Investigating and modeling the combined effects of pH and osmotic pressure on seed germination for use in phytoactivity and allelopathic research

Phytoactivity and allelopathic studies are heavily dependent on germination bioassays of water solutions of allelochemical(s), which necessarily imply that pH and osmotic pressure vary among treatments and between treatments and controls and are therefore a confounding factor in the assessment of seed germination responses to allelochemical(s). When the contribution of pH and osmotic pressure to seed germination responses is considered in experimental designs their effects are almost without exceptions examined separately being assumed, without any evidences, that pH and osmotic pressure act independently on seed germination responses. The objectives of this work were to examine experimentally such assumption using wheat, lettuce, and subterranean clover cultivars to evaluate and model the combined effects on germination of pH and osmotic pressure in the range between 3.0–6.0 and 0–100 mOsmol kg^?1, respectively. Empirical equations are fitted, discussed, and the need to consider the simultaneous effects of pH and osmotic pressure firmly established. Finally, the use of the equations fitted and its impact on conclusions is exemplified in a dose-response bioassay of water extracts of Cistus ladanifer on seed germination using subterranean clover as target species where hormesis was found before allelochemical effects were corrected for pH and osmotic pressure values of control and extracts.     

Leaf and root extracts of the invasive shrub, Lonicera maackii, inhibit seed germination of three herbs with no autotoxic effects

In addition to effects mediated by resource competition, some invasive plants may impact surrounding vegetation by secreting compounds that are directly inhibitory to growth. Lonicera maackii, an invasive Asian shrub of forests and open areas in eastern and midwestern North America, has devastating effects on understory vegetation, some of which persist even after this shrub is removed. In this study, we explored the potential of aqueous extracts of the leaves and roots of this plant to inhibit seed germination of Impatiens capensis, Alliaria petiolata, Arabidopsis thaliana, and L. maackii in Petri dish bioassays. Both L. maackii root and leaf extracts significantly decreased germination in the three herb species. This inhibitory effect generally increased with increasing extract concentration and was more pronounced with application of leaf extract than root extract. However, when the same extracts were applied to seeds of L. maackii itself, germination was delayed in some cases, but was not significantly reduced by the end of the experiment. Germination of L. maackii seeds even reached significantly higher levels in some extract treatments than in no-extract controls. This implies that L. maackii can successfully inhibit the germination of other plants with few autotoxic effects and may even promote the germination of its own seeds.     

Antibacterial properties of extracts from selected planktonic freshwater cyanobacteria – a comparative study of bacterial bioassays

Aqueous and methanol extracts from five selected cyanobacteria were examined for antibacterial properties in six different bacterial bioassays. All five cyanobacteria revealed antibacterial properties. Methanol extracts made from Tychonema bourrellyi, Aphanizomenon flos-aquae and Cylindrospermopsis raciborskii showed the most pronounced inhibitory effects. Aqueous extracts made from Microcystis aeruginosa and T. bourrellyi possessed evident antibacterial properties. The bacterial bioassays were based on agar diffusion tests and included pour-plate methods commonly used to detect residues of antibacterial substances in food. In addition, a pour-plate bioassay with Aeromonas hydrophila was developed and described. Antibacterial effects were observed in five of the six bacterial bioassays. No antibacterial effect was observed in the Micrococcus luteus bioassay. Bioassays based on Aer. hydrophila, Bacillus cereus and B. subtilis grown in Antibiotic Medium 8, pH 5·85, seemed to be sensitive and suitable. The MIC value of diluted MeOH extracts made from C. raciborskii and T. bourrellyi against Aer. hydrophila corresponded to 38 mg freeze-dried cyanobacteria. Bacillus subtilis was more sensitive when grown in a culture medium with pH 5·85 than 7·9. The antibacterial properties of extracts from the cyanobacteria examined differed from defined cyanotoxins and antibacterial substances. The pattern of inhibition in the bacterial bioassays indicated that various antibacterial substances are involved.     

