根瘤菌在大麦和水稻根上形成拟瘤的细胞结构

用3种方法使紫云英根瘤菌(Rhizobium astragali Huikui)、田菁根瘤菌(R.sesbania sp.)分别入侵大麦(hordeum vulgare L.)和水稻(Oryza sativa L.),形成拟瘤状组织。一是用一定磁场强度处理根瘤菌和植物,并接种培养。二是用含有水稻幼苗根提取物的培养基培养根瘤菌,接种水稻。三是重复别人用2,4-D外源激素处理植物,接种根瘤菌。镜检观察,用紫云英根瘤菌接种形成的大麦根拟瘤细胞结构非常精细,保持各种细胞器。有侵入线结构和根瘤菌从侵入线释放。根瘤菌被宿主细胞来源的膜包围,成为拟菌体。这些形态结构与豆科根瘤细胞相似,有共生状态特征,但拟菌体有泡状化现象。田菁根瘤菌入侵水稻根形成的拟瘤,在细胞间隙和细胞内都有细菌分布。受侵染的细胞结构粗糙,根瘤菌裸露,无胞膜包围。用2,4-D处理接种根瘤菌的拟瘤细胞结构也如此,但在维管系统内有大量密集的细菌存在。这种结构完全不同于豆科根瘤细胞结构,细菌与植物细胞的形态学相互关系是一种非共生联合作用。     

Rhizobium meliloti nodulation genes allow Agrobacterium tumefaciens and Escherichia coli to form pseudonodules on alfalfa.

Regions of the Rhizobium meliloti symbiotic plasmid (20 to 40 kilobase pairs long) containing nodulation (nod) genes were transferred to Agrobacterium tumefaciens or Escherichia coli by conjugation. The A. tumefaciens and E. coli transconjugants elicited root hair curling and the formation of ineffective pseudonodules on inoculated alfalfa plants. A tumefaciens elicited pseudonodules formed at a variable frequency, ranging from 15 to 45%, irrespective of the presence of the Ti plasmid. These pseudonodules developed characteristic nodule meristems, and in some nodules, infection threads were found within the interior of nodules. Infrequently, infection threads penetrated deformed root hairs, but these threads were found only in a minority of nodules. There was no evidence of bacterial release from the infection threads. In addition to being found within threads, agrobacteria were also found in intercellular spaces and within nodule cells that had senesced . In the latter case, the bacteria appeared to invade the nodule cells independently of infection threads and degenerated at the same time as the senescing host cells. No peribacteroid membranes enclosed any agrobacteria , and no bacteroid differentiation was observed. In contrast to the A. tumefaciens-induced pseudonodules , the E. coli-induced pseudonodules were completely devoid of bacteria; infection threads were not found to penetrate root hairs or within nodules. Our results suggest that relatively few Rhizobium genes are involved in the earliest stages of nodulation, and that curling of root hairs and penetration of bacteria via root hair infection threads are not prerequisites for nodule meristem formation in alfalfa.     

KINETIN-INDUCED PSEUDONODULES ON TOBACCO ROOTS

Arora , Nirmal , F. Skoog , and O. N. Allen . (U. Wisconsin, Madison.) Kinetin-induced pseudonodules on tobacco roots. Amer. Jour. Bot. 46(8): 610–613. Illus. 1959.—Tobacco stem segments were cultured on modified White's medium containing 0.02–0.1 mg./l. of kinetin, 2 mg./l. of IAA and 2 g./l. of casein hydrolysate. Roots grew profusely from these stem pieces. In the presence of kinetin, especially when a second supply (0.2 mg./l.) was introduced after the roots had developed, large numbers of pseudonodules were formed along the root surfaces. The protuberances were spherical in shape and were invariably associated with the axial area of lateral rootlets derived as root primordia from parent root pericycle. Development of the pseudonodules started with the division and enlargement of cortical cells. The center of each pseudonodule contained either a simple provascular strand constituting a modified rootlet with a poorly defined apex and layers of tracheids at the base, or a normal lateral root primordium capable of continued growth and eventual emergence as a rootlet. In later stages, the swellings became lobed and the mature cells showed a high starch content. Although these kinetin-induced pseudonodules arose from cortical tissue, their anatomical structure remained undifferentiated and unspecialized and bore no resemblance to that of typical nodules caused by rhizobia.     

