γ-Aminobutyric Acid Metabolism in Detached Leaves of Wheat Seedling and Leaves and Cotyledons of Sunflower

With a prerequisite of 5 hours in the light the detached leaves of wheat seedling and detached leaves and cotyledons of sunflower were able to utilize exogenous γ-aminobutyric acid, the amount of alanine and glutamine formed were increased. It was found that deamination of γ-aminobutyric acid was associated with γ-aminobutyric-pyruvate transaminase in the leaves of wheat seedling. The specific activity of this transaminase was enhanced about 5.6 fold by adsorption with calcium phosphate gel-Some properties of this transaminas were as follows: the optimum pH was 8.9. The produced amount of alanine was linear with time up to a period of one hour. The primary rate of reaction was proportional to enzyme concentration in the first hour. The relation of substrate concentration to the primary rate of alanine formation was determinated and Michaelis constant was evaluated about 2.6 × 10-3 M. The action of this transaminase in metabolism of γ-aminobutyrie acid was discussed.     

Chilling-Induced Photoinhibition in Two Oak Species: Are Evergreen Leaves Inherently Better Protected Than Deciduous Leaves?

We compared the sensitivity to cold stress, in terms of photosynthetic capacity and changes in chlorophyll fluorescence of photosystem 2 (PS2), of an evergreen and a deciduous oak species, which co-occur in the southeastern United States. We predicted that the evergreen species, Quercus virginiana, which must endure winter, is likely to have an inherently greater capacity for energy dissipation and to be less susceptible to chilling stress than the deciduous species, Quercus michauxii. Short-term cold stress in both species lead to greater than 50 % reduction in maximum photosynthetic rates, 60-70 % reduction in electron transport, and irreversible quenching of PS2 fluorescence. The kinetics of recovery in the dark after exposure to 1 h high irradiance (1000 µmol m^-2 s^-1) and chilling (5 °C) showed that the evergreen Q. virginiana exhibited more protective q_E and less irreversible quenching (q_I) than the deciduous Q. michauxii. The large q_E which we observed in Q. virginiana suggests that the capacity for photoprotection at low temperatures is not induced by a long-term acclimation to cold but preexists in evergreen leaves. This capacity may contribute to the ability of this species to maintain leaves during the winter.     

Chilling-Induced Photoinhibition in Two Oak Species: Are Evergreen Leaves Inherently Better Protected Than Deciduous Leaves?

We compared the sensitivity to cold stress, in terms of photosynthetic capacity and changes in chlorophyll fluorescence of photosystem 2 (PS2), of an evergreen and a deciduous oak species, which co-occur in the southeastern United States. We predicted that the evergreen species, Quercus virginiana, which must endure winter, is likely to have an inherently greater capacity for energy dissipation and to be less susceptible to chilling stress than the deciduous species, Quercus michauxii. Short-term cold stress in both species lead to greater than 50 % reduction in maximum photosynthetic rates, 60-70 % reduction in electron transport, and irreversible quenching of PS2 fluorescence. The kinetics of recovery in the dark after exposure to 1 h high irradiance (1000 μmol m^-2 s^-1) and chilling (5 °C) showed that the evergreen Q. virginiana exhibited more protective q_E and less irreversible quenching (q_I) than the deciduous Q. michauxii. The large q_E which we observed in Q. virginiana suggests that the capacity for photoprotection at low temperatures is not induced by a long-term acclimation to cold but preexists in evergreen leaves. This capacity may contribute to the ability of this species to maintain leaves during the winter. This revised version was published online in June 2006 with corrections to the Cover Date.     

Size Control in Plants—Lessons from Leaves and Flowers

To achieve optimal functionality, plant organs like leaves and petals have to grow to a certain size. Beginning with a limited number of undifferentiated cells, the final size of an organ is attained by a complex interplay of cell proliferation and subsequent cell expansion. Regulatory mechanisms that integrate intrinsic growth signals and environmental cues are required to enable optimal leaf and flower development. This review focuses on plant-specific principles of growth reaching from the cellular to the organ level. The currently known genetic pathways underlying these principles are summarized and network connections are highlighted. Putative non–cell autonomously acting mechanisms that might coordinate plant-cell growth are discussed.Over millions of years, plant leaves and flowers evolved into an enormous range of shapes and sizes. Likely reflecting adaptations to changing environmental conditions, even closely related species often differ dramatically in their organ sizes (Mizukami 2001). Although interspecies diversity is remarkably high, species-specific leaf and petal characteristics are often highly uniform between individuals grown under constant conditions. This suggests that tight genetic control is used to integrate intrinsic growth signals and environmental cues to enable organ growth to a defined size. This review summarizes the current knowledge of the regulatory networks of plant size control at the cellular and at the organ level. We will focus on the regulation of determinate growth of lateral plant organs, such as simple leaves and petals.     

