ALLELOPATHIC MECHANISMS OF VELVETLEAF (ABUTILON THEOPHRASTI MEDIC., MALVACEAE) ON SOYBEAN

Sampling in a soybean field established that presence of velvetleaf (A. theophrasti) weeds interfered with soybean production. Number of soybean pods and number of pods/stem were significantly lower in transect segments adjacent to velvetleaf plants. In bioassays for phytotoxicity of velvetleaf, several dilutions of aqueous extracts from fresh field-collected leaves depressed germination of radish seeds and inhibited growth of soybean seedlings. Seed germination bioassays from eluates of chromatograms developed in one dimension showed that two of three bands containing phenolic compounds were inhibitory to radish seed germination. Soybeans inhibited by aqueous velvetleaf extracts had increased diffusive resistance, suggesting partial stomatal closure. Inhibited plants also gave evidence of water stress, with leaf water potentials often as low as –20 bars and reduced water content, when compared with controls. Quantification of chlorophyll on a leaf area basis showed that chlorophyll of inhibited plants was below controls. These data demonstrate the allelopathic potential of velvetleaf and suggest that interference with water balance and chlorophyll content may be two mechanisms of inhibitory action of toxins present in the leaves of velvetleaf.     

THE ECOLOGICAL IMPACT OF ALLELOPATHY IN AILANTHUS ALTISSIMA (SIMAROUBACEAE)

Compounds inhibitory to the growth of neighboring plant species were found in significant concentrations in the leaves and stems of young Ailanthus altissima ramets. The surrounding soil also contained appreciable concentrations of similarly acting toxins. Individuals of neighboring plant species have either incorporated active portions of inhibitory compounds or responded to Ailanthus by producing growth-inhibiting substances. Under greenhouse conditions, individuals of neighboring plant species previously unexposed to Ailanthus in the field were found to be more susceptible to the Ailanthus toxins than individuals previously exposed. Moreover, seeds produced by unexposed populations were also more susceptible to Ailanthus toxins than seeds produced by previously exposed populations. These differences demonstrated that the allelochemicals of Ailanthus altissima exhibited a measurable impact upon neighboring plant species. Since the progeny of these populations displayed a differential response to Ailanthus toxin, this phenotypic difference between the two populations may have a heritable basis.     

PHYTOTOXIC EXUDATES FROM VELVETLEAF (ABUTILON THEOPHRASTI) GLANDULAR TRICHOMES

Nonvolatile exudates from velvetleaf glandular trichomes inhibited root and shoot growth of several weed and crop species in petri plate bioassays, but had no effect on seed germination per se. The exudate was efficiently collected by wiping both the stems and petioles with cotton swabs or by leaching with water, but was absent on the leaves of velvetleaf plants. Cress (Lepidium sativum L.) was the most sensitive indicator species. Four types of trichomes appeared on the stem surface as revealed by scanning electron microscopy. Water soluble globules on the apices of 12- to 15-celled glandular trichomes recurred and demonstrated their original potency within eight days after removal with cotton swabs. Both the quantity and phytotoxicity of the exudates from velvetleaf plants cultured under varying environmental conditions were determined. While total exudate production was not affected at 16, 24, or 36 C, the exudates from plants cultured at 24 and 36 C were about twice as toxic as the exudate collected from plants grown at the lower temperature. Water stress decreased the amount of exudate collected, but the phytotoxic activity was increased by approximately the same factor.     

Impact of soil stockpiling on ericoid mycorrhizal colonization and growth of velvetleaf blueberry (Vaccinium myrtilloides) and Labrador tea (Ledum groenlandicum)

