A Soil-free Plant Growth System to Facilitate Analysis of Plant Pathogen Interactions in Roots

Analysis of the interaction of pathogens with plant roots is often complicated by the growth of plants in a soil substrate. A soil-free plant growth system (SPS) was developed that removes the need for a substrate while supporting the growth of seedlings in a nutrient rich, oxygenated environment. The model legume Lupinus angustifolius was used to compare the growth of seedlings within soil and the SPS. Seedlings grown under both conditions were similar in morphology, anatomy and health (measured by leaf chlorophyll abundance) and importantly there was little difference in root growth and development although straighter and fuller root systems were achieved in the SPS. The ease of access to the root system proved efficient for the analysis of root and pathogen interactions with no interference from soil or adhering particulate matter. Following inoculation of L. angustifolius roots with Phytophthora cinnamomi the host/pathogen interaction was easily observed and tissues sampled undamaged.     

Role of Azotobacter paspali in Association with Paspalum notatum

Azotobacter paspali grows in the rhizospheres of Paspalum notatum where it is thought to fix nitrogen actively and hence improve pasture growth. In the experiments described here A. paspali improved growth primarily by producing growth regulating substances. Nitrogenase activity was not detected in rhizospheres of young plants. Its occurrence in older plants was not necessarily associated with the presence of A. paspali and was greater in the rhizopheres of control than of inoculated plants.     

Plant Growth Substances Produced by Azospirillum brasilense and Their Effect on the Growth of Pearl Millet (Pennisetum americanum L.)

Azospirillum brasilense, a nitrogen-fixing bacterium found in the rhizosphere of various grass species, was investigated to establish the effect on plant growth of growth substances produced by the bacteria. Thin-layer chromatography, high-pressure liquid chromatography, and bioassay were used to separate and identify plant growth substances produced by the bacteria in liquid culture. Indole acetic acid and indole lactic acid were produced by A. brasilense from tryptophan. Indole acetic acid production increased with increasing tryptophan concentration from 1 to 100 μg/ml. Indole acetic acid concentration also increased with the age of the culture until bacteria reached the stationary phase. Shaking favored the production of indole acetic acid, especially in a medium containing nitrogen. A small but biologically significant amount of gibberellin was detected in the culture medium. Also at least three cytokinin-like substances, equivalent to about 0.001 μg of kinetin per ml, were present. The morphology of pearl millet roots changed when plants in solution culture were inoculated. The number of lateral roots was increased, and all lateral roots were densely covered with root hairs. Experiments with pure plant hormones showed that gibberellin causes increased production of lateral roots. Cytokinin stimulated root hair formation, but reduced lateral root production and elongation of the main root. Combinations of indole acetic acid, gibberellin, and kinetin produced changes in root morphology of pearl millet similar to those produced by inoculation with A. brasilense.     

Plant Growth Substances Produced by Micro-organisms of Soil and Rhizosphere

S ummary : Micro-organisms isolated from rhizospheres and rhizoplanes of wheat plants, and from root-free soil, produced growth regulating substances with the properties of gibberellins and indolyl-3-acetic acid (IAA). Substances inhibiting extensions of pea plant internodes and lettuce hypocotyls were also produced, especially by bacteria from the root region of seedlings 6 days old. Bacteria producing growth promoting substances were most abundant on roots of older plants. Seedlings grown aseptically with added gibberellic acid (GA₃) and IAA, or grown with a soil inoculum, developed similarly and differed in their morphology from those grown aseptically without additives.     

Root Foraging Influences Plant Growth Responses to Earthworm Foraging

Interactions among the foraging behaviours of co-occurring animal species can impact population and community dynamics; the consequences of interactions between plant and animal foraging behaviours have received less attention. In North American forests, invasions by European earthworms have led to substantial changes in plant community composition. Changes in leaf litter have been identified as a critical indirect mechanism driving earthworm impacts on plants. However, there has been limited examination of the direct effects of earthworm burrowing on plant growth. Here we show a novel second pathway exists, whereby earthworms (Lumbricus terrestris L.) impact plant root foraging. In a mini-rhizotron experiment, roots occurred more frequently in burrows and soil cracks than in the soil matrix. The roots of Achillea millefolium L. preferentially occupied earthworm burrows, where nutrient availability was presumably higher than in cracks due to earthworm excreta. In contrast, the roots of Campanula rotundifolia L. were less likely to occur in burrows. This shift in root behaviour was associated with a 30% decline in the overall biomass of C. rotundifolia when earthworms were present. Our results indicate earthworm impacts on plant foraging can occur indirectly via physical and chemical changes to the soil and directly via root consumption or abrasion and thus may be one factor influencing plant growth and community change following earthworm invasion. More generally, this work demonstrates the potential for interactions to occur between the foraging behaviours of plants and soil animals and emphasizes the importance of integrating behavioural understanding in foraging studies involving plants.     

