Evidence of association of salmonellae with tomato plants grown hydroponically in inoculated nutrient solution

The possibility of uptake of salmonellae by roots of hydroponically grown tomato plants was investigated. Within 1 day of exposure of plant roots to Hoagland nutrient solution containing 4.46 to 4.65 log(10) CFU of salmonellae/ml, the sizes of the pathogen populations were 3.01 CFU/g of hypocotyls and cotyledons and 3.40 log(10) CFU/g of stems for plants with intact root systems (control) and 2.55 log(10) CFU/g of hypocotyls and cotyledons for plants from which portions of the roots had been removed. A population of > or =3.38 log(10) CFU/g of hypocotyls-cotyledons, stems, and leaves of plants grown for 9 days was detected regardless of the root condition. Additional studies need to be done to unequivocally demonstrate that salmonellae can exist as endophytes in tomato plants grown under conditions that simulate commonly used agronomic practices.     

Identification and Characterization of Rhizosphere-Competent Bacteria of Wheat

To obtain rhizosphere-competent bacteria which could subsequently be modified for the development of biological control agents, bacteria were isolated from the rhizosphere and rhizoplane of wheat and barley plants by standard techniques. Of these isolates, 60 were selected for field testing as spring wheat seed inoculants in 1985. Isolates were marked genetically for resistance to antibiotics via selection of spontaneous mutants to detect and monitor isolates in the field. Forty-three days after planting, the average log₁₀ CFU/mg (dry weight) of roots and rhizosphere soil for the mutant isolates sampled ranged from 0 to 3.4. Twenty mutant isolates were retested in 1986. A total of 4 isolates were not detected, but the other 16 had an average root colonization value of log₁₀ 2.1 CFU and a range of log₁₀ 0.9 CFU to log₁₀ 3.2 CFU when sampled 32 days after planting. The average colonization value dropped to log₁₀ 1.1 CFU 51 days later. Some isolates detected previously were not detected in the second sampling; others had root colonization values similar to those obtained in the first sampling. Mutant isolates of rhizosphere bacteria included Bacillus pumilus, Bacillus subtilis, Pseudomonas fluorescens, Streptomyces spp., Xanthomonas maltophilia, and a saprophytic coryneform. Mixtures of isolates from different genera and species were compatible on seeds and roots.     

Growth promotion of Prunus rootstocks by root treatment with specific bacterial strains

A collection of bacterial strains obtained from a wide-range origin was screened for ability to promote growth in two types of Prunus rootstocks in a commercial nursery. Only few strains promoted growth significantly and consistently, and a strong specificity for the rootstock cultivar was observed. Irrigation of plants with Pseudomonas fluorescens EPS282 and Pantoea agglomerans EPS427 significantly increased plant height and root weight of the plum Marianna 2624 and the peach–almond hybrid GF-677, respectively. Plant height showed a higher rate of growth in early stages of development (2.6–3.5 times the non-treated controls), but the effect decreased with plant age. However, in aged plants growth promotion was more significant on root weight (1.9 times the non-treated controls) than on plant height. The efficacy of growth promotion and the persistence of strains in the root environment were dependent on the bacterial inoculum concentration applied. Increases in root development were maximum at inoculum concentrations of up to 8 log₁₀ CFU ml^–1 (ca 10 log₁₀ CFU L^–1 of potting mix). Population levels at the optimum inoculum concentration were around 7 log₁₀ CFU g f.w.^–1 root material at early stages of development and decreased to 4 log₁₀ CFU g f.w.^–1 after several months of development. The best plant growth-promoting strains were very diverse in secondary metabolite production and antagonistic ability against several plant pathogens.     

抗感青枯病番茄的内生细菌数量动态分析及其对青枯病的生物防治

对番茄内生细菌数量动态及其对青枯病的生物防治研究结果表明:番茄内生细菌可来源于种子内部。番茄不同生育期,内生细菌数量最多在成株期,其中抗病品种根、茎分别为24.3×104CFU/g鲜重和22.9×104CFU/g鲜重,感病品种根、茎分别为9.8×104CFU/g鲜重和13.4×104CFU/g鲜重。抗病品种中具有拮抗青枯菌的内生细菌菌株为17个,感病品种中7个。部分内生细菌具促进番茄种子萌发和防治番茄青枯病的作用,其中5R和3R内生菌株的防病效果分别达91.7%和81.3%。     

