Ultrastructural localization of acid phosphatase in the pollen tube of Prunus avium L. (sweet cherry)

The pollen tube of Prunus avium (cherry) consists of a growth zone of vesicles at the tip and an assemblage of organelles typical of an actively metabolizing cell. Electron opaque globules are closely associated with the plasma membrane and fibrillar cell wall layer at the tip. Acid phosphatase (EC 3.1.3.2) activity is localized in the membranes of 120 nm vesicles and ER system, the lumen of 50 nm vesicles, the plasma membrane and the tube nucleus.     

Competitive interaction between two functional S-haplotypes confer self-compatibility on tetraploid Chinese cherry (Prunus pseudocerasus Lindl. CV. Nanjing Chuisi)

Self-incompatibility (SI) has been studied extensively at the molecular level in Solanaceae, Rosaceae and Scrophulariaceae, all of which exhibit gametophytic self-incompatibility (GSI). In the present study, four PpsS-haplotypes (Prunus pseudocerasus S-haplotypes) comprising at least two genes, i.e., PpsS-RNase (P. pseudocerasus S-RNase) and PpsSFB (P. pseudocerasus S-haplotype-specific F-box) have been successfully isolated in tetraploid P. pseudocerasus Lindl. CV. Nanjing Chuisi ("NC") which exhibited self-compatibility (SC), and its S-genotype was determined as S-1/S-3'/S-5/S-7. These PpsS-RNases, which were expressed exclusively in style, shared the typical structural features with S-RNases from other Prunus species exhibiting GSI. All PpsSFBs showed similar structure characteristics of SFBs from other Prunus species, and matched with the necessary conditions for pollen S-determinant. No mutations leading to dysfunction of S-haplotype were found in their full-length c-DNA sequences, except for PpsS-3'-haplotype which was not amplified by PCR. These four S-haplotypes complied with tetrasomic inheritance. Diploid pollen grains with S-genotypes S-7/S-1, S-7/S-5 and S-1/S-5 can grow the full length of the style after self-pollination, while pollen grains with S-3'/S-7, S-3'/S-1 and S-3'/S-5 cannot. These results suggest that PpsS-haplotypes-1, -5 and -7 are functional, and that competitive interaction between two of them confer self-compatibility on cultivar "NC". Furthermore, in terms of recognition specificity, diploid pollen grains carrying PpsS-3'-haplotype are equal to monoploid pollen grains carrying the other functional S-haplotype.     

Photosystem II efficiency and mechanisms of energy dissipation in iron-deficient,field-grown pear trees (Pyrus communis L.)

The dark-adapted Photosystem II efficiency of field-grown pear leaves, estimated by the variable to maximum chlorophyll fluorescence ratio, was little affected by moderate and severe iron deficiency. Only extremely iron-deficient leaves showed a decreased Photosystem II efficiency after dark adaptation. Midday depressions in Photosystem II efficiency were still found after short-term dark-adaptation in iron-deficient leaves, indicating that Photosystem II down-regulation occurred when the leaves were illuminated by excessive irradiance. The actual Photosystem II efficiency at steady-state photosynthesis was decreased by iron deficiency both early in the morning and at midday, due to closure of Photosystem II reaction centers and decreases of the intrinsic Photosystem II efficiency. Iron deficiency decreased the amount of light in excess of that which can be used in photosynthesis not only by decreasing absorptance, but also by increasing the relative amount of light dissipated thermally by the Photosystem II antenna. When compared to the controls, iron-deficient pear leaves dissipated thermally up to 20% more of the light absorbed by the Photosystem II, both early in the morning and at midday. At low light iron-deficient leaves with high violaxanthin cycle pigments to chlorophyll ratios had increases in pigment de-epoxidation, non-photochemical quenching and thermal dissipation. Our data suggest that pH could be the major factor controlling thermal energy dissipation, and that large (more than 10-fold) changes in the zeaxanthin plus antheraxanthin to chlorophyll molar ratio caused by iron deficiency were associated only to moderate increases in the extent of photoprotection.This revised version was published online in October 2005 with corrections to the Cover Date.     

Endogenous levels of abscisic acid,indole-3-acetic acid and benzyladenine during in vitro bud growth induction of Wild cherry (Prunus avium L.)