SOME EFFECTS OF KINETIN ON THE GROWTH AND FLOWERING OF INTACT GREEN PLANTS

Wittwer , S. H., and R. R. Dedolph . (Michigan State U., E. Lansing.) Some effects of kinotin on the growth and flowering of intact green plants. Amer. Jour. Bot. 50(4): 330–336. Illus. 1963.—Dry matter accumulation of aerial parts, and heights of tomato, cucumber, and pea plants were markedly reduced when kinetin was incorporated into the culture solution root medium in concentrations ranging from 10^–5 to 10^–7 M. Concentrations which suppressed top growth (height, dry weight) generally had lesser effects on root growth and, in some instances, enhanced it. Thus top/root ratios were greatly reduced and approached unity in kinetin-treated peas and tomatoes. Flowering was inhibited in tomatoes and accelerated in peas. There were marked changes in root morphology, including the formation of pseudonodules. Kinetin had an effect which was opposite to that of gibberellin on internode elongation, root extension, top/root ratios and flowering of dwarf peas. N⁶-benzyladenine was more active than kinetin in suppressing the growth of intact green plants. The data show that kinetin can markedly alter the behavior of intact plants when absorbed by the roots from culture solutions in which the concentrations are comparable to those which are biologically active on explants.     

Pseudonodules formation on barley roots induced by Rhizobium astragali

Abstract Symbiotic association Rhizobium astragali with barley roots was induced by a permanent magnetic field. Initially root hairs were deformed. Later, pseudonodules were formed, showing infected cells with infection threads, and bacteroids each enclosed within a peribacteroid membrane. The overall picture is similar to that of legume root nodules. No acetylene reduction activity could be detected in pseudonodules.     

The effect of spraying with DNOC (4,6-dinitro-o-cresol) on the growth of the roots and shoots of winter rye plants

Summary Spraying young winter rye plants with 4,6-dinitro-o-cresol (DNOC), as a contact herbicide, initially depressed the growth rate of the plants although this subsequently increased until ultimately the yield of plant material was greater than achieved by the control plants, also apart from the herbicidal effect of the treatment.It was observed that the growth rate of the roots of the treated plants recovered sooner than did the growth rate of the aerial parts. Ultimately a greater root dry weight was produced by the treated plants than by the control plants. This was achieved before the dry weights of the aerial parts of the treated plants equalled those of the untreated plants. The shoot/root ratio of the treated plants was lower than that of the control plants and the roots of the treated plants survived longer in the deeper layers of the soil than did those of the control plants.It is suggested that the subsequent increase in shoot growth in the treated plants may be a consequence of increased uptake of nutrients from the soil by a more vigorous root system. It is concluded that the increase in root growth which follows the initial depression, after treatment of the plants with DNOC, may be due to factors within rather than outside the roots.     

Shoot-to-Root Signal Transmission Regulates Root Fe(III) Reductase Activity in the dgl Mutant of Pea

