Root hairs confer a competitive advantage under low phosphorus availability

Root hairs are presumably important in the acquisition of immobile soil resources such as phosphorus. The density and length of root hairs vary substantially within and between species, and are highly regulated by soil phosphorus availability, which suggests that at high nutrient availability, root hairs may have a neutral or negative impact on fitness. We used a root-hairless mutant of the small herbaceous dicot Arabidopsis thaliana to assess the effect of root hairs on plant competition under contrasting phosphorus regimes. Wildtype plants were grown with hairless plants in a replacement series design at high (60 m phosphate in soil solution) and low (1 m phosphate in soil solution) phosphorus availability. At high phosphorus availability, wildtype and mutant plants were equal in growth, phosphorus acquisition, fecundity and relative crowding coefficient (RCC). At low phosphorus availability, hairless plants accumulated less biomass and phosphorus, and produced less seed when planted with wildtype plants. Wildtype plants were unaffected by the presence of hairless plants in mixed genotype plantings. Wildtype plants had RCC values greater than one while hairless plants had RCC values less than one. We conclude that root hairs increase the competitiveness of plants under low phosphorus availability but do not reduce growth or competitiveness under high phosphorus availability.     

Neutral changes during divergent evolution of hemoglobins

Summary A comparison of the mRNAs for rabbit and human-hemoglobins shows that synonymous changes in codons have accumulated three times as rapidly as nucleotide replacements that produced changes in amino acids. This agrees with predictions based on the so-called neutral theory. In addition, seven codon changes that appear to be single-base changes (according to maximum parsimony) are actually two-base changes. This indicates that the construction of primordial sequences is of limited significance when based on inferences that assume minimum base changes for amino acid replacements.     

Coexpression of the Soybean Vegetative Storage Protein β Subunit (S-VSPβ) Either with the Bacterial Feedback-Insensitive Dihydrodipicolinate Synthase or with S-VSPα Stabilizes the S-VSPβ Transgene Protein and Enhances Lysine Production in Transgenic Tobacco Plants

Soybean vegetative storage proteins (S-VSPs) are lysine-rich leaf proteins, originally found to accumulate to high levels in depodded soybean plants. In the present study, we overexpressed S-VSP, the ruminant stable subunit of the S-VSP genes, in transgenic tobacco plants. The S-VSP protein accumulated in all organs studied, but its level declined drastically with leaf age. This instability of S-VSP could be overcome either by elevating free lysine levels or by coexpressing S-VSP with S-VSP. High levels of rumen-stable, lysine-rich proteins is expected to improve absorption of lysine by ruminants. Furthermore, the expression of S-VSPs in heterologous plants led to a significant increase in total soluble lysine, suggesting that these proteins may also permit better assimilation of lysine by humans and monogastric animals.     

Immunochemical assay applied to mycotoxin biosynthesis: ELISA comparison of sterigmatocystin production byAspergillus versicolor andAspergillus nidulans

Conventional thin layer and instrumental methods for analyzing mycotoxins and their precursors are time-consuming and make the investigation of mycotoxin biosynthesis particularly difficult. As an alternative, sensitive enzyme-liked immunosorbent assays (ELISAs) can be utilized to analyze for these compounds. In this report, sterigmatocystin production in test tube cultures ofAspergillus versicolor ATCC 18643 andAspergillus nidulans ATCC 32610 were compared using competitive ELISA. Polyclonal antiserum that was prepared against a sterigmatocystin hemiacetal-bovine serum albumin conjugate exhibited greatest specificity for sterigmatocystin hemiacetal and sterigmatocystin with less reactivity for O-methylsterigmatocystin. The antiserum could be used to detect as little as 50 ng/ml sterigmatocystin in ELISA. Direct ELISA could be performed on diluted culture broth and on mycelial extracts solubilized with N,N-dimethylformamide.Apergillus versicolor ATCC 18643 produced more sterigmatocystin in SLS medium than in YES medium, and showed maximal levels at between 9 to 12 days incubation. Approximately 75% of sterigmatocystin was detectable in mycelium (254g/ml culture) compared to the extracellular fraction (87g/ml culture).Aspergillus nidulans exhibited qualitatively similar patterns of growth and toxigenesis in SLS medium but accumulated maximal levels of only 15g mycelial sterigmatocystin/ml culture and 5g extracellular sterigmatocystin/ml broth, respectively.     

