Showing papers on "Shoot published in 1995"

Phytoextraction: The Use of Plants To Remove Heavy Metals from Soils

Abstract: A small number of wild plants which grow on metal contaminated soil accumulate large amounts of heavy metals in their roots and shoots This property may be exploited for soil reclamation if an easily cultivated, high biomass crop plant able to accumulate heavy metals is identified Therefore, the ability of various crop plants to accumulate Pb in shoots and roots was compared While all crop Brassicas tested accumulated Pb, some cultivars of Brassica juncea (L) Czern showed a strong ability to accumulate Pb in roots and to transport Pb to the shoots (1083 mg Pb/g DW in the roots and 345 mg Pb/g DW in the shoots) B juncea was also able to concentrate Cr{sup -6}, Cd, Ni, Zn, and Cu in the shoots 58, 52, 31, 17, and 7 fold, respectively, from a substrate containing sulfates and phosphates as fertilizers The high metal accumulation by some cultivars of B juncea suggests that these plants may be used to clean up toxic metal-contaminated sites in a process termed phytoextraction

A developmental switch sufficient for flower initiation in diverse plants

Abstract: We have generated transgenic plants in which the flower-meristem-identity gene LEAFY of Arabidopsis is constitutively expressed. LEAFY is sufficient to determine floral fate in lateral shoot meristems of both Arabidopsis and the heterologous species aspen, with the consequence that flower development is induced precociously. Our results also suggest a new level of regulation during flower development, as indicated by the competence of the main shoot to respond to LEAFY activity.

A gene triggering flower formation in Arabidopsis

Abstract: In Arabidopsis, the apical shoot meristem produces lateral meristems that develop into either shoots or flowers. The decision to form flowers instead of shoots is mediated by the action of floral-meristem-identity genes, such as APETALA1 (AP1) and LEAFY (LFY), which specify meristem fate. Here we show that transgenic plants which constitutively express the AP1 gene show transformations of apical and lateral shoots into flowers, and that these plants flower much earlier than wild-type plants. These results indicate that AP1 alone can convert infloresence shoot meristems into floral meristems, and that ectopic AP1 expression can dramatically reduce the time to flowering.

Growth and shoot: Root ratio of seedlings in relation to nutrient availability

Abstract: The influence of mineral nutrient availability, light intensity and CO2 on growth and shoot:root ratio in young plants is reviewed. Special emphasis in this evaluation is given to data from laboratory experiments with small Betula pendula plants, in which the concept of steady-state nutrition has been applied.

Plant stems : physiology and functional morphology

Abstract: Part 1 Roles of stem architecture in plant performance: plant stems - biomechanical adaption for energy capture and influence on species distributions, T.J. Givnish opportunities and constraints in the placement of flowers and fruits, D.M. Waller and D.A. Steingraeber the biomechanical optimum in woody stems, C. Mattheck shrub stems - form and function, B.F. Wilson. Part 2 Roles of stems in transport and storage of water: limitations on stem water transport and their consequences, J.S. Sperry patterns of xylem variation within a tree and their hydraulic and mechanical consequences, B.L. Gartner stem water storage, N.M. Holbrook. Part 3 Roles of live stem cells in plant performance: role of stems in transport, storage and circulation of ions and metabolites by the whole plant, J.S. Pate and W.D. Jeschke the low profile directors of C- and N-economy in plants - the parenchyma cells associated with translocation channels, A.J.E. van Bel stem photosynthesis - extent, patterns and role in plant carbon economy, E.T. Nilsen microflora and microfauna on stems and trunks - diversity, foodwebs and effects on plants, E.R. Ingham and A.R. Moldenke developmental potential of shoot buds, J.P. Stafstrom respiratory gas exchange and cambial function in tree stems, T.W. Kimmerer and J. Stringer hormonal control of radial and longitudinal growth in the tree stem, C.H.A. Little and R.P. Pharis. Part 4 Roles of stems in preventing or reacting to responses to plant injury: stems and fires, A.M. Gill response of stem growth and function to air pollution, J.A. Weber and N.E. Grulke chemical antiherbivore defense, J.S. Bryant and K.F. Raffa stem defense against pathogens, L. Shain synthesis, T.M. Hinckley and P.S. Schulte.

