Induction of nitrate reductase by cytokinin and ethylene in Agrostemma githago L. embryos

In dark-grown, isolated embryos of Agrostemma githago, a transient period of nitrate-reductase (NR) (NADH: nitrate oxidoreductase, EC 1.6.6.1) activity occurred from 6 to 36 h after the start of imbibition. During this period, NR activity was enhanced by nitrate, 6-benzylamino-purine and ethylene. Ethylene and 6-benzylamino-purine acted synergistically, whereas ethylene had no effect on nitrate induction. Aminoethoxyvinyl-glycine, an inhibitor of ethylene biosynthesis, inhibited the cytokinin-induced increase of NR activity, but had no effect on the nitrate-induced increase. The inhibition by aminoethoxyvinylglycine was overcome completely by ethylene. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid had the same effect on NR activity as ethylene. Our data indicate that NR induction by cytokinins only occurs in the presence of ethylene, and that nitrate enhances NR activity through a mechanism which is distinct from the induction by hormones.Abbreviations ACC 1-aminocycloproparte-1-carboxylic acid - AVG aminoethoxyvinylglycine - BAP 6-benzylaminopurine - c.p. cotyledonary pair - NR nitrate reductase This article was finalized by the second author two weeks before his death. It was translated and adapted by Dr. G.J. de Klerk, Research School of Biological Sciences, Australian National University, Canberra. Reprint requests should be sent to Dr. de Klerk at his present address: Bulb Research Centre, Vennestraat 22, 2160 AB Lisse, The NetherlandsDeceased 4 September 1985     

Increase of protein synthesis after isolation in dormant and afterripened Agrostemma githago L. embryos

Isolated embryos are more suitable for in vivo study of protein synthesis than non-isolated embryos because, after isolation, the uptake of labeled amino acids is about 1000 times higher. However, isolation also stimulates protein synthesis: Up to 4 h after isolation, the capacity to incorporate labeled amino acids increased 7 times. Therefore, data on incorporation obtained with isolated embryos cannot be extended to non-isolated embryos. The increase of protein synthesis was not due to synthesis of specific proteins, but was a general increase. Furthermore, ripening, dormant, and afterripened embryos showed the same degree of increase. Isolation therefore stimulates protein synthesis nonspecifically. When embryos were kept under anaerobic conditions after isolation, protein synthesis did not increase. Therefore, higher oxygen consumption after removal of the seedcoat is probably the cause of the higher incorporation capacity. Furthermore, the activation of protein synthesis lagged several hours behind the increase of oxygen consumption.Abbreviations A afterripened - D dormant - pre-rRNA precursor of ribosomal RNA     

高温加速老化过程中甜菜种子线粒体小分 子量热激蛋白22的变化

甜菜(BetavulgarisLcv.Loke)种子的人工老化(30℃,100％RH)导致种子的干重、生活力和活力逐渐丧失,线粒体的呼吸速率、细胞色素c氧化酶和苹果酸脱氢酶的活性下降。线粒体蛋白质随着种子老化而显著变化,小分子量热休克蛋白(LMWHSP)22从老化的0d到30d增加,然后从30d到90d下降。可以认为甜菜种子人工老化过程中线粒体活性和LMWHSP22的含量变化与种子活力密切相关。     

Changes in dormancy levels ofFraxinus excelsior L. embryos at different stages of morphological and physiological maturity

The dormancy status ofFraxinus excelsior embryos at different developmental stages under environmental conditions was examined over a period of 2 years. For each sampling date the length of the fruit, of the seed, and of the embryo were measured, and the embryological stage determined. The depth of dormancy was assayed by the germination behaviour of isolated embryos under aseptic conditions on an agar medium without nutrients. As an approach towards a quantitative estimate of the dormancy status, the degree of inhibiton of germinative growth in the embryonic organs was evaluated on the basis of four categories from none to full germinative growth. From these ratings a dormancy index was calculated, expressing the mean dormancy status of the embryos at a given date. Embryo dormancy already became apparent during embryogenesis and reached its highest level during the later phase of reserve deposition in the seed. A marked loss of embryo dormancy occurred during the phase of maturation drying in autumn, followed by a moderate increase in winter. In hydrated seeds in spring the embryo was gradually released from dormancy and enlarged further. In maintaining the embryo ofF. excelsior in a developmental but not germinative mode, dormancy mechanisms within the embryo and the endosperm, combined with environmental factors, may be involved.     