Soil stockpiling is a common practice prior to the reclamation of surface mines. In this study, velvetleaf blueberry and Labrador tea plants were grown from seed in fresh soil, stockpiled soil (1 year), and autoclaved stockpiled soil (1 year) obtained from the Canadian boreal forest. After 7 months of growth, the root colonization intensity with ericoid mycorrhizal (ERM) fungi in both plants growing in stockpiled soil was lower compared to plants growing in the fresh soil. The diversity of ERM fungal species in roots also decreased due to soil stockpiling and Pezoloma ericae was absent from the plants growing in stockpiled soil. Changes in the ERM root colonization in plants growing in stockpiled soil were accompanied by decreases in root and shoot dry weights. Leaf chlorophyll, nitrogen, and phosphorus concentrations of velvetleaf blueberry were higher in fresh soil compared to 1‐year stockpiled soil. Plants grown in the autoclaved stockpiled soil became colonized by the thermotolerant ERM fungus Leohumicola verrucosa and showed higher root and shoot biomass compared to the nonautoclaved stockpiled soil. The results point to the importance of ERM fungi for growth of ericaceous plants, even under favorable environmental conditions and adequate fertilization, and suggest that reduced ERM colonization intensity and ERM fungal diversity in roots likely contributed to the negative effects of soil stockpiling on growth of velvetleaf blueberry and Labrador tea.     

INDETERMINATE GROWTH OF LEAVES IN GUAREA (MELIACEAE): A TWIG ANALOGUE

Leaves of seed plants are generally characterized as organs of determinate growth. In this regard, Guarea and related genera seem unusual in that the pinnately compound leaves of these plants contain a bud at their tip from which new pinnae expand from time to time. Previous studies (based upon superficial examinations of leaf-tip buds) have produced contradictory conclusions regarding how long the leaf apex remains meristematic and produces new pinna primordia. In order to determine whether leaf development in Guarea is truly indeterminate, we microscopically examined leaf-tip buds of G. guidonia and G. glabra. In both species, the leaf apex remains meristematic and continues to produce new pinna primordia as the leaf ages. Unexpanded leaves of G. guidonia contained an average of 23 pinna primordia, while the oldest leaves we examined had initiated an average of 44 total pinnae. In G. glabra, unexpanded leaves contained 8 pinnae, whereas an average of 28 pinnae had been initiated on the oldest leaves. These results indicate that leaf development in Guarea is truly indeterminate. Periodic examination of individual intact leaves indicated that the leaves commonly continue their growth for 2 or more years (observed maximum = 51 months). As new leaflets are initiated at the shoot apex (and subsequently expand in rhythmic flushes), older (basal) leaflets may abscise. In addition, the petiole and rachis of the leaf thicken and become woody as a result of the activity of a vascular cambium. Guarea leaves therefore seem to function as the analogue of a typical twig (stem) in general habit as well as in their indeterminate apical growth and secondary thickening.     

Nitrate reduction and nitrate content in ash trees (Fraxinus excelsior L.): distribution between compartments,site comparison and seasonal variation

Summary Nitrate reductase activity (NRA), nitrate content and biomass components of leaflets, leaf stalks, old stem, current-year stem and roots of ash trees (Fraxinus excelsior L.) growing in their natural habitats were investigated. In addition, NRA, total nitrogen and nitrate concentration were analyzed in the leaves and roots of ash trees from four different field sites. The highest NRA per gram biomass and also per total compartment biomass was found in the leaflets, even though root biomass was much higher than total leaflet biomass. The highest nitrate concentrations were found in the leaf stalks. Correlations between nitrate availability in the soil and NRA in leaves were not significant due to high variability of the actual soil nitrate concentrations. The seasonal variation in foliar NRA, nitrate concentration and total nitrogen concentration is much smaller in F. excelsior than reported for herbaceous species and is mainly caused by changes in the actual soil nitrate availability and by senescence of the leaves.     

REPRODUCTIVE STRATEGY OF CLEISTES DIVARICATA (ORCHID ACEAE)

In Cleistes divaricata, a hinged anther dispenses a sequence of loosely aggregated pollen tetrad masses onto the dorsal thorax of Bombus and Megachile workers. This mechanism allows more than one bee to receive pollen from a single flower. To determine the effectiveness of this strategy, plants in bud were caged and hand pollinated using pollen from sequential releases. Capsules produced from a flower's first three pollen dumps were significantly larger and heavier and contained more seeds than those produced by later pollen deposits with fewer tetrads. Decreasing pollen dosage did not affect fruit set, capsule development, individual seed weight, or percentage of healthy looking embryos per fruit. Fruit set for artificial pollinations was 93% for pollen dumps 1–3 and 97% for dumps 4–18. As set of naturally pollinated marked plants was only 38%, low frequency of pollinator visits apparently limited seed production. Efficacy of infrequent visits is maximized, however, because a flower's first pollen releases contain the most pollen, but later low-dosage dumps can produce some seeds. An unexpected cost was a higher investment of pericarp per seed in low-dosage capsules (130 ng pericarp seed^-1 fresh weight) than in high-dosage pollinations (only 27 ng pericarp seed^–1). Flower fading in plants receiving low pollen dosage was as slow as that in caged, unpollinated controls, thus increasing opportunity for additional pollination.     