Comparative effects of gibberellic acid and N6-benzyladenine on dry matter partitioning and osmotic and water potentials in seedling organs of dwarf watermelon

Apical applications of 0.2 μg N⁶-benzyladenine (BA), a synthetic cytokinin, or 5 μg of gibberellic acid (GA₃) significantly enhanced hypocotyl elongation in intact dwarf watermelon seedlings over a 48-h period. Accompanying the increase in hypocotyl length was marked expansion of cotyledons in BA-treated seedlings and inhibition of root growth by both compounds. A study on dry matter partitioning indicated that both growth regulators caused a preferential accumulation of dry matter in hypocotyls at the expense of the roots; however, GA₃ elicited a more rapid and greater change than did BA. In comparison to untreated seedlings, BA decreased total translocation of metabolites out of the cotyledons. Water potentials of cotyledons and hypocotyls were determined by allowing organs to equilibrate for 2 h in serial concentrations of polyethylene glycol 4000. Osmotic potentials were determined by thermocouple psychrometry. During periods of rapid growth in cotyledons and hypocotyls of BA-treated seedlings and in hypocotyls of GA-treated seedlings, the osmotic potential increased and the turgor pressure decreased in relation to untreated seedlings, indicating that cell wall extensibility was being increased. Osmotic potentials were lower in hypocotyls of GA-treated than in those of BA-treated seedlings, even though growth rates were higher in GA-treated seedlings, indicating that the latter treatment was generating more osmotically active solutes in hypocotyls.     

Comparative effects of gibberellic acid and N6-benzyladenine on dry matter partitioning and osmotic and water potentials in seedling organs of dwarf watermelon

Apical applications of 0.2 g N⁶-benzyladenine (BA), a synthetic cytokinin, or 5 g of gibberellic acid (GA₃) significantly enhanced hypocotyl elongation in intact dwarf watermelon seedlings over a 48-h period. Accompanying the increase in hypocotyl length was marked expansion of cotyledons in BA-treated seedlings and inhibition of root growth by both compounds. A study on dry matter partitioning indicated that both growth regulators caused a preferential accumulation of dry matter in hypocotyls at the expense of the roots; however, GA₃ elicited a more rapid and greater change than did BA. In comparison to untreated seedlings, BA decreased total translocation of metabolites out of the cotyledons. Water potentials of cotyledons and hypocotyls were determined by allowing organs to equilibrate for 2 h in serial concentrations of polyethylene glycol 4000. Osmotic potentials were determined by thermocouple psychrometry. During periods of rapid growth in cotyledons and hypocotyls of BA-treated seedlings and in hypocotyls of GA-treated seedlings, the osmotic potential increased and the turgor pressure decreased in relation to untreated seedlings, indicating that cell wall extensibility was being increased. Osmotic potentials were lower in hypocotyls of GA-treated than in those of BA-treated seedlings, even though growth rates were higher in GA-treated seedlings, indicating that the latter treatment was generating more osmotically active solutes in hypocotyls.Scientific Contribution No. 1219 from the New Hampshire Agricultural Experiment Station.     

Developmental and environmental regulation of tissue- and cell-specific expression for a pea protein farnesyltransferase gene in transgenic plants

Farnesylation mediates membrane targeting and in vivo activities of several key regulatory proteins such as Ras and Ras-related GTPases and protein kinases in yeast and mammals, and is implicated in cell cycle control and abscisic acid (ABA) signaling in plants. In this study, the developmental expression of a pea protein farnesyl-transferase (FTase) gene was examined using transgenic expression of the β-glucuronidase (GUS) gene fused to a 3.2 kb 5′ upstream sequence of the gene encoding the pea FTase β subunit. Coordinate expression of the GUS transgene and endogenous tobacco FTase β subunit gene in tobacco cell lines suggests that the 3.2 kb region contains the key FTase promoter elements. In transgenic tobacco plants, GUS expression is most prominent in meristematic tissues such as root tips, lateral root primordia and the shoot apex, supporting a role for FTase in the control of the cell cycle in plants. GUS activity was also detected in mature embryos and imbibed embryos, in accordance with a role for FTase in ABA signaling that modulates seed dormancy and germination. In addition, GUS activity was detected in regions that border two organs, e.g. junctions between stems and leaf petioles, cotyledons and hypocotyls, roots and hypocotyls, and primary and secondary roots. GUS is expressed in phloem complexes that are adjacent to actively growing tissues such as young leaves, roots of light-grown seedlings, and hypocotyls of dark-grown seedlings. Both light and sugar (e.g. sucrose) treatments repressed GUS expression in dark-grown seedlings. These expression patterns suggest a potential involvement of FTase in the regulation of nutrient allocation into actively growing tissues.     