Root to shoot ratio of crops as influenced by CO2

Abstract: Crops of tomorrow are likely to grow under higher levels of atmospheric CO2. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO2 concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO2 concentration will affect roots and shoots of crop plants proportionally. Since elevated CO2 can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO2 on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability. Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO2 and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO2 enrichment will add substantially to the global change response data base.

Salt tolerance of maize (Zea mays L.): the role of sodium exclusion

Abstract: The influence of NaCl and Na 2 SO 4 on growth of two maize cultivars (Zea mays cv. Pioneer 3906 and cv. Across 8023) differing in Na + uptake was investigated in two greenhouse experiments. Na + treatment with different accompanying anions (Cl - /SO 4 2- ) showed that ion toxicity was caused by Na + . While shoot growth of the two cultivars was markedly affected by salt in comparison to the control during the first 2-3 weeks, there were only slight differences between the cultivars. The shoot Ca 2+ concentration was reduced in both cultivars, and the youngest leaves contained an even lower concentration compared with the rest of the shoot. During this first phase, Across 8023 tended to have higher concentrations of Ca 2+ than Pioneer 3906. The Na + -excluding cultivar Pioneer 3906 showed continuous, although reduced, growth compared with the control, while the Na + concentration in the shoot decreased until flowering. Cultivar Across 8023 accumulated Na + until flowering: the reduction in the growth of stressed plants was greater than that for Pioneer 3906. Leaves of cultivar Across 8023 showed clear toxic symptoms, while those of the more salt-tolerant cultivar Pioneer 3906 did not. It is concluded that Na + exclusion contributes to the salt tolerance of maize.

Importance of seed Zn content for wheat growth on Zn-deficient soil. I: Vegetative growth

Abstract: Seed nutrient reserves may be important for an early establishment of crops on low-fertility soils. This glasshouse pot study evaluated effects of seed Zn content on vegetative growth of two wheat (Triticum aestivum L.) genotypes differing in Zn efficiency. Low-Zn (around 250 ng Zn per seed) and high-Zn seed (around 700 ng Zn per seed on average) of Excalibur (Zn efficient) and Gatcher (Zn inefficient) wheats were sown in a Zn-deficient siliceous sand fertilised with 0, 0.05, 0.2, 0.8 or 3.2 mg Zn kg -1 soil. After 3 weeks, plants derived from the high-Zn seed had better root and shoot growth; the cv. Excalibur accumulated more shoot dry matter than the cv. Gatcher. After 6 weeks, greater root and shoot growth of plants grown from the high-Zn seed compared to those from the low-Zn seed was obvious only at nil Zn fertilisation. A fertilisation rate of 0.2 mg Zn kg -1 soil was required for achieving 90% of the maximum yield for plants grown from the high-Zn seed compared to 0.8 mg Zn kg -1 soil for plants derived from the low-Zn seed. The critical Zn level in youngest expanded leaves for 90% maximum yield was 16 mg Zn kg -1 dry matter for both genotypes. Zn-efficient Excalibur had greater net Zn uptake rates compared to Zn-inefficient Gatcher after 3 weeks but they were not different at the 6-week harvest. Zinc-deficient plants had greater net uptake rates of Cu, Mn, B, P, and K but a reduced uptake rate of Fe. It is concluded that higher seed Zn content acted similar to a starter-fertiliser effect by improving vegetative growth and dissipating differences in Zn efficiency of wheat genotypes.

Short‐term effects of boron, germanium and high light intensity on membrane permeability in boron deficient leaves of sunflower

