Genetic and morphological diversity of Finnish tansy (Tanacetum vulgare L., Asteraceae)

 Morphological and genetical differences of twenty Finnish tansy (Tanacetum vulgare) genotypes were studied. The genotypes were distinguishable by morphology, and number of flower heads, which correlated positively with height of the plant and height of the corymb. The mean nuclear DNA content in the leaves of tissue-cultured tansy plantlets was 8.86 pg, and variation between genotypes was 27%. The genotypes were also distinguishable on the basis of their RAPD patterns. The RAPD and morphological data were subjected to analysis of principal components, according to which the genotypes were separated into two main groups. Group I included 7 genotypes from southern Finland and 2 genotypes from the eastern lake district. They started to flower later, had more flower heads and nodes per stem, and the corymb was longer than in the other genotypes that originated in the western and central part of Finland and formed group II. Our data are supported by previous studies and suggest that group I may represent native tansy populations in Finland, whereas group II may represent tansy genotypes that have been transported to other parts of Finland through agriculture and attempts of domestication. Received: 19 November 1997 / Accepted: 25 November 1997     

Alterations in growth of tissue-cultured tansy (Tanacetum vulgare L.) treated with antibiotics

Effects of three antibiotics (cefotaxime, rifampicin and gentamicin) were tested on in vitro shoots cultures of tansy (Tanacetum vulgare L.)- These antibiotics were selected because endophytic bacteria isolated from the in vitro shoot cultures of tansy showed that all bacteria were Gram-negative and their growth was reduced by these three antibiotics. Five isolates were Enterobacteriaceae, three were fluorescent Pseudomonas, and two were aerobic bacteria. Increased concentrations of antibiotics caused usually linear or quadratic changes on the initiation of shoot growth, shoot number, growth rate, and shoot height. These changes and changes in pH of the culture media were tansy genotype-dependent following treatments with gentamicin. Also, the treatment with rifampicin or cefotaxime showed a genotype-dependent effect, because they resulted in significantly higher percentage of rooted plants in one of the three tansy genotypes tested. The growth rate and length of shoots were reduced in the media containing both gentamicin and rifampicin, but less so than in media containing both gentamicin and cefotaxime.     

Chemical Diversity of the Natural Populations of Dalmatian Pyrethrum (Tanacetum cinerariifolium (Trevir.) Sch.Bip.) in Croatia

Dalmatian pyrethrum (Tanacetum cinerariifolium (Trevir. ) Sch.Bip. ) is a plant species endemic to the east Adriatic coast. The bioactive substance of Dalmatian pyrethrum is a natural insecticide, pyrethrin, a mixture of six active components (pyrethrins I and II, cinerins I and II, and jasmolins I and II). The insecticidal potential of pyrethrin was recognized decades ago, and dried and ground flowers have traditionally been used in Croatian agriculture and households. A total of 25 Dalmatian pyrethrum populations from Croatia were studied to determine the pyrethrin content and composition, and to identify distinct chemotypes. The total pyrethrin content ranged from 0.36 to 1.30% (dry flower weight; DW) and the pyrethrin I/pyrethrin II ratio ranged from 0.64 to 3.33%. The statistical analyses revealed that the correlations between the percentage of pyrethrin I and of all the other components were significant and negative. The total pyrethrin content was positively correlated with the percentage of pyrethrin I and negatively correlated with cinerin II. The multivariate analysis of the chemical variability enabled the identification of five chemotypes among 25 Dalmatian pyrethrum populations. The chemical characterization of indigenous Dalmatian pyrethrum populations may serve as a good background for future breeding and agricultural exploitation.     

High frequency plant regeneration from mature embryo explants of highland barley (Hordeum vulgare L. var. nudum Hk. f.) under endosperm-supported culture

An in vitro protocol for efficient plant regeneration has been developed from mature embryo explants of highland barley (Hordeum vulgare L. var. nudum Hk. f.) under endosperm-supported culture. Embryos with (endosperm-supported culture, ES) or without endosperm (non-endosperm-supported culture, NES) were excised from mature seeds and cultured on MS medium supplemented with various concentrations of 2,4-D (1–5 mg l⁻¹) for callus induction. The percentage of callus induction from ES explants was significantly (P < 0.05) lower than that from NES. The highest frequency (97.6%) of callus induction was obtained from NES explants on MS medium containing 3 mg l⁻¹ 2,4-D. When the primary calli were maintained at a reduced concentration of 2,4-D (0.5 mg l⁻¹) for 3 weeks, embryogenic calli were formed. The embryogenic calli were then transferred to MS medium supplemented with different concentrations of BA (1–5 mg l⁻¹) and 500 mg l⁻¹ casein hydrolysate (CH) for shoot regeneration. However, the capacity of plant regeneration from ES explant-derived calli was significantly (P < 0.05) higher than that from NES. The best response (81.3%) was observed from ES explant-derived calli on MS medium containing 2 mg l⁻¹ BA. Regenerated plantlets with well-developed root systems were transferred to pots where they grew well, attained maturity and produced fertile seeds. This method could be employed for genetic manipulation studies.     