Age-related Changes in the Ultrastructure and Membrane Properties of Brassica napus L. Seeds

The ultrastructure was studied of imbibed non-aged winter rape(Brassica napus L.) seeds in comparison with that of artificiallyaged seeds in which viability was partially or completely impaired.In parallel, measurements were made of lipid-phosphorus content,the leakage of phosphate from the seeds and their vigour andgerminability. Decreases in lipid-phosphorus which accompaniedthe loss of viability corresponded to an increase in phosphateleakage, suggesting damage to cellular membranes. Three ultrastructuralsymptoms possibly related to age-induced membrane deteriorationwere observed: (i) the lowering of electron contrast in allcellular membranes excluding plasmalemma; (ii) coalescence ofsmall storage lipid bodies to larger units presumably as a resultof the degradation of enclosing half-unit membranes; and (iii)the appearance of protoplasmic inclusions inside the storageprotein bodies, possibly resulting from rupture of the enclosingunit membranes. It is suggested that the presence of enlarged fibrillar centresin nucleoli of low viability seeds observed here for the firsttime in aged seed material may be the morphological manifestationof age-induced damage to nucleic acids. Brassica napus L, seeds, accelerated ageing, ultrastructure, leakage     

Gibberellins and the photoperiodic control of stem elongation in the long-day plant Agrostemma githago L.

Agrostemma githago is a long-day rosette plant in which transfer from short days (SD) to long days (LD) results in rapid stem elongation, following a lag phase of 7–8 d. Application of gibberellin A₂₀ (GA₂₀) stimulated stem elongation in plants under SD, while 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride (AMO-1618, an inhibitor of GA biosynthesis) inhibited stem elongation in plants exposed to LD. This inhibition of stem elongation by AMO-1618 was overcome by simultaneous application of GA₂₀, indicating that GAs play a role in the photoperiodic control of stem elongation in this species. Endogenous GA-like substances were analyzed using reverse-phase high-performance liquid chromatography and the d-5 corn (Zea mays L.) assay. Three zones with GA-like activity were detected and designated, in order of decreasing polarity, as A, B, and C. A transient, 10-fold increase in the activity of zone B occurred after 8–10 LD, coincident with the transition from lag phase to the phase of rapid stem elongation. After 16 LD the activity in this zone had returned to a level similar to that under SD, even though the plants were elongating rapidly by this time. However, when AMO-1618 was applied to plants after 11 LD, there was a rapid reduction in the rate of stem elongation, indicating that continued GA biosynthesis was necessary following the transient increase in activity of zone B, if stem elongation was to continue under LD. It was concluded that control of stem elongation in A. githago involves more than a simple qualitative or quantitative change in the levels of endogenous GAs, and that photoperiodic induction alters both the sensitivity to GAs and the rate of turnover of endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - LD long day(s) - LDP long-day plant(s) - SD short day(s)     

Changes in the activities of the protoheme-synthesizing system during the growth of yeast under different conditions.

The levels of some enzymatic activities involved in protoheme synthesis have been measured in subcellular fractions obtained at different stages of the growth of the yeast Saccharomyces cerevisiae grown anaerobically and aerobically with glucose (50 or 6 g/ liter), and ethanol (20 g/liter) as the carbon source. The degree of repression of the respiratory system is estimated by the respiratory capacity of whole cells, by the activities of succinate-cytochrome c reductase and cytochrome c oxidase of the mitochondrial particles, and by the cytochrome spectra. The results show that (i) the more porphyrins (cytochromes) that are synthesized by the cells, the lower is the specific activity of δ-aminolevulinic acid (ALA) synthetase and the higher is the specific activity of ALA dehydratase, the activity ratio ALA synthetase/ALA dehydratase decreasing at least 10-fold compared to the repressed cells; (ii) the amount of intracellular ALA found under all conditions tested (from 0.05 to 1.5 mm in the cell sap) correlates well with the measured ALA synthetase activity; its presence argues against a rate-limiting function for ALA synthetase and rather favors such a role for the ALA dehydratase in the formation of heme in yeast; (iii) the rate of porphyrin synthesis measured in vitro is higher in the case of cells with high cytochrome contents; and (iv) the specific activities of succinyl CoA synthetase and protoheme ferrolyase are always present in nonlimiting amounts. Some experiments are described showing that the values of the activities which are calculated from these in situ and in vivo experiments compare well with the values measured in vitro in the acellular extracts. The results concerning the enzymatic activities, together with (i) the excretion of coproporphyrin(ogen) and the accumulation of protoporphyrin + Zn-protoporphyrin in anaerobiosis, (ii) the presence of protoporpho(di)methene (P503) in anaerobic and repressed cells, and (iii) the presence of intracellular ALA under all growth conditions, are discussed in terms of possible control(s) of heme synthesis in yeast.     

