[Show abstract][Hide abstract] ABSTRACT: Genus Suaeda (family Chenopodiaceae, subfamily Suaedoideae) has two structural types of Kranz anatomy consisting of a single compound
Kranz unit enclosing vascular tissue. One, represented by Suaeda taxifolia, has mesophyll (M) and bundle sheath (BS) cells distributed around the leaf periphery. The second, represented by Suaeda eltonica, has M and BS surrounding vascular bundles in the central plane. In both, structural and biochemical development of C4 occurs basipetally, as observed by analysis of the maturation gradient on longitudinal leaf sections. This progression in
development was also observed in mid-sections of young, intermediate, and mature leaves in both species, with three clear
stages: (i) monomorphic chloroplasts in the two cell types in younger tissue with immunolocalization and in situ hybridization showing ribulose bisphosphate carboxylase oxygenase (Rubisco) preferentially localized in BS chloroplasts,
and increasing in parallel with the establishment of Kranz anatomy; (ii) vacuolization and selective organelle positioning
in BS cells, with occurrence of phosphoenolpyruvate carboxylase (PEPC) and immunolocalization showing that it is preferentially
in M cells; (iii) establishment of chloroplast dimorphism and mitochondrial differentiation in mature tissue and full expression
of C4 biochemistry including pyruvate, Pi dikinase (PPDK) and NAD-malic enzyme (NAD-ME). Accumulation of rbcL mRNA preceded its peptide expression, occurring prior to organelle positioning and differentiation. During development there
was sequential expression and increase in levels of Rubisco and PEPC followed by NAD-ME and PPDK, and an increase in the 13C/12C isotope composition of leaves to values characteristic of C4 photosynthesis. The findings indicate that these two forms of NAD-ME type C4 photosynthesis evolved in parallel within the subfamily with similar ontogenetic programmes.
Preview · Article · Feb 2011 · Journal of Experimental Botany
[Show abstract][Hide abstract] ABSTRACT: The interest in renewable, plant-derived, bioenergy/biofuels has resulted in a renaissance of plant cell-wall/lignin research. Herein, effects of modulating lignin monomeric compositions in a single plant species, Arabidopsis, are described. The earliest stage of putative "AcBr/Klason lignin" deposition was apparently unaffected by modulating p-coumarate 3-hydroxylase or ferulate 5-hydroxylase activities. This finding helps account for the inability of many other studies to fully suppress the reported putative levels of lignin deposition through monolignol biosynthesis manipulation, and also underscores limitations in frequently used lignin analytical protocols. The overall putative lignin content was greatly reduced (circa 62%) in a plant line harboring an H-(p-hydroxyphenyl) enriched lignin phenotype. This slightly increased H-monomer deposition level apparently occurred in cell-wall domains normally harboring guaiacyl (G) and/or syringyl (S) lignin moieties. For G- and S-enriched lignin phenotypes, the overall lignification process appeared analogous to wild type, with only xylem fiber and interfascicular fiber cells forming the S-enriched lignins. Laser microscope dissection of vascular bundles and interfascicular fibers, followed by pyrolysis GC/MS, supported these findings. Some cell types, presumably metaxylem and possibly protoxylem, also afforded small amounts of benzodioxane (sub)structures due to limited substrate degeneracy (i.e. utilizing 5-hydroxyconiferyl alcohol rather than sinapyl alcohol). For all plant lines studied, the 8-O-4' inter-unit frequency of cleavable H, G and/or S monomers was essentially invariant of monomeric composition for a given (putative) lignin content. These data again underscore the need for determination of lignin primary structures and identification of all proteins/enzymes involved in control of lignin polymer assembly/macromolecular configuration.
No preview · Article · Mar 2010 · Molecular BioSystems
[Show abstract][Hide abstract] ABSTRACT: Our studies on the enigmatic genus Bienertia (Chenopodiaceae), with its C4 photosynthesis and lack of Kranz anatomy, led us to the discovery of a second species of this previously-supposed monotypic genus. The new species is named Bienertia sinuspersici after its main range around the Persian Gulf countries and the northern side of the Gulf of Oman. Bienertia sinuspersici occurs in hot climates and is a vicariant of Bienertia cycloptera, which is found at higher latitudes and elevations in temperate and cold deserts of the region. Like Bienertia cycloptera, the new species has unique chlorenchyma cells with dimorphic chloroplasts and single cell C4 photosynthesis. However, it differs anatomically by having mostly one to two layers of chlorenchyma cells, versus two to three layers in Bienertia cycloptera. Furthermore, the new species has longer cotyledon leaves, larger seeds, larger flowers, and larger chromosomes, and differs in a set of micro-morphological features. All of this supports our conclusion that this widely distributed, novel plant is an overlooked new species. Bienertia sinuspersici grows well in very hot climates, under conditions which most species can barely tolerate. Its wide distribution indicates that its novel C4 photosynthesis may confer advantages for CO2 fixation in these habitats not found in C4 species having conventional Kranz anatomy.