Plant regeneration from embryogenic suspension-derived protoplasts of ginger (Zingiber officinale Rosc.)

A procedure is described to regenerate plants from embryogenic suspension-derived protoplasts of ginger (Zingiber officinale Rosc.). Somatic embryogenic calli were induced from ginger shoot tips on solid MS medium with half the concentration of NH₄NO₃ and supplemented with 1.0 mg l⁻¹ 2,4-Dichloroacetic acid (2, 4-D) and 0.2 mg l⁻¹ Kin. Rapid-growing and well-dispersed suspension cultures were established by subculturing the embryogenic calli in the same liquid medium. Protoplasts were isolated from embryogenic suspensions with an enzyme solution composed of 4.0 mg l⁻¹ cellulase, 1.0 mg l⁻¹ macerozyme, 0.1 mg l⁻¹ pectolyase, 11% mannitol, 0.5% CaCl₂ and 0.1% 2-(N-morpholino) ethane sulphonic acid (MES) for 12–14 h at 27°C with a yield of 6.27 × 10⁶ protoplasts g⁻¹ fresh weight. The protoplasts were cultured initially in liquid MS medium with 1.0 mg l⁻¹ 2, 4-D and 0.2 mg l⁻¹ Kin. Then the protoplast-derived calli (1.5 cm²) were transferred to a basal MS medium containing 0.2 mg l⁻¹ 2, 4-D, 5.0 mg l⁻¹ benzyladenine (BA), 3% sucrose and 0.7% agar. The white somatic embryos were transferred to MS medium lacking growth regulators for shoot development. Shoots developed into complete plantlets on a solid MS medium supplemented with 2.0 mg l⁻¹ BA and 0.6 mg l⁻¹ α-Naphthaleneacetic acid (NAA). In addition, the effects of AgNO₃, activated charcoal (AC) and ascorbic acid (AA) on browning of protoplast-derived calli are discussed.     

Use of an industrial effluent as a carbon source for denitrification of a high-strength wastewater

Denitrification of a high-strength synthetic wastewater (150 g NO^- ₃ l^-1) was carried out using a wine distillery effluent as an example of an industrial carbon source (22.7 g chemical oxygen demand l^-1). Two configurations were tested: one consisted of an acidogenesis reactor followed by a denitrifying reactor and the other was a single reactor directly fed with the raw effluents. In both cases, denitrification was achieved at a nitrate load of 9.54 g NO^- ₃ l^-1 day^-1 (2.19 g N as NO^- ₃ l^-1 day^-1) with good specific reduction rates: 32.6 mg and 35.2 mg N as NO _x  g volatile suspended solids h^-1, calculated on a single day, for the two-step and the one-step process respectively. Dissimilatory nitrate reduction to ammonium did not occur, even in the one-step process. Received: 26 October 1995/Received revision: 15 February 1996/Accepted: 20 February 1996     

Plantlet regeneration from protoplast-derived embryogenic calli of Crocus cancellatus

Plant regeneration from protoplast culture of Crocus cancellatus was investigated using regenerable embryogenic calli obtained from shoot meristem culture on LS (Linsmaier and Skoog, 1965) medium containing 4 mg l⁻¹ kinetin and 1 mg l⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D). Protoplasts were isolated directly from embryogenic calli. The best protoplast growth was found on those embedded in Ca-alginate beads and cultured with nurse cells in MS (Murashige and Skoog, 1962) medium supplemented with 2 mg l⁻¹ kinetin, 1 mg l⁻¹ 2,4-D and 100 mg l⁻¹ ascorbic acid at 25 °C in darkness. After 4–5 weeks of culture, microcalli appeared on the surface of the Ca-alginate beads, but the protoplasts without immobilization in Ca-alginate beads showed very low cell division. Growth of the microcalli in the medium with nurse cells was much better than in the medium without nurse cells. Transferring beads onto half strength MS medium supplemented with 0.2 mg l⁻¹ kinetin and 0.1 mg l⁻¹ 2,4-D, increased the growth of embryogenic calli. Somatic embryo development was observed either on half strength MS medium growth regulator free or with 1 mg l⁻¹ abscisic acid. Matured embryos germinated on half strength MS medium containing 25 mg l⁻¹ of gibberelic acid. Plantlet formation was obtained on half strength MS medium containing 1 mg l⁻¹ 6-benzyladenine and 1 mg l⁻¹ α-naphthaleneacetic acid at 20 °C in a 16/8 h light/dark cycle. This revised version was published online in June 2006 with corrections to the Cover Date.     

