Promoted Root Elongation Research Articles

Persistence in soil of the plant growth promoting rhizobacterium Pseudomonas putida GR12-2 and genetically manipulated derived strains

Transformation of the plant growth promoting rhizobacterium Pseudomonas putida GR12-2 with broad-host-range vectors can affect the growth of the bacterium, its ability to promote root elongation of canola seedlings under gnotobiotic conditions, and its persistence in soil. Plasmid transformants, and a transposon-mutagenized derivative of P. putida GR12-2, fell into two classes with respect to these three attributes: strains that were clearly diminished in these capabilities and strains that behaved like the nontransformed wild type. These differences can be accounted for by the imposition of a metabolic load that is created by some types of genetic modification that results in a physiological impairment of the modified bacterium and decreases its ability to function as a plant growth promoting rhizobacterium.Key words: plant growth promoting rhizobacteria, PGPR, bacterial fertilizer, soil bacteria, soil persistence, microcosm.

Comparative structural study ofQuercus serrata andQ. acutissima formed byPisolithus tinctorius andHebeloma cylindrosporum

Ectomycorrhizas were synthesized in pots and growth pouches betweenQuercus serrata, Q. acutissima, and two ectomycorrhizal fungi,Pisolithus tinctorius andHebeloma cylindrosporum. Root morphology and the structure of the mantle and Hartig net were compared using light, fluorescence, scanning and transmission electron microscopy.P. tinctorius initially colonized root cap cells, and eventually produced a highly branched lateral root system with a complete mantle, whereasH. cylindrosporum promoted root elongation with few hyphae on the root apex surface indicating that interaction between roots differs with fungal species. Hartig net structure and hyphal inclusions varied between all the combinations tested. There were structural differences between mycorrhizas ofH. cylindrosporum/Q. acutissima grown in soil and growth pouches, which indicate that the growth pouch environment can induce artefacts in roots. Fruit bodies ofH. cylindrosporum developed in pots withQ. acutissima. AlthoughP. tinctorius has been used to inoculate oak seedlings in the nursery, results of this study indicate thatH. cylindrosporum may also be an effective ectomycorrhizal fungus forQ. serrata andQ. acutissima.

Plant Regeneration from Root Tissue and Establishment of Root Culture of Japanese White Birch (Betula platyphylla var. japonica).

Protocols for in vitro regeneration from root explants and for rapid elongation of root cultures were established on Betula platyphylla var. japonica. Adventitious shoots were differentiated on IS medium supplemented with BAP and NAA from root explants. The highest differentiation rate (50%) was attained on the medium containing 0.8mg/l BAP and 0.03mg/l NAA. The adventitious shoots successfully regenerated perfect plantlets on the rooting medium. Root culture was established from root segments excised from intact plantlets grown in vitro in liquid IS, B5 and WP media containing 1-3% sucrose. B5 medium supported maximum root elongation among the tested media. The use of 100mg/l PVP in B5 medium successfully prevented browning of roots and promoted root elongation. There was no significant difference in the rate of adventitious shoot formation between root explant obtained from root culture and that obtained from intact root from plantlets.

Partial purification and characterization of 1-aminocyclopropane-1-carboxylate deaminase from the plant growth promoting rhizobacterium Pseudomonas putida GR12-2

The plant growth promoting rhizobacterium Pseudomonas putida GR12-2 can utilize 1-aminocyclopropane-1-carboxylate (ACC) as a sole nitrogen source because it possess the unusual enzyme ACC deaminase, which hydrolyzes ACC to ammonia and α-ketobutyrate. This enzyme, which is thought to be intimately involved in the mechanism that the bacterium uses to promote root elongation in developing canola seedlings, was partially purified and characterized. The native form of the enzyme is a trimer with a molecular mass of 105 kDa and a subunit molecular mass of 35 kDa. ACC deaminase activity is found in the cytoplasm of the bacterium, is induced by low levels (i.e., 100 nM) of ACC, and has a temperature optimum at approximately 30 °C and a pH optimum of 8.5. These properties are very similar to those reported for ACC deaminase from another soil bacterium, Pseudomonas sp. strain APC.Key words: 1-aminocyclopropane-1-carboxylate, ACC, plant growth promoting rhizobacteria, PGPR, ACC deaminase, bacterial fertilizer.