To understand the root, shoot, and Fe-nutritional factors that regulate root Fe-acquisition processes in dicotyledonous plants, Fe(III) reduction and net proton efflux were quantified in root systems of an Fe-hyperaccumulating mutant (dgl) and a parental (cv Dippes Gelbe Viktoria [DGV]) genotype of pea (Pisum sativum). Plants were grown with (+Fe treated) or without (-Fe treated) added Fe(III)-N,N'-ethylenebis[2-(2-hydroxyphenyl)-glycine] (2 [mu]M); root Fe(III) reduction was measured in solutions containing growth nutrients, 0.1 mM Fe(III)-ethylenediaminetetraacetic acid, and 0.1 mM Na2-bathophenanthrolinedisulfonic acid. Daily measurements of Fe(III) reduction (d 10-20) revealed initially low rates in +Fe-treated and -Fe-treated dgl, followed by a nearly 5-fold stimulation in rates by d 15 for both growth types. In DGV, root Fe(III) reductase activity increased only minimally by d 20 in +Fe-treated plants and about 3-fold in -Fe-treated plants, beginning on d 15. Net proton efflux was enhanced in roots of -Fe-treated DGV and both dgl growth types, relative to +Fe-treated DGV. In dgl, the enhanced proton efflux occurred prior to the increase in root Fe(III) reductase activity. Reductase studies using plants with reciprocal shoot:root grafts demonstrated that shoot expression of the dgl gene leads to the generation of a transmissible signal that enhances Fe(III) reductase activity in roots. The dgl gene product may alter or interfere with a normal component of a signal transduction mechanism regulating Fe homeostasis in plants.     

Interaction between iron plaque and root border cells ameliorates aluminum toxicity of Oryza sativa differing in aluminum tolerance

Root border cells (RBCs), which are generated during plant growth and surround the root cap, and iron plaque (IP), ubiquitously formed on the root surfaces of rice, are known to alleviate aluminum (Al) toxicity. To verify the interactive effects of IP and RBCs on ameliorating Al toxicity, two rice cultivars differing in Al resistance were used to compare Al tolerance between cultivars. Additionally, root elongation, Al uptake and RBCs viability were measured as indicators of the effects of Al. The amounts of DCB-extractable Fe and Al on the root surfaces were much higher in the presence of IP than the absence. IP presence significantly decreased Al-induced inhibition of root elongation and Al contents in roots and root tips. The removal of RBCs from the root tips caused a more severe inhibition of root elongation and a higher Al accumulation in rice roots and root tips. Furthermore, root growth inhibition and Al contents in roots and root tips were significantly lower in roots with a combination of IP and RBCs than in roots with IP or RBCs only. The formation of IP on the root surface maintained higher RBCs viability and depressed mucilage exudation in an Al-tolerant rice cultivar. The results suggest that both IP and RBCs ameliorate Al toxicity, and IP has a greater capacity for Al resistance. The combination of IP and RBCs exhibited a synergistic effect associated with Al resistance.     

Origin and development in vitro of shoot buds and somatic embryos from intact roots of Helianthus annuus x H. tuberosus

A variant clone of the tetraploid (2n = 4x = 68) interspecific hybrid Helianthus annuus x H. tuberosus derived by in vitro tissue culture showed a deviation from the usual pattern of organization of the plant body. This variant developed shoot-like structures and somatic embryos from intact adventitious roots of in vitro-grown plantlets. The morphogenetic structures were not normally able to differentiate complete plants. They did show cellular proliferation with the inception of additional secondary embryos, leaf-like structures and unorganized masses of callus. Nevertheless, some ectopic structures isolated from roots and transferred onto fresh basal medium without growth regulators were able to produce plantlets that exhibited the same phenotype as the original clone. Histological analyses demonstrate that they originate from cortical cells in association with the development of lateral root primordia.     

Induction of early bolting in Arabidopsis thaliana by triacontanol, cerium and lanthanum is correlated with increased endogenous concentration of isopentenyl adenosine (iPAdos)