Sesquiterpene and long chain ester from Tanacetum longifolium

A new naturally occurring linear sesquiterpene (tanacetene) (1). having irregular non-head- to- tail attachment of isoprene units, a new long chain ester (2). and 10 known compounds have been isolated from hexane and chloroform extracts of the roots and aerial parts of Tanacetum longifolium wall. The structure of (tanacetene) (1). was established as (2E,6E,10E)-2,6,11-trimethyl-dodeca-2,6,10-triene and that of (2). as heptatriacontanyl eicosanoate by spectroscopic methods along with 10 known compounds. From the oily fraction twelve volatile compounds were identified by GC-MS. The roots of this plant were found to be a new major source of Z-spiroketalenol ether-6,7-epoxy-diyne in 3.2% yield on dry weight basis.     

Non-host plant odor (Tanacetum vulgare; Asteracea) affects the reproductive behavior ofLobesia botrana Den. et Schiff (Lepidoptera: Tortricidae)

Females ofLobesia botrana Den. et Schiff. (Lepidoptera Tortricidae) are attracted in natural conditions by volatiles released by a nonhost plant: tansy (Tanacetum vulgare L.; Asteracea). We have shown that both tansy flowers and their odor inhibit oviposition behavior and mating behavior and reduce adult longevity. The mean number of eggs laid per female isolated with tansy flowers was reduced by up to 50% every 2 days during the 6 days of exposure. This reduction was maintained after the tansy was removed. In the presence of tansy essential oil, the egg-laying reduction ranged from about 30 to 80% according to the odor concentration. The number of spermatophores found in females isolated with tansy flowers was also reduced twofold compared to the control treatment, indicating that the presence of tansy reduced mating activity. This mating activity is strongly reduced, by two-thirds, when adults face the highest dose of essential oil compared to controls. The number of eggs laid by the controls cannot be explained by the number of spermatophores. Therefore, the reduction in oviposition has been attributed to the presence of tansy flowers or to the tansy odor. Tansy flowers and tansy odor increased male mortality during the exposure (10% in the control, 50% in the tansy treatment, and up to 98% in the odor treatment). The highest rates of male mortality occurred during the 4- to 6-day period of exposure to flowers or odor. Repellence resulting in sustained locomotor activity is a possible cause of such a mortality. Female mortality was increased only in response to the highest dose of odor. This increase might be due to egg retention, and not directly to a plant effect. We discuss the effects of tansy flower odor on different patterns relative to the reproductive behavior ofL. botrana and, especially, on oviposition behavior in the ecological context of plant selection and polyphagy.     

Plant regeneration through organogenesis from callus induced from mature zygotic embryos of loblolly pine

Mature zygotic embryos from three seed sources of loblolly pine were cultured on callus induction medium containing 10 mg l^–1 α-naphthaleneacetic acid, 4 mg l^–1 benzyladenine (BA), 400 mg l^–1 casein hydrolysate, and 400 mg l^–1 glutamine for 6 weeks. Light-yellow, loose, glossy, globular callus was formed, and the highest frequency was 35.7%. The highest differentiation frequency of callus on adventitious bud induction medium was 62.1%. After culture of calli with adventitious buds on elongation medium for 6 weeks, adventitious shoots more than 1.0 cm in height were selected for rooting. On rooting medium supplemented with 0.1 mg l^–1 indole-3-butyric acid, 1 mg l^–1 BA, and 0.5 mg l^–1 gibberellic acid, the highest rooting frequency of adventitious shoots was 46% in a culture period of 6 weeks. Established plants survived following transfer to soil at a frequency of 71%. Received: 14 May 1997 / Revision received: 25 September 1997 / Accepted: 11 October 1997     

Organellar segregation,rearrangement and recombination in protoplast fusion-derived Brassica oleracea calli