1-Aminocyclopropane-1-carboxylic acid deaminase mutants of the plant growth promoting rhizobacterium Pseudomonas putida GR12-2 do not stimulate canola root elongation

The plant growth promoting rhizobacterium Pseudomonas putida GR12-2 was mutagenized with nitrosoguanidine and three separate mutants that were unable to utilize 1-aminocyclopropane-1-carboxylic acid (ACC) as a sole nitrogen source were selected. These mutants are devoid of the ACC deaminase activity that is present in wild-type P. putida GR12-2 cells. Only wild-type cells, but not any of the ACC deaminase mutants, promoted root elongation of developing canola seedlings under gnotobiotic conditions. These results are interpreted in terms of a model in which P. putida GR12-2 promotes root elongation by binding to germinating seeds and sequesters and hydrolyzes some of the unbound ACC, thereby lowering the level of ACC and hence the endogenous ethylene concentration, allowing the roots to grow longer.Key words: 1-aminocyclopropane-1-carboxylate, ACC, plant growth promoting rhizobacteria, PGPR, ACC deaminase, bacterial fertilizer.

Comparative Growth and Gravitropsim Studies in Auxin Response Mutants of Arabidopsis thaliana

We used a video digitizer system to measure the kinetics of promotion and inhibition of root elongation by applied auxin in roots of intact seedlings of Arabidopsis thaliana. We determined the dose response relationship for auxin action on elongation in roots of wild type seedlings and seedlings of four mutants with altered auxin responsiveness. Roots of all four mutants maintained more rapid rates of elongation in the presence of inhibitory concentrations of auxin than did roots of the wild type. The latent period preceding the change in elongation rate after auxin application was the same in the mutants as in the wild type indicating that the differences in the auxin response between the wild type and the mutants are not due to differences in hormone uptake. Low concentrations of auxin induced substantial promotion of root elongation in the wild type and in the mutants aux1-7 and axr2 but not in axr1-3 or axr1-12. The mutants aux1-7 and axr2 showed no gravitropic curvature when stimulated at 90°. The mutants axr1-3 and axr1-12 exhibited rates of gravitropism intermediate between the non-responsive mutants and the wild type. For these intermediate mutants there was an inverse relationship between growth rate and rate of gravitropic curvature.

Root development of in vitro hybrid walnut microcuttings in a vermiculite-containing gelrite medium

Quantitative and qualitative improvements in root development have been obtained in six clones of hybrid walnut trees propagated by tissue culture and selected for multiplication and rooting abilities. A mixture of diluted gelified medium (DKW, macroelements 14) and vermiculite, used in the proportions 250200 (v/v), strongly promoted root elongation (two to seven-fold) and the development of secondary roots of induced shoots (IBA 24.6 μM) after 2 weeks of culture. Furthermore, rooting rates were enhanced (from 15 to 50%) and the number of primary roots per rooted explant was from two to six-fold higher. Distilled water added to vermiculite always gave the poorest rooting. Vermiculite promoted penetration and aeration of the roots more than gelrite alone, and its effect was better than that of perlite. This procedure resulted in 80–100% rooting for five hybrid clones.

Promotion of root elongation by phosphorus deficiency

Decrease of culture solution pH and increase in cation/anion ratio in the plant were observed when horsegram (Macrotyloma uniflorum (Lam.) Verdc.) was grown in solution culture deficient in phosphorus. The effux of H+ from the roots of −P plants was observed in bromocresol purple agar. The length of root cells was considerably increased by −P treatment. Thus a close correlation between H+ excretion, length of the root cells and root elongation in response to P deficiency was established.