Abstract: The effects of varied boron (B) supply (0.01-50 μM) and light intensity (100-580 μmol m -1 s -1 ) on plant growth, leaf symptoms and membrane permeability of leaves were studied in sunflower plants over a 10-day-period of growth in nutrient solution. Membrane permeability was measured by incubating isolated young leaves in aerated distilled water. Additional experiments showed the effect of short-term supply (20 min to 2 h) of B and germanium (Ge) on membrane permeability of B-deficient leaves incubated in distilled water. Low supply of B decreased shoot and root growth and caused brown-purple pigmentation of young leaves, particularly under high light intensities. Leakage of K + from leaves increased with severity of B deficiency whereas, in B-sufficient leaves, leakage of solutes was low. Also leakage of phenolics, amino acids and sucrose was enhanced by B deficiency. Compared to B-sufficient leaves, the leakage from B-deficient leaves was 35-fold higher for K + , 45-fold higher for sucrose and 7-fold higher for phenolics and amino acids. Increases in solute leakage were marked in leaf areas with brown-purple pigmentation and particularly pronounced by increasing light intensity or by exposure of leaves to continuous light. In severely B-deficient leaves grown under high light intensity, treatment with B and Ge up to 1 000 μM for 20 min resulted in an immediate decrease in K + efflux to about the same levels as in B-sufficient leaves. Similar rapid decreases in K + efflux were also found in B-deficient leaves when exposed to darkness for 16 h or 30 h before the leakage measurement. The results demonstrate a particular role for B in maintaining the integrity of plasma membranes. Boron presumably stabilizes the structure of the plasma membrane by complexing membrane constituents. It also has a protective effect on membrane constituents by complexing phenolics, so that oxidation of phenolics to highly toxic quinones and oxygen free radicals is prevented or limited. In these functions, boron seems to be to a large extent replaceable by germanium.

Effect of High Temperature on Plant Growth and Carbohydrate Metabolism in Potato

Abstract: This study was undertaken to determine the role of sucrose-metabolizing enzymes in altered carbohydrate partitioning caused by heat stress. Potato (Solanum tuberosum L.) genotypes characterized as susceptible and tolerant to heat stress were grown at 19/17[deg]C, and a subset was transferred to 31/29[deg]C. Data were obtained for plant growth and photosynthesis. Enzyme activity was determined for sucrose-6-phosphate synthase (SPS) in mature leaves and for sucrose synthase, ADP-glucose pyrophosphorylase, and UDP-glucose pyrophosphorylase in developing tubers of plants. High temperatures reduced growth of tubers more than of shoots. Photosynthetic rates were unaffected or increased slightly at the higher temperature. Heat stress increased accumulation of foliar sucrose and decreased starch accumulation in mature leaves but did not affect glucose. SPS activity increased significantly in mature leaves of plants subjected to high temperature. Changes in SPS activity were probably not due to altered enzyme kinetics. The activity of sucrose synthase and ADP-glucose pyrophosphorylase was reduced in tubers, albeit less quickly than leaf SPS activity. There was no interaction of temperature and genotype with regard to the enzymes examined; therefore, observed differences do not account for differences between genotypes in heat susceptibility.

Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

Abstract: In two pot-culture experiments with maize in a silty loam (P2 soil) contaminated by atmospheric deposition from a metal smelter, root colonization with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were investigated. Soil was γ-irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatment, whereas in experiment 2 the irradiated soil was inoculated with spores of a fungal culture from P2 soil or a laboratory reference culture, Glomus mosseae. Light intensity was considerably higher in experiment 2 and resulted in a fourfold higher shoot and tenfold higher root biomass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in the mycorrhizal plants than in the nonmycorrhizal plants, suggesting a protection against metal toxicity. In contrast, in experiment 2, biomass did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concentration was significantly increased with the indigenous P2 fungal culture. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treatments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not altered between treatments. Cu and Zn, but not Pb and Cd root-shoot translocation increased with mycorrhizal colonization. The results show that the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be generalized. It is suggested that metal-tolerant mycorrhizal inoculants might be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimized conditions of normal agricultural practice, however, AM colonization even may increase plant metal absorption from polluted soils.

Shoot and Root Development in Rice Related to the Phyllochron

Abstract: In grasses, construction of a growing plant is determined primarily by the rate of leaf development in the shoot apex and the timing of tillering and rooting of individual phytomers relative to leaf development. Our purpose is to review shoot and root growth in relation to emergence of leaves in rice (Oryza sativa L.). Development of the leaf, tiller bud, and adventitious roots of each phytomer proceeds in order, at a rate that depends on leaf initiation rate at the shoot apex. Consequently, initiation, leaf emergence, tillering, and rooting of each tiller are closely synchronized with leaf emergence on the main stem. Leaves that emerge simultaneously are similar in size. Tillers whose leaf emergence is retarded from this synchronization will generally die before anthesis. Inflorescence development is closely correlated with development of the subtending leaves in each tiller, resulting in a higly predictable phenology in relation to leaf emergence. Because of these relationships, the leaf number concept provides researchers with an effective index for studying development of shoot and root systems in rice, including the prediction of tiller morphology, the estimation of potential tiller increase, and analysis of root system dynamics