Accumulation of copper by roots,hypocotyls, cotyledons and leaves of sunflower (Helianthus annuus L.)

The effects of different concentrations of copper sulfate on the growth of and the accumulation of Cu2+ by root, hypocotyl, cotyledon and leaf growth of sunflower (Helianthus annuus L.) were examined in this study. The concentrations of copper sulfate (CuSO4 x 5H2O) used were in the range from 10(-5) to 10(-3) M. Seedlings exposed to 10(-5) M Cu2+ solution exhibited a 33% increase in growth (P < 0.005) when compared with the root length of the control. The seedlings treated with 10(-3) M Cu2+ were significantly inhibited in shoot growth (P < 0.005). The Cu2+ content in roots, hypocotyls, cotyledons and leaves increased with increasing solution Cu2+ concentration. The roots of plants exposed to 10(-3) M Cu2+ accumulated a large amount of Cu (1070 microgram/g DW), and the Cu2+ level was approximately 25 fold higher than that of control. The Cu2+ contents in sunflower roots treated with 10(-4) and 10(-5) M Cu2+ were about 3.3 and 2.6 fold higher than the control, respectively. Also, the Cu2- level of the roots exposed to 10(-3) M Cu2+ was approximately 7.7 and 9.8 fold respectively, in comparison with the roots of plants grown in 10(-4) and 10(-5) M Cu2+. At 10(-3) M Cu2+, the Cu accumulated mainly in the roots (about 73%), and small amounts of Cu2+ (27%) were translocated to the hypocotyls, cotyledons and leaves. The Cu2+ concentration in the roots was less than that of the above parts of seedlings in treated groups with 10(-5) - 10(-4) M Cu2+. H. annuus has potential ability to accumulate Cu without being overly sensitive to Cu toxicity.     

The role of light and polar auxin transport in root regeneration from hypocotyls of tomato seedling cuttings

A relationship between light conditions, auxin transport and adventitious root formation by hypocotyls of tomato seedling cuttings was demonstrated. Effective rooting of tomato seedling cuttings was observed under continuous white light (WL) irradiation. However, root formation was reduced in darkness or under red (RL) or blue light (BL). At least 3/4-day-long irradiation treatment with (WL) was necessary to increase the number of roots formed in comparison with control cuttings grown in darkness. Light was most effective if applied during the first half of the 13-day-long rooting period. The role of photoreceptor-dependent light perception in the light-regulation of rooting was tested using tomato photomorphogenic mutants: aurea (au) and high pigment (hp). When exposed to WL both mutants generated fewer roots then their isogenic wild type (WT). In darkness or under BL and RL less roots were formed on all plants and no difference was observed between mutants and WT plants. TIBA (2,3,5-triiodobenzoic acid) inhibited rooting in a dose-dependent manner both in darkness and under WL. However, although rooting was suppressed by 0.75 M TIBA in the dark, 8 M TIBA was necessary to block root formation in continuous WL. Inhibition of rooting by TIBA was most efficient when applied at the initial period of rooting, a 1-day-long treatment with TIBA being sufficient to suppress rooting if given during the first 2 days of culture. Later treatment had much less effect on the root formation.     

Narrow-band light regulation of ethylene and gibberellin levels in hydroponically-grown <Emphasis Type="Italic">Helianthus annuus</Emphasis> hypocotyls and roots