Summary Cauliflower protoplasts were fused to determine the effect of protoplast source and pretreatment on organellar segregation in fusion products. Mitochondrial and chloroplast type were determined for over 250 calli from eight fusions between iodoacetate-treated or -irradiated leaf or hypocotyl protoplasts with fertile or Ogura cytoplasms. Organelles in fusion-derived calli were identified with five mitochondrial probes and one chloroplast probe. Mitochondrial and chloroplast segregation were independent but biased. Most calli had B. oleracea chloroplasts, but more calli had Ogura mitochondria than B. oleracea ones. Neither protoplast source nor pretreatment alone affected organelle segregation. However, iodoacetate treatment of hypocotyl protoplasts reduced their mitochondrial contribution to the fusion products although it did not affect chloroplast segregation. Over half of the calli had mitochondrial genomes distinct from those of either fusion partner; many of these contained the complete mitochondrial genome of one partner along with some mitochondrial DNA from the other. Out of 258 calli, 83 showed evidence of mitochondrial recombination, most commonly by formation of a novel 11-kb PstI fragment near the atp9 region.     

Improved callus formation and plant regeneration for shed microspore culture in asparagus (Asparagus officinalis L.)

 To establish an efficient asparagus microspore culture system, experiments were conducted to investigate the effects of medium components, period of cold pretreatment for flower buds, and period of anther co-culture on culture response. All factors affected the frequency of asparagus microspore division and the yields of microspore-derived calli. The best results were obtained by pretreating genotype G459 flower buds at 4  °C for 7–9 days, co-culturing anthers with shed microspores for 14 days, and including 6% sucrose, 2 mg l^–1α-naphthaleneacetic acid and 1 mg l^–1 N⁶-benzylaminopurine in the culture medium. After 4 days of culture, most shed microspores contained starch-like bodies and died. The 2% of shed microspores lacking these structures divided to produce microcalli. For the best treatments in the different experiments, about 140 calli per 100 anthers were recovered. Cultured on four different regeneration media, 19.6–21% and 3.9–8.0% of microspore-derived calli produced shoots and embryos, respectively, and ultimately plantlets, among which 49% were haploid, 34% diploid, 4% triploid and 11% tetraploid. Received: 3 September 1998 / Revision received: 25 November 1998 / Accepted: 5 December 1998     

Friable embryogenic callus and somatic embryo formation from cotyledon explants of African marigold (Tagetes erecta L.)

Embryogenic callus and somatic embryos were induced from cotyledonary explants of African marigold (Tagetes erecta L.). Cotyledons were first cultured on MS medium supplemented with 2.0 mg l^–1 2,4-D and 0.2 mg l^–1 kinetin. After 5 weeks, calli were transferred to MS medium supplemented with 0.02 mg l^–1 thidiazuron where compact embryogenic callus developed. Friable embryogenic callus developed when the compact embryogenic callus was transferred to medium containing 2,4-D and subcultured every 2 weeks. Friable embryogenic callus has been maintained for more than 2 years without losing the capacity to generate embryos. Embryo development was obtained when friable embryogenic callus was transferred to MS medium supplemented with 3 mg l^–1 ABA and 60 g l^–1 sucrose. The addition of 10–30 mM l-glutamine improved embryo development. Received: 13 May 1997 / Revision received: 24 February 1998 / Accepted: 28 March 1998     

Biomass, production and heterotrophic activity of bacterioplankton in the Great Astrolabe Reef lagoon (Fiji)

 Biomass, production and heterotrophic activity of bacterioplankton were determined for two weeks in the Great Astrolabe Reef lagoon, Fiji. Bacterial and Bacterial activities were distributed homogeneously throughout the water column (20 to 40 m deep) and varied little from site to site inside the lagoon. Bacterioplankton biomass and production also varied little over a diel period with coefficients of variation of 9 and 22%, respectively. On average, over the whole study, bacterial abundance was 0.77×10⁹ cells l^-1 and bacterial production averaged 0.36 μg-at. C l^-1 d^-1. Bacterial abundance and production were greater in the lagoon than in oceanic waters. Attachment to particles seems to provide an advantage for bacterioplankton growth because specific growth rates for attached bacterioplankton were, on average, significantly greater than that of the free community. Growth efficiency, determined by correlating the net increase of bacterial biomass and the net decrease of dissolved organic carbon (DOC) in dilution cultures, was very low (average 6.6%). Using carbon growth efficiency and bacterial production rates, heterotrophic activity was estimated to average 5.4 μg-at. C l^-1 d^-1. The turn-over rate of DOC (average 114 μg-at. C l^-1) due to bacterial consumption was estimated to be 0.048 d^-1 during the period of study. Accepted: 25 July 1998     