Effect of seasonal water availability on phenology and the annual shoot carbohydrate cycle of tropical forest shrubs

Abstract: Summary 1. The effect of seasonal water availability on phenology and shoot total non-structural carbohydrate (TNC) of three Psychotria species was investigated by irrigating two large plots of mature tropical forest in Panama during the dry season for five consecutive years. This study reports results for the fifth and final year of irrigation. 2. Irrigation did not affect total production of leaves, inflorescences or infructescenes but did advance the timing of leaf production in all Psychotria, and advanced the timing of inflorescence production in l? furcata and P. marginata and infructescence production in P. furcata. Irrigation also reduced shoot TNC levels. 3. Shoot TNC levels in all three species of Psychotria showed similar depressions at the end of the dry season and maximum levels near the end of the wet season. Depletion of shoot TNC occurred just before or during peak leaf production but did not coincide with production of inflorescences or infructescences. Therefore, we hypothesize that shoot TNC supported part of the cost of new leaf production but production of inflorescences and infructescences was most likely supported by current photosynthate. 4. Tropical plants generally show less seasonal variation in TNC than plants from more variable climates but stored carbon still plays an important role in the growth of Psychotria, although its direct role in reproduction appears limited.

Root hair length determines beneficial effect of a Glomus species on shoot growth of some pasture species

Abstract: SUMMARY Differences between plant species in the benefit derived from arbuscular mycorrhizal colonization have often been attributed to differences in physical properties of their roots, especially in root hair development. To test this hypothesis, the growth response to phosphate of five pasture species which differed markedly in the length of their root hairs was measured. Plants in the mycorrhizal treatments were inoculated with a Glomus sp. (isolate WUM 10(1)) while non-mycorrhizal plants received control inoculum. Benefit was described as the relative effectiveness of phosphorus (P) for the mycorrhizal plants compared with non-mycorrhizal plants. The beneficial effect of Glomus sp. was inversely related to root hair length of the host plant but it was not well related to root diameter, root length per plant or root/shoot ratio. It is suggested that root hairs and external hyphae of Glomus sp. act as alternative, similar ways of shortening the distance for the diffusion of phosphate in soils.

Regeneration of transgenic plants from the commercial apple cultivar Royal Gala

Abstract: A transformation system was developed for the commercial apple (Malus X domestica Borkh.) cultivar Royal Gala. Leaf pieces from in vitro-grown shoots were cocultivated for 2 days with Agrobacterium tumefaciens strain LBA4404 containing the binary vectors pKIWI105 or pKIWI110. Shoots were produced on a shooting medium containing kanamycin (50 mg·L(-1)). A 2-day incubation period on kanamycin-free medium prior to antibiotic selection enhanced the regeneration of kanamycin-resistant shoots. The majority of the kanamycin-resistant shoots also expressed GUS (β-glucuronidase) activity. The putatively transformed shoots were rooted on a medium containing kanamycin (50 mg·L(-1)). Rooted plants were established in a greenhouse, and plants transformed with pKIWI110, which contains a mutant Arabidopsis acetolactate synthase gene, were shown to be resistant to the herbicide Glean(™). Integration of T-DNA into the apple genome was confirmed by PCR and Southern hybridization analyses.

Mechanisms underlying the suppression of forb seedling emergence by grass (Poa pratensis) litter

Abstract: We investigated the mechanism by which grass litter (dead Poa pratensis L. shoots) suppressed the emergence of seedlings of four old-field forbs (Centaurea nigra L., Dipsacus sylvestris Huds., Hypericum perfioratum L., Verbascum thapsus L.) by determining the effect of litter on their seed germination and shoot extension. When seeds were placed beneath litter (715 g m -2 ) that had been collected from an old-field, the germination of all species except Verbascum was reduced significantly by 26% to 41% compared to a no-litter control. When seeds were placed in plastic dishes containing a leachate solution made from litter (7 g dish -1 ), the germination of two species (i.e. Centaurea and Dipsacus) was reduced significantly by 10% to 34% compared to the distilled water control. When germinated seeds were placed beneath litter, the emergence of seedlings of all species was reduced significantly by 95% to 100% compared to a no-litter control. These results indicate that grass litter may suppress forb seedling emergence by reducing seed germination and (or) by preventing shoot extension and that these effects are species dependent.