植物生长调节剂对鹿角杜鹃扦插繁殖的影响

以腐殖土为基质,研究了5种植物生长调节剂的4个浓度处理、以及萘乙酸(NAA)不同浓度与浸泡时间处理对鹿角杜鹃(Rhododendron latoucheae)当年生枝条扦插繁殖12个育苗指标的影响及各指标间的相关性,并运用隶属函数法对各处理组合的育苗效果进行了综合评价。结果表明:5种生长调节剂中,赤霉素(GA3)、吲哚丁酸(IBA)处理在大部分育苗指标上表现良好,为鹿角杜鹃扦插育苗的理想调节剂,吲哚乙酸(IAA)效果次之,6-苄氨基嘌呤(6-BA)、NAA处理的育苗指标表现较差;4个浓度水平上,愈伤率、腐烂率及老叶留存率总体以低浓度处理最佳,随着浓度升高效果下降;其它9个指标对浓度的响应因生长调节剂种类而异。各指标相关性分析发现,4个根系生长指标,即不定根数、最长不定根长、总根数及根系直径之间呈极显著正相关,但它们与愈伤率、腐烂率、生根率及老叶留存率、新梢率间的相关性较弱。隶属函数综合评价表明,50 mg/L GA3处理为鹿角杜鹃扦插育苗的最佳组合,其次为100 mg/L GA3和400 mg/L IBA处理。本研究为杜鹃花产业化育苗提供了科学依据。     

Inhibition of Plant Root Growth by Enzymes and Histones

It has been shown previously that root growth can be inhibited by basic, animal proteins. In an effort to see if a plant histone was more efficacious than the animal protein, roots were grown in the presence of wheat histone. Otber basic polymers were also tested. Polycations, including salmine, lysozyme, ribonuclease, wheat germ histone, thymus histone and polylysine inhibit root elongation of barley and wheat. Polyglutamate and lysylglycine at comparable weight concentrations are not inhibitory. No difference in the efficacy of tbe plant and the animal histones could be found with either plant, which suggests that the action is non-specific. Growth of roots inhibited by histone, trypsin, or lysozyme can resume after removal of the polycation. The mechanism whereby polycations influence root growth is not known, but it is clear that the polymeric state of ionic functional groups is of paramount importance in the binding of the polycations to cell surfaces.     

丛枝菌根真菌对植物生长影响的研究

菌根是自然界中一种极为普遍和重要的共生现象,其中分布最为广泛的菌根类型就是丛枝菌根,可以增强植物从土壤中获取水分的能力,改善植物根系对磷、镉等矿质元素及养分的吸收,从而促进植物的生长。本文综述了丛枝菌根真菌对植物生长影响的概况。有关丛枝菌根真菌对植物水分和矿质营养的利用,尤其是磷素营养的研究较为深入,而对植物光合特性的研究较少,这些研究工作为深入理解菌根真菌与植物的相互关系提供基础资料。     

Biocontrol Activity and Plant Growth Promotion Exerted by Aureobasidium pullulans Strains

The most common leguminous plants’ diseases are caused by soil-borne pathogens leading to important economic losses worldwide. Strains L1 and L8, belonging to Aureobasidium pullulans species, were tested in vitro and in vivo as biocontrol agents (BCAs) against Rhizoctonia solani (Rs1) (AG-4) and as plant growth promoters (PGPs). The non-volatile metabolites produced by L1 and L8 strains inhibited the pathogen mycelial growth by 87.9% on average, with no significant differences between the two strains. The lower pathogen diametric growth inhibition was displayed by both yeasts’ volatile metabolites (VOCs) that significantly reduced the colony growth of R. solani, and similarly to the control, with an average of 10.5%. By in vivo assay, L1 and L8 strains showed the ability to control the pathogen virulence probably through the biofilm formation around the bean and soybean plant roots, as confirmed by scanning electron microscope (SEM) analysis. The spectroscopic analysis highlighted the composition of non-volatile compounds: complex carbohydrates (pullulan), degrading enzymes, siderophores and antifungals (aureobasidins). Moreover, the ability of L1 and L8 strains to stimulate the bean and soybean plant roots, stems, and leaves growth was investigated, showing that these yeasts could have an application not only as BCAs but also as plant growth biostimulator.