Levels of endogenous growth substances (abscisic acid: ABA; indole-3-acetic acid: IAA) and applied benzyladenine (BA) were quantified during the eight first days of in vitro propagation of Wild Cherry (Prunus avium L.). Axillary buds from the middle part of the explants started to grow at day 2, thus were released from apical dominance. Hormone levels were measured in the apical, median and basal parts of the explants using an avidin-biotin based enzyme-linked immunosorbent assay (ELISA) after a purification of the extracts by high performance liquid chromatography (HPLC). All hormones showed rapid and considerable changes during the first eight days of growth. Exogenous IBA was probably transformed into IAA mainly in the basal part of the explant, and BA penetrated quickly. ABA levels were transiently enhanced in the apical part of the explants bearing young leaves. These phenomena are discussed in connection with the axillary bud reactivation.     

Construction of an intra-specific sweet cherry (<Emphasis Type="Italic">Prunus avium</Emphasis> L.) genetic linkage map and synteny analysis with the <Emphasis Type="Italic">Prunus</Emphasis> reference map

Linkage maps of the sweet cherry cultivar ‘Emperor Francis’ (EF) and the wild forest cherry ‘New York 54’ (NY) were constructed using primarily simple sequence repeat (SSR) markers and gene-derived markers with known positions on the Prunus reference map. The success rate for identifying SSR markers that could be placed on either the EF or NY maps was only 26% due to two factors: a reduced transferability of other Prunus-species-derived markers and a low level of polymorphism in the mapping parents. To increase marker density, we developed four cleaved amplified polymorphic sequence markers (CAPS), 19 derived CAPS markers, and four insertion–deletion markers for cherry based on 101 Prunus expressed sequence tags. In addition, four gene-derived markers representing orthologs of a tomato vacuolar invertase and fruit size gene and two sour cherry sorbitol transporters were developed. To complete the linkage analysis, 61 amplified fragment length polymorphism and seven sequence-related amplified polymorphism markers were also used for map construction. This analysis resulted in the expected eight linkage groups for both parents. The EF and NY maps were 711.1 cM and 565.8 cM, respectively, with the average distance between markers of 4.94 cM and 6.22 cM. A total of 82 shared markers between the EF and NY maps and the Prunus reference map showed that the majority of the marker orders were the same with the Prunus reference map suggesting that the cherry genome is colinear with that of the other diploid Prunus species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Microsatellite analysis of relationships among North American plums (Prunus sect. Prunocerasus, Rosaceae)

Fifteen microsatellite primer pairs developed in sweet cherry and peach were used to explore genetic relationships among North American plums (Prunus section Prunocerasus). In all, 186 putative alleles were detected with a mean value of 12.4 per locus. The Jaccard coefficient of similarity was calculated between all pairs of accessions and their genetic similarities represented by a UPGMA dendrogram. Despite the apparent closeness among native American plums as evidenced by their ability to hybridize freely and their very similar ITS and trnL-trnF nucleotide sequences, all pairs of accessions among the North American plums shared fewer than half of their alleles. Some of the relationships suggested by the UPGMA dendrogram are congruent with current taxonomic hypotheses, but others are difficult to interpret. Further resolution of relationships among American plums will require molecular markers more variable than ITS yet less variable than microsatellites.     

Growth and development of embryo parts during the germination of caryopses of the wild oat (Avena fatua L.)

Wild oat (Avena fatua L.) caryopses were germinated on moist filter paper and under water in the presence and absence of hydrogen peroxide (H₂O₂). The sequential growth and development of embryo parts were studied. Germination, as indicated by radicle emergence, was least and slowest in caryopses submerged in deoxygenated water. The coleorhiza in such caryopses elongated much earlier than the root, in contrast to the other treatments where the coleorhiza and the root emerged at about the same time. In caryopses incubated on moist filter paper all embryo parts showed considerable growth. In H₂O₂ treated caryopses only the epicotyl showed substantial growth over the experimental period. In all treatments the first mitotic peaks were noticed at the same period. The occurrence of these early nuclear divisions may be due to release of 4 C nuclei from inhibition by the uptake of water during caryopsis imbibition. The mitosis continued in the radicle of the embryo in those caryopses germinating on moist filter paper, indicating occurrence of DNA synthesis. In the other two treatments, however, few divisions were detected. Here the early growth of the root, causing caryopsis germination, was due to cell elongation, especially in the proximal part of the root.     