Relationship between the distribution of soil macropores and root elongation

Abstract We studied the role of soil macropores in the promotion of root elongation. The roots of maize plants were grown in undisturbed soil columns 30 cm in diameter and 10 cm in height. The number of visible macropores with or without roots was counted in horizontal sections cut every 2–3 cm. The soils used were taken from the BC and C horizons of a Brown Lowland Soil, the BCg and Cg horizons of a Pseudogley and the B horizon of an Ordinary Andosol. The distribution patterns of the soil macropores varied with the soil types. Brown Lowland Soil was characterized by a large number of tubular macropores with a clustered distribution pattern. Ordinary Andosol was characterized by a small number of tubular macropores with a scattered distribution. Pseudogley was characterized by a linked distribution of interstitial macropores. The degree of clustering or linking of the macropores was more pronounced in the B horizons of both the Brown Lowland Soil and Pseudogley than in the C horizons. χ2 test revealed that the root elongation depended on the presence of macropores in each type of soil. Moreover, the distribution of the roots corresponded fairly well with the distribution of the macropores. The proportion of roots that elongated into macropores was higher in the soils with abundant clusters or linkages of macropores. To analyze this relationship, we introduced the concept of entropy as an index to characterize the distribution of macropores. The more pronounced the degree of clustering or linking of the macropores, the lower the value of entropy. The value of entropy, however, was also affected by the mean density of the macropores, and the larger the number of the macropores the higher the value of entropy. To eliminate the influence of the mean density, the ratio of the actual entropy (S′) to the entropy (S) calculated on the assumption that all the macropores were distributed independently. The values of S′/S were low in the B horizons of the Brown Lowland Soil and Pseudogley while high in the Ordinary Andosol. The values of S′/S showed a strong negative correlation with the proportion of the roots penetrating the clustered or linked macropores. This fact suggests that the distribution patterns of the macropores may reflect the mechanical strength, bulk density, and other factors in the soil which hamper root elongation.

Tn 5 -Mediated Cloning of a Genetic Region from Pseudomonas putida Involved in the Stimulation of Plant Root Elongation

Transposon (Tn5) mutagenesis was applied to Pseudomonas putida GR12-2R3, which promotes root elongation (a phenotype designated Pre) of Brassica campestris under gnotobiotic conditions. Of 3,000 Tn5 transconjugants, only one mutant that lost Pre activity but remained prototrophic and capable of plant root colonization was detected. This mutant was complemented by plasmid pRE53, which contained a 15.0-kilobase DNA insert isolated from a parental strain. The complemented mutant regained full Pre activity comparable to that of the wild type.

Involvement of IAA in the interaction betweenAzospirillum brasilense andPanicum miliaceum roots

The possible involvement of IAA in the effect thatAzospirillum brasilense has on the elongation and morphology ofPanicum miliaceum roots was examined by comparing in a Petri dish system the effects of inoculation with a wild strain (Cd) with those of an IAA-overproducing mutant (FT-326). Both bacterial strains produced IAA in culture in the absence of tryptophan. At the stationary growth phase, production of IAA by FT-326 wasca. 12 times greater than that of Cd. When inoculation was made with bacterial concentrations higher than, 106 colony forming units ml−1 (CFU ml−1), both strains inhibited root elongation to the same extent. At lower concentrations Cd enhanced elongation, by 15–20%, while FT-326 was ineffective. Both strains promoted root-hair development, and root-hairs were produced nearer the root tip the higher the bacterial concentration (e. g. root elongation region was reduced). Effects of FT-326 on root-hair development were greater than those of Cd. Acidified ether extracts of Cd and FT-326 cultures had inhibitory or promoting effects on root elongation depending on the dilution applied. At low dilutions, extracts from FT-326 were more inhibitory for elongation than those from Cd. At higher dilutions root elongation was promoted, but FT-326 extracts had to be more diluted than those from Cd. Dilutions that promoted root elongation contained supra-optimal concentrations of IAA, 1–3 orders of magnitude higher than those required for optimal enhancement by synthetic IAA. It is suggested that the bacteria produce in culture an IAA-antagonist or growth inhibitor that decreases the effectiveness of IAA action. The large variability reported for the effects ofAzospirillum on root elongation could be the result of the opposite effects on root elongation of IAA and other compounds, produced by the bacteria.

Organ correlation in long-day flowering ofPharbitis nil

Pharbitis nil, strain Kidachi and Violet, were grown at 20° C under continuous light in various cases of different sizes, containing the nutrient solution or tap water. Kidachi initiated flowers when seedlings were cultured in small cases containing nutrient solution but did not flower in large cases. The application of NAA, kinetin, ABA or 5-chlorobenzoiec acidvia roots in large cases caused flowering, Floral initiation was always accompanied by the suppression of root elongation. The promotion of root elongation by aeration inhibited flowering. Root cutting inhibited flowering. On the other hand, Kidachi did not flower in tap water irrespective of vessel size. Violet did not flower in the nutrient solution even in small vessels, but initiated floral buds in tap water irrespective of vessel size, though the plants grown in large cases developed very long roots. In both types of flowering, cotyledons are necessary to induce flowering and the removal of cotyledons before the 16th day after the start of culture in Kidachi and before the 12th day in Violet completely inhibited flowering. GA3 promoted stem elongation without preventing flowering of Kidachi.