小桐子枝叶提取物对植物病原真菌的生物活性

采用菌丝生长抑制法,测定了小桐子枝叶6种不同溶剂提取物对小麦赤霉病菌、稻瘟病菌、烟草疫霉菌和辣椒疫霉菌的抑制作用,从中筛选出抑制作用最强的粗提物进行进一步的活性组分分离和抑菌活性测定。结果表明小桐子枝叶的乙醇提取物对4种植物病原菌抑制活性最高,在浓度为0.8 g·L^-1时,小桐子枝叶的乙醇提取物对小麦赤霉病菌、稻瘟病菌、烟草疫霉菌、辣椒疫霉菌菌丝生长抑制率分别为：87.1%、90.3%、86.4%、77.9%,其抗菌活性与农药世高均无显著差异;在小桐子枝叶乙醇提取物的不同溶剂萃取物对稻瘟病菌和烟草疫霉病菌进行生物活性追踪测试中发现,石油醚和水萃取物都具有较好的活性,当浓度为0.8 g·L^-1时,石油醚和水萃取物对两种病菌抑制率都达50%以上。表明小桐子枝叶含有丰富的抗植物病原真菌活性物质,且主要存在于小桐子枝叶乙醇提取物的石油醚相和水相中。     

Seaweed extract stimuli in plant science and agriculture

Both micro- and macroalgae have long been used to augment plant productivity and food production in various regions of the world through their beneficial effects when applied to soils. Interactions of algae with the soil community undoubtedly are complex and benefits are dependent on the crop and the local environmental conditions. This has resulted in much speculation as to mechanisms involved as well as the validity of the results reported. It is now 60 years since the first commercial seaweed extract was manufactured for agricultural use. These aqueous extracts allowed for the first time the direct application of soluble seaweed constituents to specific plant organs such as leaves and roots. The earlier concept that benefits of seaweeds and their extracts were due mainly to their manurial value or to their micronutrient suites is no longer tenable. Seaweeds likewise have been used for millennia as fodder supplements to improve animal nutrition and productivity. Recent research is focusing on their mode of action, specific health benefits, and the mechanisms of action in animals. Improved analytical techniques and instrumentation coupled with the use of molecular genetic tools are establishing that seaweed extracts can modify plant and animal responses at a fundamental level. It therefore seems appropriate to review key developments over the years and to remark on novel findings. A new and exciting vista has opened for seaweed extracts in both plant and animal applications.     

Phytotoxicity induced by Phragmites australis: an assessment of phenotypic and physiological parameters involved in germination process and growth of receptor plant

This study investigated the possible phytotoxicity induced by Phargmites australis on phenotypic and physiological parameters of recipient plants with identification of major inhibitors in the donor plant. This was achieved using aqueous extracts of different organs and root exudates of P. australis in laboratory and greenhouse experiments with Lactuca sativa as the model test plant. The observed reduced liquid imbibition and altered resource mobilization in seeds of L. sativa, in particular an insufficient carbohydrate supply, demonstrated that the onset of germination might be negatively affected by phytotoxicity. Dose-response studies pointed out that oxidative stress through reactive oxygen species production could potentially cause the observed germination and seedling growth reductions. The osmotic effects by mannitol solution on germination as well as growth and physiology at a level of ?0.57 and ?0.45 bar, respectively, demonstrated that the results from aqueous plant extracts were partially induced by the osmotic potential on and above those levels. Overall, the relative strength of inhibition on measured parameters was the highest in leaf extract, followed by rhizome, root, stem, and inflorescence. Root exudates of P. australis also had negative impacts by reducing germination and growth of plant. High-performance liquid chromatography (HPLC) analysis revealed gallic acid, a potent phytotoxin, as a major compound with an order of leaf >inflorescence>rhizome>root>stem.     

Inhibitory effect of leachate from Helianthus annuus on germination and growth of Kharif crops and weeds

Allelopathic potential of sunflower (Helianthus annuus L.) fresh plant tissues aqueous extraction in bioassay, rhizosphere soil in pot experiment and phytotoxicity of decomposed sunflower plant biomass in bioassay against Vigna radiata, Pennisetum glaucum, Trianthema portulacastrum and Parthenium hysterophorum was investigated. In bioassay aqueous extracts of fresh sunflower plant tissue inhibited the germination, seedling growth (shoot and root) and dry matter accumulation of test plant species. In pot study sunflower rhizosphere soil inhibited growth attributes (plant height, population, number of branches) and yield attributes (grain yield, biomass yield) of selected crops and weeds. Phytotoxicity of decomposed sunflower biomass showed inhibitory effect on selected plant species. The fresh plant tissues was greatest inhibitory to test plants and followed by that of the decomposed biomass extracts in all bioassays. Significant reductions in the root and shoot growth were observed as the extract concentration was increased. The concentrations of extract fraction of fresh sunflower was determined, since nine compounds i.e. ferulic, p-coumaric, syringic, chlorogenic acid, isochlorogenic acid, neochlorogenic acid, vanillic acid, p-hydroxybenzoic acid, caffeoylquinic acid, found to be main growth inhibitors in sunflower plant tissue. These results suggested that sunflower plants may possess allelopathic potential, and the plant tissues may be potentially useful for weed management.     