The microbial plankton of Lake Fryxell,southern Victoria Land,Antarctica during the summers of 1992 and 1994

 Samples collected from Lake Fryxell, southern Victoria Land, Antarctica in January 1992 and 1994 were analysed for the abundance of bacterioplankton and the diversity and abundance of protistan plankton. At the times of sampling, 14 ciliate species and 10 species of autotrophic flagellate were recorded. The samples contained two species of rotifer (Philodina spp.), which formed the first record of planktonic metazoans in the Dry Valley lakes of this region of Antarctica. Bacterial concentrations ranged between 1.0 and 3.8×10⁸ l^-1 in the upper oxic waters increasing to 20×10⁸ l^-1 in the anoxic waters. Heterotrophic flagellates decreased in abundance down the oxygenated water column, disappearing completely at 9 m, and ranged between 0.28 and 7.39×10⁵ l^-1 in abundance. Autotrophic flagellates were much more abundant exhibiting a number of distinct peaks down the water column (1.89–25.3×10⁸ l^-1). The ciliated protozoa were very abundant (up to 7720 l^-1) in relation to flagellate and bacterial numbers, typical of oligotrophic lakes world-wide. The distribution of the protistan plankton showed marked zonation, probably in response to the differing salinity and temperature gradients in the water column. Possible trophic interactions are discussed and comparisons with other continental Antarctic lakes made. Received: 29 November 1995/Accepted: 18 February 1996     

Production of poly(3-hydroxyalkanoates) by Pseudomonas putida KT2442 in continuous cultures

 The synthesis of poly(3-hydroxyalkanoates) (PHA) by Pseudomonas putida KT2442 growing on long-chain fatty acids was studied in continuous cultures. The effects of the growth rate on the biomass and polymer concentration were determined and it was found that the PHA concentrations decreased with increasing growth rates. The highest volumetric productivity was 0.13 g PHA l^-1 h^-1 at a specific growth rate (μ) of 0.1 h^-1. The molecular mass of the polymer remained constant at all growth rates but changes in the monomeric composition of the PHA synthesized were observed. Variation of the carbon to nitrogen (C/N) ratio of the substrate feed at μ=0.1 h^-1 revealed optimal PHA formation at C/N=20 mol/mol. In order to optimize PHA production P. putida KT2442 was cultivated to high cell densities in oxygen-limited continuous cultures. In this way a maximum biomass concentration of 30 g/l containing approximately 23% PHA was achieved. This corresponds to a volumetric productivity of 0.69 g  l^-1 h^-1. Received: 14 December 1995 / Received revision: 18 April 1996 / Accepted: 22 April 1996     

Mutation induced by ethylmethanesulphonate (EMS), in vitro screening for salt tolerance and plant regeneration of sweet potato (<Emphasis Type="Italic">Ipomoea</Emphasis><Emphasis Type="Italic">batatas</Emphasis> L.)

Salt tolerant cultivars of sweet potato (Ipomoea batatas L.) can be obtained from induced mutation. The objective of the present study was to induce mutation for salt tolerance using ethylmethanesulphonate (EMS) in calli of sweet potato, followed by cell line selection and subsequent plant regeneration. Calli initiated from leaf explants were treated with 0.5% EMS for 0, 1, 1.5, 2, 2.5 and 3 h, followed by rinsing with sterile distilled water for four times. Preliminary experiments showed that 200 mM NaCl could be used as selection pressure. Salt tolerant calli were sub-cultured on medium supplemented with 200 mM NaCl for selection of mutant cell lines and this process repeated 5 times (20 days each). The selected calli were transferred onto somatic embryo formation medium, which was Murashige and Skoog (MS) medium supplemented with 4 mg l⁻¹ abscisic acid (ABA), 10 mg l⁻¹ gibberellic acid (GA). After 15 days, somatic embryos were transferred onto MS medium supplemented with 0.05 mg l⁻¹ ABA, 0.2 mg l⁻¹ zeatin (ZT) for regeneration. Plants designated as ML1, ML2 and ML3 were regenerated from the somatic embryos formed by calli treated with 0.5% EMS for 2 and 2.5 h. After propagation, salt tolerance of these mutants was investigated. Data suggested the mutants were more salt tolerant than control plants.     