Transformation of wheat (Triticum aestivum L.) through electroporation of protoplasts

Protoplasts isolated from embryogenic suspension cultures of wheat (Triticum aestivum cv. Hartog) were electroporated in the presence of plasmid pEmuGN and/or pEmuPAT, which contained the reporter gene gus and selectable marker gene bar, respectively. Under optimised electroporation conditions, up to 0.9% of viable protoplasts displayed gus activity two days after electroporation. To select for phosphinothricin (PPT) resistant colonies, electroporated protoplasts were incubated for six weeks in a medium containing 10 g/ml PPT. The cells surviving the selection were maintained as individual colonies on solid medium or as suspension cultures. More than 60% of these colonies exhibited tolerance to 40 g/ml PPT when tested 10 months after initial selection. To date, 57 green plants have been regenerated from these colonies and 24 have been transferred to soil. Southern blot analyses of colonies and plants, using the bar gene sequence as the probe, confirmed transformation of the cells. Positive PAT assays of both regenerated colonies and plants indicated the presence of the bar gene product. These results provide a basis for the establishment of routine procedures for transformation of wheat by direct gene transfer into protoplasts.Abbreviations gus -glucuronidase - PAT phosphinothricin N-acetyltransferase - PPT phosphinothricin - MS Murashige and Skoog medium     

Micropropagation of candelilla,Euphorbia antisyphilitica Zucc

Axillary shoot proliferation was induced in vitro from shoot explants of greenhouse grown candellila (Euphorbia antisyphilitica Zucc). Optimum shoot proliferation was obtained by supplementing a modified Murashige and Skoog [7] medium with 0.13 M naphthalene-acetic acid and 4.44 M 6-benzylaminopurine. Rooting occurred on 100% of shoots transferred to a medium containing half strength salts supplemented with 0.49 M indole-3-butyric acid. Fully rooted plants were transferred to potting soil and established under greenhouse conditions without special acclimatization techniques.     

Agrobacterium-mediated inoculation of plants with tomato golden mosaic virus DNAs

We have adapted the agroinfection procedure of Grimsley and co-workers [4,5] to develop a simple, efficient, reproducible infectivity assay for the insect-transmitted, split-genome geminivirus, tomato golden mosaic virus (TGMV). Agrobacterium T-DNA vectors provide efficient delivery of both components of TGMV when used in mixed inoculation of wild-type host plants. A greater increase in infection efficiency can be obtained by Agrobacterium delivery of the TGMV A component to permissive transgenic plants. These permissive plants contain multiple tandem copies of the B component integrated into the host genome. An inoculum containing as few as 2000 Agrobacterium cells can produce 100% infection under these conditions. Further, our results show that there is a marked effect of the configuration of the TGMV A components within the T-DNA vector on time of symptom development. We have also found that transgenic plants carrying tandem copies of the A component do not complement the B component. Possible mechanisms to explain these results and the potential use of this system to further study the functions of the geminivirus components in infection are discussed.     