Full-text · Article · Jan 2009 · Systematic Botany
[Show abstract][Hide abstract] ABSTRACT: Two putative Kunitz-type chymotrypsin inhibitor genes (WCI2 and WCI5) were isolated from winged bean (Psophocarpus tetragonolobus (L.) DC). While WCI2 has previously been characterized, WCI5 represents a new member of the WCI family. WCI5 was exclusively expressed in winged bean seeds. Theoretical translation of both the genes resulted into polypeptides of 207 amino acids with 86% sequence similarity. The polypeptide sequences contain four half-cysteine residues and a well-conserved Leu(65)-Ser(66) reactive site, typical for chymotrypsin inhibitors. WCI5 and WCI2 were expressed in Pichia pastoris and the recombinant proteins were assayed against various proteinases. Both the inhibitors strongly inhibited commercially available bovine chymotrypsin. More importantly, gut proteinases of Helicoverpa armigera larvae that damage many important crop plants, were inhibited by WCI2 and WCI5. In addition, both proteinase inhibitors demonstrated significant reduction of growth of H. armigera larvae after feeding on inhibitor incorporated artificial diets. The inhibitory effects of WCI2 and WCI5 on activity of proteinases and larval growth make these proteins and their genes promising candidates for enhancing plant defense against H. armigera using transgenic plants.
[Show abstract][Hide abstract] ABSTRACT: A leaf anatomical survey was conducted to gather critical data for interpreting relationships among 32 species of annual Muhlenbergia. Phenetic analyses, utilizing 14 anatomical characters, support recognition of four major species groups. These four major species groups are not concordant with previously reported groups. Muhlenbergia brandegei, known only from three islands in Baja California Sur, is believed to be more closely related to M. appressa, M. microsperma, and M. tenuifolia, rather than, M. biloba, as suggested in prior publication. Muhlenbergia diversiglumis is morphologically similar to species of Pereilema and does not show close affinities with other annual species of Muhlenbergia. Anatomically, M. ciliata, M. pectinata, and M. tenella are very similar and form the most distinctive group among the annual Muhlenbergia.
No preview · Article · Mar 2008 · Nordic Journal of Botany
[Show abstract][Hide abstract] ABSTRACT: Among dicotyledon families, Chenopodiaceae has the most C4 species and the greatest diversity in structural forms of C4. In subfamily Salicornioideae, C4 photosynthesis has, so far, only been found in the genus Halosarcia which is now included in the broadly circumscribed Tecticornia. Comparative anatomical, cytochemical, and physiological studies on these taxa, which have near-aphyllous photosynthetic
shoots, show that T. pergranulata is C3, and that two subspecies of T. indica (bidens and indica) are C4 (Kranz-tecticornoid type). In T. pergranulata, the stems have two layers of chlorenchyma cells surrounding the centrally located water storage tissue. The two subspecies
of T. indica have Kranz anatomy in reduced leaves and in the fleshy stem cortex. They are NAD-malic enzyme-type C4 species, with mesophyll chloroplasts having reduced grana, characteristic of this subtype. The Kranz-tecticornoid-type anatomy
is unique among C4 types in the family in having groups of chlorenchymatous cells separated by a network of large colourless cells (which may
provide mechanical support or optimize the distribution of radiation in the tissue), and in having peripheral vascular bundles
with the phloem side facing the bundle sheath cells. Also, the bundle sheath cells have chloroplasts in a centrifugal position,
which is atypical for C4 dicots. Fluorescence analyses in fresh sections indicate that all non-lignified cell walls have ferulic acid, a cell wall
cross-linker. Structural–functional relationships of C4 photosynthesis in T. indica are discussed. Recent molecular studies show that the C4 taxa in Tecticornia form a monophyletic group, with incorporation of the Australian endemic genera of Salicornioideae, including Halosarcia, Pachycornia, Sclerostegia, and Tegicornia, into Tecticornia.