Orotidine-5′-Phosphate Decarboxylase and Pyrophosphorylase of Bean Leaves

This report includes results demonstrating the existence of orotidine-5'-phosphate decarboxylase and orotidine-5'-phosphate pyrophosphorylase in plant leaves. The decarboxylase enzyme, purified 8 fold from leaves of etiolated pinto beans (Phaseolus vulgaris L.), had a pH optimum of 6.3. It was strongly inhibited by 6-azauridine-5'-phosphate; a concentration of 12 mum decreased the reaction rate 60%. The enzyme was not dependent upon magnesium ions or inhibited by p-chloromercuribenzoate. It was present in other parts of the bean plant and was found in young leaves of tomato (Lycopersicon esculentum Mill.) and Canada thistle (Cirsium arvense L.)The enzyme orotidine-5'-phosphate pyrophosphorylase, which catalyzes the formation of orotidine-5'-phosphate from orotic acid and 5-phosphoribosyl-1-pyrophosphate, was found in the etiolated bean leaves, and was also present in the leaves of tomato and Canada thistle. It was stimulated by manganous or magnesium ions and had a pH optimum of 7.2. The K(m) value obtained by varying the concentrations of 5-phosphoribosyl-1-pyrophosphate was 75 mum, and when orotic acid was varied the resulting K(m) was 3.5 mum.The presence of these 2 enzymes in higher plants, combined with previous results with inhibitors and labeled metabolites, indicates that the normal pathway of pyrimidine nucleotide synthesis in higher plants proceeds through orotic acid and OMP.     

Cotton Leaf Curl Virus： Ionic Status of Leaves and Symptom Development

In the present study, the relationship between the nutritional status of leaves and the development of symptoms of cotton leaf curl virus （CLCuV） in two cotton （Gossypium hirsutum L.） cuItlvars （I.e. CIM-240 and S-12） was Investigated. The incidence of disease attack was found to be 100% In the S-12 cuItlvar and 16% in the CIM-240 cuItivar. Geminivirus particles in infected leaves were confirmed by transmission electron microscope examination of highly specific geminivirus coat protein antlsera-treated cell sap. The CLCuV Impaired the accumulation of different nutrients in both cuItivars. A marked decrease in the accumulation of Ca^2＋ and K^＋ was observed in infected leaves. However, the disease had no effect on leaf concentrations of Na^＋, N, and P. It was observed that the curling of leaf margins in CLCuV-Infected plants was associated with the leaf Ca^2＋ content; leaf curling was severe in plants with a significant reduction In Ca^2＋ content. Moreover, leaf K＆＋ content was found to be associated with resistance/susceptibility to CLCuV infection.     

Studies on Some Properties of the Apoplastic β-N-Acetyl-D-Hexosaminidase from Tomato Leaves

Some properties of the β-N-acetyl-D-hexosaminidase purified from intercellular fluid of tomato leaves after the plant was systematically infected by TMV (tobacco mosaic virus) were studied. When pNP β-D-GlcNAc (p nitrophenyl-N-aeetyl β-D-glucosaminide) or pNP β-D- GalNAc (p-nitrophenyl-N-acetyl-β-D galactosaminide) was used as the substrate, it showed the optical pH between 4. 8--5.0 and optical temperature between 44— 47℃. Studies of thermostabillty indicated that the enzyme had a biphasic denaturation curve. Using pNP-β-D-GIcNAc or pNP-β-D GalNAc as the substrate, the Km value of the enzyme was 0. 36 and 0. 67 mmol/L respectively. N acetyi-D glucosamine and N acetyl-D-galactosamine were competitive inhibitors of the enzyme activities. Ag+ and Hg2+ were sensitive inhibitors and Fe2+ . Fe3+ and Cu2+ were also inhibitors enzyme activities.     