Wheat genotypes differ in Zn efficiency when grown in chelate-buffered nutrient solution

Abstract: Ten Triticum aestivum and two Triticum turgidum conv. durum genotypes were grown in chelate-buffered nutrient solution at Zn supplies ranging from deficient to sufficient (free Zn activities from 2 to 200 pM, pZn from 11.7 to 9.7). The critical level of Zn ion activity in solution for healthy growth of wheat plants was around 40 pM. Genotypes differed in the growth response: those classified as Zn-efficient suffered less reduction of shoot growth and did not change the rate of root growth at a Zn supply quite deficient for Zn-inefficient genotypes. Root growth of Zn-inefficient genotypes increased at deficient Zn supply. The shoot/root ratio was the most sensitive parameter of Zn efficiency; Zn-efficient genotypes showed less reduction in the ratio when grown at deficient compared to sufficient Zn supply. Classification of wheat genotypes into Zn-efficient and Zn-inefficient groups after screening in chelate-buffered nutrient solution corresponded well with classification obtained in field experiments on Zn-deficient soil.

Nitrogen incorporation and remobilization in different shoot components of field-grown winter oilseed rape ( Brassica napus L.) as affected by rate of nitrogen application and irrigation

Abstract: The seasonal course of nitrogen uptake, incorporation and remobilization in different shoot components of winter oilseed rape (Brassica napus L.) was studied under field conditions including three rates of 15N labelled nitrogen application (0, 100 or 200 kg N ha-1) and two irrigation treatments (rainfed or watered at a deficit of 20 mm). The total amount of irrigation water applied was 260 mm, split over 13 occasions in a 7-week-period ranging from 1 week before onset of flowering until 4 weeks after flowering. Nitrogen application and irrigation increased plant growth and nitrogen accumulation. Irrespective of N and irrigation treatment more than 50% of total shoot N was present in the stem when flowering started. At the end of flowering, pod walls were the main N store containing about 30–40% of shoot N. The quantities of N remobilized from stems and pod walls amounted in all treatments to about 70% of the N present in these organs at mid-flowering. At harvest, stem and pod walls each contained about 10% of total shoot N, the remaining 80% being incorporated into seeds. The main component contributing to the response of seed N accumulation to nitrogen application and irrigation was pods in axillary racemes. Up to 20 kg N ha-1, corresponding to about 10% of final shoot N content, was lost from the plants by leaf drop. Irrigation increased the recovery at harvest of applied N from 30% to about 50%, while the level of N application did not affect the N recovery. 15N labelled (fertilizer derived) nitrogen constituted a greater proportion of the N content in old leaves than in young leaves and increased with age in the former, but not in the latter. Relative to soil N, fertilizer derived N also contributed more to the N content of vegetative than to that of reproductive shoot components. Small net changes in shoot N content after flowering reflected a balance between N import and export, leading to continuous dilution of 15N labelled N with unlabelled N.

Effect of apex excision and replacement by 1-naphthylacetic acid on cytokinin concentration and apical dominance in pea plants

Abstract: As known from literature lateral buds from pea (Pisum sativum) plants are released from apical dominance when repeatedly treated with exogenous cytokinins. Little is known, however, about the endogenous role of cytokinins in this process and whether they interact with basipolar transported IAA, generally regarded as the main signal controlling apical dominance. This paper presents evidence that such an interaction exists. The excision of the apex of pea plants resulted in the release of inhibited lateral buds from apical dominance (AD). This could be entirely prevented by applying 1-naphthylacetic acid (NAA) to the cut end of the shoot. Removal of the apex also resulted in a rapid and rather large increase in the endogenous concentrations of zeatin riboside (ZR), isopentenyladenosine (iAdo) and an as yet unidentified polar zeatin derivative in the node and internode below the point of decapitation. This accumulation of ZR and iAdo, was strongly reduced by the application of NAA. The observed increase in cytokinin concentration preceded the elongation of the lateral buds, suggesting that endogenous cytokinins play a significant role in the release of lateral buds from AD. However, the effect of NAA on the concentration of cytokinins clearly demonstrated the dominant role of the polar basipetally transported auxin in AD. The results suggest a mutual interaction between the basipolar IAA transport system and cytokinins obviously produced in the roots and transported via the xylem into the stem of the pea plants.