Interspecific hybridization between the cultivated potato Solanum tuberosum subspecies tuberosum L. and the wild species S. circaeifolium subsp. circaeifolium Bitter exhibiting resistance to Phytophthora infestans (Mont.) de Bary and Globodera pallida (Stone) Behrens

Summary Somatic fusions between the cultivated potato Solanum tuberosum and the wild species S. circaeifolium subsp. circaeifolium Bitter were produced in order to incorporate desirable traits into the potato gene pool. Selection of the putative hybrids was based on a difference in callus morphology between the hybrids and their parents, with the hybrids showing typical purple-colored cells in otherwise green calli. In all, 17 individual calli regenerated to plants. Of the nine plants that could be transferred to the greenhouse, eight showed a hybrid and one a parental morphology. Restriction fragment length polymorphism (RFLP) analysis confirmed the hybrid character in the former group. Chloroplast counts in stomatal guard cells and flow cytometric determination of nuclear DNA content showed that four hybrid plants were tetraploid (4x), one was mixoploid (5x–8x), and the others were polyploid (6x; 8x). Three out of four tetraploid hybrids were found to be fully resistant to Phytophthora infestans, and all four hybrids were resistant to Globodera pallida pathotypes Pa2 and Pa3. It was further observed that the type and amount of steroidal glycoalkaloids varied among the tubers of the parents and the hybrids. Using the hybrids as female parents in crosses with S. tuberosum, viable seeds could be obtained. This demonstrates the potential of these hybrids in practical plant breeding.     

Transfer of resistance to the beet cyst nematode (Heterodera Schachtii Schm.) from Sinapis alba L. (white mustard) to the Brassica napus L. gene pool by means of sexual and somatic hybridization

Summary Sexual and somatic hybrid plants have been produced between Sinapis alba L. (white mustard) and Brassica napus L. (oil-seed rape), with the aim to transfer resistance to the beet cyst nematode Heterodera schachtii Schm. (BCN) from white mustard into the oil-seed rape gene pool. Only crosses between diploid accessions of S. alba (2n = 24, S_a1S_a1) as the pistillate parent and several B. napus accessions (2n = 38, AACC) yielded hybrid plants with 31 chromosomes. Crosses between tetraploid accessions of S. alba (2n = 48, S_a1S_a1S_a1S_a1) and B. napus were unsuccessful. Somatic hybrid plants were also obtained between a diploid accession of S. alba and B. napus. These hybrids were mitotically unstable, the number of chromosomes ranging from 56 to more than 90. Analysis of total DNA using a pea rDNA probe confirmed the hybrid nature of the sexual hybrids, whereas for the somatic hybrids a pattern identical to that of B. napus was obtained. Using chloroplast (cp) and mitochondrial (mt) DNA sequences, we found that all of the sexual F₁ hybrids and somatic hybrids contained cpDNA and mtDNA of the S. alba parent. No recombinant mtDNA or cpDNA pattern was observed. Three BC₁ plants were obtained when sexual hybrids were back-crossed with B. napus. Backcrossing of somatic hybrids with B. napus was not successful. Three sexual hybrids and one BC₁ plant, the latter obtained from a cross between a sexual hybrid and B. napus, were found to show a high level of BCN resistance. The level of BCN resistance of the somatic hybrids was in general high, but varied between cuttings from the same plant. Results from cytological studies of chromosome association at meiotic metaphase I in the sexual hybrids suggest partial homology between chromosomes of the AC and S_a1 genomes and thus their potential for gene exchange.     

Arsenic hyperaccumulation and localization in the pinnule and stipe tissues of the gold-dust fern (Pityrogramma calomelanos (L.) Link var. austroamericana (Domin) Farw.) using quantitative micro-PIXE spectroscopy