Subcellular Localization and Properties of L-Galactono-γ-lactone Dehydrogenase in Spinach Leaves

L-Galactono-γ-lactone dehydrogenase, which catalyzes the final step of the biosynthesis of L-ascorbate, is bound to spinach mitochondrial membrane, as confirmed by linear sucrose density gradient centrifugation. The solubilized enzyme was very labile, but stabilized in the presence of L-galactono-γ-lactone under anaerobic conditions. The enzyme reduced cytochrome c and phenazine methosulfate in the presence of L-galactono-γ-lactone, but not when L-gulono-γ-lactone was used as an electron donor. The K_ms of the enzyme for L-galactono-γ-lactone and cytochrome c were 192 μM and 180 μM, respectively.     

Carbon Monoxide： A Novel Antioxidant Against Oxidative Stress in Wheat Seedling Leaves

Carbon monoxide （CO）, an endogenous signaling molecule in animals, also provides potent cytoprotective effects including attenuation of lung lipid peroxidation induced by oxidant in the mouse. Our recent work demonstrated that 0.01 μmol/L hematin （a CO donor） treatment of wheat plants alleviated salt-induced oxidative damage in seedling leaves. In this report, we further discovered that hematin pretreatment （≤ 0.1 μmol/L） could delay wheat leaf chlorophyll loss mediated by further treatment of H202 and paraquat, two reactive oxygen species （ROS） sources, in dose-and even time-dependent manners. Also, compared with the control samples, seedling leaves pretreated with 0.01 or 0.1 μmol/L hematin for 24 h exhibited lower levels of H2O2 and lipid peroxidation, as well as higher contents of chlorophyll and activities of antioxidant enzymes. Such beneficial effects exerted by hematin were mimicked by the pretreatment of antioxidant butylated hydroxytoluene （BHT）, and differentially reversed when CO scavenger hemoglobin （Hb）, or CO specific synthetic inhibitor ZnPPIX was added, respectively. Taken together, the results presented In this paper directly illustrate for the first time that CO is able to strongly protect plants from oxidative damage caused by the overproduction of ROS, and strengthens the evidence that CO is a potent antioxidant in various abiotic and biotic stresses, as similar results have been shown in animal tissues.     

Do Invertebrate Activity and Current Velocity Affect Fungal Assemblage Structure in Leaves?

In this study we assessed the effect of current velocity and shredder presence, manipulated in artificial channels, on the structure of the fungal assemblage colonizing alder (Alnus glutinosa (L.) Gaertner ) leaves incubated in coarse and fine mesh bags. Fungal sporulation rates, cumulative conidial production and number of species of aquatic hyphomycetes were higher in leaves exposed to high rather than to low current velocity. The opposite was observed regarding Simpson's index (D) on the fungal assemblage. Some species of aquatic hyphomycetes were consistently stimulated in high current channels. No effect of shredders or of mesh type was observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Environmental Conditions on the α-Glucosidase Inhibitory Activity of Mulberry Leaves

Mulberry leaves have been used as the sole food for silkworms in sericulture, and also as a traditional medicine for diabetes prevention. Mulberry leaf components, for example 1-deoxynojirimycin (1-DNJ), inhibit the activity of α-glucosidase and prevent increased blood glucose levels, and they are highly toxic to caterpillars other than silkworms. The α-glucosidase inhibitory activity of mulberry leaves changes with the season, but it is unknown which environmental conditions influence the α-glucosidase inhibitory activity. We investigated in this study the relationship between the α-glucosidase inhibitory activity and environmental conditions of temperature and photoperiod. The results demonstrate that low temperatures induced decreasing α-glucosidase inhibitory activity, while the induction of newly grown shoots by the scission of branches induced increasing α-glucosidase inhibitory activity. These results suggest that the α-glucosidase inhibitory activity was related to the defense mechanism of mulberry plants against insect herbivores.     

Diurnal Changes in Metabolite Levels and Crassulacean Acid Metabolism in Kalanchoë daigremontiana Leaves

Diurnal changes in levels of selected metabolites associated with glycolysis, the C₃ cycle, C₄-organic acids, and storage carbohydrates were analyzed in active Kalanchoë daigremontiana Crassulacean acid metabolism leaves. Three metabolic transition periods occurred each day. During the first two hours of light, nearly all of the metabolite pools underwent transient changes. Beginning at daylight, stomata opened transiently and closed again within 30 minutes; malate synthesis continued for about 1 hour into the light; C₃ photosynthesis began within 30 minutes; and net quantities of starch and glucan began to accumulate after 2 hours, continuing linearly throughout the rest of the day.     