Full-text · Article · Feb 2008 · Journal of Experimental Botany
[Show abstract][Hide abstract] ABSTRACT: C (4) species of family Chenopodiaceae, subfamily Suaedoideae have two types of Kranz anatomy in genus Suaeda, sections Salsina and Schoberia, both of which have an outer (palisade mesophyll) and an inner (Kranz) layer of chlorenchyma cells in usually semi-terete leaves. Features of Salsina (S. AEGYPTIACA, S. arcuata, S. taxifolia) and Schoberia type (S. acuminata, S. Eltonica, S. cochlearifoliA) were compared to C (3) type S. Heterophylla. In Salsina type, two layers of chlorenchyma at the leaf periphery surround water-storage tissue in which the vascular bundles are embedded. In leaves of the Schoberia type, enlarged water-storage hypodermal cells surround two layers of chlorenchyma tissue, with the latter surrounding the vascular bundles. The chloroplasts in Kranz cells are located in the centripetal position in Salsina type and in the centrifugal position in the Schoberia type. Western blots on C (4) acid decarboxylases show that both Kranz forms are NAD-malic enzyme (NAD-ME) type C (4) species. Transmission electron microscopy shows that mesophyll cells have chloroplasts with reduced grana, while Kranz cells have chloroplasts with well-developed grana and large, specialized mitochondria, characteristic of NAD-ME type C (4) chenopods. In both C (4) types, phosphoenolpyruvate carboxylase is localized in the palisade mesophyll, and Rubisco and mitochondrial NAD-ME are localized in Kranz cells, where starch is mainly stored. The C (3) species S. heterophylla has Brezia type isolateral leaf structure, with several layers of Rubisco-containing chlorenchyma. Photosynthetic response curves to varying CO (2) and light in the Schoberia Type and Salsina type species were similar, and typical of C (4) plants. The results indicate that two structural forms of Kranz anatomy evolved in parallel in species of subfamily Suaedoideae having NAD-ME type C (4) photosynthesis.
[Show abstract][Hide abstract] ABSTRACT: A major goal currently in Arabidopsis research is determination of the (biochemical) function of each of its approximately 27,000 genes. To date, however, 12% of its genes actually have known biochemical roles. In this study, we considered it instructive to identify the gene expression patterns of nine (so-called AtCAD1-9) of 17 genes originally annotated by The Arabidopsis Information Resource (TAIR) as cinnamyl alcohol dehydrogenase (CAD, EC 188.8.131.52) homologues [see Costa, M.A., Collins, R.E., Anterola, A.M., Cochrane, F.C., Davin, L.B., Lewis N.G., 2003. An in silico assessment of gene function and organization of the phenylpropanoid pathway metabolic networks in Arabidopsis thaliana and limitations thereof. Phytochemistry 64, 1097-1112.]. In agreement with our biochemical studies in vitro [Kim, S.-J., Kim, M.-R., Bedgar, D.L., Moinuddin, S.G.A., Cardenas, C.L., Davin, L.B., Kang, C.-H., Lewis, N.G., 2004. Functional reclassification of the putative cinnamyl alcohol dehydrogenase multigene family in Arabidopsis. Proc. Natl. Acad. Sci. USA 101, 1455-1460.], and analysis of a double mutant [Sibout, R., Eudes, A., Mouille, G., Pollet, B., Lapierre, C., Jouanin, L., Séguin A., 2005. Cinnamyl Alcohol Dehydrogenase-C and -D are the primary genes involved in lignin biosynthesis in the floral stem of Arabidopsis. Plant Cell 17, 2059-2076.], both AtCAD5 (At4g34230) and AtCAD4 (At3g19450) were found to have expression patterns consistent with development/formation of different forms of the lignified vascular apparatus, e.g. lignifying stem tissues, bases of trichomes, hydathodes, abscission zones of siliques, etc. Expression was also observed in various non-lignifying zones (e.g. root caps) indicative of, perhaps, a role in plant defense. In addition, expression patterns of the four CAD-like homologues were investigated, i.e. AtCAD2 (At2g21730), AtCAD3 (At2g21890), AtCAD7 (At4g37980) and AtCAD8 (At4g37990), each of which previously had been demonstrated to have low CAD enzymatic activity in vitro (relative to AtCAD4/5) [Kim, S.