Sucrose in storage media and cultivar affects post-storage regrowth of <Emphasis Type="Italic">in vitro</Emphasis> Hosta propagules

The goal of this research was to investigate if culturing in high sucrose (5%) liquid media during multiplication phase (stage II) would enhance endogenous sugar levels and dry matter sufficiently to allow storage of in vitro plants in sugar free media without adversely affecting post-storage recovery. Hosta tokudama Newberry Gold (NBG) and Hosta Striptease were cultured in Murashige and Skoog (MS) media containing 5% sucrose during stage II and transferred to rooting phase (stage III) in MS medium without (0%) sucrose or with 3% sucrose for 4weeks. At the end of stage III, cultures were stored, with the remaining media, at 10°C with 5molm^–2s^–1 photosynthetic photon flux (PPF) from cool white fluorescent lamps for 7 or 14weeks with or without a 2-week dark period prior to removal from storage. In both cultivars, stage III plants cultured in 3% sucrose media had higher soluble sugar levels and greater shoot and root biomass than those cultured in 0% sucrose media. Shoot and root soluble sugars decreased during storage. Shoot growth ceased during storage in both media. Root dry matter continued to increase in plants stored in 3% sucrose media but did not change in 0% sucrose media. Plants cultured in 3% sucrose media had less leaf chlorosis and less mortality after 7 or 14weeks of low temperature storage than the plantlets from sugar free media. Extending the storage period from 7 to 14weeks or introduction of 2-week dark period at the end of storage did not affect leaf chlorosis or plant mortality during acclimatization. Post-storage growth varied with the cultivar. Benefit of having sucrose in storage media was to develop a strong root system that aided the acclimatization and post-storage growth following 7 or 14week storage. Sucrose loading by culturing plants in liquid media containing 5% sucrose did not allow storage in sugar free media without adversely affecting post-storage growth in both cultivars.     

Agrobacterium tumefaciens mediated gene transfer in peanut (Arachis hypogaea L.)

Transgenic peanut plants were produced using Agrobacterium mediated gene transfer. Primary leaf explants of peanut were co-cultivated with Agrobacterium tumefaciens LBA 4404 harbouring the binary plasmid pBI 121 (conferring -glucuronidase activity and resistance to kanamycin) and cultured on regeneration medium supplemented with kanamycin to select putatively transformed shoots. They were rooted and plants were transferred to soil. Stable integration and expression of the transgenes were confirmed by NPT II assay, Southern blot hybridization and GUS assay.Abbreviations BA 6-benzyladenine - GUS -glucuronidase - IAA indole-3-acetic acid - NAA -naphthaleneacetic acid - NOS nopaline synthase - NPT II neomycin phosphotransferase II - SDS Lauryl sulfate     

Axillary shoot induction and plant regeneration in Plantago ovata Forssk

Axillary shoot induction and plant regeneration were obtained in Plantago ovata. The optimum medium for inducing axillary shoots was Murashige & Skoog (MS) medium [5] supplemented with 4.6 M kinetin and 0.05 M NAA. Rooting of shoots was best on half-strength MS medium containing 5.0 M IBA and 0.05 M kinetin. The regenerated plants were similar to the control plants in karyotypic and phenotypic details.     

Silicon amelioration of aluminium toxicity in teosinte (Zea mays L. ssp. mexicana)

The influence of different Al concentrations, (0, 60 and 120 M Al) on growth and internal concentrations of Al, Si and selected organic acids was analysed in plants of teosinte (Zea mays L. ssp. mexicana), a wild form of maize from acid soils from Mexico. The plants were grown in nutrient solutions (pH 4.0) with or without 4 M silicon. Analysis with the GEOCHEM speciation program did not reveal differences between free activities of Al³⁺ in solutions with and without 4 M Si, but solutions with Si yielded lower concentrations of monomeric Al species, [Al]_mono, when analysed by a modified aluminon method. Plants grown on solutions with similar [Al]_mono, but differing in silicon, showed highly significant differences in growth and tissue concentrations of Al and organic acids. Silicon prevented growth inhibition at [Al]_mono concentrations as high as 35 M, while plants grown without Si suffered severe growth reductions with 33 M [Al]_mono. In solutions with similar [Al]_mono concentrations plants with Si had lower tissue Al concentrations and higher concentrations of malic acid than plants without Si. In view of both the significant influence of Si on the response of plants to Al toxicity and the fact that some soluble Si is always present in soil solutions, the addition of low Si concentrations to nutrient solutions used for Al-tolerance screening is recommended.     