The effects of triacontanol (TRIA), applied singly or in combination with cerium nitrate and lanthanum nitrate, on bolting of Arabidopsis thaliana were studied. Triacontanol (0.1 to 0.6 microM) added to the culture medium induced early bolting. TRIA (0.3 microM) applied with low concentrations of cerium and lanthanum caused a synergistic stimulation of bolting. In medium containing 0.3 microM TRIA, 0.1 microM cerium nitrate and 0.1 mM lanthanum nitrate, 82% of the plants bolted 20 d after seed sowing compared to only 8.6% in basal medium and 47.8% in medium with TRIA only. The changes in the endogenous concentrations of total cytokinins of the isopentenyl adenine (IP) subfamily in the leaf and root tissues were correlated with TRIA-induced early bolting. The combined treatment of TRIA (0.3 microM), cerium nitrate (0.1 microM) and lanthanum nitrate (0.1 mM) resulted in a significant increase in the endogenous concentrations of total cytokinins of the IP subfamily in the root and leaf tissues compared to plants growing in the basal medium and medium with TRIA. The exogenous application of six natural cytokinins to the plants revealed that only isopentenyl adenosine (iPAdos) was as effective as TRIA on floral bud formation. iPAdos was also found to have similar effects as TRIA on root growth and reproductive growth. These results suggest a correlation between the early bolting induced by TRIA, cerium and lanthanum and the production of higher concentrations of endogenous iPAdos.     

Rhizobium meliloti exopolysaccharide Mutants Elicit Feedback Regulation of Nodule Formation in Alfalfa

Nodule formation by wild-type Rhizobium meliloti is strongly suppressed in younger parts of alfalfa (Medicago sativum L.) root systems as a feedback response to development of the first nodules (G Caetano-Anollés, WD Bauer [1988] Planta 175: 546-557). Mutants of R. meliloti deficient in exopolysaccharide synthesis can induce the formation of organized nodular structures (pseudonodules) on alfalfa roots but are defective in their ability to invade and multiply within host tissues. The formation of empty pseudonodules by exo mutants was found to elicit a feedback suppression of nodule formation similar to that elicited by the wild-type bacteria. Inoculation of an exo mutant onto one side of a split-root system 24 hours before inoculation of the second side with wild-type cells suppressed wild-type nodule formation on the second side in proportion to the extent of pseudonodule formation by the exo mutants. The formation of pseudonodules is thus sufficient to elicit systemic feedback control of nodulation in the host root system: infection thread development and internal proliferation of the bacteria are not required for elicitation of feedback. Pseudonodule formation by the exo mutants was found to be strongly suppressed in split-root systems by prior inoculation on the opposite side with the wild type. Thus, feedback control elicited by the wild-type inhibits Rhizobium-induced redifferentiation of host root cells.     

Quinine and quinidine production by cinchona leaf,root and unorganized cultures

Serially propagated Cinchona ledgeriana and C. succirubra (Rubiaceae) leaf, root and unorganized suspension cultures established from germinated seeds were studied for quinine and quinidine production. Leaf organ cultures were grown and subcultured in Murashige and Skoog's Revised Tobacco Medium supplemented with benzyladenine; root organ cultures were grown on the same medium supplemented with indolebutyric acid; and unorganized suspension cultures were grown on the same medium supplemented with 2,4-dichlorophenoxyacetic acid and benzyladenine. On a dry weight basis, leaf organ cultures of C. ledgeriana contained 0.06 % quinine and 0.05 % quinidine and of C. succirubra contained 0.04 % quinine and 0.04 % quinidine. No quinine and quinidine were detected in either root organ or unorganized suspension cultures.     

Plant defence and delayed infection of alfalfa pseudonodules induced by an exopolysaccharide (EPS I)-deficient Rhizobium meliloti mutant