     

不同有机肥影响菠萝生长的生理生化机制

以菠萝品种'澳大利亚卡因'为材料,研究了施用不同有机肥对菠萝长叶期和抽蕾期植株生长量、生理生化指标以及土壤酶活性、微生物等的影响,以探讨不同有机肥对菠萝生长的影响机理.结果显示:(1)在花生麸处理中菠萝株高、青叶数、地上部和根鲜重较对照(施用化肥)提高,而在鸡粪和水肥处理中株高、青叶数、地上部鲜重较对照降低.(2)花生麸处理的菠萝叶片细胞膜透性较对照降低,而叶绿素含量、根系活力以及叶片和根系的可溶性糖、可溶性蛋白含量、SOD活性均较对照提高;鸡粪和水肥处理的叶片细胞膜透性和根系SOD酶活性较对照提高,而叶绿素含量、根系活力、长叶期叶片和根系的可溶性糖含量、长叶期和抽蕾期叶片的可溶性蛋白含量、叶片SOD酶活性均比对照降低.(3)花生麸能提高土壤脲酶、转化酶和过氧化氢酶的活性及土壤微生物数量;鸡粪和水肥能降低土壤脲酶、蛋白酶活性,却能增强土壤转化酶、过氧化氢酶活性,鸡粪使土壤微生物数量增加,水肥使长叶期土壤微生物数量增加,但使抽蕾期的减少.研究表明,施用花生麸能提高菠萝叶绿素含量、根系活力以及叶片和根系的可溶性糖、可溶性蛋白含量,并增强根和叶的SOD活性,同时增加了土壤相关酶活性和微生物数量,从而有效促进菠萝植株生长.     

Root Exudate-Induced Alterations in Bacillus cereus Cell Wall Contribute to Root Colonization and Plant Growth Promotion

The outcome of an interaction between plant growth promoting rhizobacteria and plants may depend on the chemical composition of root exudates (REs). We report the colonization of tobacco, and not groundnut, roots by a non-rhizospheric Bacillus cereus (MTCC 430). There was a differential alteration in the cell wall components of B. cereus in response to the REs from tobacco and groundnut. Attenuated total reflectance infrared spectroscopy revealed a split in amide I region of B. cereus cells exposed to tobacco-root exudates (TRE), compared to those exposed to groundnut-root exudates (GRE). In addition, changes in exopolysaccharides and lipid-packing were observed in B. cereus grown in TRE-amended minimal media that were not detectable in GRE-amended media. Cell-wall proteome analyses revealed upregulation of oxidative stress-related alkyl hydroperoxide reductase, and DNA-protecting protein chain (Dlp-2), in response to GRE and TRE, respectively. Metabolism-related enzymes like 2-amino-3-ketobutyrate coenzyme A ligase and 2-methylcitrate dehydratase and a 60 kDa chaperonin were up-regulated in response to TRE and GRE. In response to B. cereus, the plant roots altered their exudate-chemodiversity with respect to carbohydrates, organic acids, alkanes, and polyols. TRE-induced changes in surface components of B. cereus may contribute to successful root colonization and subsequent plant growth promotion.     

Plant Growth and Morphogenesis in vitroIs Promoted by Associative Methylotrophic Bacteria

The effects of aerobic methylotrophic bacteria Methylovorus mayson growth and morphogenesis were studied in in vitropropagated tobacco, potato, and flax. Colonization of plant explants with the methylo-trophic bacteria led to the stable association of bacteria and plants and enhanced the growth and the capacity of the latter for regeneration and root formation. When colonized by the methylotrophic bacteria, the rootless transgenic tobacco plants carrying the agrobacterial cytokinin gene iptrestored their ability to form roots. These data indicate the possibility to employ methylotrophic bacteria as a tool in experimental biology and plant biotechnology.     

