Involvement of ethylene on growth and plant regeneration in callus cultures of Heliconia psittacorum L.f.

The level of ethylene accumulated in morphogenic callus cultures of Heliconia psittacorum L.f. was only one quarter that of non-morphogenic cultures. The rate of ethylene production in the morphogenic callus cultures during early stages of differentiation of protocorm-like bodies leading to plantlet regeneration was 10-fold higher than that during callus proliferation. In cultures sealed with gastight serum caps, fresh weight gain was reduced 2-to 3-fold compared to those that were closed with Kaputs. Treatment with 1-aminocyclopropane-1-carboxylic acid ( 100 M) caused complete inhibition of plant regeneration from the morphogenic callus on subsequent culture under inductive conditions. Silver nitrate and aminoethoxyvinylglycine also reduced plant regeneration. These results indicate that while high levels of ethylene were inhibitory, a low level of endogenous ethylene production may be necessary during the plant regeneration phase in callus cultures of Heliconia.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - AC activated charcoal - ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - BM basal medium - CH casein hydrolysate - DM development medium - MM maintenance medium - PLB protocorm-like body     

Effect of salicylic acid on protein composition of Tatar buckwheat Fagopyrum tataricum calluses with different ability for morphogenesis

The effect of salicylic acid on the content of soluble proteins and individual polypeptides in Tatar buckwheat Fagopyrum tataricum calluses differing in ability for morphogenesis was studied. Changes in the protein composition of the calluses cultivated in the dark and in the light indicated the higher sensitivity of the non-morphogenic callus. Different response of callus cultures to salicylic acid and conditions of cultivation (light, darkness) is suggested to be associated with the antioxidant defense system, which is, in particular, characterized by the hydrogen peroxide content in the calluses. Salicylic acid increased the H₂O₂ content in non-morphogenic calluses more strongly than in morphogenic calluses, and the difference was more significant for the calluses cultivated in the light.Translated from Biokhimiya, Vol. 70, No. 3, 2005, pp. 390–396.Original Russian Text Copyright © 2005 by Maksyutova, Galeeva, Rumyantseva, Viktorova.     

桥山林区麻栎种群不同发育阶段空间格局及关联性

为探究麻栎种群不同发育阶段的空间分布特征及关联性,以黄土高原南部桥山林区麻栎天然次生林为研究对象,用L(r)函数对麻栎种群不同发育阶段空间分布特征及关联性进行分析。结果表明:(1)样地内麻栎种群各发育阶段数量结构均为不规则倒"J"型,种群结构稳定,能实现持续更新。(2)麻栎种群总体的空间分布特征受生境异质性影响较大,纯林样地中,种群在0—10 m尺度上表现为高强度聚集分布,5—35 m尺度表现为低强度聚集;混交林样地中,0—5 m尺度上表现为高强度聚集分布,5—35 m尺度上则表现为低强度聚集分布。(3)随着种群的发育及尺度的增大,麻栎种群空间聚集强度减弱,纯林样地内,麻栎幼苗在0—6 m的小尺度表现为聚集分布,6—12 m尺度上表现为随机分布;幼树在各尺度上均表现为聚集分布;中龄树与成龄树在各尺度上均表现为随机分布。混交林样地中,仅幼苗在0—6 m尺度上表现为聚集分布,其余各阶段在各尺度下均趋于随机分布。(4)种群不同发育阶段不同尺度空间关联性不同,纯林样地中,幼苗与幼树在1—2 m小尺度上呈负相关,幼树与中龄树在8 m尺度呈正相关,其余各生长阶段之间在任意尺度上均无关联性;混交林样地中,幼树与中龄树在2—12 m尺度上表现为正相关,其余各生长阶段之间在各尺度上均无关联。在未来的森林经营中,应对不同发育阶段、不同生境的种群进行不同抚育措施,促进种群良性发育。     

Organization of actin filaments in regenerating and outgrowing subprotoplasts from pollen tubes ofNicotiana tabacum L.