Response of traplining bumble bees to competition experiments: shifts in feeding location and efficiency

Summary In field experiments, we mapped the regular foraging routes (traplines) of marked bumble bees visiting Aralia hispida. When other bees were removed to create localized competitive vacuums, the marked bees shifted their feeding activity toward the removal areas. Bees foraging in these competitive vacuums probed more flowers per inflorescence than control bees. One bee's foraging was studied intensively before and after its local competitors were removed. Compared to four nestmates foraging elsewhere, the focal bee's trip times were shorter (p<0.005) and its food collection rate was marginally higher (P=0.064) during the removal, although all the bees foraged similarly before the removal. These observations indicate that traplining bumble bees opportunistically modify their use of space in response to the activities of other bees in a highly competitive environment.     

Isotopic equilibration of calcium-45 with labile soil calcium

Summary When soils are suspended in solutions of labelled calcium chloride isotopic exchange with the labile soil calcium occurs rapidly. This may be followed by a slow secondary exchange reaction, but its magnitude is not great and equilibrium is nearly, if not completely, attained within 7 days.When, however, plants are grown in soil throughout which carrier-free calcium-45 has been thoroughly mixed, it is found that the calcium-45 absorbed by the plants has equilibrated with a quantity of soil calcium larger than that which undergoes isotopic exchange when soils are suspended in solutions of labelled calcium chloride. The analysis of plants grown for varying periods shows that equilibration can continue for several weeks, and that the quantity of soil calcium with which the calcium-45 is associated can be increased both by the addition of electrolytes to the soil and by growing plants under exhaustion conditions. In 5 soils the extra calcium which equilibrated with calcium-45 in this way never exceeded 3.5 per cent of the total soil calcium, and was usually considerably lower.The continued equilibration of calcium-45 with soil calcium causes the specific activity (Ca⁴⁵/stable Ca) of the calcium entering plants to decrease. Because the calcium in plant roots has, on average, been absorbed more recently than that in shoots, the latter show higher specific activities.The causes of these effects are discussed and consideration is given to their significance in the interpretation of results of experiments involving the use of calcium-45 as a tracer in soils.     

Utilisation of soil organic P by agroforestry and crop species in the field,western Kenya

A field experiment in western Kenya assessed whether the agroforestry species Tithonia diversifolia (Hemsley) A. Gray, Tephrosia vogelii Hook f., Crotalaria grahamiana Wight & Arn. and Sesbania sesban (L) Merill. had access to forms of soil P unavailable to maize, and the consequences of this for sustainable management of biomass transfer. The species were grown in rows at high planting density to ensure the soil under rows was thoroughly permeated by roots. Soil samples taken from beneath rows were compared to controls, which included a bulk soil monolith enclosed by iron sheets within the tithonia plot, continuous maize, and bare fallow plots. Three separate plant biomass samples and soil samples were taken at 6-month intervals, over a period of 18 months. The agroforestry species produced mainly leaf biomass in the first 6 months but stem growth dominated thereafter. Consequently, litterfall was greatest early in the experiment (0–6 months) and declined with continued growth. Soil pH increased by up to 1 unit (from pH 4.85) and available P increased by up to 38% (1 g P g^–1) in agroforestry plots where biomass was conserved on the field. In contrast, in plots where biomass was removed, P availability decreased by up to 15%. Coincident with the declines in litterfall, pH decreased by up to 0.26 pH units, plant available P decreased by between 0.27 and 0.72 g g^–1 and P_o concentration decreased by between 8 and 35 g g^–1 in the agroforestry plots. Declines in P_o were related to phosphatase activity (R²=0.65, P<0.05), which was greater under agroforestry species (0.40–0.50 nmol MUB s^–1 g^–1) than maize (0.28 nmol MUB s^–1 g^–1) or the bare fallow (0.25 nmol MUB s^–1 g^–1). Management of tithonia for biomass transfer, decreased available soil P by 0.70 g g^–1 and P_o by 22.82 g g^–1. In this study, tithonia acquired P_o that was unavailable to maize. However, it is apparent that continuous cutting and removal of biomass would lead to rapid depletion of P stored in organic forms.     