生姜水浸液对生姜幼苗根际土壤酶活性、微生物群落结构及土壤养分的影响

本文以生姜为材料,研究生姜不同部位（根茎、茎和叶）、不同浓度（10、20、40和80 g L-1）的水浸液对生姜幼苗根际土的微生物数量、土壤酶活性及土壤养分含量的影响,并通过HPLC定量分析了生姜各部位水浸液中所含酚酸类（香草酸、丁香酸、对羟基苯甲酸、香豆酸和阿魏酸）、香豆素类（伞花内脂和7-甲氧基香豆素）化合物的含量。结果表明：三种生姜水浸液对所测六种土壤酶活性均产生了不同程度的影响,其中影响最大的是酸性磷酸酶和蔗糖酶,在10 g L-1 时就达到了显著性差异水平,并且所有酶均有随着水浸液浓度的增加而呈增大的趋势;相同部位的水浸液随着浓度的增加,细菌和真菌的数量呈增加趋势,而放线菌的数量呈减少趋势;三种生姜水浸液均随着浓度的增加降低了土壤中有机质的含量,加剧了土壤中硝态氮含量的积累,根茎水浸液对土壤有效磷、速效钾和铵态氮均显示出低浓度提高其含量而高浓度降低其含量的趋势,而茎和叶水浸液则随着浓度的增加均降低了其含量。生姜水浸液中主要化感成分包括：根茎水浸液主要是丁香酸和伞花内脂;茎水浸液主要是阿魏酸,且其含量最高为73.4 ug/g;叶水浸液除了阿魏酸,其他六种物质均被检测出,但含量较高的主要有丁香酸、伞花内脂和香豆酸。     

Allelopathic potentials of exotic invasive and native trees over coexisting understory species: the soil as modulator

Ailanthus altissima and Robinia pseudoacacia are two aggressive exotic tree species invading riparian ecosystems in Central Spain. We explored their allelopathic potentials as a possible mechanism explaining their success in these ecosystems. Specifically, we aimed (1) to compare the phytotoxic effects of the exotic and native (Fraxinus angustifolia and Populus alba) trees on the fitness of several understory plants coexisting in riparian ecosystems, and (2) to assess the capacity of the riparian soil to modulate the phytotoxic effects. In laboratory bioassays, aqueous leaf litter extracts from the donor tree species at field-realistic concentrations were tested on different fitness indicators of 13 understory target species, using germination paper and soil as substrates in petri dishes. Using germination paper, we found species-specific effects between donor and target species, but the phytotoxicity of the exotic trees as a group was not greater than that of the natives. Nevertheless, the exotic R. pseudoacacia was the most effective donor species reducing the radicle growth of the target species. Over riparian soil substrate, the aqueous leaf litter extracts did not produce any phytotoxic effect on the target species, except in one case. Altogether, our results highlight the importance of using both a native control when assessing the phytotoxicity of nonnative plants and also the natural soil in the modulation of phytotoxic effects. Ignoring both factors in laboratory bioassays would have led to the overestimation of the phytotoxicity of the exotic species as a mechanism contributing to their invasion success.     

Changes in content of free,conjugated and bound polyamines and osmotic adjustment in adaptation of vetiver grass to water deficit

Osmotic adjustment and alteration of polyamines (PAs) have been suggested to play roles in plant adaptation to water deficit/drought stress. In this study, the changes in cell intactness, photosynthesis, compatible solutes and PAs [including putrescine (Put), spermidine (Spd) and spermine (Spm) each in free, conjugated and bound forms] were investigated in leaves of vetiver grass exposed to different intensity of water deficit stress and subsequent rewatering. The results showed that, when vetiver grass was exposed to the moderate (20% and 40% PEG-6000 solutions) and severe (60% PEG solution) water deficit for 6 days, the plant injury degree (expressed as the parameters of plant growth, cell membrane integrity, water relations and photosynthesis) increased and contents of free and conjugated Put decreased with the rise of PEG concentration. Under the moderate water deficit, the plants could survive by the reduced osmotic potential (ψ_s), increased free and conjugated Spd and Spm in leaves. After subsequent rewatering, the osmotic balance was re-established, most of the above investigated physiological parameters were fully or partly recovered to the control levels. However, it was not the case for the severely-stressed and rewatering plants. It indicates that, vetiver grass can cope well with the moderate water deficit/drought stress by using the strategies of osmotic adjustment and maintenance of total contents of free, conjugated and bound PAs in leaves.     