Spatial distribution patterns of arsenic (As) in the tissues of a lesser-known As hyperaccumulating fern Pityrogramma calomelanos (L.) Link var. austroamericana (Domin) Farw. (Pteridaceae) have been studied. Quantitative micro-proton-induced X-ray emission (micro-PIXE) spectroscopy was employed to examine As localization in pinnule and stipe cross-sections of this species. In addition, As hyperaccumulation status of P. calomelanos var. austroamericana was compared with the well-known As hyperaccumulating fern Pteris vittata L. Both species were grown in pots under controlled conditions and exposed to four levels of As (0–500 mg As kg⁻¹) for 20 weeks. Pityrogramma calomelanos var. austroamericana accumulated up to 16 415 mg As kg⁻¹ dry weight (DW), however, phytotoxicity symptoms such as necrotic pinnule tips and margins, appeared in fronds with concentrations >3,008 mg As kg⁻¹ DW. Arsenic was readily translocated to fronds, with concentrations up to 75 times greater in fronds than in roots. Quantitative elemental maps of As generated using micro-PIXE analysis revealed that As concentrations in pinnule cross-sections were higher than in stipe cross-sections with concentrations of 3.7 × 10³ and 1.6 × 10³ mg As kg⁻¹ DW, respectively (as determined by region selection analysis; RSA). In pinnules, RSA revealed variable concentrations of As, however did not resolve a clear pattern of compartmentalization across different anatomical regions. In stipe tissues, As concentrations followed the order vascular bundle > cortex > epidermis (as determined by RSA). Our results show that P. calomelanos var. austroamericana is an As hyperaccumulator and has the potential for use in phytoremediation of soils with low levels (up to 50 mg kg⁻¹) of As contamination.     

Abortion and determination of stages for embryo rescue in crosses between sweet-potato,Ipomoea batatas Lam. (2n=6x=90) and its wild relative,I. trifida (H. B. K.) G. Don. (2n=2x=30)

Summary The frequency of aborted fruits and the changes and abnormalities that occur during the embryo development in intraspecific crosses of sweet-potato Ipomoea batatas (2n=6x=90) and interspecific crosses between I. batatas and I. trifida (2n=2x=30) were investigated in order to study the causes of the low seed production. Three genotypes of I. batatas and 18 genotypes of I. trifida were intermated. The frequency of aborted fruits was below 25% in the intraspecific crosses and over 90% in the interspecific crosses. Paraffin sections were used to examine the developmental stages of fruits and seeds. Embryos in different developmental stages were observed to determine the stage of abortion. These observations permitted the identification of developmental stages of embryo rescue in interspecific crosses. There were no significant differences in the frequency of embryo abortion before the early globular stage among female sweet-potato progenitors for the intraspecific and interspecific crosses. The frequency of the late occurrence of embryo abortion (when embryo abortion occurs after the pre-globular stage) was higher in interspecific crosses (19.1%) than in intraspecific crosses (5.5%). The frequency of the late occurrence of embryo abortion in interspecific crosses was higher at the globular stage (9.6%) than at the heart stage (4.3%). Providing that embryo rescue is conducted in interspecific crosses, the estimated number of potentially viable embryos could be increased: 30 times with embryos at the globular stage; 20 times with embryos at the heart stage; and 11 times if embryos at the torpedo stage were used for the rescue with respect to the seed set. The results suggested that the appropriate time for embryo rescue in interspecific crosses is at the globular stage. If embryos could be rescued at the globular stage, it would be possible to increase the number of surviving embryos up to 30 times in interspecific crosses and 0.02 times in intraspecific crosses with respect to natural conditions without embryo rescue.This research was initiated during sabbatical of M.I. at the Asian Vegetable Research and Development Center (AVRDC) in Taiwan     

Characterization of biomass production,cytology and phenotypes of plants regenerated from embryogenic callus cultures of Pennisetum americanum x P. purpureum (hybrid triploid napiergrass)

Summary Five hundred and twenty-four plants of a triploid, sexually sterile hybrid napiergrass (Pennisetum americanum x P. purpureum; 3x=21) were regenerated from embryogenic callus cultures obtained from segments of young inflorescences. Replicated field trials were conducted for two consecutive years to compare the biomass yield, phenotype and cytology of tissue culture regenerants (TC) and vegetatively propagated (V) plants. In the first year total biomass yield of TC plants was significantly greater than V plants but there was no significant difference in the second year. TC plants had more tillers compared to V plants. V plants did not show any morphological variability. The TC population also exhibited a high degree of phenotypic stability (96%). There were 23 phenotypic variants in the TC population of 524, most of them being more dwarf and late-flowering. Detailed morphological analysis of the TC-variant plants suggests that they very likely arose from only a few variant cell lines. Cytological analysis indicated stability of the triploid status in randomly selected regenerants. Two of the morphological variants were hexaploids (6x=42). It is concluded that embryogenic callus cultures can provide useful alternative for the rapid propagation of hybrid napier-grass which is commonly propagated by cuttings.     