Variation in volatile compounds from tansy (Tanacetum vulgare L.) related to genetic and morphological differences of genotypes

Air-dried flower heads of 20 Finnish tansy genotypes were extracted with petroleum ether and analyzed using GC-MS. A total of 55 volatile compounds were detected, and 53 were identified. Of the tansy genotypes studied, 15 were well defined and five were mixed chemotypes. Complete linkage analysis differentiated the populations into six clusters. The most frequently found monoterpene was camphor with or without several satellite compounds such as camphene, 1,8-cineole, pinocamphone, chrysanthenyl acetate, bornyl acetate and isobornyl acetate. In 13 genotypes, camphor concentration exceeded 18.5% and in seven genotypes, camphor was less than 7.2%. Other chemotypes rich in trans thujone, artemisia ketone, 1,8-cineole, or davadone-D were also identified. Davadone-D and a mixed chemotype, containing tricyclene and myrcene, were identified from a Finnish tansy for the first time. Geographically, most chemotypes containing camphor originated from Central Finland, whereas chemotypes without camphor such as artemisia ketone, davadone D and myrcene-tricyclene originated from South or Southwest Finland. Morphologically, the 20 tansy chemotypes based on the groups formed from complete linkage cluster analysis, were compared. The group containing the highest concentration of camphor chemotypes had the tallest shoots. The groups consisting from chemotypes containing davadone-D or artemisia ketone, which originated from Southwest Finland, produced the highest number of flower heads, had the tallest corymb, and were last to flower. Also, the group consisting from chemotypes with a high concentration of camphor and originated from South Finland started to flower late. The correlation between the genetic distance matrices based on RAPD patterns reported previously (Keskitalo et al., 1998. Theo. Appl. Genet. 96, 1141-1150.) and the chemical distance matrices of the present study of the same tansy genotypes was highly significant (0.41, P<0.0001).     

Diurnal changes in assimilate concentrations and fluxes in the phloem of castor bean (Ricinus communis L.) and tansy (Tanacetum vulgare L.)

Reports about diurnal changes of assimilates in phloem sap are controversial. We determined the diurnal changes of sucrose and amino acid concentrations and fluxes in exudates from cut aphid stylets on tansy leaves (Tanacetum vulgare), and sucrose, amino acid and K(+) concentrations and fluxes in bleeding sap of castor bean pedicel (Ricinus communis). Approximately half of the tansy sieve tubes exhibited a diurnal cycle of sucrose concentrations and fluxes in phloem sap. Data from many tansy plants indicated an increased sucrose flux in the phloem during daytime in case of low N-nutrition, not at high N-nutrition. The sucrose concentration in phloem sap of young Ricinus plants changed marginally between day and night, whereas the sucrose flux increased 1.5-fold during daytime (but not in old Ricinus plants). The amino acid concentrations and fluxes in tansy sieve tubes exhibited a similar diurnal cycle as the sucrose concentrations and fluxes, including their dependence on N-nutrition. The amino acid fluxes, but not the concentrations, in phloem sap of Ricinus were higher at daytime. The sucrose/amino acid ratio showed no diurnal cycle neither in tansy nor in Ricinus. The K(+)-concentrations in phloem sap of Ricinus, but not the K(+) fluxes, decreased slightly during daytime and the sucrose/K(+)-ratio increased. In conclusion, a diurnal cycle was observed in sucrose, amino acid and K(+) fluxes, but not necessarily in concentrations of these assimilates. Because of the large variations between different sieve tubes and different plants, the nutrient delivery to sink tissues is not homeostatic over time.     

Asymmetric protoplast fusion between sweet potato and its relatives,and plant regeneration

Experiments were conducted to asymmetrically fuse protoplasts from sweet potato (Ipomoea batatas L. Lam.) and its wild relativesI. trifida Don. andI. lacunosa L. Protoplasts of sweet potato were treated with iodoacetamide, whereas those ofI. trifida Don. andI. lacunosa L. were irradiated with X-rays. The asymmetric protoplast fusion was carried out by the electrofusion method and by polyethylene glycol treatment. Electrically-fused protoplasts initiated cell division, and then formed calli earlier than the polyethylene glycol-fused protoplasts. Plant regeneration occurred only in electrofused calli, suggesting that polyethylene glycol had some toxic effect on plant regeneration ability. Analysis of peroxidase isozymes confirmed the interspecific hybrid characteristics of both the fusion-derived calli and regenerated plants.