Differential Rhizosphere Establishment and Cyanide Production by Alginate-Formulated Weed-Deleterious Rhizobacteria

The effects of Pseudomonas putida ATH2-1RI/9 and Acidovorax delafieldii ATH2-2RS/1 on rhizosphere colonization, cyanide production, and growth of velvetleaf and corn was examined. When formulated in alginate beads and inoculated onto velvetleaf and corn plants (10⁹ CFU/plant), only P. putida ATH2-1RI/9 consistently reduced velvetleaf growth. Neither isolate inhibited corn growth. Interestingly the levels of P. putida ATH2-1RI/9 in the velvetleaf rhizosphere were 1000-fold higher (7 × 10⁷ CFU/g root) than the A. delafieldii ATH2-2RS/1 populations. Cyanide (53–68 mM/g root) was recovered from the P. putida ATH2-1RI/9-inoculated velvetleaf plants. In contrast both A. delafieldii ATH2-2RS/1 and P. putida ATH2-1RI/9 colonized the corn rhizosphere to the same extent (1–5 × 10⁷ CFU/g root), producing 1 mM and 14 mM/g root respectively. These results suggest that bacterial formulation methods can influence the effectiveness of deleterious rhizobacteria in reducing weed growth.     

Climatic and anthropogenic factors affect Ailanthus altissima invasion in a Mediterranean region

Ailanthus altissima is an aggressive invasive tree worldwide, but the ecological factors that lead to the spread of this species in Mediterranean ecosystems are still unclear. Here we aim to identify such factors, focusing on the interaction of human activity with climatic conditions. We determined the occurrence and abundance of Ailanthus in 240 sites and studied their relationship with 20 variables representing climatic, geographic, and topographic factors, as well as land use, in the region of Campania (southern Italy). Overall, we found that temperature and rainfall in Campania are suitable for Ailanthus, with the only major constraint being the temperature at an altitude exceeding 900 m a.s.l.. We found that Ailanthus is unable to spread where the mean annual temperature is lower than 11.1 °C. By contrast, precipitation variables showed poor correlation with Ailanthus distribution, suggesting that rainfall in the selected study sites is suitable to sustain the growth of this tree. About land use variables, roads were the primary landscape feature along which this species spread and invaded new areas. Roads probably combine high propagule pressure and favorable growing conditions in terms of available resources i.e., light, water, and mineral nutrients, that allow Ailanthus to establish and spread along roadside edges in different ecosystems. In conclusion, we found that climate and human-associated variables are correlated with the current occurrence of Ailanthus, with the temperature being more influential at high elevation sites and road distance playing a prominent role in low elevation areas.

     

ON THE MECHANISMS OF LIGHT-INDUCED GERMINATION INHIBITION OF PHACELIA TANACETIFOLLV

Germination of seed of Phacelia tanacetifolia is inhibited by several mechanisms. In addition to physical restraints imposed by the seed coats, the seed contains a water-soluble inhibitor which is independent of light or temperature for its activity. Available evidence also points to the presence of 1 or more light-activated inhibitors which are not easily leached from the seed. The blue-light-activated inhibition can be negated by high oxygen tensions or mechanical abrasion of the micropylar end of the seed. The suppression of germination by far-red or red light can be negated by abrasion but is only partially reversed by oxygen. Combinations of abrasion and high oxygen tensions negate both light-induced and temperature-induced inhibitions of germination.     