EDTA-assisted heavy-metal uptake by poplar and sunflower grown at a long-term sewage-sludge farm

Little information is available concerning the efficacy of chelates applied to biosolids (sewage-sludge)-treated soil for heavy-metal removal. The purpose of the experiment was to determine the availability to sunflower (Helianthus annuus L.) and hybrid poplar (Populus deltoides Marsh. × P. nigra L.) seedlings, of non-essential (Cd, Ni, Pb) and essential heavy metals (Cu, Fe, Mn, Zn) in field soil injected with biosolids since 1976 and treated with ethylenediamine-tetraacetic acid (EDTA) in 2001. Sunflower was grown at two densities, 20000 and 60000 plants/ha, and poplar at 10000 plants/ha. The tetrasodium salt of EDTA was applied at rates of 0, 0.5, 1, and 2 g EDTA salt per kg surface (25-cm depth) soil. The EDTA did not affect uptake by poplar of the three non-essential (Cd, Ni, Pb) and four essential (Cu, Fe, Mn, Zn) heavy metals. For sunflower, the 1.0 g/kg rate of chelate addition resulted in maximal removal of the three non-essential heavy metals (Cd, Ni, Pb). Uptake of the essential heavy metals by sunflower was little affected by the EDTA. At the 20000 plants/ha density, leaves of sunflower grown with 1.0 g EDTA Na₄2H₂O per kg soil accumulated more Cd, Ni, and Pb than leaves of sunflower grown without the EDTA salt. At this density, concentrations of Cd in leaves of sunflower without EDTA and with 1.0 g/kg EDTA salt were 2.2 and 6.5 g/g, respectively; for Ni, they were 6.7 and 19.2 g/g, respectively; and for Pb, they were 15.6 and 46.9 g/g, respectively. At the 60000 plants/ha density, stems of sunflower grown with 1.0 g EDTA Na₄2H₂O per kg soil accumulated more Cd, Ni, and Pb than stems of sunflower grown without the EDTA salt. At this density, concentrations of Cd in stems of sunflower without EDTA and with 1.0 g/kg EDTA salt were 0.6 and 4.6 g/g, respectively; for Ni, they were 1.7 and 17.6 g/g, respectively; and for Pb, they were 5.2 and 42.8 g/g, respectively. Removal of the non-essential heavy metals by sunflower was greater at the higher plant density (60000 plants/ha) compared to the lower one (20000 plants/ha).     

Evidence for the direct involvement ofβ-hemolysin inAeromonas hydrophila enteropathogenicity

Culture filtrates of 19 of 21 (90%) -hemolytic isolates ofAeromonas hydrophila caused fluid accumulation in permanently ligated rabbit ileal loops, whereas no fluid was accumulated with filtrates of eight non--hemolytic isolates. Antiserum to purified -hemolysin neutralized the ileal loop activity of culture filtrates from four of four -hemolytic isolates, and treatment at 56°C for 10 min eliminated the loop activity of six additional isolates. These results support the conclusion that -hemolysin alone causes significant changes in intestinal permeability and that it is a more common pathogenic mechanism than the heat-stable cytotonic enterotoxin. Electrophoretic and serological assays showed evidence for production of only one species of -hemolysin byA. hydrophila.     