The dynamics of actin-filament organization in pollen-tube subprotoplasts ofNicotiana tabacum L. cv. Samsun during regeneration and outgrowth was examined using phalloidin probes and a non-fixation method. A succession of actin arrays was examined during subprotoplast regeneration that strongly resembled the actin dynamics described for developing microspores by Van Lammeren et al. (1989, Planta178, 531–539) and activated pollen by Tiwari and Polito (1988, Protoplasma147, 5–15). At the end of the succession the actin filaments often became extended between two opposite polar foci. The ordering of the cortical actin filaments reflected a polarity in the subprotoplasts which determined the plane of outgrowth. The site of outgrowth was often marked by a ring of actin filaments. As growth proceeded and tube-like structures were formed, the arrangement of cortical actin filaments was found to be transverse to the elongation axis. Since the patterns of actin distribution were identical in both caryoplasts and cytoplasts, it was concluded that the pollen-tube cytoplasm has the intrinsic capacity of reorganizing actin filaments and imposing polarity on the spherical subprotoplasts.     

Phenology of first and peak emergence of Aphthona lacertosa and A. nigriscutis: Two flea beetles introduced for biological control of leafy spurge, Euphorbia esula L.

Nonlinear models were used to estimate first emergence and peak abundance dates for Aphthona lacertosa Rosenhauer and A. nigriscutis Foudras, two flea beetles introduced to control leafy spurge, Euphorbia esula L., in North America. For model development, 26 field sites were sampled for flea beetle abundance at weekly intervals for eight weeks in three western Minnesota counties in 2000, 2001, and 2002. A three-parameter Weibull function, fit to observed cumulative probability distributions, were used to predict accumulated degree-days (ADD) to first emergence. Bias testing indicated the Weibull function provided a useful estimate of first emergence for A. lacertosa (304 ADD, lower developmental threshold 7.5 °C), but failed to produce a useful estimate for A. nigriscutis. A third-order polynomial was used to approximate seasonal abundance and predict peak abundance for each species. Estimated ADD to peak abundance of A. lacertosa was 594 ± 24 (DD > 7.5 °C) and 670 ± 15 (DD > 9.3 °C) for A. nigriscutis. Models were validated with additional data sets from Minnesota, Montana, and North Dakota. Estimated date of peak emergence provided useful predictions of peak emergence for Minnesota and North Dakota, but failed to predict peak emergence in Montana. We speculate that variation in climate and environmental conditions between Midwestern states and Montana were responsible for differing emergence patterns. We conclude that phenology models should be developed regionally to provide useful predictions of peak emergence for land managers. Maps were developed for Minnesota to spatially display predicted dates of peak abundance for A. lacertosa and A. nigriscutis.     

Ingestion of the dinoflagellate, Pfiesteria piscicida, by the calanoid copepod, Acartia tonsa

The dinoflagellate, Pfiesteria piscicida, can form harmful algal blooms in estuarine environments. The dominant copepod species usually found in these waters is Acartia tonsa. We tested the ability of A. tonsa to graze the non-toxic zoospore stage of P. piscicida and thus serve as a potential biological control of blooms of this algal species. A. tonsa grazed the non-toxic zoospore stages of both a non-inducible P. piscicida strain (FDEPMDR23) and a potentially toxic strain (Tox-B101156) at approximately equal rates. Ingestion of P. piscicida increased with cell concentration and exhibited a saturated feeding response. Both the maximum number of cells ingested (I_max) and the slope of the ingestion curve (α) of A. tonsa feeding on P. piscicida were comparable to these ingestion parameters for A. tonsa fed similar-sized phytoplankton and protozoan species. When these laboratory ingestion rates were combined with abundance estimates of A. tonsa from the Pocomoke Estuary and Chesapeake Bay, we found that significant grazing control of the non-toxic zoospore stage of P. piscicida by A. tonsa would only occur at high copepod abundances (>10 copepods L⁻¹). We conclude that under most in situ conditions the potential biological control of blooms of P. piscicida is exerted by microzooplankton grazers. However, in the less saline portions of estuaries where maximum concentrations of copepods often occur with low abundances of microzooplankton, copepod grazing coefficients can be similar to the growth rates of P. piscicida.     