The Growth Substances separated from Plant Extracts by Chromatography. I

Methods for the chromatographic separation on paper of indolecompounds and for the direct biological assay of the chrornatograinsusing the Avena coleoptile straight-growth method are described.Reagents for the detection of the indole-3-carboxylic acids,indole-3-acetonitrile, and gramirte as coloured spots on chromatogramsare compared and the areas of such spots are shown to be proportionalto the logarithms of the quantities of substance present. The procedure of chromatography described is shown not to involvea loss of indole-3-acetic acid activity if chromatography isdone in darkness and chrornatograms are not stored in lightand air. Methods are described for the extraction of growth aubstancesfrom plant materials, the purification and chromatography, onpaper, of the extracts and the bioassay of the chromatogramsusing Avena coleoptile sections. The ether extracts, containing acidic substances, of etiolatedbroad bean and pea shoots and roots, etiolated sunflower shoots,maize roots, and potato etiolated shoots and tuber have beenchromatographed and the chromatograms bioassayed. On all chromatogramsthree areas active in Avena coleoptile section growth are found.One area of growth promotion is shown due to indole-3-aceticacid [IAA]. Another area of growth promotion and, one of growthinhibition are due to unknown substances, which are named accelerator () and inhibitor ß (ß) respectively. On chromatograms of potato tuber a fourth growth-promoting area,in addition to those described above, is detected and is shownto be probably due to indole-3-acetonitrile [IAN]. IAN or indole-3-pyruvicacid may occpr together with IAA on chrormatograms of extractsof immature maize kernels and cauliflower head respectively. On cabbage extract chromatograms the growth-promoting activitycorresponding in position with IAA is shown to be due to IAAand to IAA alone. In etiolated broad bean shoots IAA is the predominating growthsubstance in the stem and ß predominates in the firstlateral bud. The latter is suggested as an explanation of apicaldominance, and the predominance of ß in potato tuberskin is suggested as an explanation of dormancy in tubers. In the broad bean root the acidic growth-substance patterns,for the whole root and for the sections 0–2 cm. and 2–4cm. from the tip, are the same. The acidic growth substances extractable from broad bean shootsare the same whether the plant material is boiled or frozenbefore extraction.     

硝态氮（NO3^—）对水稻侧根生长及其氮吸收的影响

侧根是植物吸收利用土壤养分的重要器官 ,其生长发育受内部遗传因子和外部环境矿质养分的影响。通过琼脂分层培养发现 :局部供应NO-3 可以诱导水稻 (OryzasativaL .)主根或不定根上侧根的生长。为研究旱种条件下NO-3 对水稻侧根发育及其N吸收的影响 ,设置了 3个蛭石培养实验 :分根处理、全株缺N、全株供N处理。分根处理 (一半根系供应 3mmol/LKNO3,另一半根系供应 3mmol/LKCl)结果表明 :局部供应NO-3 能够促进水稻侧根生长。而在全株处理下 ,N饥饿诱导了侧根的伸长。水稻根系对NO-3 的这两种反应都存在着显著的基因型差异。同时对地上部N浓度、可溶性总糖含量及N含量分析表明 ,这些生理指标在分根处理与全株加N处理中的差异均不显著 ,表明分根处理也能基本满足植株正常生长对N的需求。在分根处理中 ,水稻的N含量与分根处理中供N一侧的平均侧根长度存在显著正相关 ,这表明在养分不均一的介质中 ,侧根长度对水稻N素吸收具有十分重要的作用。而在N素充足的条件下 ,两者之间的相关性并不显著 ,这暗示在养分充足的环境下 ,侧根长度可能并不是决定根系吸收N素的主要因素     

Influence of Plant Growth Promoting Rhizobacterial Inoculation on Wheat Productivity Under Soil Salinity Stress

Soil salinity affects the growth and yield of crops. The stress of soil salinity on plants can be mitigated by inoculation of plant growth promoting bacteria (PGPR). The influence of PGPR inoculation on wheat (Triticum aestivum L.) crop productivity under salinity stress has not been properly addressed so far. Therefore, the present study was conducted to investigate the effects of various PGPR strains (W14, W10 and 6K; alone and combined) at several growth attributes of wheat plant under different soil salinity gradients (3, 6 and 9 dS m-1). The growth attributes of wheat (height, roots, shoots, spikes, grains quality, biological and economical yield, nutrients nitrogen, phosphorus and potassium in grains) were highly affected by salinity and decreased with increasing salinity level. The PGPR inoculation substantially promoted growth attributes of wheat and prominent results were observed in W14 × W10 × 6K treatment at all salinity levels. The results suggest that inoculation of PGPR is a potential strategy to mitigate salinity stress for improving wheat growth and yield.     

Zinc Accumulation and Tolerance in Solanum nigrum are Plant Growth Dependent

Zinc tolerance, accumulation, and organic acid production by Solanum nigrum, a known Zn accumulator, was studied during pre- and post-flowering stages of development. The plants, when challenged with Zn concentrations lethal to plantlets, showed an increase in tolerance from pre-flowering to post-flowering, which was accompanied by a reduction of Zn translocation to the aerial plant parts. Treatment with Zn induced a differential response in organic acids according to the plant organ and developmental stage. In the roots, where Zn concentrations were similar in pre- and post-flowering plants, a general decrease in organic acid in pre-flowering roots contrasted with the increase observed in post-flowering plants. In the stems, Zn induced a generalized increase in organic acids at both growth stages while in the leaves, a slight increase in malic and shikimic was observed in pre-flowering plants and only shikimic acid levels were significantly increased in post-flowering plants. This work shows that Zn accumulation and tolerance in S. nigrum vary during plant development – an observation that may be important to improve the efficiency of phytoremediation approaches. Furthermore, the data suggest the involvement of specific organic acids in this response.     