SEED GERMINATION OF AMERICAN POKEWEED (PHYTOLACCA AMERICANA). I. LABORATORY TECHNIQUES AND AUTOTOXICITY

Seeds of pokeweed (Phytolacca americana L.), an underinvestigated species, were studied to determine optimal conditions for laboratory germination. Soaking seeds in acid solutions prior to sowing increased rates of germination. Concentrated (conc) H₂SO₄ was more effective than conc NO₃ or conc HCl acids. Physiological evidence from seed germination studies suggests that autotoxicity, or intraspecific inhibition, exists in pokeweed, a species known to possess several biologically active compounds. Seed germination was investigated in the laboratory with aqueous extracts of vegetative and reproductive structures of the plant. The presence of extracts from most plant parts correlated with reduced or no germination by seeds of its own species, whereas the presence of distilled water correlated with high percentages of germination by control seeds. Whether diluted with water by 5-fold (20% v/v) or undiluted, juice of pokeweed fruits completely inhibited the laboratory germination of pokeweed seeds. Also, extracts of freshly harvested mature leaves, stems, and immature fruits inhibited seed germination. However, results with root extracts, obtained from a single individual, depended more on concentration, since the highest concentration (50% v/v) inhibited germination, and lower concentrations (10 and 20% v/v) increased germination percentages over control samples. Results with extracts of juvenile leaves correlated with neither inhibition nor promotion of germination. Thus, except for juvenile leaves and the root, most extracts of the pokeweed plant inhibited seed germination with more mature structures exerting more inhibition and less mature structures exerting less or no inhibition. The ecological implication of autotoxicity is that seeds are more dispersed through time and space. In regard to seed germination by other species, especially those taxa known to possess biologically active compounds, these and other results suggest that the phenomenon of autotoxicity might be more widespread than previously suspected.     

树兰原球茎内生细菌群落多样性及功能分析

【目的】通过分析树兰原球茎内生细菌群落组成、多样性特征和促生功能,探究树兰种子萌发相关的核心细菌类群及生物学功能。【方法】以树兰原球茎(树兰种子在树皮基质上共生萌发、在树叶基质上共生萌发、在MS1培养基上非共生萌发)和共生萌发基质(松树皮、腐熟树叶)共5个样本为研究材料,采用高通量测序技术分析不同萌发条件下原球茎内生细菌的16S rRNA基因多样性,比较分析细菌群落多样性和物种组成特征,通过传统的内生细菌分离方法获得共生萌发原球茎内生细菌菌株,并进行促生潜力评价。【结果】从5个研究样本中共获得2 735个可操作分类单元(operational taxonomic unit, OTU),属于41门453科876属,其中变形菌门(Proteobacteria)和放线菌门(Actinobacteria)为优势门。主坐标分析(principal coordinates analysis, PCoA)结果表明,树兰原球茎与萌发基质细菌群落结构存在差异,非共生萌发原球茎与在树皮基质上共生萌发原球茎内生细菌群落结构最为接近。功能预测表明,在树叶基质上共生萌发的原球茎内生细菌固氮功能显著高于其他萌发条件。通过分离培养,共获得内生细菌19株,分属12属16种,其中鞭毛膨胀芽孢杆菌(Tumebacillus flagellatus)、Bradyrhizobium cenepequi和人参腐殖土魏茨曼氏菌(Weizmannia ginsengihumi)为共生萌发原球茎共有种;韩国假单胞菌(Pseudomonaskoreensis)和 W. ginsengihumi兼具有溶磷、产吲哚乙酸(indole-3-acetic acid, IAA)和铁载体的潜在能力。【结论】在不同环境中萌发的树兰原球茎均有丰富的内生细菌群落定殖;从共生萌发原球茎中分离的内生细菌具有固氮、溶磷、产IAA和铁载体等促生功能。本研究为兰科植物种子萌发相关微生物资源挖掘及兰科植物与微生物互作研究提供科学依据。     

A mechanism for promoting the germination of Zinnia elegans seeds by hydrogen peroxide

H(2)O(2) promotes seed germination of cereal plants such as barley, wheat and rice, and several mechanisms have been proposed for its action [Naredo et al. (1998) Seed Sci. Technol. 26: 675-689]. We investigated the role of H(2)O(2) in the germination of Zinnia elegans seeds. H(2)O(2) promoted seed germination in a dose-dependent manner as did respiratory inhibitors, indicating that H(2)O(2) itself possibly promotes seed germination rather than O(2). Seed germination was promoted by removal of pericarp from seeds or by removal of ethanol-soluble compounds from the seeds with pericarp. The ethanol-soluble compounds suppressed the germination of seeds having no pericarp, and this effect was reversed by H(2)O(2). These findings indicate that oxidation of the germination inhibitor(s) present in the pericarp by H(2)O(2) promotes seed germination. Antioxidants which are derivatives of well-known germination inhibitors suppressed seed germination in a dose-dependent manner, suggesting that, to initiate seed germination, a germination inhibitor(s) should be decomposed by an oxidant such as H(2)O(2).     