Both hypocotyl and root growth of sunflower (Helianthus annuus) were examined in response to a range of narrow-band width light treatments. Changes in two growth-regulating hormones, ethylene and gibberellins (GAs) were followed in an attempt to better understand the interaction of light and hormonal signaling in the growth of these two important plant organs. Hydroponically-grown 6-day-old sunflower seedlings had significantly elongated hypocotyls and primary roots when grown under far-red (FR) light produced by light emitting diodes (LEDs), compared to narrow-band red (R) and blue (B) light. However, hypocotyl and primary root lengths of seedlings given FR light were still shorter than was seen for dark-grown seedlings. Light treatment in general (compared to dark) increased lateral root formation and FR light induced massive lateral root formation, relative to treatment with R or B light. Levels of ethylene evolution (roots and hypocotyls) and concentrations of endogenous GAs (hypocotyls) were assessed from both 6-day-old sunflower plants either grown in the dark, or treated with FR, R or B light. Both R and B light had similar effects on hypocotyl and root growth as well as on ethylene and on hypocotyl GA levels. Dark treatment resulted in the highest ethylene levels, whereas FR treatment significantly reduced ethylene evolution for both hypocotyls and roots. R- and B-light treatments elevated ethylene evolution relative to FR light. Endogenous GA₅₃ and GA₁₉ levels in hypocotyls were significantly higher and GA₄₄, GA₂₀ and GA₁ levels significantly lower, for dark and FR light treatments compared to R and B light-treatments. The patterns seen for changes in GA concentrations indicate FR-, R- and B-light-mediated effects [differences] in the metabolism of the early C₂₀ GAs, GA₅₃ → GA₄₄ → GA_19. Surprisingly, GA₂₀, GA₁ and GA₈ levels in hypocotyls were very much reduced by treatment of the plants with FR light, relative to B and R-light treatments, e.g. the increased hypocotyl elongation induced by FR light was correlated with reduced levels of all three of the downstream C₁₉ GAs. The best explanation, albeit speculative, is that a more rapid metabolism, i.e. GA₂₀ → GA₁ → GA₈ → GA₈ conjugates occurs under FR light. Although this study provided no evidence that elevated ethylene evolution by roots or hypocotyls of sunflower is controlling growth via endogenous GA biosynthesis, there are differences between soil-grown and hydroponically-grown sunflower seedlings with regard to trends seen for hypocotyl GA concentrations and both root and hypocotyl ethylene evolution in response to narrow band width R and FR light signaling.     

Effects of root anaerobiosis on ethylene production, epinasty, and growth of tomato plants

Experiments were performed to determine the source(s) of ethylene-causing epinasty in flooded tomato plants (Lycopersicon esculentum Mill.). Simultaneous measurements were made of ethylene synthesized by the roots and shoots of tomato plants exposed to either aerobic or anaerobic atmospheres in the root zone. When the root zone was made anaerobic by a flowing stream of N₂ gas, petiole epinasty and accelerated ethylene synthesis by the shoots were observed. In soil-grown plants, ethylene synthesis by the root-soil complex increased under anaerobic conditions; but when grown in inert media under the same conditions, ethylene synthesis by roots remained constant or declined during the period of rapid epinastic growth by the petioles. Other characteristic symptoms of flooding, e.g. reduced growth and chlorosis, were also observed in plants with anaerobic roots. Pretreatment of plants with AgNO₃, an inhibitor of ethylene action, completely prevented epinasty, demonstrating that ethylene is the agent responsible for waterlogging symptoms. These results indicate that deprivation of O₂ to the roots is the primary effect of soil flooding, and that this is sufficient to cause increased ethylene synthesis in the shoot. The basis of the observed root-shoot communication is unknown, but root-synthesized hormones or specific ethylene-promoting factors may be involved.     

Altered lignin composition in phenylalanine ammonia-lyase-inhibited radish seedlings: implications for seed-derived sinapoyl esters as lignin precursors

We earlier reported that when phenylalanine ammonia-lyase (PAL) activity in radish seedlings was inhibited by the competitive inhibitor 2-aminoindan-2-phosphonic acid (AIP), soluble sinapoyl esters carried over from the seed were converted to wall-bound esters in young cotyledons. We now report that these soluble sinapoyl esters may also be converted into lignin in the cotyledons. When radish seedlings were grown in the presence of 100 microM AIP, lignin formation (determined as lignothioglycolic acid) was inhibited ca. 74% in the cotyledons and ca. 80% in hypocotyls plus roots. The syringyl to guaiacyl (S/G) ratio in the lignin of AIP-grown plants, as determined by alkaline cupric oxidation and from Fourier-transform infrared (FT-IR) spectra, was higher in cotyledons, but lower in hypocotyls plus roots, as compared to plants grown on distilled water. These results support the view that soluble sinapoyl esters preformed in seeds may contribute to the syringyl moiety of lignin in cotyledons during early seedling development and that there is no appreciable transport of soluble sinapoyl esters from cotyledons to the hypocotyls and roots.     