Mutants of the symbiotic soil bacterium Rhizobium meliloti that fail to synthesize the acidic exopolysaccharide EPS I were unable to induce infected root nodules on Medicago sativa L. (alfalfa). These strains, however, elicited pseudonodules that contained no infection threads or bacteroids. The cortical cell walls of the pseudonodules were abnormally thick and incrusted with an autofluorescent material. Parts of these cell walls and wall appositions contained callose. Biochemical analysis of nodules induced by the EPS I-deficient R. meliloti mutant revealed an increase of phenolic compounds bound to the nodule cell walls when compared with the wild-type strain. These microscopic and biochemical data indicated that a general plant defence response against the EPS I-deficient mutant of R. meliloti was induced in alfalfa pseudonodules. Following prolonged incubation with the EPS I-deficient R. meliloti mutant, the defence system of the alfalfa plant could be overcome by the rhizobium mutant. In the case of the delayed infections, the mutants colonized lobes of the pseudonodules, but the infection threads in these nodules had an abnormal morphology. They were greatly enlarged and did not contain the typical gum-like matrix inside. The bacteria were tightly packed. Based on the mechanism of phytopathogenic interactions, we propose that EPS I or a related compound may act as a suppressor of the alfalfa plant defence system, enabling R. meliloti to infect the plant.     

Rhizobacteria improve sugarcane growth and photosynthesis under well‐watered conditions

Morpho‐physiological changes caused by particular plant growth‐promoting rhizobacteria were evaluated in sugarcane plants under varying water availability. Under well‐watered conditions, we have found one rhizobacteria isolate (IAC‐RBcr5) able to enhance root dry matter and photosynthesis of sugarcane plants. The IAC‐RBcr5 genome was sequenced and high similarity was found with Pseudomonas putida GB‐1. Based on increased root system size of inoculated plants, we hypothesised that sugarcane plants inoculated with IAC‐RBcr5 would have improved performance under water deficit. Although IAC‐RBcr5 had improved plant leaf CO₂ assimilation under water shortage, inoculation caused reduction of biomass accumulation in sugarcane. The negative influence of water deficit on shoot growth rate and root traits such as volume, area, diameter, length and specific root area was higher in plants treated with IAC‐RBcr5 as compared to non‐inoculated ones. However, rhizobacteria‐induced improvements in leaf and root proline contents would represent a strategy for storing carbon and nitrogen during low water availability and helping both organisms to resume their metabolism after rehydration. In conclusion, we found and identified a rhizobacterium able to improve growth and photosynthesis of sugarcane plants. Such benefit for plant growth was lost under low water availability as a likely consequence of increased carbon‐energy demand by rhizobacteria and their sensitivity to drought.     

Vascularization is a general requirement for growth of plant and animal tumours

Solid-tumour growth in animals as in humans depends on angiogenesis. Tumours that fail to induce the formation of new blood vessels do not enlarge beyond a few millimetres in diameter. Plant tumours induced by Agrobacterium tumefaciens can reach diameters of more than 100 mm, thus raising the question of how they are sufficiently supplied with nutrients and water. Until recently, these rapidly growing tumours were considered unorganized or partly organized masses. However, in analogy to animal and human tumours, growth of leaf and stem tumours depends on neovascularization. Plant tumour cells induce the formation of a sophisticated vascular network consisting of water-conducting vessels and assimilate-transporting sieve elements. Similar to animal and human tumours that overexpress angiogenic growth factors, plant tumours overexpress the T-DNA-encoded vascularization-promoting growth factors auxin and cytokinin upon AGROBACTERIUM: infection. High auxin levels induce ethylene emission from the tumours, which has a strong impact on tumour and host stem, as well as on root structure and function. Ethylene apparently stimulates abscisic acid synthesis in the leaves above the tumour, which reduces transpiration and thus protects the host plant from rapid wilting. Hence, for the elucidation of phytohormone-dependent vascular development in plants, such tumours are regarded as an excellent model system. The comparison of analogous requirement of neovascularization for tumour growth in plants, as in animals and humans, is discussed in terms of interdisciplinary strategies of possible prevention and therapy.     