Correlation between Long-Day Flowering and Root Elongation in <italic>Pharbitis nil</italic>, Sfrain Kidachi

Long-day flowering of Pharbitis nil, dwarf strain Kidachi, at 20°C was greatly influenced by the size of the culture vessel and the number of plants per vessel. The smaller the vessel, the greater the flowering response. The volume of nutrient solution per plant was not decisive for long-day flowering. For instance, plants cultured singly in 200-ml beakers flowered, but those cultured in 5,000-ml vessels (33×26×11.5 cm, 48 plants per vessel) did not, even though there was only about 100 ml of nutrient solution per plant. Long-day flowering was always accompanied by the suppression of root elongation, but not by a decrease in the dry weight of roots or shoots, or in the rate at which the leaf primordia appeared (plastochrone). Aeration of the nutrient solution or culture in vermiculite promoted root elongation even in small vessels, thereby inhibiting long-day flowering. Thus the suppression of root elongation seems to be necessary for long-day flowering. Removal of the roots or cotyledons; however, suppressed long-day flowering even when root elongation was inhibited by culture in small vessels. When plants were cultured at 24°C, suppression of root elongation (culture in a small vessel) did not induce long-day flowering; but, short-day treatment induced flowering without suppressing root elongation.

Root Elongation and Plant Growth in a Basal Till Compact Soil Treated with 3,5‐Diiodo‐4‐Hydroxybenzoic Acid and Gibberellic Acid1

AbstractSoils developed on basal till have very dense compact subsoil, which may extend many meters below the topsoil. To improve their moisture storage and other physical conditions, deep subsoiling is usually practiced. In most instances, the beneficial effect of subsoiling is short‐lived and the operation has to be repeated every few years. The spiralling costs of fossil fuel may make repeated subsoiling operations prohibitive. Therefore, as an alternative management technique, the use of small quantities of 3,5‐diiodo‐4‐hydroxybenzoic acid (DIHB) and gibberellic acid (GA3) in the top‐soil to promote root elongation and enhance crop yields was compared with loosening the sub‐soil and also with incorporating limestone in the subsoil after loosening.A growth chamber study showed that roots of alfalfa (Medicago saliva L.) ‘Saranac’ penetrated the dense subsoil, bulk density 1.9 g cm−3, of a poorly drained basal till soil (Fera Luvic Gleysol) when 1,700 g topsoil was treated with 200 ml of 10−2M DIHB or with GA3. However, the roots in loosened subsoil and to which limestone at 11.2 metric ton/ha had been added and incorporated went deeper. The treatments in order of their superiority were: loosened sub‐soil plus limestone > loosened sub‐soil > top‐soil treated with DIHB > topsoil treated with GA3 > control. Mean root lengths of the alfalfa plants in the various treatments were 66.3, 61.0, 51.2, 49.0, and 33.2 cm, respectively. Corresponding mean dry weight yields of shoots in each treatment were 7.05, 6.08, 5.59, 4.65, and 3.08 g.Should the spiraling costs of energy make periodic subsoiling operations uneconomical, the use of small quantities of DIHB in the topsoil may provide an alternate management technique for agricultural lands with dense subsoil.

Interacting effects of subsoil acidity and water on the root behaviour and shoot growth of some genotypes of lucerne (Medicago sativa L.)