Cadmium toxicity in tomato (Lycopersicon esculentum) plants grown in hydroponics

The effects of Cd have been investigated in tomato (Lycopersicon esculentum) plants grown in a controlled environment in hydroponics, using Cd concentrations of 10 and 100 μM. Cadmium treatment led to major effects in shoots and roots of tomato. Plant growth was reduced in both Cd treatments, leaves showed chlorosis symptoms when grown at 10 μM Cd and necrotic spots when grown at 100 μM Cd, and root browning was observed in both treatments. An increase in the activity of phosphoenolpyruvate carboxylase, involved in anaplerotic fixation of CO₂ into organic acids, was measured in root extracts of Cd-exposed plants. Also, significant increases in the activities of several enzymes from the Krebs cycle were measured in root extracts of tomato plants grown with Cd. In leaf extracts, significant increases in citrate synthase, isocitrate dehydrogenase and malate dehydrogenase activities were also found at 100 μM Cd, whereas fumarase activity decreased. These data suggest that at low Cd supply (10 μM) tomato plants accumulate Cd in roots and this mechanism may be associated to an increased activity in the PEPC–MDH–CS metabolic pathway involved in citric acid synthesis in roots. Also, at low Cd supply some symptoms associated with a moderate Fe deficiency could be observed, whereas at high Cd supply (100 μM) effects on growth overrule any nutrient interaction caused by excess Cd. Cadmium excess also caused alterations on photosynthetic rates, photosynthetic pigment concentrations and chlorophyll fluorescence, as well as in nutrient homeostasis.     

In vitro plant regeneration via organogenesis of cowpea [Vigna unguiculata (L.) Walp.]

Shoot regeneration via organogenesis was achieved from axenic cowpea [Vigna unguiculata subsp. unguiculata L. (Walp.) Verde.] hypocotyls and cotyledons of advanced breeding lines and varieties. Cotyledons and embryos were excised from green immature pods. The apical parts of the embryos were removed and the hypocotyls were transferred to regeneration media. Cotyledons and hypocotyls were tested on media with gradients of several hormonal and putrescine combinations. Cowpea cotyledons and hypocotyls exhibited a pattern of shoot formation that occurred in three distinct phases. Multiple shoots developed within 45 days from the wounded region of the primary hypocotyl and cotyledons in different media containing a high cytokinin concentration. The induced plant explants were then grown for 20 days in low-intensity light (10 μmol m^–2 s^–1) on the same medium and numerous shoot buds emerged de novo from the upper part of the hypocotyl and the wounded part of the cotyledons. These buds had no apparent vascular connection with the parent tissues. The plant regeneration capability of this procedure was tested with several cowpea genotypes, five of which (83D-442, 86D-1010, 93K-624, Vita 3 and Ife Brown) responded positively with shoot development and were able to form roots and whole plants. Some somaclonal variation was observed. Received: 14 June 1996 / Revision received: 14 December 1996 / Accepted: 25 January 1997     

Fate of Clavibacter michiganensis ssp. sepedonicus, the Causal Organism of Bacterial Ring Rot of Potato, in Weeds and Field Crops

Crops and weeds were tested for their ability to host Clavibacter michiganensis ssp. sepedonicus (Cms), the causal agent of bacterial ring rot in potato. Ten crops grown in rotation with potato in Europe, namely maize, wheat, barley, oat, bush bean, broad bean, rape, pea and onion and five cultivars of sugar beet were tested by stem and root inoculation. About 6–8 weeks after inoculation, Cms could be detected in most crops except onion and sugar beet, in larger numbers in stems (10⁵–10⁶ cells/g of tissue) than in roots (≤10³ cells/g of tissue) in immunofluorescence cell‐staining (IF). Cms was successfully re‐isolated only from IF‐positive stem samples of maize, bush bean, broad bean, rape and pea, but not from roots. Twelve solanaceous weeds and 13 other weeds, most commonly found in potato fields in Europe, were tested in IF as hosts of Cms by stem and root inoculations. Only in Solanum rostratum, a weed present in northern America, Cms persisted in high numbers (10⁸ cells/g tissue) in stems and leaves, where it caused symptoms. In the other solanaceous weeds, Cms persisted at low numbers (approximately 10⁵ cells/g of tissue) in stems but less so in roots. The bacteria could be frequently re‐isolated from stem but not from root tissues. In 2 consecutive years, plants from 14 different weed species were collected from Cms‐contaminated potato field plots and tested for the presence of Cms by dilution plating or immunofluorescence colony‐staining (IFC), and by AmpliDet RNA, a nucleic acid‐based amplification method. Cms was detected in roots but not in stems of Elymus repens plants growing through rotten potato tubers, and in some Viola arvensis and Stellaria media plants, where they were detected both in stems and roots, but more frequently by AmpliDet RNA than by IFC.     