Relationships Amongst the Fast-growing Rhizobia of Lablab purpureus, Leucaena leucocephala, Mimosa spp., Acacia farnesiana and Sesbania grandiflora and their Affinities with Other Rhizobial Groups

Colony characteristics, growth in litmus milk, precipitation in calcium glycerophosphate medium and utilization of carbon sources of the root-nodule bacteria isolated from the tropical legumes Leucaena, Mimosa, Acacia, Sesbania and Lablab were similar to fast-growing rhizobia of temperate legumes, particularly Rhizobium meliloti. In agglutination tests, isolates from each host shared antigens with one or more of five Rhizobium strains from Leucaena. Infective characteristics of the fast-growing rhizobia were studied in modified Leonard jars and in agar culture. Cross-infections by rhizobia between these plants were common and the association often effective. Lablab was effectively nodulated by its own fast-growing isolate but only formed root swellings, possibly ineffective pseudonodules, with the other isolates. Slow-growing rhizobia which were able to nodulate Macroptilium atropurpureus were unable to form nodules on these legumes except Lablab which was considered more akin to the cowpea group. All fast-growing isolates nodulated, often effectively, Vigna unguiculata and V. unguiculata ssp. sesquipedalis. The isolate from Lablab also effectively nodulated a number of other tropical legumes which have previously only been reported to nodulate with slow-growing nodule bacteria and it also produced ineffective nodulation on Medicago sativa. This is the first record of an effective fast-growing isolate from Lablab.     

Nuclear instability and chromosomal mosaicism in the polyploids ofTrigonella foenum-graecum

It was observed that the polyploids ofTrigonella foenum-graecum produced by seed treatment with 0·2% colchicine died after two cotyledonary stage, while the ones produced by seedling treatment survived. The root and shoot of seed treated plants were found to be mixoploids. The root tips exhibited 2n to 12n chromosomes and with the passage of time there is a regular decrease in the frequency of cells with lower chromosomes. The frequency of dividing cells decreases considerably towards the end of the 6th day due to the highploidy of most of the ploid plants. In case of seedling treatment the first formed tissue was mixoploid of high level similar to that of seed treated ones but in some cases the growing tip reverted to low level of ploidy which lead to more or less normal growth. Since the difference in the constitution of seed and seedling treated plants lies in their root system, it has been suggested that probably highploidy of root system in the former may be responsible for the 100% mortality of plants.     

Cadmium induced oxidative stress and changes in soluble and ionically bound cell wall peroxidase activities in roots of seedling and 3–4 leaf stage plants of <Emphasis Type="Italic">Brassica juncea</Emphasis> (L.) czern

Metabolic adaptations to heavy metal toxicity in plants are thought to be related with developmental growth stage and the type of metal by which plant is affected. In the present study, changes in ionically bound CWP, soluble peroxidase activity, H(2)O(2) level and Malonaldehyde content in roots of cadmium and copper stressed seedlings and cadmium stressed 3-4 leaf stage plants of Brassica juncea were investigated. Cadmium inhibits root growth and reduces fresh biomass. The reduction in root growth and fresh biomass is correlated with increased lipid peroxidation and reduced tolerance. Treatment with cadmium resulted in an increase in ionically bound CWP activity in roots of seedlings but no significant change in its activity was found in roots of 3-4 leaf stage plants. Increased level of H(2)O(2) in roots of cadmium and copper treated seedlings, show a direct correlation with increased activity of ionically bound CWP. H(2)O(2) level in 3-4 leaf stage plant roots was found to be very low. Soluble peroxidase activity decreased in cadmium (50 and 100 mu-icroM) treated seedlings but it was ineffective to cause any change in its activity in 3-4 leaf stage plants. Copper treated seedlings showed an increase in ionically bound CWP activity, H(2)O(2) level and MDA content. Ascorbic acid (50 mM) pretreated seedlings shows significant decrease in ionically bound CWP activity when exposed to 50 muM cadmium. Hence, it is concluded that inhibition of root growth in Brassica juncea seedlings by cadmium, is associated with CWP catalyzed H(2)O(2) dependent reactions which are involved in metabolic adaptations to heavy-metal stress.