Plant Competition and Herbivory in Relation to Vegetation Biomass

Abstract: We tested whether effects of competition and herbivory on plant growth depend on the aboveground biomass of vegetation. Our objective was to test theoretical predictions about the site-dependence of biotic mechanisms of plant population regulation. Biomass ranged from a mean of 64 to 776 g/m2 at the eight study sites, which included six old fields and two herbaceous plant communities near water. To measure effects of competition, 4-5 wk old plants of a perennial grass (Poa compressa) were transplanted into plots where neighboring plants were either left intact or removed and after 4 mo the shoot mass of transplants was compared in the two treatments. Transplants were caged in both treatments to exclude herbivores. Removing neighbors increased transplant shoot mass significantly at all sites, indicating that transplants experienced less competition for re- sources when their neighbors were removed. Regression analysis indicated that the increase in shoot mass due to neighbor removal was significantly greater at sites with higher biomass. This result supports theories that predict competition should increase with increasing bio- mass. To measure effects of herbivory, the growth of caged and uncaged plants was com- pared. Caging transplants did not increase their shoot mass significantly at the two sites with the lowest biomass. However, shoot mass was significantly greater for caged transplants than for uncaged transplants at all other sites. Caged transplants lost less tissue to herbivores such as small mammals and molluscs. Regression analysis indicated that the increase in shoot mass due to caging was significantly greater at sites with higher biomass. The com- bined effect of herbivory and competition was measured by comparing transplant growth in plots where transplants were caged and neighbors were removed with the growth of transplants in plots where transplants were not caged and neighbors were left intact. Trans- plant shoot mass was significantly greater where herbivores were excluded and neighbors were removed, especially at sites with high biomass. Our results indicate that competition and herbivory each have a greater effect on plant growth at sites with higher biomass and that herbivory has less effect than competition on plant growth at sites with relatively low biomass.

Natural Herbicide Potential of Alfalfa Residue on Selected Weed Species

Abstract: Alfalfa (Medicago sativa L.) contains water-soluble substances that are toxic to itself (autotoxicity) and to other species (allelopathy). Experiments were conducted to determine the potential of using alfalfa residue as a natural herbicide for inhibition of weed seed germination, seedling growth, and development. Various weed species were germinated in aqueous extracts from dried alfalfa using cold (5°C), warm (24°C), and hot (80°C) treatments. Results indicated that inhibition of weed seed germination was dependent on the aqueous extraction method, residue application rate (w/v or w/w), and weed species. The greatest inhibition of germination was 44%, when 60% (w/v) warm aqueous extract was applied to lambsquarters (Chenopodium album L.). Seedling growth was also inhibited by residue application at various rates. Root length was more inhibited than increase in shoot length. In terms of total seedling length, giant foxtail (Setaria faberii Herrm.) was the most resistant species and lambsquarters was the most susceptible among the weed species studied to alfalfa aqueous extracts. Weed seed germination percentage decreased as incubation time increased from 8, 16, 24, and 48 h. An alfalfa aqueous extract incubated for 48 h caused the greatest inhibition of velvetleaf (Abutilon theophrasti Medic.) seed germination (25%). When alfalfa residue was incorporated with silica sand, the growth and development of lambsquarters, pigweed (Amaranthus retroflexus L.), velvetleaf, and crabgrass [Digitaria sanguinalis (L.) Scop.], as measured by plant height, leaf area, and total, shoot, leaf, and root dry weight, were significantly inhibited as the rate increased from 0.0 to 2.0 g kg -1 . Dried alfalfa residue significantly stimulated plant height, leaf area, and total dry weight including shoot, leaf, and root of giant foxtail and cheatgrass (Bromus secalinus L.). Results suggest that alfalfa residue has a contrasting effect on weed growth and development due to water-soluble allelochemicals present in the residue.