The extrafloral nectaries of cowpea (Vigna unguiculata (L.) Walp): I. Morphology,anatomy and fine structure

The cowpea bears two distinctive types of extrafloral nectaries. One, on the stipels of trifoliolate leaves, consists of a loosely demarcated abaxial area (1–2 mm diameter) of widely-spaced trichomes (papillae) borne on a stomata-free epidermis, and lacking a specific vascular supply. Each trichome has up to eight apical (head) cells, two to four intermediate cells, and a single large stalk cell. The secretory faces of the apical cells bear wall ingrowths and an easily detached cuticle. The wall separating the stalk cell and the underlying epidermal cell(s) has a mean plamodesmatal frequency of 25/m². The second type of nectary consists of a large elliptical mound of tissue (short and long axes about 2 mm and 4 mm) formed between a pair of flowers on an inflorescence stalk. It comprises four to eight cone-shaped subnits of secretory tissue, each with a circular secretory orifice and an individual supply of phloem, but not of xylem. Cells of the secretory tissue of the nectary subunits separate as they mature, and nectar flows to the orifice through the resulting intercellular spaces. Intact secretory cells and cellular debris are extruded into the nectar. Some of the sieve elements terminating in the inner secretory tissue exhibit open sieve pores. Each mature secretory cell contains many small (2 m diameter) spherical protein bodies and one to three large (up to 2–3 m diameter 15 m long), paracrystalline bodies. These inclusions are absent or not fully developed in inner, less mature regions of the secretory tissue. Mechanisms of secretion are proposed for the two classes of nectary, including estimates of flux of sugar into the trichomes of the stipel nectary.     

Influence of plant growth regulators on growth, morpho-physiological characters and yield of summer sesame (Sesamum indicum L. cv. Rama) under moisture stress

Field experiments were conducted with sesame (Sesamum indicum L. cv. Rama) for two years (1997 and 1998) to study the effect of three level of irrigation (F+C, B+C, B+F+C) and two growth regulators (CCC, 200 ppm CCC; 100 ppm and BX-112, 100 ppm; BX-112, 50 ppm) on growth (root and shoot length, average number of primary branches/plant), morpho-physiological growth parameters(LAI, LAD, CGR and NAR), yield attributing parameters(average number of capsule/plant, average number of seeds/capsule) and seed yield. Irrigation at B+F+C stage showed significant effect on these parameters. Among the growth regulators, CCC, 200 ppm showed remarkable results on these parameters and seed yield. Seed yield in CCC, 200 ppm treatment was more than 53% in comparison to water soaked seeds. The interaction between irrigation and PGR showed better seed yield and it was concluded that the growth regulator CCC might be utilized for enhancement of seed yield of summer sesame under field condition.     

Compartmentation of soluble carbohydrates,of starch and of malate in motor organs (pulvini) and other parts of Phaseolus coccineus L. leaves

Quantitative histochemistry was used to investigate the tissue-specific compartmentation of soluble carbohydrates (sucrose, glucose, fructose), starch and malate in the laminar pulvinus, leaf blade and petiole of Phaselous coccineus L. at day and night positions of diurnal leaf movement. Total carbohydrate levels measured in a series of cross sections along individual pulvini of 24-d-old plants showed only small differences between the day and night positions of the respective leaf. In contrast, the level of malate changed during diurnal leaf movement, especially in the central part of a pulvinus. The levels of glucose and fructose in the pulvinus increased towards the transition zones between the pulvinus and lamina, and pulvinus and petiole, and this trend was even more pronounced for starch. By contrast, sucrose levels were highest in the pulvinus proper. The transverse compartmentation of metabolites was studied in distinct, approx. 0.5-mm-thick tissue slices from the central part of a pulvinus. These were dissected further into up to 14 distinct subsamples (bundle, bundle sheath, motor tissues, flanks). Irrespective of the position of the leaf (day or night), the central vascular core and the surrounding bundle sheath had high levels of sucrose (up to 500 mmol-(kg DW)^–1) and low levels of glucose and fructose (below 100 mmol-(kg DW)^–1), while in the cortex the situation was reversed. In the night position the level of sucrose decreased by approx. 30% in the bundle sheath and the central vascular core but not in the other sections. We thus suggest that because of the relatively small diurnal changes in their cortical pools, soluble sugars are not involved in the osmotic processes resulting in leaf movement. In contrast, pulvini from 14-d-old plants showed an interesting diurnal change in starch and malate pools in the outermost layer of the extensor. Here starch increased at night while the malate pool was lowered nearly stoichiometrically. Inverse pool sizes were found in the day position of the respective leaves. Although less significant, the opposite diurnal variation occurred in samples taken from the flexor region. We thus were able to locate areas of different carbohydrate activities in the laminar pulvinus of P. coccineus. The central vascular core, including the bundle sheath, is involved in temporary storage of photoassimilates, and the cortical regions are responsible for osmotically driven leaf movement. The results are discussed with respect to guard-cell physiology.Abbreviations CLP cut-leaf pulvini - ILP intact-leaf pulvini This work was supported by a grant from the Deutsche Forschungsgemeinschaft.     