-J., Kim, M.-R., Bedgar, D.L., Moinuddin, S.G.A., Cardenas, C.L., Davin, L.B., Kang, C.-H., Lewis, N.G., 2004. Functional reclassification of the putative cinnamyl alcohol dehydrogenase multigene family in Arabidopsis. Proc. Natl. Acad. Sci. USA 101, 1455-1460.]. Neither AtCAD2 nor AtCAD3, however, were expressed in lignifying tissues, with the latter being found mainly in the meristematic region and non-lignifying root tips, i.e. indicative of involvement in biochemical processes unrelated to lignin formation. By contrast, AtCAD7 and AtCAD8 [surprisingly now currently TAIR-annotated as probable mannitol dehydrogenases, but for which there is still no biochemical or other evidence for same] displayed gene expression patterns largely resembling those of AtCAD4/5, i.e. indicative perhaps of a quite minor role in monolignol/lignin formation. Lastly, AtCAD1 (At1g72680), AtCAD6 (At4g37970) and AtCAD9 (At4g39330), which lacked detectable CAD catalytic activities in vitro, were also expressed predominantly in vascular (lignin-forming) tissues. While their actual biochemical roles remain unknown, definition of their expression patterns, nevertheless, now begins to provide useful insights into potential biochemical/physiological functions, as well as the cell types in which they are expressed. These data thus indicate that the CAD metabolic network is composed primarily of AtCAD4/5 and may provisionally, to a lesser extent, involve AtCAD7/8 based on in vitro catalytic properties and (promoter regions selected to obtain) representative gene expression patterns. This analysis has, therefore, enabled us to systematically map out bona fide CAD gene involvement in both the assembly and differential emergence of the various component parts of the lignified vascular apparatus in Arabidopsis, as well as those having other (e.g. putative plant defense) functions. The data obtained also further underscore the ongoing difficulties and challenges as regards current limitations in gene annotations versus actual determination of gene function. This is exemplified by the annotation of AtCAD2, 3 and 6-9 as purported mannitol dehydrogenases, when, for example, no in vitro studies have been carried out to establish such a function biochemically. Such annotations should thus be discontinued in the absence of reliable biochemical and/or other physiological confirmation. In particular, AtCAD2, 3, 6 and 9 should be designated as dehydrogenases of unknown function. Just as importantly, the different patterns of gene expression noted during distinct phases of growth and development in specific cells/tissues gives insight into the study of the roles that these promoters have.
[Show abstract][Hide abstract] ABSTRACT: Each photosynthetic palisade cell in the leaves of shade-adapted Peperomia glabella contains a druse calcium oxalate crystal which we hypothesize is involved in dispersing light to the chloroplasts. The effect of light intensity on druse size, number and position, relative to growth and phototsynthesis was determined. Peperomia glabella grew best at 50-100 μE m-2s -1, and at 300-400 μE m-2s-1 had smaller leaves with considerable yellowing. Plants grown under lower light had well developed chloroplasts while at 300-400 μE m-2s-1 the chloroplasts accumulated plastoglobuli and showed thylakoid swelling. Chlorophyll content, chlorophyll a/b, and photosynthetic rate decreased with increasing light intensity. Druse crystals were produced in palisade cells under all light conditions but crystal diameter changed, being greatest at 100 μE m-2 s-1 and decreasing with higher light. The position of the crystals also changed with light intensity. Under 50 and 100 μE m -2s-1 the crystals were predominantly located at the bottom or middle of cells while at 300 and 400 μE m-2s -1 they were at the top of cells. The data indicate an adaptive role of calcium oxalate crystals in photosynthesis in Peperomia.