橘小实蝇与番石榴实蝇卵及蛹的种间竞争

【背景】实蝇的竞争可能发生在生活史的各个阶段,但未见卵和蛹的种间竞争的相关报道。【方法】将橘小实蝇与番石榴实蝇的卵及蛹按照相应的比例或龄期分别进行混合培养,分析2种实蝇的卵或蛹混合后的发育历期和存活率是否受到彼此影响。【结果】橘小实蝇与番石榴实蝇的卵同龄等量混合,对彼此卵的历期和孵化率无影响。当橘小实蝇和番石榴实蝇的蛹为新鲜蛹时,分别与比它们蛹龄大1 d的对方蛹混合,蛹的羽化率分别为(87.67±3.61)%和(84.33±2.56)%,显著小于对照,说明在此混合蛹处理中,后化蛹者的发育可能受到先化蛹者的抑制。【结论与意义】总体上,在卵和蛹期,橘小实蝇与番石榴实蝇未产生竞争作用;但不排除蛹期竞争的可能性,这种竞争可能存在于特定的蛹期。     

下延叉蕨和芽胞叉蕨配子体发育的研究

利用光学显微镜详细观察了叉蕨属(Tectaria)下延叉蕨(Tectaria decurrens)和芽胞叉蕨(T.fauriei)的配子体发育过程,记录了配子体各发育阶段的特征。结果表明:(1)下延叉蕨和芽胞叉蕨的孢子均为单裂缝,具周壁,由周壁形成纹饰,孢子极面观椭圆形,赤道面观豆形或肾形。(2)孢子萌发方式为向心型。(3)原叶体发育方式为三叉蕨型。(4)成熟原叶体心脏形,两翼向斜上方扩展。(5)均具单细胞和多细胞毛状体,在丝状体或片状体阶段出现。研究认为,从配子体发育角度看,叉蕨属是较进化的陆生真蕨类;毛状体的类型、位置和出现时间等特征在叉蕨属种间存在差异,可作为该属种间分类的特征。     

Survivin protein expression in bovine follicular oocytes and their in vitro developmental competence

This study examined the relationship between survivin expression and the stage of development of in vitro cultured bovine oocytes and embryos; and whether survivin expression is affected by the quality of cumulus–oocyte complexes (COCS) or the quality of pre-implantation embryos. A polyclonal antibody was prepared using recombinant bovine survivin protein. Expression of survivin mRNA and protein was analyzed by real-time quantitative RT-PCR and immunocytochemistry. In the first experiment, survivin mRNA expression was examined at developmental stages from germinal vesicle (GV) oocyte to blastocyst, it was significantly decreased after fertilization of matured oocytes (P < 0.05), then increased slightly to the 8-cell stage followed by rapid increases at the morula and blastocyst stages (P < 0.05). In the second experiment, the effect of oocyte quality on survivin protein, pro-apoptotic (bax, caspase-3) and anti-apoptotic (survivin, bax inhibitor) mRNA expression was examined. Survivin protein was more strongly expressed in good quality COCS than in poor quality COCS. The expression of the anti-apoptotic genes, survivin and bax inhibitor, was significantly higher (P < 0.05) and that of the pro-apoptotic genes, bax and caspase-3, was significantly lower (P < 0.05) in good compared to poor quality COCS. The developmental competence of good quality COCS (30.4% blastocysts) was significantly better than that of poor quality COCS. In the last experiment also, we confirmed that significantly higher expression of survivin and bax inhibitor genes and significantly lower expression of bax and caspase-3 genes was resulted in good quality blastocysts than in poor quality blastocysts (P < 0.05). It was concluded that the expression of survivin was related to the quality of COCS, their developmental competence and the quality of in vitro produced blastocysts. Consequently, survivin may be a good candidate marker for embryo quality.     

Confirmation and identification of parasitic stages of obligate endobionts (Harpellales) in blackflies (Simuliidae) by means of rRNA sequence data

Over the last 35 y, the life cycle of endosymbiotic gut fungi (Harpellales) has been expanded to include cyst stages associated with the developing ovaries. Ovarian cysts (chlamydospore stages) have been identified after germination and production of asexual trichospores in vitro, but germination is not always successful, and spores exhibit morphological variation. Sequence data (for partial 18S and 28S rRNA genes) were generated for these putative stages of Harpellales using ungerminated cysts from adult blackflies and germinated cysts associated with field-collected blackfly egg masses. Cladistic analyses of the 18S and 28S rRNA sequences confirmed that ovarian cysts are stages in the life cycle of Harpellales. Ungerminated cysts, from a blackfly collected from New York state were identified as Pennella simulii and two samples from Newfoundland Prosimulium mixtum adults were identified as Harpella melusinae. Cysts with bipolar germ tubes, associated with field-collected Simulium egg masses from Newfoundland, were also identified as H. melusinae. Two other samples of cysts could not be matched with available sequences of gut fungi from larval hosts. The potential use of this approach to identify pathogenic stages associated with adult ovaries or field-collected egg masses among other host groups is highlighted and promoted as a tool to test the hypothesis that ovarian cysts are a dispersal stage common to all genera of Harpellales.     