Root-shoot interaction in the greening of wheat seedlings grown under red light

Abstract: Wheat seedlings grown with roots exposed to constant red light (300-500 micromoles m-2 s-1) did not accumulate chlorophyll in the leaves. In contrast, seedlings grown with their roots shielded from light accumulated chlorophylls. Chlorophyll biosynthesis could be induced in red-light-grown chlorophyll-deficient yellow plants by either reducing the red-light intensity at the root surface to 100 micromoles m-1 s-1 or supplementing with 6% blue light. The inhibition of chlorophyll biosynthesis was due to impairment of the Mg-chelatase enzyme working at the origin of the Mg-tetrapyrrole pathway. The root-perceived photomorphogenic inhibition of shoot greening demonstrates root-shoot interaction in the greening process.

Effects of a vesicular-arbuscular mycorrhizal fungus and other soil microorganisms on growth, mineral nutrient acquisition and root exudation of soil-grown maize plants

Abstract: Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-μm nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shoot∶root ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.

Hormonal control of radial and longitudinal growth in the tree stem

Abstract: Publisher Summary This chapter reviews the evidence implicating the currently recognized hormone classes in the regulation of radial and longitudinal growth in the stem and shoots of woody species. Emphasis is placed on investigations that used temperate-zone tree species as the experimental material, and modern physicochemical or immunoassay techniques to identify and measure endogenous hormone levels. Understanding the roles of hormones, and the mechanisms regulating their absolute and relative levels, not only would significantly increase our basic knowledge about how trees grow and develop, but could also have practical applications, for example, in the development of methods for early screening of inherently fast growth in breeding programs, and for using genetic engineering to alter traits such as wood quantity, and quality and tree form. Auxins, gibberellins, cytokinins, and abscisic acid have been conclusively identified, typically, by combined gas chromatography–mass spectrometry either in whole shoots or more specifically in buds, leaves, stem, cambial region, or xylem sap. The significance of hormones in the regulation of cambial and longitudinal growth in woody shoots is still unknown, although at least some of them most likely play key roles. The use of genotypes with different growth capacity and crown form is increasing and should help in defining the role of each hormone. It seems likey that IAA and GAs are essential for the division of cambial cells and the differentiation of their derivatives; that CKs are necessary for bud expansion; with GAs and optimal levels of IAA being required for rapid shoot elongation.

Carbon allocation and partitioning in aspen clones varying in sensitivity to tropospheric ozone.

Abstract: Clones of aspen (Populus tremuloides Michx.) were identified that differ in biomass production in response to O(3) exposure. (14)Carbon tracer studies were used to determine if the differences in biomass response were linked to shifts in carbon allocation and carbon partitioning patterns. Rooted cuttings from three aspen Clones (216, O(3) tolerant; 271, intermediate; and 259, O(3) sensitive) were exposed to either charcoal-filtered air (CF) or an episodic, two-times-ambient O(3) profile (2x) in open-top chambers. Either recently mature or mature leaves were exposed to a 30-min (14)C pulse and returned to the treatment chambers for a 48-h chase period before harvest. Allocation of (14)C to different plant parts, partitioning of (14)C into various chemical fractions, and the concentration of various chemical fractions in plant tissue were determined. The percent of (14)C retained in recently mature source leaves was not affected by O(3) treatment, but that retained in mature source leaves was greater in O(3)-treated plants than in CF-treated plants. Carbon allocation from source leaves was affected by leaf position, season, clone and O(3) exposure. Recently mature source leaves of CF-treated plants translocated about equal percentages of (14)C acropetally to growing shoots and basipetally to stem and roots early in the season. When shoot growth ceased (August 16), most (14)C from all source leaves was translocated basipetally to stem and roots. At no time did mature source leaves allocate more than 6% of (14)C translocated within the plant to the shoot above. Ozone effects were most apparent late in the season. Ozone decreased the percent (14)C translocated from mature source leaves to roots and increased the percent (14)C translocated to the lower stem. In contrast, allocation from recently mature leaves to roots increased. Partitioning of (14)C among chemical fractions was affected by O(3) more in source leaves than in sink tissue. In source leaves, more (14)C was incorporated into the sugar, organic acid and lipids + pigments fractions, and less (14)C was incorporated into starch and protein fractions in O(3)-treated plants than in CF-treated plants. In addition, there were O(3) treatment interactions between leaf position and clones for (14)C incorporation into different chemical fractions. When photosynthetic data were used to convert percent (14)C transported to the total amount of carbon transported on a mass basis, it was found that carbon transport was controlled more by photosynthesis in the source leaves than proportional changes in allocation to the sinks. Ozone decreased the total amount of carbon translocated to all sink tissue in the O(3)-sensitive Clone 259 because of decreases in photosynthesis in both recently mature and mature source leaves. In contrast, O(3) had no effect on carbon transport from recently mature leaves to lower shoots of either Clone 216 or 271, had no significant effect on transport to roots of Clone 216, and increased transport to roots of Clone 271. The O(3)-induced increase in transport to roots of Clone 271 was the result of a compensatory increase in upper leaf photosynthesis and a relatively greater shift in the percent of carbon allocated to roots. In contrast to those of Clone 271, recently mature leaves of Clone 216 maintained similar photosynthetic rates and allocation patterns in both the CF and O(3) treatments. We conclude that Clone 271 was more tolerant to O(3) exposure than Clone 216 or 259. Tolerance to chronic O(3) exposure was directly related to maintenance of high photosynthetic rates in recently mature leaves and retention of lower leaves.