<Emphasis Type="Italic">Terminalia chebula</Emphasis> Retz. Fruit Extracts Inhibit Bacterial Triggers of Some Autoimmune Diseases and Potentiate the Activity of Tetracycline

Terminalia chebula Retz. is a northern Indian plant species known for its anti-inflammatory and antimicrobial properties. T. chebula fruit powder was extracted with solvents of varying polarity and screened for bacterial growth inhibition by disc diffusion assay. The minimum inhibitory concentration (MIC) was quantified by both liquid dilution and disc diffusion techniques. To screen for combinatorial effects, the T. chebula fruit extracts were combined with a range of conventional antibiotics and tested against each bacteria using a liquid dilution assay. Where synergy was detected, the optimal ratios were determined using isobologram analysis. Toxicity was examined using Artemia nauplii and HDF bioassays. T. chebula fruit methanolic, aqueous and ethyl acetate extracts displayed strong antimicrobial activity against the bacterial triggers of all autoimmune inflammatory diseases except K. pneumoniae, for which only moderate inhibition was observed. Indeed, MIC values as low as 195 μg/mL were measured for the aqueous extract against a resistant strain of P. aeruginosa. Of further note, both the aqueous and ethyl acetate extracts interacted synergistically in combination with tetracycline against K. pneumoniae (Σ FIC 0.38 and 0.25 respectively). All extracts were nontoxic in the Artemia and HDF toxicity assays, further indicating their potential for medicinal use.     

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 electrical resistance of epithelia in the presence of osmotic and hydrostatic pressure gradients

The electrical resistance has been determined for aqueous channels through thick walls which separate electrolyte solutions of different concentrations under hydrostatic and osmotic pressure gradients. It is shown that the variation of the conductivity of epithelial layers under various constraints can be subjected to a similar analysis. Although the treatment is quantitative, concomitant morphological changes in the tissue could also take place which would introduce a non-predictive element. An awareness of both effects appears essential, when osmotic and/or hydrostatic pressure gradients are applied across epithelia.     

Priority effects: How the order of arrival of an invasive grass,Bromus tectorum,alters productivity and plant community structure when grown with native grass species

Theories and models attempt to explain how and why particular plant species grow together at particular sites or why invasive exotic species dominate plant communities. As local climates change and human‐use degrades and disturbs ecosystems, a better understanding of how plant communities assemble is pertinent, particularly when restoring grassland ecosystems that are frequently disturbed. One such community assembly theory is priority effects, which suggests that arrival order of species into a community alters plant–plant interactions and community assembly. Theoretically, priority effects can have lasting effects on ecosystems and will likely be altered as the risk of invasion by exotic species increases. It is difficult to predict how and when priority effects occur, as experimental reconstruction of arrival order is often difficult in adequate detail. As a result, limited experimental studies have explored priority effects on plant community assembly and plant invasions. To determine if and how priority effects affect the success of invasive species, we conducted a greenhouse study exploring how the arrival order of an invasive grass, Bromus tectorum, affects productivity and community composition when grown with native grasses. We found evidence for priority effects, as productivity was positively related to dominance of B. tectorum and was greater the earlier B. tectorum arrived. This suggests that priority effects could be important for plant communities as the early arrival of an invasive species drastically impacted the productivity and biodiversity of our system at the early establishment stages of plant community development.     

Responses of the sweetpotato whitefly, Bemisia tabaci, to the chinaberry tree (Melia azedarach L.) and its extracts

Host preference bioassays for adults of the sweetpotato whitefly were performed with leaves of the chinaberry tree Melia azedarach L., tomato, cucumber and bean. Fruit and leaf extracts of the chinaberry tree were tested against adults of the sweetpotato whitefly. Fruit extracts were tested against eggs, first and second instar nymphs, and pupae of the insect. Treatments included aqueous, methanol, and acetone fruit extracts of 200 mg ml^?1 and serial dilutions of 20.0 and 2.00 mg ml^?1, ether extract, the botanical insecticides Azatin® and Margosan® ‐O and the control, water or water with Triton®. Mortality data was collected at 6, 7, and 8 days after treatment of the eggs, nymphs and pupae, respectively. Results of the host preference bioassays indicated a significantly lower number of live insects on leaves of the chinaberry tree vs leaves of bean, cucumber, and tomato after 24 h. This indicates that M. azedarach is not a good host for the sweetpotato whitefly. Adults of the insect were significantly more repelled from tomato plants treated with the undiluted extracts when compared to the control after 72 h. There were significant differences in percent mortality of nymphal instars when exposed to the undiluted extracts compared to other extracts and the control. However, there was no significant effect of the fruit extracts on the egg and pupa instars. Thus M. azedarach extracts were found to be repellent to the whitefly adults, while the fruit extracts have shown a significant detrimental effect against early nymphal instars. In general, the methanol extracts were more active against B. tabaci than extracts with other solvents.     