Poly(A)+ RNA and cytoskeleton during cyst formation in the cap ray of Acetabularia peniculus

Summary. The configuration and distribution of polyadenylated RNA (poly(A)⁺ RNA) during cyst formation in the cap rays of Acetabularia peniculus were demonstrated by fluorescence in situ hybridization using oligo(dT) as a probe, and the spatial and functional relationships between poly(A)⁺ RNA and microtubules or actin filaments were examined by immunofluorescence microscopy and cytoskeletal inhibitor treatment. Poly(A)⁺ RNA striations were present in the cytoplasm of early cap rays and associated with longitudinal actin bundles. Cytochalasin D destroyed the actin filaments and caused a dispersal of the striations. Poly(A)⁺ RNA striations occurred in the cytoplasm of the cap rays up to the stage when secondary nuclei migrated into the cap rays, but they disappeared after the secondary nuclei were settled in their positions. At that time, a mass of poly(A)⁺ RNA was present around each of the secondary nuclei and accumulated rRNA. This mass colocalized with microtubules radiating from the surface of each secondary nucleus and disappeared when the microtubules were depolymerized by butamifos, which did not affect the configuration of actin filaments. These masses of poly(A)⁺ RNA continued to exist even after the cap ray cytoplasm divided into cyst domains. Thus two distinct forms of poly(A)⁺ RNA population, striations and masses, appear in turn at consecutive stages of cyst formation and are associated with distinct cytoskeletal elements, actin filaments and microtubules, respectively. Correspondence and reprints: Graduate School of Kuroshio Science, Kochi University, 2-5-1 Akebono-cho, Kochi 780-8520, Japan.     

A systematic study on hemocyte identification and plasma prophenoloxidase from Culex pipiens quinquefasciatus at different developmental stages

Culexpipiens quinquefasciatus (C. quinquefasciatus) is an important vector that can transmit human diseases such as West Nile virus, lymphatic filariasis, Japanese encephalitis and St. Louis encephalitis. However, very limited research concerning the humoral and cellular immune defenses of C. quinquefasciatus has been done. Here we present the research on hemocyte identification and plasma including hemocyte prophenoloxidase from C. quinquefasciatus at all developmental stages in order to obtain a complete picture of C. quinquefasciatus innate immunity. We identified hemocytes into four types: prohemocytes, oenocytoids, plasmatocytes and granulocytes. Prophenoloxidase (PPO) is an essential enzyme to induce melanization after encapsulation. PPO-positive hemocytes and plasma PPO were observed at all developmental stages. As for specific hemocyte types, prophenoloxidase was found in the plasmatocytes at larval stage alone and in the smallest prohemocytes during almost all developmental stages. Moreover, the granulocytes were PPO-positive from blood-fed female mosquitoes and oenocytoids were observed PPO-positive in pupae and in adult females after blood-feeding. As for plasma, there were different patterns of PPO in C. quinquefasciatus at different developmental stages. These results are forming a basis for further studies on the function of C. quinquefasciatus hemocytes and prophenoloxidase as well as their involvement in fighting against mosquito-borne pathogens.     

Pyrus pyrifolia stylar S-RNase induces alterations in the actin cytoskeleton in self-pollen and tubes in vitro