Growth regulation of Eurasian watermilfoil with flurprimidol

Studies were conducted in 55-liter aquariums under controlled environment conditions to evaluate growth regulator effects of flurprimidol [-(1-methylethyl)--[4-(trifluoromethoxy) phenyl]-5-pyrimidinemethanol] on Eurasian watermilfoil (Myriophyllum spicatum L.). Treatments included flurprimidol concentrations ranging from 0 to 500 g L^-1, with exposure times varying from 0.25 to 28 days. Extending the flurprimidol contact time increased the growth inhibitory response. Flurprimidol-treated shoots were 14–64% shorter than untreated plants at 14 DAT (days after treatment). Growth inhibition persisted 56 DAT for plants exposed to 25 and 100 g L^-1 flurprimidol for 28 days or 200 g L^-1 flurprimidol for 10 days. Growth-inhibited plants accumulated starch in shoots and roots, whereas plants showing little or no growth suppression utilized available assimilate for growth. Treatments that most effectively suppressed shoot length accumulated up to 68% more total nonstructural carbohydrate compared with untreated plants. Shoot and root dry weight biomass were unaffected by flurprimidol.Abbreviations PGR(s) plant growth regulator(s) - TNC total non-structural carbohydrate - DAT days after treatment - PVC polyvinyl chloride - DW dry weight - BOD biological oxygen demand - DMSO dimethyl sulfoxide - LSD least significant difference     

Heavy metal tolerance and accumulation of Cd, Cr and Ni by Cannabis sativa L.

Experiments in semi-natural conditions were undertaken to assess hemp metal tolerance and its ability to accumulate cadmium, nickel and chromium. Cannabis sativa was grown in two soils, S1 and S2, containing 27, 74, 126 and 82, 115, 139 g g^–1 of Cd, Ni and Cr, respectively. After two months from germination and at ripeness, no significant alteration in plant growth or morphology was detected. On the contrary, a high hemp reactivity to heavy metal stress with an increase in phytochelatin and DNA content was observed during development, suggesting the Cannabis sativa ability to avoid cell damage by activating different molecular mechanisms. Metals were preferentially accumulated in the roots and only partially translocated to the above-ground tissues. The mean shoot Cd content was 14 and 66 g g^–1 for S1 and S2 soil, respectively. Although not negligible concentrations they were about 100 times lower than those calculated for the hyperaccumulator Thlaspi caerulescens. Similarly Ni uptake was limited if compared with that of the Ni-hyperaccumulator Alyssum murale. Chromium uptake was negligible. As expected on the base of the metal concentration detected in ripe plants, no statistically significant variation in soil metal content was detected after one crop of hemp. Nevertheless, a consistent amount (g) of Cd and Ni is expected to be extracted by 1 ha biomass of hemp (about 10 t) per year and along the time a slow restoration of deeper soil portions can be obtained by its wide root system (at least 0,5 m deep). In addition, the possibilities of growing hemp easily in different climates and using its biomass in non-food industries can make heavy metal contaminated soils productive. This means economical advantage along with a better quality of soil.     

Indole alkaloids in clonal propagules of Rauwolfia serpentina benthe ex kurz

Plantlets were succesfully regenerated from shoot cultures of Rauwolfia serpentina initiated from auxillary meristems on medium containing BA (4.44 M) + NAA (0.54 M). Rooting was initiated in White's basal medium supplemented with NAA (0.54 M). Tissue culture derived piants of R. serpentina (RSTC) were similar to normal plants (RS) in their morphological characteristics and chemical consitution. The biomass of the RSTC plants was higher (47.11 gms) than the normal plant (18.23 gms) on a dry weight basis. Five RSTC plants were cloned and the cloned plants were similar in biomass and alkaloid content to the normal plant.Abbreviations BA benzyl adenine - NAA naphthalene acetic acid - MS Murashige and Skoog - TLC thin layer chromatography - HPLC high performance liquid chromatography - F.W. fresh weight - D.W. dry weight - RS normal field grown plant established from stem cuttings - RSTC tissue culture plants established from shoot cultures - R reserpine - Aj ajmalicine - A ajmaline - S serpentine