No preview · Article · Apr 2007 · Botanical Studies
[Show abstract][Hide abstract] ABSTRACT: In conifer stems, formation of chemical defenses against insects or pathogens involves specialized anatomical structures of the phloem and xylem. Oleoresin terpenoids are formed in resin duct epithelial cells and phenolics accumulate in polyphenolic parenchyma cells. Ethylene signaling has been implicated in the induction of these chemical defenses. Recently, we reported the cloning of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) from spruce (Picea spp.) and Douglas fir (Pseudotsuga menziesii). ACO protein was constitutively expressed in Douglas fir and only weakly induced upon wounding. We now cloned seven full-length and one near full-length cDNA representing four distinct 1-aminocyclopropane-1-carboxylic acid synthases (ACS; ACS1, ACS2, ACS3, and ACS4) from spruce and Douglas fir. Cloning of ACS has not previously been reported for any gymnosperm. Using gene-specific, quantitative real-time polymerase chain reaction, we measured constitutive expression for the four ACS genes and the single-copy ACO gene in various tissues of Sitka spruce (Picea sitchensis) and in white spruce (Picea glauca) somatic embryos. ACO and ACS4 were ubiquitously expressed at high levels; ACS1 was predominantly expressed in developing embryos and ACS2 and ACS3 were expressed only at very low levels. Insect attack or mechanical wounding caused strong induction of ACS2 and ACS3 in Sitka spruce bark, a moderate increase in ACO transcripts, but had no effect on ACS1 and ACS4. ACS protein was also strongly induced following mechanical wounding in Douglas fir and was highly abundant in resin duct epithelial cells and polyphenolic parenchyma cells. These results suggest that ACS, but not ACO, is a regulated step in ethylene-induced conifer defense.
[Show abstract][Hide abstract] ABSTRACT: Leaves and cotyledons of the terrestrial C-4 plants, Bienertia cycloptera Bunge ex Boiss. and Suaeda aralocaspica (Bunge) Freitag & Schutze (Chenopodiaceae), accomplish C-4 photosynthesis within individual chlorenchyma cells: each species having a unique means of intracellular spatial partitioning of biochemistry and organelles. In this study the chlorenchyma tissue in flowers and stems of these species was investigated. Flowers have an outer whorl of green tepals with a layer of chlorenchyma cells, which are located on the abaxial side, exposed to the atmosphere. Anatomical, immunocytochemical, western blots and starch analyses show that the chlorenchyma cells in tepals are specialised for performance of single-cell C-4 photosynthesis like that in leaves. In the tepals of B. cycloptera, chlorenchyma cells have a distinctive central cytoplasmic compartment, with chloroplasts which contain Rubisco, separated by cytoplasmic channels from a peripheral chloroplast-containing compartment, with phosphoenolpyruvate carboxylase (PEPC) distributed throughout the cytoplasm. In the tepals of S. aralocaspica, chlorenchyma cells have chloroplasts polarised towards opposite ends of the cells. Rubisco is found in chloroplasts towards the proximal end of the cell and PEPC is found throughout the cytoplasm. Also, green stems of B. cycloptera have a single layer of the specialised C-4 type chlorenchyma cells beneath the epidermis, and in stems of S. aralocaspica, chlorenchyma cells are scattered throughout the cortical tissue with chloroplasts around their periphery, typical of C-3 type chlorenchyma. During reproductive development, green flowers become very conspicuous, and their photosynthesis is suggested to be important in completion of the life cycle of these single-cell C-4 functioning species.
Full-text · Article · Jan 2007 · Functional Plant Biology
[Show abstract][Hide abstract] ABSTRACT: Eleocharis contains many amphibious species, and displays diversity of photosynthetic mechanism (C3, C4 or C3-C4 intermediates). A unique feature of Eleocharis is the plasticity in the photosynthetic,mechanism,of some,species in response to the environment. In this study, we have examined the culm anatomy and photosynthetic property of several Eleocharis species grown,terrestrially and the changes,in the newly,produced,culms,over a short period time frame after switching from terrestrial to submerged condition. Eleocharis baldwinii (Torrey) Chapman is C4-like in terrestrial habitat, exhibiting O2 inhibition of photosynthesis,with Rubisco expressed,in both mesophyll,and bundle sheath cells and PEPC strictly in the mesophyll cells, but switches to C3-C4 intermediacy when submerged. In addition to Eleocharis vivipara Link type 1 (which switches from C4-like to C3), two other photosynthetic types examined in this study were shown to have different responses to growth,in either terrestrial or submerged,conditions. E. vivipara type 2 is a typical C4 plant in the terrestrial habitat, but becomes a C3-C4 intermediate under submerged conditions. Further, terrestrially, E. vivipara type 3i s aC 3-C4 intermediate, but when submerged the δ,C value increases to −6.7‰, indicating its use of bicarbonate as a major carbon source. The submerged,form of this plant exhibited about three times higher photosynthetic,O2 evolution rate, compared to the C3 species Eleocharis erythropoda Steudel. These Eleocharis species possess different molecular switches for regulating C4 gene expression in response to environmental stimuli both between different species, and in E. vivipara among,different populations. The apparent expression of a bicarbonate transport system,by E. vivipara type 3 while submerged,represents a unique adaptation to low CO2 availability.