Inheritance of qualitative and quantitative trypsin inhibitor variants in Pisum

A trypsin inhibitor locus (Tri) has been mapped close to Vc-2 on Pisum (pea) linkage group 5 using recombinant inbred lines derived from crosses of genotypes showing qualitative variation in seed trypsin inhibitors. F₂ seed populations derived from crosses between lines showing qualitative variation in trypsin inhibitors as well as quantitative variation in inhibitor activity showed an association between the segregation of the structural variation and relative activity levels. Clones complementary to Pisum trypsin inhibitor mRNA were used in hybridization analyses which showed that the segregation of protein polymorphisms reflected directly the segregation of polymorphisms associated with the structural genes.     

LEAF DEVELOPMENT AND CROWN GEOMETRY OF TWO IRIARTEOID PALMS

We examined changes in pinnately compound leaf morphology and crown geometry that occur during height growth of the iriarteoid palms Socratea exorrhiza and Iriartea deltoidea in tropical wet forest of Costa Rica. Although light availability increased with height, the number of leaves per plant was relatively constant. Total leaf area, however, was much larger in taller individuals. Increases in linear dimensions of leaves (length and width) was responsible for less than half of this greater surface area. More important was the transition from a basically dorsiventral display of leaflets in small individuals to a more radial display in taller plants. Production of leaflets in more than one plane resulted in leaves whose surface area was more than twice the horizontally projected area and whose lateral light interception was greatly enhanced. S. exorrhiza, a faster-growing and more light-demanding species, undergoes this transformation in leaf morphology at heights between 3 and 6 m; whereas in the slower-growing and more shade-tolerant I. deltoidea this occurs at heights between 10 and 20 m. Pinnate leaves, with dense radial packing of leaflets along the rachis, are functionally comparable to branches of dicotyledonous trees and may have been important for the evolution of arborescence in palms.     

Biocontrol of Ailanthus altissima: inoculation protocol and risk assessment for Verticillium nonalfalfae (Plectosphaerellaceae: Phyllachorales)

Verticillium nonalfalfae has been proposed as a biocontrol for invasive Ailanthus altissima (tree-of-heaven) in Ohio, Pennsylvania and Virginia. However, previous studies evaluating this potential biocontrol utilised a conidial suspension with a short shelf life as inoculum. Anticipating future expanded use of V. nonalfalfae, we evaluated other inoculum formulations, inoculation protocols and sensitivity of non-target (non-Ailanthus) plant species within Pennsylvania. The most effective inoculum formulation, with an extended shelf life, was prepared by mixing water with stored, refrigerated soil containing V. nonalfalfae. Less successful, but positive infections were obtained by simply using infected Ailanthus wood and leaves as inoculum. Monthly inoculation of Ailanthus trees demonstrated that the optimal time for successful inoculations was April to May, but limited infections were achieved during all months, including the winter. The health of Ailanthus and non-target species was evaluated within a decade-old natural Verticillium wilt epicentre, where all mature Ailanthus trees had been killed by V. nonalfalfae. Verticillium wilt was observed on a few small Ailanthus trees, likely newly established seedlings, whereas non-target species were asymptomatic. Our findings reveal that soil formulated and natural inocula are effective biocontrols against Ailanthus, and V. nonalfalfae appears to pose little threat to non-target plants.     