Synergistic and molecular interactions between the formamidine amitraz and copper(II) sulfate,used against the mite Varroa jacobsoni O., a parasite of the honeybee Apis mellifera L.

Toxicological field assays have shown that the shock-treatment efficacy of the formamidine pesticide amitraz, used against the parasitic mite Varroa jacobsoni, is synergistically improved by the administration of copper(II) sulfate through feeding of the honeybees. Amitraz is autoxidized and this process is accompanied by chemiluminescence. The emission is enhanced in the presence of low concentrations of H₂O₂. A dose-related inhibition of the chemiluminescence by CuSO₄ was observed; consistent with the formation of copper-amitraz complexes evidenced in vitro. The results suggest the possibility that a protection of amitraz by cupric ions might be at the origin of the enhancement of its toxicity and thus makes a contribution to the observed synergy.     

Simultaneous substitution of Gly96 to Ala and Ala183 to Thr in 5-enolpyruvylshikimate-3-phosphate synthase gene of <Emphasis Type="Italic">E. coli</Emphasis> (k12) and transformation of rapeseed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) in order to make tolerance to glyphosate

Glyphosate is a non-selective broad-spectrum herbicide that inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). This is a key enzyme in the aromatic amino acid biosynthesis pathway of microorganisms and plants. The manipulation of bacterial EPSPS gene in order to reduce its affinity for glyphosate, followed by its transfer to plants is one of the most effective approaches for the production of glyphosate-tolerant plants. In this study, we chose to focus on amino acid residues glycine96 and alanine183 of the E. coli (k12) EPSPS enzyme. These two amino acids are important residues for glyphosate binding. We used site directed mutagenesis (SDM) to induce point mutations in the E. coli EPSPS gene, in order to convert glycine96 to alanine (Gly96Ala) and alanine183 to threonine (Ala183Thr). After confirming the mutation by sequencing, the altered EPSPS gene was transferred to rapeseed (Brassica napus L.) via Agrobacterium-mediated transformation. The transformed explants were screened in shoot induction medium containing 25 mg L⁻¹ kanamycin. Glyphosate tolerance was assayed in putative transgenic plants. Statistical analysis of data showed that there was a significant difference between the transgenic and control plants. It was observed that transgenic plants were resistant to glyphosate at a concentration of 10 mM whereas the non-transformed control plants were unable to survive 1 mM glyphosate. The presence and copy numbers of the transgene were confirmed with PCR and Southern blotting analysis, respectively.     

Characteristics of adventitious root formation in cotyledon segments of mango (Mangifera indica L. cv. Zihua): two induction patterns, histological origins and the relationship with polar auxin transport

Cotyledon segments derived from zygote embryos of mango (Mangifera indica L. cv. Zihua) were cultured on agar medium for 28 days. Depending on different pre-treatments with plant growth regulators, two distinct patterns of adventitious roots were observed. A first pattern of adventitious roots was seen at the proximal cut surface, whereas no roots were formed on the opposite, distal cut surface. The rooting ability depended on the segment length and was significantly promoted by pre-treatment of embryos with indol-3-acetic acid (IAA) or indole-3-butyric acid (IBA) for 1 h. A pre-treatment with the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) completely inhibited adventitious root formation on proximal cut surfaces. A second pattern of roots was observed on abaxial surfaces of cotyledon segments when embryos were pre-treated with 2,700 μM 1-naphthalenacetic acid (NAA) for 1 h. Histological observations indicated that both patterns of adventitious roots originated from parenchymal cells, but developmental directions of the root primordia were different. A polar auxin transport assay was used to demonstrate transport of [³H] indole-3-acetic acid (IAA) in cotyledon segments from the distal to the proximal cut surface. In conclusion, we suggest that polar auxin transport plays a role in adventitious root formation at the proximal cut surface, whereas NAA levels (influx by diffusion; carrier mediated efflux) seem to control development of adventitious roots on the abaxial surface of cotyledon segments.