Summary. Pears (Pyrus pyrifolia L.) have an S-RNase-based gametophytic self-incompatibility system, and S-RNases have also been implicated in self-pollen or genetically identical pollen rejection. Tip growth of the pollen tube is dependent on a functioning actin cytoskeleton. In this study, configurations of the actin cytoskeleton in P. pyrifolia pollen and effects of stylar S-RNases on its dynamics were investigated by fluorescence and confocal microscopy. Results show that actin filaments in normal pollen grains exist in fusiform or circular structures. When the pollen germinates, actin filaments assembled around one of the germination pores, and then actin bundles oriented axially throughout the shank of the growing tube. There was a lack of actin filaments 5–15 μm from the tube tip. When self-stylar S-RNase was added to the basal medium, pollen germination and tube growth were inhibited. The configuration of the actin cytoskeleton changed throughout the culturing time: during the first 20 min, the actin configurations in the self-pollen and tube were similar to the control; after 20 min of treatment, the actin filaments in the pollen tube gradually moved into a network running from the shank to the tip; finally, there was punctate actin present throughout the whole tube. Although the actin filaments of the self-pollen grain also disintegrated into punctate foci, the change was slower than in the tube. Furthermore, the alterations to the actin cytoskeleton occurred prior to the arrest of pollen tube growth. These results suggest that P. pyrifolia stylar S-RNase induces alterations in the actin cytoskeleton in self-pollen grains and tubes. Correspondence: Shao-ling Zhang, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu 210095, People’s Republic of China.     

Monitoring <Emphasis Type="Italic">ALS1</Emphasis> and <Emphasis Type="Italic">ALS3</Emphasis> Gene Expression During In Vitro <Emphasis Type="Italic">Candida albicans</Emphasis> Biofilm Formation Under Continuous Flow Conditions

ALS1 and ALS3 encode cell-surface associated glycoproteins that are considered to be important for Candida albicans biofilm formation. The main goal of the present study was to monitor ALS1 and ALS3 gene expression during C. albicans biofilm formation (on silicone) under continuous flow conditions, using the Centers for Disease Control biofilm reactor (CDC reactor). For ALS1, we found few changes in gene expression until later stages of biofilm formation (72 and 96 h) when this gene appeared to be downregulated relative to the gene expression level in the start culture. We observed an induction of ALS3 gene expression in the initial stages of biofilm formation (0.5, 1, and 6 h), whereas at later stages, this gene was also downregulated relative to the gene expression level in the start culture. We also found that biofilms of an als3/als3 deletion mutant contained less filaments at several time points (1, 6, 24, and 48 h), although filamentation as such was not affected in this strain. Together, our data indicate an important role for ALS3 in the early phases of biofilm formation in the CDC reactor, probably related to adhesion of filaments, while the role of ALS1 is less clear.     

Cell-type-specific disruption and recovery of the cytoskeleton in Arabidopsis thaliana epidermal root cells upon heat shock stress

Summary. The cytoskeleton in plant cells plays an important role in controlling cell shape and mediating intracellular signalling. However, almost nothing is known about the reactions of cytoskeletal elements to heat stress, which represents one of the major environmental challenges for plants. Here we show that living epidermal root cells of Arabidopsis thaliana could cope with short-term heat shock stress showing disruption and subsequent recovery of microtubules and actin microfilaments in a time-dependent manner. Time-lapse imaging revealed a very dynamic behavior of both cytoskeletal elements including transient depolymerization and disassembly upon heat shock (40–41 °C) followed by full recovery at room temperature (20 °C) within 1–3 h. Reaction of microtubules, but not actin filaments, to heat shock was dependent on cell type and developmental stage. On the other hand, recovery of actin filaments, but not microtubules, from heat shock stress was dependent on the same parameters. The relevance of this adaptive cytoskeletal behavior to intracellular signalling is discussed. Correspondence and reprints: Institute of Cellular and Molecular Botany, University of Bonn, Kirschallee 1, 53115 Bonn, Federal Republic of Germany.     

The transmembrane protein,Tincar, is involved in the development of the compound eye in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

We previously cloned and characterized the Drosophila gene, tincar (tinc), which encodes a novel protein with eight putative transmembrane domains. Here, we have studied the expression pattern and functions of tinc during developmental processes. tinc mRNA is expressed in the central and peripheral nervous systems, and midgut during embryogenesis. In the third-instar larval eye disc, tinc mRNA is strongly expressed in all the differentiating ommatidial cells within and in the vicinity of the morphogenetic furrow. Loss-of-function analysis using the RNA-interference method revealed severe defects of eye morphogenesis during the late developmental stages. Our results suggested that tinc may have an indispensable role in the normal differentiation of ommatidial cells.Edited by C. Desplan     

Relationships between peroxidases and in vitro bulbification in garlic (Allium sativum L.)