Full-text · Article · Jan 2007 · Functional Plant Biology
[Show abstract][Hide abstract] ABSTRACT: Many plant species accumulate calcium oxalate crystals in specialised cells called crystal idioblasts. In one species of crystal-forming plants (Pistia stratiotes L.; forming raphide crystals), it has been shown that ascorbic acid is the primary precursor of oxalic acid. The question remains if this is true of other calcium oxalate crystal-forming plants. One way of answering the above question is by examining ascorbic acid as the oxalic acid precursor in diverse species with a variety of crystal types. In this study we tested ascorbic acid as the primary precursor of oxalic acid in four different species, each forming one of the four, thus far, unexamined crystal types: water hyacinth, styloid (and raphide); tomato, crystal sand; winged-bean, prismatic; water lily, astrosclereids with surface prismatic crystals. Pulse-chase feeding of 1-[C-14]-ascorbic acid followed by resin embedding, microautoradiography and light microscopy were employed to examine incorporation of label into calcium oxalate crystals. For the species and crystal types studied, ascorbic acid is the primary precursor of oxalic acid and further, oxalic acid is added to crystals in patterns that correlate with the age and type of crystal involved.
No preview · Article · Jan 2007 · Functional Plant Biology
[Show abstract][Hide abstract] ABSTRACT: Recently, three Chenopodiaceae species, Bienertia cycloptera, Bienertia sinuspersici, and Suaeda aralocaspica, were shown to possess novel C(4) photosynthesis mechanisms through the compartmentalization of organelles and photosynthetic enzymes into two distinct regions within a single chlorenchyma cell. Bienertia has peripheral and central compartments, whereas S. aralocaspica has distal and proximal compartments. This compartmentalization achieves the equivalent of spatial separation of Kranz anatomy, including dimorphic chloroplasts, but within a single cell. To characterize the mechanisms of organelle compartmentalization, the distribution of the major organelles relative to the cytoskeleton was examined. Examination of the distribution of the cytoskeleton using immunofluorescence studies and transient expression of green fluorescent protein-tagged cytoskeleton markers revealed a highly organized network of actin filaments and microtubules associating with the chloroplasts and showed that the two compartments in each cell had different cytoskeletal arrangements. Experiments using cytoskeleton-disrupting drugs showed in Bienertia and S. aralocaspica that microtubules are critical for the polarized positioning of chloroplasts and other organelles. Compartmentalization of the organelles in these species represents a unique system in higher plants and illustrates the degree of control the plant cell has over the organization and integration of multiorganellar processes within its cytoplasm.
[Show abstract][Hide abstract] ABSTRACT: Members of the Pinaceae family have complex chemical defense strategies. Conifer defenses associated with specialized cell types of the bark involve constitutive and inducible accumulation of phenolic compounds in polyphenolic phloem parenchyma cells and oleoresin terpenoids in resin ducts. These defenses can protect trees against insect herbivory and fungal colonization. The phytohormone ethylene has been shown to induce the same anatomical and cellular defense responses that occur following insect feeding, mechanical wounding, or fungal inoculation in Douglas fir (Pseudotsuga menziesii) stems (Hudgins and Franceschi in Plant Physiol 135:2134-2149, 2004). However, very little is known about the genes involved in ethylene formation in conifer defense or about the temporal and spatial patterns of their protein expression. The enzyme 1-aminocyclopropane-1-carboxylate oxidase (ACO) catalyzes the final step in ethylene biosynthesis. We cloned full-length and near full-length ACO cDNAs from three conifer species, Sitka spruce (Picea sitchensis), white spruce (P. glauca), and Douglas fir, each with high similarity to Arabidopsis thaliana ACO proteins. Using an Arabidopsis anti-ACO antibody we determined that ACO is constitutively expressed in Douglas fir stem tissues and is up-regulated by mechanical wounding, consistent with the wound-induced increase of ethylene levels. Immunolocalization showed cytosolic ACO is predominantly present in specialized cell types of the wound-induced bark, specifically in epithelial cells of terpenoid-producing cortical resin ducts, in polyphenolic phloem parenchyma cells, and in ray parenchyma cells.
