photosynthetic rate to internal CO₂ concentrations were determined on selected occasions during the drought and re-watering treatments and compared between species and photosynthetic types.

Key Results

Leaves of C₄ species of grasses maintained their photosynthetic advantage until water deficits became severe, but lost their water-use advantage even under conditions of mild drought. Declining C₄ photosynthesis with water deficit was mainly a consequence of metabolic limitations to CO₂ assimilation, whereas, in the C₃ species, stomatal limitations had a prevailing role in the drought-induced decrease in photosynthesis. The drought-sensitive metabolism of the C₄ plants could explain the observed slower recovery of photosynthesis on re-watering, in comparison with C₃ plants which recovered a greater proportion of photosynthesis through increased stomatal conductance.

Conclusions

Within the Panicoid grasses, C₄ (NADP-ME) species are metabolically more sensitive to drought than C₃ species and recover more slowly from drought.