Kaempferol glycosides and enzymes of flavonol biosynthesis in leaves of a soybean strain with low photosynthetic rates

Soybean (Glycine max L.) strains which accumulate kaempferol 3-(2^G-glucosylgentiobioside) in their leaves fix CO₂ at rates significantly lower than those lacking this compound (Buttery, Buzzell 1976 Crop Sci 16: 547-550), and kaempferol aglycone is a well known inhibitor of photosynthesis in vitro. However, since neither kaempferol nor any of its glycosides could be detected in mesophyll cells isolated from mature soybean leaves we suspect that kaempferol 3-(2^G-glucosylgentiobioside) has no direct inhibitory effect on photosynthesis. The most rapid stage of flavonoid accumulation, and the highest level of activity for several enzymes of phenolic biosynthesis, occurs in leaflets 2.5 to 3 centimeters long. Mesophyll cells isolated from these leaflets contain about 70% of the whole leaf activity for shikimate dehydrogenase, 24% of the 4-coumarate:CoA ligase activity, 35% of the activity for chalcone-flavanone isomerase, but no demonstrable activity for phenylalanine ammonialyase. Our results suggest a highly tissue-specific pattern of secondary phenolic metabolism in soybean leaves.     

EFFECT OF CARBON DIOXIDE ENRICHMENT ON DEVELOPMENT OF THE FIRST SIX MAINSTEM LEAVES IN SOYBEAN

Many conclusions concerning plant responses to CO₂ enrichment have been based on assumptions of increased leaf size derived from observations of average leaf area measured at some time well into the growth period. The objectives of this study were to study the effect of elevated CO₂ on 1) the timing of mainstem leaflet appearance, 2) the rate and duration of leaflet expansion, and 3) the final area of individual leaflets of soybeans (Glycine max [L.] Merr. cv. Bragg) grown from seed at 348, 502, and 645 μl 1^–1 CO₂ concentrations. Central leaflet areas from mainstem trifoliolates 1–6 were measured every two days from time of appearance to full expansion. Leaflets tended to appear earlier in elevated CO₂ treatments; leaflets 2 through 6 appeared an average of 0.4 days earlier in the 502 μl 1^–1 treatment and 1.2 days earlier in the 645 μl 1^–1 treatment than in the 349 μl 1^–1 treatment. Relative rates of expansion were different among leaflets in their response to elevated CO₂; expansion rates of leaflets 1 and 4 were significantly higher at the highest CO₂ concentration. However, final area of leaflets was not affected by CO₂, or (in leaflet 5 only) was slightly smaller at the highest CO₂ treatment. Apparently, higher expansion rates of leaflets 1 and 4 at high CO₂ were offset by a tendency for decreased duration of expansion. It appears that there are morphological constraints on final leaflet area in soybean seedlings which limit the effects of elevated CO₂ on the early development of mainstem leaf area.     

Significato dei Tegumenti in Cariossidi di Triticum Durum Desf. Trattate Con Raggi X

Abstract

Significance of integuments in caryopses of « Triticum durum » Desf. treated with X-rays. Experiments were carried out on Triticum durum « Cappelli », to test the influence of seed coats on the damage by X-rays. The damage was evaluated in terms of germination, seedling growth and chromosomal aberrations. Seeds in which the embryo was covered (with pericarp and spermoderm), uncovered (without pericarp) and bared (without pericarp and spermoderm), were irradiated at the total exposure of 1000, 2000 and 4000 R of X-rays. The growth of seedlings coming from covered and uncovered embryos, X-rayed at 1000 R, results better than that of bared embryos. The chromosomal aberrations analysis carried out in root meristem cells at anaphase, during the first mitotic cycle, show the highest damage in seedlings coming from uncovered and bared embryos and the type of aberrations was almost chromatidic (B'). We therefore forward the hypothesis that the removal of the integuments (pericarp and spermoderm) could possibly accelerate the process of germination, and could also produce in the embryo a greater sensitivity to X-rays.     

刺楸种子中性与酸性抑制物质的研究

本文研究了刺楸种子抑制物质的提取,分离和鉴定方法,并测定了抑制物质的相对活性及其含量。结果表明,刺揪种子中除含高水平的酸性抑制物外,还存在一种中性抑制物。该中性抑制物同酸性抑制物相似,有较强的生物活性,不但可以抑制白菜种子的萌发与胚根生长,而且对已解除休眠的刺楸种子也有显著作用。利用纸层析,薄层层析,颜色反应和高效液相色谱等手段,证明中性抑制物质为香豆素类物质;酸性抑制物质的主要成分为脱落酸。种子各部位均含这两种抑制物质,但含量有所不同,随种子贮藏时间的延长,抑制物会发生转移。本文还讨论了用不同溶剂提取中性抑制物的效果。