[Show abstract][Hide abstract] ABSTRACT: Species having C4 photosynthesis belonging to the phosphoenolpyruvate carboxykinase (PEP-CK) subtype, which are found only in family Poaceae, have the most complex biochemistry among the three C4 subtypes. In this study, biochemical (western blots and immunolocalization of some key photosynthetic enzymes) and structural analyses were made on several species to further understand the PEP-CK system. This included PEP-CK-type C4 species Urochloa texana (subfamily Panicoideae), Spartina alterniflora and S. anglica (subfamily Chloridoideae), and an NADP-ME-type C4 species, Echinochloa frumentacea, which has substantial levels of PEP-CK.
Urochloa texana has typical Kranz anatomy with granal chloroplasts scattered around the cytoplasm in bundle sheath (BS) cells, while the Spartina spp. have BS forming long adaxial extensions above the vascular tissue and with chloroplasts in a strictly centrifugal position. Despite some structural and size differences, in all three PEP-CK species the chloroplasts in mesophyll and BS cells have a similar granal index (% appressed thylakoids). Immunolocalization studies show PEP-CK (which catalyses ATP-dependent decarboxylation) is located in the cytosol, and NAD-ME in the mitochondria, in BS cells, and in the BS extensions of Spartina. In the NADP-ME species E. frumentacea, PEP-CK is also located in the cytosol of BS cells, NAD-ME is very low, and the source of ATP to support PEP-CK is not established.
Representative PEP-CK species from two subfamilies of polyphyletic origin have very similar biochemistry, compartmentation and chloroplast grana structure. Based on the results with PEP-CK species, schemes are presented with mesophyll and BS chloroplasts providing equivalent reductive power which show bioenergetics of carbon assimilation involving C4 cycles (PEP-CK and NAD-ME, the latter functioning to generate ATP to support the PEP-CK reaction), and the consequences of any photorespiration.
[Show abstract][Hide abstract] ABSTRACT: The Chenopodiaceae includes taxa with both C3 and C4 photosynthesis with diverse kinds of Kranz anatomy and single-celled C4 species without Kranz anatomy; thus, it is of key importance for understanding evolution of C4 photosynthesis. All of the C4 genera except Atriplex, which belongs to Chenopodioideae, are in the Salicornioideae / Suaedoideae / Salsoloideae s.l. (including Camphorosmeae and Sclerolaeneae) clade. Our study focused on the relationships of the main lineages within this clade with an emphasis on the placement of the single cell functioning C4 genus Bienertia using maximum parsimony, maximum likelihood, and Bayesian inference phylogenetic analyses of the nuclear ribosomal ITS and five chloroplast DNA regions (atpB-rbcL, matK, psbB-psbH, rbcL, and trnL-trnF). Further we provide a detailed phylogeny of Alexandra and Suaeda based on ITS, atpB-rbcL, and psbB-psbH. Our molecular data provide strong statistical support for the monophyly of: (1) a Salicornioideae / Suaedoideae / Salsoloideae s.l. clade; (2) a Salicornioideae / Suaedoideae clade; (3) the subfamilies Salicornioideae, Suaedoideae (including Bienertia) and Salsoloideae s.l.; (4) the tribes Suaedeae, Salsoleae, and Camphorosmeae; (5) the Salicornieae if Halopeplideae is included; and (6) Suaeda if Alexandra is included. Alexandra lehmannii is therefore reclassified as Suaeda lehmannii and a new section of Suaeda is created, section Alexandra. There are four independent origins of C4 photosynthesis within the Suaedoideae including two parallel origins of Kranz C4 anatomy (in Suaeda sections Salsina s.l. and Schoberia) and two independent origins of C4 systems without Kranz anatomy (in Bienertia and in Suaeda section Borszczowia).