Changes in the antioxidative systems of Ocimum basilicum L. (cv. Fine) under different sodium salts

The effects of different sodium salts on some physiological parameters and antioxidant responses were investigated in a medicinal and aromatic plant, Ocimum basilicum L. (cultivar Fine). Plants were subjected to an equimolar concentration of Na₂SO₄ (25?mM) and NaCl (50?mM) for 15 and 30?days. Growth, oxidative stress parameters [electrolyte leakage, peroxidation, and hydrogen peroxide (H₂O₂) concentration], antioxidant enzyme activities [ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and peroxidases (POD, EC 1.11.1.7)], as well as antioxidant molecules [ascorbate and glutathione] were determined. The two salts affected leaf growth rates to the same extent, after 15 or 30?days of treatment, indicating a similar effect of Na₂SO₄ and NaCl salinity on growth, even if different (enzymatic and non-enzymatic) antioxidant mechanisms were involved in H₂O₂ detoxification. However, under both salts, the efficiency of the antioxidant metabolism seemed to be sufficient to avoid the deleterious effects of reactive oxygen species (ROS). Indeed, both ion leakage and peroxidation did not change under either Na₂SO₄ or NaCl salinity. As a whole, these data suggest that a cooperative process between the antioxidant systems is important for the tolerance of Ocimum basilicum L., cv. Fine to Na₂SO₄ and NaCl salinity.     

Changes in endogenous polyamines during the formation of somatic embryos from isogenic lines of Dactylis glomerata L. with different regenerative capacities

The endogenous levels of polyamines (PAs) in leaf-base explants isolated from plants of two isogenic lines of Dactylis glomerata L., differing in their competence for somatic embryogenesis, were compared. Leaf-bases isolated from plants with a high level of competence for somatic embryogenesis (HEC) contained four times the level of polyamines compared to those isolated from plants with a low level of competence for somatic embryogenesis (LEC). When the levels of individual polyamines in the HEC and LEC lines were compared, leaf-bases from plants of the HEC line had much lower PUT/SPD ratios than those from the LEC line. When changes in the levels of PAs were monitored during the first 28 d of culture, on a medium which promotes initiation of somatic embryogenesis, leaf-base cultures from plants of the HEC line showed a 50% increase in the levels of PAs during the first 7 d of culture, after which time levels began to decline. By day 21, levels had dropped below those found in freshly isolated leaf bases. While PUT and SPM levels increased by about 30%, the greatest increase was shown by SPD, which increased by more than 100% during the first 7 d of culture, before declining. In contrast much smaller changes in PA levels were found when leaf-bases from plants of the LEC line were cultured.     

Inhibition of stem growth and gibberellin production in Agrostemma githago L. by the growth retardant tetcyclacis

The effects of the new growth retardant tetcyclacis (TCY) on stem growth and endogenous gibberellin (GA) levels were investigated in the long-day rosette plant Agrostemma githago. Application of TCY (10 ml of a 5·10^-5M solution daily) to the soil suppressed stem elongation in Agrostemma grown under long-day conditions. A total of 10 g GA₁ (1 g applied on alternate days) per plant overcame the growth retardation caused by TCY.Control plants and plants treated with TCY were analyzed for endogenous GAs after exposure to nine long days. The acidic extracts were fractionated by high-performance liquid chromatography. Part of each fraction was tested in the d-5 maize bioassay, while the remainder was analyzed by combined gas chromatography-selected ion monitoring. The bioassay results indicated that the GA content of plants treated with TCY was much lower than that of untreated plants. The data obtained by gas chromatography-selected ion monitoring confirmed that the levels of seven GAs present in Agrostemma were much reduced in TCY-treated plants when compared with the levels in control plants: GA₅₃ (13%), GA₄₄ (0%), GA₁₉ (1%), GA₁₇ (33%), GA₂₀ (15%), GA₁ (4%), and epi-GA₁ (13%). These results provide evidence that TCY inhibits stem growth in Agrostemma by blocking GA biosynthesis and thus lowering the levels of endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - HPLC high-performance liquid chromatography - TCY Tetcyclacis (5-[4-chlorophenyl]-3,4,5,9,10-pentaaza-tetracyclo-5,4,1,0^2,6,0^8,11-dodeca-3,9-diene)     

Changes in the Molecular-size Distribution of Carbohydrates during Ripening in Attached and Detached Seeds of Lolium temulentum L.