Cytotoxic and α-Glucosidase Inhibitory Xanthones from Garcinia mckeaniana Leaves and Molecular Docking Study

A new racemic xanthone, garmckeanin A ( 1 ), and eight known analogs 2 – 9 were isolated from the ethyl acetate (AcOEt) extract of the Vietnamese Garcinia mckeaniana leaves. Their structures were determined by MS and NMR spectral analyses and compared with the literature. The AcOEt extract showed good cytotoxicity against cancer cell lines KB, Lu, Hep-G2 and MCF7, with IC₅₀ values of 5.40–8.76 μg/mL, and it also possessed α-glucosidase inhibitory activity, with an IC₅₀ value of 9.17 μg/mL. Garmckeanin A ( 1 ) exhibited inhibition of all cancer cell lines, with an IC₅₀ value of 7.3–0.9 μM. Allanxanthone C ( 5 ) successfully controlled KB growth, with an IC₅₀ value of 0.54 μM, higher than that of the positive control, ellipticine (IC₅₀ 1.22 μM). Norathyriol ( 8 ) was a promising α-glucosidase inhibitor, with an IC₅₀ value of 0.07 μM, much higher than that of the positive control, acarbose (IC₅₀ 161.0 μM). The interactions of the potential α-glucosidase inhibitors with the C- and N-terminal domains of human intestinal α-glucosidase were also investigated by molecular docking study. The results indicated that bannaxanthone D ( 2 ), garcinone E ( 4 ), bannaxanthone E ( 6 ), and norathyriol ( 8 ) exhibit higher binding affinity to the C-terminal than to the N-terminal domain through essential residues in the active sites. In particular, compound 8 could be assumed to be the most potent mixed inhibitor.     

Purification of an Apoplastic β-N-Acetyl-D-Hexosaminidase from Tomato Leaves Infected with Tobacco Mosaic Virus

Systematic infection of tomato (Lycopersicon esculenturn) leaves by tobacco mosaic virus (TMV) increased the levels of β-N-acetyl-D-hexosaminidase activity. The enzyme was purified from intercellular fluid by --20℃ acetone precipitation, CM-Sephadex C-25 ion exchange chromatography, Polybuffer Exchanger 94 chromatofocusing and Sephadex G-150 gel filtration column to homogeneity. The molecular weight obtained by SDS-PAGE and Sephadex G-150 gel filtration was 75 kD and 145 kD respectively. The enzyme hydrolysed p-nitrophenyl-N-acetyl-β-glucosaminide and p-nitrophenyl-N-acetyl-β-galaetosaminide, it was a glycoprotein. Most of the enzyme activity in the TMV-infected tomato leaves was found in the intercellular spaces.     

Anatomy,Histochemistry and Phytochemistry of Leaves inAloe vera var. chinensis

A multidisciplinary approach—anatomy, histochemistry and phytochemistry—was used to investigate the leaf structure, the content and the storage location of barbaloin in the leaves of Aloe vera L. var. chinensis (Haw.) Berg. Xeromorphic characteristics including secondary thickened epidermal cell walls, thicker cuticle, ambiguous differentiation of spongy and palisade tissues in the chlorenchyma, and well-developed aquiferous tissue could be seen in the leaves. Several large parenchymatous cells were observed at the phloem pole of the first ring of vascular bundles. The secondary ring of vascular bundles in the leaf base and the stomata, which are surrounded by five cells, have some classification significance in this species. The density of vascular bundles, the content of barbaloin and the intensity of histochemical reaction differed among leaf numbers L1 (annual leaf), L2 (biennial leaf), L3 (triennial leaf) and L4 (quadrennial leaf), and in different parts of the leaf. These three factors were highest in the youngest leaf, L1, and top parts of all the leaves and lowest in the basal parts and the oldest leaf, L4. The density of vascular bundles had a positive correlation to the content of barbaloin. The histochemical results revealed that the small sheath cells that surrounded the bundles might be the location of barbaloin synthesis and the large parenchymatous cells beneath the sheath might be the storage places of this metabolite.     