Full-text · Article · Jun 2006 · Systematic Botany
[Show abstract][Hide abstract] ABSTRACT: Abstract Axenic Lemna minor plants, which form numerous calcium oxalate crystals, were exposed to [14C]-glycolic acid, -glyoxylic acid, -oxalic acid and -ascorbic acid and prepared for microautoradiography by a technique that preserves only insoluble label to determine specifically the pathway leading to oxalic acid used for crystal formation. Label from glycolic, glyoxylic, and oxalic acids was incorporated into crystals. Label from oxalic acid was also found in starch when exposure to label was done in the light but not dark, while plastids specialized for lipid storage were heavily labelled under both conditions. Incorporation of label from glycolic and glyoxylic acids, but not oxalic acid, was inhibited in the presence of the glycolate oxidase inhibitors, αHPMS (2-pyridylhydroxy methanesulphonic acid) and mHBA (methyl 2-hydroxy-3-butynoic acid), and inhibition of labelling was not due to an effect on uptake. These studies show that the glycolate oxidase pathway to oxalic acid is operational in L. minor and that the product is available for crystal formation. Dark-grown plants form almost four times as many crystal cells (idioblasts) as do light-grown plants, indicating crystal formation is not in response to photorespiratory glycolate production. Label from [1-14C]ascorbic acid was also incorporated into crystals and labelling was inhibited by mHBA, indicating glycolic acid and/or glyoxylic acid are possible intermediates of ascorbic acid catabolism.
The effect of nitrogen source on crystal formation was also investigated. Significantly more crystal idioblasts were formed, on a surface area basis, by plants grown on ammonium than by plants grown on nitrate nitrogen. When grown with mixed ammonium and nitrate, an intermediate number of crystal idioblasts were formed.
No preview · Article · Apr 2006 · Plant Cell and Environment
[Show abstract][Hide abstract] ABSTRACT: Photoassimilate export from the mesophyll and the processes underlying phloem loading are central to the efficient growth,
competitive ability, and reproductive success of a plant. The assimilate flux out of the leaf is regulated on a number of
levels. For example, structural aspects including the spatial organization of individual cell types within the leaf and the
extent of the symplasmic connections between these cell types control these fluxes at the cellular level. Phloem loading can
follow a symplasmic route, or involve an apoplasmic step within the vicinity of the companion cell-sieve element (CC-SE) complex.
In the latter case, apoplasmic transfer is regulated by the capacity of the individual cell types to engage in efflux or uptake
(retrieval) of photoassimilates. Within the autotrophic tissues of the leaf, photoassimilate flow may be regulated through
feed-back mechanisms that can modify biochemical pathways, plasmodesmal conductivity, and membrane transport properties. At
the membrane transport level, molecular techniques have led to the isolation and characterization of transporters operating
at the site of phloem loading. These studies allowed for the molecular manipulation of such transport systems and now offer
a powerful method to advance our understanding of the events that underlie both phloem loading and photoassimilate allocation.
The recent discovery that plasmodesmata can mediate the cell-to-cell transport of macromolecules suggests that these unique
structures may play a role not only in assimilate transport, but also in the integration of cellular processes. A model is
proposed where regulatory macromolecules move cell to cell, within the leaf, as well as long-distance, via the phloem, to
serve in the coordination and regulation of physiological events taking place in source and sink tissues.
[Show abstract][Hide abstract] ABSTRACT: Differentially expressed genes in chickpea, (Cicer arietinum L.) during root infection by Fusarium oxysporum f sp. ciceri Race1, were identified using cDNA-RAPD and cDNA-AFLP approaches. The former employed decamer primers on cDNA template and revealed nine differentially expressed transcripts in the resistant-infected chickpea variety. Among the 2000 transcript-derived fragments (TDFs) screened by cDNA-AFLP, 273 were differentially expressed in chickpea roots during Fusarium infection. Only 13.65% of the TDFs were differentially regulated during pathogen challenge, while the other 86% were expressed non-differentially during the process of pathogen infection in chickpea roots. Nineteen TDFs, which expressed differentially in the resistant-infected chickpea variety were cloned and sequenced. Two of these TDFs were similar to transcription factors like WRKY proteins and 14-3-3 proteins, while three TDFs represented the NBS-LRR-type gene sequences. Two TDFs had sequence identity to genes known to have function in defense. The RAPD TDF CaFRi60 showed sequence identity to gamma-glutamyl-cysteine synthetase. Among the TDFs examined by cDNA-AFLP, 19 were confirmed by Reverse Northern blot to be differentially expressed. The data confirms the effectiveness of the cDNA-AFLP technique in detecting differentially expressed genes during pathogenesis.
No preview · Article · Apr 2006 · Physiological and Molecular Plant Pathology