Seed samples of Lolium temulentum L. were harvested at variousstages of maturity and subjected to successive cold- and hot-waterextractions. These extracts were then fractionated by gel-filtrationand the changes in the carbohydrate elution pattern with increasingseed maturity were characterized. Extracts of seeds from earlyharvests contained only free sugars, but the mean chain-lengthincreased with maturity. The hot-water fraction contained nosalient features until 17 days after anthesis but, after thispoint, a completely excluded, high-molecular-weight polysaccharideaccumulated. Infiltration studies using ^I4C-sucrose and detached seeds showedthat sugar was readily incorporated into polysaccharide, butthat the degree of uptake was directly proportional to the developmentalstage of the seed at the time of detachment. Hydrolysis dataon the various components are given and the results are discussedin terms of their practical significance.     

Water Status Changes During Development in Relation to the Germination and Desiccation Tolerance of Aesculus hippocastanum L. Seeds

Seed growth characteristics of Aesculus hippocastanum were examinedin detail during development from about 70 to 140 d after anthesis(DAA), mainly in 1988 and 1989. Mean fresh and dry weights increasedfor both the axis and the whole seed up to the time of peakseed fall at 135 DAA with no cessation before fruit abscission.Water per seed increased up to 100 DAA, after which no furtherincrease occurred; moisture content declined for the embryonicaxis and whole seed respectively from above 75 and 65% at 95DAA to 65 and 50% at 130 DAA. At fruit shedding in 1990 waterpotential values of -1·2, -2·6 and -1·1MPa were observed for the testa, cotyledon and axis tissuesrespectively; relevant sorption isotherms are presented. Decreases in seed moisture content during development were accompaniedby increases in desiccation tolerance and in germinability,both reaching their maximum at the time of peak seed fall. Atmaturity, only about 10% viability was retained on drying seedto 20% moisture content; it is confirmed that the seeds are'recalcitrant'. The exact relationship between moisture contentand germination during development was dependent on the deptof dormancy, as judged by the period of chilling required; eachduration of chilling at 2°C within the range 3-12 weeksyields a curve of sigmoid shape. No germination occurred at26°C without chilling, but nearly full germination can beobserved for samples collected at 6 weeks before maximum seedfall with 12 weeks chilling. The rate of moisture loss duringdesiccation at 15°C and 15% rh becomes reduced during development.The ontogeny of these 'recalcitrant' seeds is compared withthat of 'orthodox' seeded species and the implication of sigmoid-shapedcurves for the relationship between seed moisture content andgermination are considered.Copyright 1993, 1999 Academic Press Aesculus hippocastanum L., horse chestnut, seed development, water status, germination, desiccation intolerance, desiccation rate     

Changes of the actin filament system in the green algaMicrasterias denticulata induced by different cytoskeleton inhibitors

Summary Two different techniques have been adapted forMicrasterias denticulata to depict the actin cytoskeleton of both untreated and inhibitor-treated developing cells: the quickstaining method, where the cells are fixed in a mixture of glutaraldehyde and formaldehyde followed by staining with phalloidin without embedding, and the methacrylate method, where the cells are also fixed by aldehydes and where the embedding medium is removed prior to incubation with an actin antibody. Both methods produce sufficient preservation and visualization of actin microfilaments (MFs) and confirm earlier observations on the presence of a cortical actin MF network in both the growing and the nongrowing semicell as well as of a basketlike MF arrangement around the migrating nucleus. The results show that a network of actin MFs is essential for the proper development of the young lobes ofM. denticulata. Early developmental stages expanding uniformly at the beginning of growth lack any netlike actin MF arrangement. The actin cytoskeleton in developing cells treated with the actin-targeting agents cytochalasin D and latrunculin B is markedly influenced. Cytochalasin D, which produces the most pronounced effects, causes a breakdown of the network of actin MFs, resulting in bright actin clusters as well as in short and abnormally thick actin fragments particularly in cortical cell regions. In latrunculin B-treated cells remnants of the former actin MF network are still visible, yet most of the actin cytoskeleton appears collapsed and is reduced to short filament pieces. The disturbance of the actin MF system visualized in the present study correlates with the severe morphological and ultrastructural changes occurring in desmid cells as a consequence of both drugs. The dinitroanilin herbicide oryzalin, known to deploymerize cytoplasmic microtubules, causes also an impairment of the actin cytoskeleton inM. denticulata though not sufficient to influence normal cell growth and differentiation.Abbreviations CB cytochalasin B - CD cytochalasin D - DMSO dimethyl sulfoxide - FA formaldehyde - GA glutaraldehyde - LAT-A latrunculin A - LAT-B latrunculin B - MFs microfilaments - MT microtubule Dedicated to Professor Walter Gustav Url on the occasion of his 70th birthday     