Single-plant,Sterile Microcosms for Nodulation and Growth of the Legume Plant Medicago truncatula with the Rhizobial Symbiont Sinorhizobium meliloti

Rhizobial bacteria form symbiotic, nitrogen-fixing nodules on the roots of compatible host legume plants. One of the most well-developed model systems for studying these interactions is the plant Medicago truncatula cv. Jemalong A17 and the rhizobial bacterium Sinorhizobium meliloti 1021. Repeated imaging of plant roots and scoring of symbiotic phenotypes requires methods that are non-destructive to either plants or bacteria. The symbiotic phenotypes of some plant and bacterial mutants become apparent after relatively short periods of growth, and do not require long-term observation of the host/symbiont interaction. However, subtle differences in symbiotic efficiency and nodule senescence phenotypes that are not apparent in the early stages of the nodulation process require relatively long growth periods before they can be scored. Several methods have been developed for long-term growth and observation of this host/symbiont pair. However, many of these methods require repeated watering, which increases the possibility of contamination by other microbes. Other methods require a relatively large space for growth of large numbers of plants. The method described here, symbiotic growth of M. truncatula/S. meliloti in sterile, single-plant microcosms, has several advantages. Plants in these microcosms have sufficient moisture and nutrients to ensure that watering is not required for up to 9 weeks, preventing cross-contamination during watering. This allows phenotypes to be quantified that might be missed in short-term growth systems, such as subtle delays in nodule development and early nodule senescence. Also, the roots and nodules in the microcosm are easily viewed through the plate lid, so up-rooting of the plants for observation is not required.     

Phospholipids as Plant Growth Regulators

In this paper the potential to use phospholipids and lysophospholipids as plant growth regulators is discussed. Recent evidence shows that phospholipids and phospholipases play an important signalling role in the normal course of plant development and in the response of plants to abiotic and biotic stress. It is apparent that phospholipase A (PLA), C (PLC) and D (PLD), lysophospholipids, and phosphatidic acid (PA) are key components of plant lipid signalling pathways. By comparison, there is very little information available on the effect of exogenously applied phospholipids on plant growth and development. This paper serves to introduce phospholipids as a novel class of plant growth regulator for use in commercial plant production. The biochemistry and physiology of phospholipids is discussed in relation to studies in which phospholipids and lysophospholipids have been applied to plants and plant parts. Implicit in the observations is that phospholipids impact the hypersensitive response and systemic acquired resistance in plants to improve crop performance and product quality. Based on published data, a scheme outlining a possible mode of action of exogenously applied phospholipids is proposed.     

Effects of Capsaicin on Plant Growth

Rice (Oryza sativa L.) seedlings inhibited the growth of hypocotyls and roots of cress (Lepidium sativum L.) seedlings when both seedlings were grown together. Two growth inhibiting substances were found in the culture solution in which rice seedlings were hydroponically grown for 14 d. One growth inhibitor was further purified. This suggests that the rice seedlings may produce growth inhibiting substances, acting as allelochemicals to other plants, and release them from their roots into the environment.     

植物生长延缓剂对盆栽月季生长发育的影响

采用不同质量浓度的3种植物生长延缓剂多效唑(PP333)、矮壮素(CCC)、缩节胺(DPC),运用叶喷和灌根两种处理方式,通过测定植株的形态指标(株高、节间长、叶片长与宽、花枝长、花梗长、花径及初花期等)和生理生化指标(叶绿素含量、光合速率、蒸腾速率、叶片酶活性及可溶性糖含量等),研究3种药剂对盆栽月季‘世纪之春’生长发育的影响。结果表明:(1)不同药剂的使用浓度和方式对盆栽月季的形态和生理指标有不同程度的影响,适宜浓度和方式处理能缩短植株节间长度来降低株高,使株型饱满,开花正常,提高观赏价值;同时可以增加叶片叶绿素含量,提高光合效率,增加叶片超氧化物歧化酶和过氧化物酶活性及可溶性糖含量,对改善盆栽月季观赏品质有重要影响;(2)叶面喷洒700mg.kg-1 PP333和灌根300mg.kg-1 PP333的调控效果最好,喷洒1 200mg.kg-1CCC和300mg.kg-1 DPC效果次之,均能达到有效降低株高和提高观赏效果的目的。