外来入侵植物银胶菊水提物对三叶鬼针草和茶条木种子萌发的化感作用

以伴生草本植物三叶鬼针草和能源木本植物茶条木为受试植物,初步研究了外来入侵植物银胶菊根、茎、花水浸提液对二者种子萌发的化感效应。根据发芽率、化感效应敏感指数、发芽速率可以看出,银胶菊不同部位的浸提液在不同浓度下对三叶鬼针草的种子萌发的影响力不同;而对茶条木种子萌发无明显的作用。为选择适宜植物,生物替代防治银胶菊提供依据。     

反枝苋水浸提液与挥发油对黄瓜根尖的影响

采用悬空气法研究了在入侵植物反枝苋(Amaranthus retroflexus L.)水浸提液和挥发油作用下,黄瓜根缘细胞活性、根冠果胶甲基酯酶(PME)、根尖过氧化氢酶(CAT)、过氧化物酶(POD)、超氧化物歧化酶(SOD)以及丙二醛(MDA)含量的变化规律.结果表明:反枝苋水浸提液对黄瓜根的生长无显著性影响而挥发油显著抑制黄瓜根的生长,且随浓度增大抑制作用显著增强.PME活性随着水浸提液浓度的增大呈先上升后下降趋势,而随着挥发油浓度的升高呈现逐渐上升的趋势;水浸提液和挥发油均降低了对根缘细胞的存活率,这种抑制作用随浓度的增加而增大;随着处理液浓度增大,黄瓜根尖中MDA含量、CAT活性整体表现为增加,SOD活性先升高后降低,POD活性与对照差异不显著.反枝苋挥发油的化感效应大于水浸提液的化感效应.     

Olfactory <Emphasis Type="Italic">versus</Emphasis> Contact Cues in Host Plant Recognition of a Monophagous Chrysomelid Beetle

The importance of olfactory versus contact cues for host plant recognition was investigated in the tortoise beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae), which is strictly monophagous on meadow sage. The reaction of adult beetles to olfactory and contact host cues was tested using three bioassays (locomotion compensator, six-chamber-olfactometer, ‘stem arena’) to account for different behavioral contexts. Bioassay-guided fractionation of plant extracts was elaborated to characterize the nature of contact stimuli. The beetles were only slightly attracted to odors from small amounts of leaf material. However, when contact cues were provided additionally, the beetles showed strong preferences for samples of their host plant over controls. Bioassay-guided fractionation led to isolation of at least two non-polar contact stimuli acting in concert that are sufficient for host plant identification in C. canaliculata.     

毛竹浸提液对苦槠幼苗生长的化感效应

为探讨毛竹(Phyllostachys edulis)扩张过程中潜在的化感作用,选择苦槠(Castanopsis sclerophylla(Lindl)Schott)为研究对象。采用水浸提的方法,用毛竹茎叶、枯落物和土壤3部分浸提液浇灌苦槠幼苗,以蒸馏水处理作为对照,对比分析质量浓度分别为0.1、0.05、0.02 g/mL的3个浓度梯度浸提液处理下苦槠幼苗生长指标及各项光合生理指标的差异。结果表明,毛竹浸提液对苦槠幼苗苗高、地径和叶绿素相对含量的影响大体上呈现高浓度抑制低浓度促进的双重浓度效应。不同来源毛竹浸提液的化感效应不尽相同,土壤浸提液对苦槠幼苗生长和光合生理均呈现抑制作用,而茎叶、枯落物浸提液低浓度时为促进作用。毛竹潜在的化感作用,在其扩张过程中可能会干扰森林主要树种更新,从而对森林群落产生威胁。     

油蒿(Artemisia ordosica)的化感作用研究

通过对鄂尔多斯高原毛乌素沙地油蒿（Ａｒｔｅｍｉｓｉａ ｏｒｄｏｓｉｃａ）化感作用研究,发现油蒿茎叶的水浸提液对几种受体植物种子的萌发率,幼苗长和根长生长均有不同程度的抑制作用,随水浸提液浓度的增加抑制作用逐步增加;用油蒿茎叶水浸提液进行盆栽试验,受体植物的出苗率,苗高,根长和干物重也受到抑制,苗的形态也与对照有较明显的差异;