The effects of additions of calcium carbonate to a low-calcium, acidic subsoil, underlying a fertilized, limed surface soil, on the root and shoot growth of four lucerne genotypes were studied in deep (85 cm) soil columns. Separate surface and subsoil watering treatments were included after plants were established. A comparison showed that, at low rates of addition, calcium carbonate was more effective than magnesium carbonate in promoting root elongation, but more generally the increase in pH appeared to be the important factor. Surface droughting reduced shoot growth, but the response to subsoil lime continued as long as subsoil moisture was supplied, in accordance with the increased root penetration and ability for water uptake. Thus shoot growth under surface drought reflected (r = 0.973) the total length of deep roots (> 60 cm depth) over all genotypes and lime treatments. The genotypes, which included three from cv. Hunter River and one from cv. Siro Peruvian, differed in several respects. Our selections from Hunter River varied in root morphology, shoot:root ratios and type of response to subsoil lime. The Siro Peruvian genotype produced abundant deep, fine roots and good shoot growth under surface drought.

Root growth ofLolium perenneL.

Abstract The suppression of root elongation of Lolium perenne plants after defoliation to 25 mm above the base of the shoot was accompanied by a decrease in soluble carbohydrates in the roots. The addition of sugar to the root medium largely countered the suppression of root elongation, indicating that the depletion of soluble carbohydrates in the roots was the prime cause of the suppression. Placing undefoliated plants in the dark produced a similar effectto defoliating to 25 mm, indicating that the photosynthetic function of the shoot was more important than the storage function in promoting root elongation. The level of soluble carbohydrates in the roots of plants harvested when elongation of most roots had ceased was found to be comparable with that which supported normal root elongation in other experiments. That under such circumstances the application of sugar to the root medium largely countered the suppression of elongation indicates a shortage of soluble carbohydrates at the root apex, i.e., a failure of translocation from elsewhere in the roots. Such a mechanism which results in the suppression of root elongation before the soluble carbohydrates in the roots are exhausted would aid in the survival of grazed plants through increasing the amount of soluble carbohydrates available for regrowth of the shoot. No explanation was found for the partial suppression of root elongation which still occurred when sugar was supplied to the root medium after defoliation.

Root growth ofLolium perennel.

Abstract The suppression of root elongation of Lolium perenne plants after defoliation to 25 mm above the base of the shoot was accompanied by a decrease in soluble carbohydrates in the roots. The addition of sugar to the root medium largely countered the suppression of root elongation, indicating that the depletion of soluble carbohydrates in the roots was the prime cause of the suppression. Placing undefoliated plants in the dark produced a similar effectto defoliating to 25 mm, indicating that the photosynthetic function of the shoot was more important than the storage function in promoting root elongation. The level of soluble carbohydrates in the roots of plants harvested when elongation of most roots had ceased was found to be comparable with that which supported normal root elongation in other experiments. That under such circumstances the application of sugar to the root medium largely countered the suppression of elongation indicates a shortage of soluble carbohydrates at the root apex, i.e., a f...

Effect of Auxin upon Loss of Calcium from Cell Walls

In 1955, Bennet-Clark (2) and Carlier and Buffel (4) independently suggested that auxin induces elongation of stem and coleoptile tissues by removing calcium from the cell wall. According to this calciumbridge hypothesis, the factor which limits cellular expansion is the number of calcium ions which crosslink the pectin chains of the cell wall. Removing such cross-linkages by auxin would result in elongation. It has been suggested that auxin brings about this removal of calcium by chelation (2, 9, 19) or by methylation of the carboxyl groups to which the calcium is attached (12, 13). Considerable evidence from work with stems and coleoptiles has been used to support such a theory. Calcium increases the rigidity of cell walls (1, 15) and inhibits elongation (8, 16, 19). Ethylenediamine tetraacetic acid (EDTA), which might be expected to remove calcium from the wall by chelation, promotes elongation (2, 9, 19). Auxin induces an increase in the transfer of methyl groups from methionine to the pectin of Avena (12,13) and maize (6) coleoptile cell walls. The fact that calcium promotes root elongation suggests that calcium bridges do not control the elongation of root cells (3). If this theory is correct, adding auxin to a tissue should result in a loss of calcium from the cell walls. The loss of calcium from whole Avena coleoptile tissues has been examined by Thimann and Takahashi. Initial experiments suggested that the combination of auxin and EDTA enhanced this calcium loss (17) but subsequent experiments have indicated that the increase is not significant (Thimann, personal communic.) This calcium-bridge hypothesis has now been directly tested. The effect of auxin on the loss of Ca45 from cell walls has now been determined in Avena coleoptile and maize mesocotyl tissue.