Summary The relationship between in vitro bulbification and peroxidase activities of garlic (Allium sativum L.) was studied. Two stages could be distinguished during in vitro bulb formation characterized by the peroxidase activity, isoenzymatic patterns especially of the soluble fractions, dry weight, and bulbification index (BI). The first stage, called the morphogenic stage, started after planting until 30d of culture with a maximum soluble peroxidase activity, BI=1–0.5 and low dry weight. At that time axillary buds preformed at the base of the leaves grew and the in vitro bulb was generated. The second stage (filling in and bulb maturation) started when the BI reached 0.5 at 30 d of the ontogenic cycle, as a result of the bulb assimilate accumulation phenomenon. During the morphogenic stage the soluble peroxidase activity was maximum and the zymograms showed higher intensity bands. The second stage presented anodic ionic peroxidases and substantial increase in staining of the anodic covalent peroxidase fraction. The putative role of the different isoforms of peroxidases in relation to the bulbification process is discussed.     

Morphology,biology, and systematics ofCryptochlora perforans (Chlorarachniophyta), a phagotrophic marine alga

The life cycle ofCryptochlora perforans is described under culture conditions, including the following stages: Naked and walled amoebae, cysts, coccoid, palmelloid and flagellate stages. Phagotrophy of living diatoms, movement and reproduction are documented. Amoebae ofCryptochlora are chemotactically attracted by damaged algal filaments, perforate and penetrate such filaments, and subsequently engulf part of their contents. A comparison is made with a culture ofChlorarachnion reptans Geitler, according to earlier and own observations. Chloroplast structure as well as zoospore morphology confirm close affinities betweenCryptochlora andChlorarachnion. Generic characters as well as possible phylogenetic affinities with amoeboidXanthophyta andProtozoa are discussed.     

Cultivation of the green alga, Codium fragile (Suringar) Hariot, by artificial seed production in Korea

Codium fragile (Suringar) Hariot is an edible green alga farmed in Korea using seed stock produced from regeneration of isolated utricles and medullary filaments. Experiments were conducted to reveal the optimal conditions for nursery culture and out-growing of C. fragile. Sampling and measurement of underwater irradiance were carried out at farms cultivating C. fragile at Wando, on the southwestern coast of Korea, from October 2004 to August 2005. Growth of erect thalli and underwater irradiance were measured over a range of depths for three culture stages. During the nursery cultivation stage (Stage I), growth rate was greatest at 0.5 m depth (0.055 ± 0.032 mm day⁻¹), where the average midday irradiance over 60 days was 924 ± 32 μmol photons m⁻² s⁻¹. During the pre-main cultivation stage (Stage II), the greatest growth rate occurred at a depth of 2 m (0.113 ± 0.003 mm day⁻¹) with an average irradiance of 248 ± 116 μmol photons m⁻² s⁻¹. For the main cultivation stage (Stage III) of the alga, thalli achieved the greatest increase in biomass at 1 m depth (7.2 ± 1.0 kg fresh wt m⁻¹). These results suggest that optimal growth at each cultivation stages of C. fragile could be controlled by depth of cultivation rope.     

Morphogenesis induction and organogenic nodule differentiation in <Emphasis Type="Italic">Populus euphratica</Emphasis> Oliv. leaf explants

Populus euphratica Oliv. is a deciduous poplar species, occurring mainly in riparian areas of China and Middle Eastern countries, and presenting high tolerance to extreme temperatures and high soil salinity. In this study, an optimized protocol for development and propagation of P. euphratica from leaf explants is reported, based on a morphogenic process that involves organogenic nodule differentiation. Adventitious shoot regeneration of P. euphratica from organogenic nodules of leaf explants was achieved within a range of concentrations of α-naphtalenacetic acid and 6-benzylaminopurine, at a fixed 2:1 ratio. Cambial cells started to divide 5 days after inoculation on culture medium and, after 12 days, several organizing centres were already formed. Non-friable callus tissue, together with organization centres, formed structures that evolved to nodules after about 40 days which were, then, able to regenerate new shoots after 50–60 days. The nodules did not separate from the mother explants and were able to successfully give rise to new adventitious shoots. These were rescued and successfully grown and rooted in different culture media, and fully developed plants were obtained. The regeneration system here described for P. euphratica is innovative, reproducible and data from histological studies of the morphogenic process support the classification of the regenerative structures as organogenic nodules.