The effect of nitrogen and growth regulators on stem and root characteristics associated with lodging in two cultivars of winter wheat

Abstract: The effects of nitrogen and plant growth regulators (stem shorteners) on root and shoot characteristics associated with lodging resistance were investigated in two winter wheat (Triticum aestivum L.) cultivars of contrasting lodging resistance: the susceptible Galahad and the resistant Hereward. The morphology and mechanical strength of the stems and anchorage systems grown at two levels of nitrogen and with or without growth regulators were measured and related to the incidence of lodging recorded in a field trial. In both cultivars high levels of nitrogen increased the height of the stem, thereby increasing the 'self-weight' moment transmitted into the ground and weakened both the stems and the anchorage coronal roots. As a result, the anchorage strength was also reduced, plants failing in the root system in simulated lodging tests. Growth regulators, in contrast, had little effect on the bending strength of the shoots and root systems, but reduced plant height so that the overturning moments generated by the weight of the shoot were less. There were also differences between cultivars: Galahad plants had weaker anchorage due to the smaller number and lower strength of the coronal roots. The morphological and mechanical measures were used to calculate a safety factor against both stem and root lodging. Five factors were found to influence the safety factors, these were: cultivar type, the type of lodging, the rate of nitrogen and growth regulator application, and time, being lowest in Galahad plants at high levels of nitrogen and without growth regulators and at grain filling when the ears were heaviest. This was consistent with the observed pattern of lodging: root lodging occurred at grain filling and only in Galahad which had been treated with high nitrogen rates, most strongly in plants without growth regulators.

Increased 1-Aminocyclopropane-1-Carboxylic Acid Oxidase Activity in Shoots of Flooded Tomato Plants Raises Ethylene Production to Physiologically Active Levels.

Abstract: Soil flooding increased 1-aminocyclopropane-1-carboxylic (ACC) acid oxidase activity in petioles of wild-type tomato (Lycopersicon esculentum L.) plants within 6 to 12 h in association with faster rates of ethylene production. Petioles of flooded plants transformed with an antisense construct to one isoform of an ACC oxidase gene (ACO1) produced less ethylene and had lower ACC oxidase activity than those of the wild type. Flooding promoted epinastic curvature but did so less strongly in plants transformed with the antisense construct than in the wild type. Exogenous ethylene, supplied to well-drained plants, also promoted epinastic curvature, but transformed and wild-type plants responded similarly. Flooding increased the specific delivery (flux) of ACC to the shoots (picomoles per second per square meter of leaf) in xylem sap flowing from the roots. The amounts were similar in both transformed and wild-type plants. These observations demonstrate that changes in ACC oxidase activity in shoot tissue resulting from either soil flooding or introducing ACC oxidase antisense constructs can influence rates of ethylene production to a physiologically significant extent. They also implicate systemic root to shoot signals in regulating the activity of ACC oxidase in the shoot.