Nitrate Assimilation and Crassulacean Acid Metabolism in Leaves of Kalanchoë fedtschenkoi Variety Marginata

The enzymes necessary to assimilate ammonia either via glutamine synthetase and glutamate synthase or via the glutamate dehydrogenase pathways are present in both green and white leaf tissues of Kalanchoë fedtschenkoi. Nitrate reductase activity develops to a maximum in a Crassulacean acid metabolism (CAM) plant canopy before either ribulose 1,5-bisphosphate carboxylase, or phosphoenolpyruvate carboxylase, or CAM. Nitrate reductase also is activated each morning and is inactivated late in the day as in other plants. However, there does not appear to be any direct relationship between nitrate reductase activity and the level of acid, its daily pattern or the amplitude of CAM. Though nitrate reductase is activated maximally each day by light, in Kalanchoë leaves for six days the activity followed a precise daily pattern independent of continuous light or dark.     

Effect of β-Aminobutyrie Acid on Anthocyanin of Leaves of Arabidopsis thaliana (Cruciferae)

To analyze the effect of β aminobutyrie acid (BABA) on anthocyanin of leaves of Arabidopsis, 30 old plants were sprayed with BABA while the control were sprayed with water. After treated with BABA, the content of anthocyanin was significantly lower than that of control. Furthermore, the results from RT PCR showed that CHS, LDOX, UF3GT were down regulated compared with contro1, while PAL showed an opposite trend. At the same time, the activity of PPO, which played an important role in the degradation of anthocyanin, showed higher level than control. In addition, the antioxidant capacity, the death rate of cells and electrical conductivity of leaves were also decreased with BABA treatment. All results suggested that BABA might inhibit the accumulation of anthocyanin in leaves of Arabidopsis in vitro.     

Apoplastic β-1, 3-Glucanases in Leaves of Tomato Systematically Infected by TMV

Apoplastic β-1, 3-glucanase was purified from leaves of tomato (Lycopersicon esculentum Mill. ) which were systematically infected by TMV (tobacco mosaic virus). The enzyme obtained through -20℃ acetone precipitation, CM-Sephadex C-25 ion exchange chromatography, DEAE-Sephadex A-25 ion exchange chromatography and Sephadex G-75 gel filtration, showed homogeneity in PAGE, and SDS-PAGE which had two isoenzymes of 27 kD and 36 kD. The enzyme hydrolysed laminarin at an optimum pH of 4.8--5.2 and was stable between pH 4--8 and at an optimum temperature between 30--40℃, and stable at 40℃ after 1 hour of incubation, It had a Km of 9. 2 mg/mL. SDS-PAGE profiles of the proteins in the tomato leaf intercellular fluid had the bands of 22 kD, 27 kD and 36 kD that were β-1, 3-glucanases.     

Does Apoplastic Sucrose Induce the Ability for Sucrose Loading in Developing Leaves of Sugarbeet?

Dark-grown sugarbeet (Beta vulgaris L.) leaves were used toinvestigate a possible role of apoplastic sucrose in the inductionand development of the putative phloem-located sucrose carrierin relation to minor vein loading and export capacity. Unlabeledsucrose was introduced to the leaf apoplast after which veinaccumulation of [¹⁴C]sucrose was determined by autoradiogra-phy.Western blotting was used to detect the putative carrier. Anaffinity purified antibody against the sucrose binding proteinof soybean did not cross-react with the protein in a plasmalemma-enrichedfraction from sugarbeet leaves. Challenging the apoplast ofleaf discs with buffer plus sucrose for 6 h (induction) resultedin decreased [¹⁴C]sucrose uptake. When induction treatmentswere conducted with detached intact leaves in the dark, sucroseand glucose, but not buffer alone enhanced [¹⁴C]sucrose uptake.Detached leaves induced under laboratory light conditions for24 h showed enhanced [¹⁴C]sucrose uptake even in the absenceof any sugar introduced to the apoplast (buffer only). The datasuggested that in the etiolated tissue, sucrose was not a directand specific inducer of its putative carrier; instead sugarsmay have provided the energy for vein loading. Furthermore,the data suggested a role for light in the development of theputative sucrose carrier and vein accumulation of sucrose intransitional leaves of sugarbeet. The role of light may alsobe related to tissue energy level. ¹Contribution No. D-15192-1-91 from the New Jersey AgriculturalExperiment Station. This work was funded in part by the BeetSugar Development Foundation and Rutgers University ResearchCouncil and was submitted as partial fulfillment for M.S. degreeby Lynne H. Pitcher. (Received February 19, 1991; Accepted May 13, 1991)