Phytophthora cryptogea root rot of tomato in rockwool nutrient culture:

The effect of root temperature on growth and yield of rockwool-grown tomato plants infected with Phytophthora cryptogea was investigated. Measurements of shoot and root growth were taken at high (25^oC) and low (15^oC) root temperatures during the generative phase of growth. The growth of roots of healthy and P. cryptogea-infected tomato plants in rockwool blocks was higher in plants grown with roots at 25^oC than at 15^oC after 60 days and a similar effect was found in slabs after 98 days. Under sub-optimal conditions for growth the disease became severe when root temperatures were low. Growth of roots was greatest when roots were maintained at a high temperature in combination with an ambient air temperature of c. 15^oC and the response was greater in cv. Counter than cvs Calypso and Marathon. Water-soluble carbohydrates of roots were higher in those produced in blocks than slabs and were reduced by infection compared to healthy plants with roots at 15^oC and 25^oC. Reduced transpiration rates were found 17 days after inoculation in symptomless plants grown at a root temperature of 25^oC. Infection, regardless of the temperature of the roots or cultivar, led to reduced stem growth. The plants grown at 25^oC were taller than those with a root temperature of 15^oC. After 9 wk of harvest, the cumulative fruit yields in infected cvs Counter and Calypso grown at 25^oC were comparable to that in healthy plants grown at either temperature and cumulative fruit numbers followed a similar pattern. High root temperatures led to delayed fruit ripening between weeks 3–10 and a larger number of unripe fruit. The weight of unripe fruit from infected plants grown at 25^oC at the terminal harvest was higher than from healthy plants with roots maintained at 15^oC.     

NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO2

The effect of elevated atmospheric CO₂ on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton (¹H) nuclear magnetic resonance (NMR) imaging. Exposure of 24-d-old plants to atmospheric CO₂-enriched air at 650 cm³ m^?3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short-term drying-stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO₂ (350 m³ m^?3), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO₂ does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO₂ environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate.     

Effect of phosphate fertiliser and plant density on phosphate inflow into ryegrass roots in soil

Summary Ryegrass plants were grown in pots of Horotiu sandy loam, either singly or as a dense sward, with a range of P fertiliser rates and regular harvests. Plants were non-mycorrhizal. P inflows into roots increased with P fertiliser rate. Sward plants absorbed up to 14.3% of the P fertiliser added, and single plants up to 7.6%. Sward plants absorbed most of the fertiliser P available to them within two weeks of germinating. After that, root growth ceased except at the highest P fertiliser rate used, and P inflow into roots decreased from 10^–15 to 10^–16 mole/cm/sec. Single plants, however, had continuous root growth and P uptake throughout the two month experiment, except for those at the two lowest fertiliser rates. Singly grown plants absorbed much more P than each plant in the dense swards. In single plants, root length/root weight ratio increased with increasing P fertiliser. Plant growth was dependant on continued P uptake by the roots, which only occurred if new roots were continally produced and new volumes of soil tapped for P. Non-growing root systems absorbed very little P. re]19760201     

Somatic embryogenesis and plant regeneration from cotyledons of walnut,Juglans regia L.

Immature cotyledons of open-pollinated seeds from five walnut (Juglans regia L.) cultivars were excised from fruits at 6–11 weeks after full pistillate bloom and grown on a sequence of media to induce somatic embryogenesis. Globular, heart, cotyledonary and complete somatic embryos were obtained. Embryogenic cultures were maintained for more than a year by repetitive embryogenesis in which the roots, cotyledons and hypocotyls of somatic embryos formed additional adventive somatic embryos. Mature somatic embryos required a cold treatment of 8–10 weeks at 2–4°C to overcome apical dormancy. Selected plantlets derived from these somatic embryos were grown to young plants in soil. In addition, somatic embryogenesis was induced in J. hindsii (Jeps.), Jeps., and in Pterocarya sp., another member of the Juglandaceae.