利用荧光共振能量转移检测外源信号分子对拟南芥ATP水平的影响

本研究使用ATP特异性荧光共振能量转移(Fluorescence resonance energy transfer,FRET)为基础的荧光蛋白传感器(Ateam1.03-nD/nA),分析了4种外源信号分子(细胞外ATP、Ca²⁺、H₂O₂和NO)对拟南芥(Arabidopsis thaliana(L.)Heynh.)幼苗叶绿体和细胞质中ATP水平的影响。结果显示,细胞质ATP水平整体高于叶绿体,在4种不同浓度的信号分子处理下,叶绿体Ateam1.03-nD/nA的FRET比值仅在1.2 ~ 1.8波动;细胞质Ateam1.03-nD/nA 的FRET比值仅在2.2 ～ 3.0之间波动,未产生显著变化。结果表明在以上外源信号分子的作用下,植物细胞质和叶绿体ATP均维持在较为稳定的水平。     

外源信号物质对肉苁蓉种子萌发与吸器形成内源激素水平变化的影响

利用外源信号物质氟草敏（norflurazon）和2,6-二甲氧基对苯醌（2,6-DMBQ）分别诱导肉苁蓉种子萌发与吸器形成,研究它们在此过程中对内源激素脱落酸（ABA）、赤霉素（GA3）、吲哚乙酸（IAA）、玉米素核苷（ZR）水平变化的影响。结果表明：在诱导肉苁蓉种子萌发时,经norflurazon处理0～168h后,种子中ABA水平呈现显著降低的变化趋势,GA3、IAA、ZR水平呈现显著升高的变化趋势。在诱导肉苁蓉种子萌发体吸器形成时,经2,6-DMBQ处理0～72h后,肉苁蓉种子萌发体ABA水平变化不显著,GA3、IAA、ZR水平均呈现显著升高的变化趋势。表明在肉苁蓉种子萌发与吸器形成中外源信号物质nor-flurazon和2,6-DMBQ能影响内源激素水平的变化。     

Activity of the Pentose Phosphate Pathway and Changes in Nicotinamide Nucleotide Content during Germination of Seeds of Cicer arietinum L.

Changes in the level of nicotinamide nucleotides, rate of ¹⁴CO₂output from [1^–14C] or [6¹⁴ C₆/C₁ ratios, glucose-6-phosphatedehydrogenase, 6-phosphogluconate dehydrogenase, and NAD kinaseactivities were determined during the first 72 h of germinationof seeds of Cicer arietinum L. The level of oxidized and reducedforms of nicotinamide nucleotides, together with the activityof glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase,NAD kinase, and C₆/C₁ ratios, suggest that the pentose phosphatepathway is activated during early germination in cotyledonsof chick pea seeds. The results obtained in embryonic axes seemsto indicate a lower participation of the PP pathway, probablydue to the development of the activity of the glycolytic-TCApathway.     

Asymmetric distribution of the plasma-membrane H+-ATPase in embryos of Vicia faba L. with special reference to transfer cells

The ultrastructural localization of the plasma-membrane H⁺ -ATPase by immunocytochemistry was studied in Vicia faba embryos which absorb nutrients from the maternal organism through the transfer cells of their external epidermis. The samples were embedded in LR White resin and the specificity of immunolabelling was checked by inhibition in the presence of purified H⁺-ATPase. The following results were obtained: (i) The H⁺-ATPase density varied according to the cell type, being higher in transfer cells than in other cell types, especially the non-modified cells of the internal epidermis. (ii) There was a marked polarity in transfer cells as proton pumps were more numerous in the area of plasmalemma infoldings where active nutrient uptake is assumed to take place, (iii) No clear immunolabelling occurred on the plasma membrane of plasmodesmata. These results demonstrate that in transfer cells the area of plasmalemma infoldings is highly specialized for active solute transport; they also support the idea of specific structural properties of the plasmalemma in plasmodesmata.This work was supported by the Centre National de la Recherche Scientifique (URA CNRS 574). We express our gratitude to Dr M.G. Palmgren (Royal Veterinary and Agricultural University, Copenhagen, Denmark) for his gift of purified H⁺-ATPase. We wish to thank J.C. Fromont for his skillful technical assistance with the immunological procedures. We are grateful to J.M. Perault and C. Besse of the Electron Microscopy Service (Service Universitaire de Microscopie Electronique Appliquée à la Biologie Poitiers, France) for their contribution to the microscopical techniques.     

Changes of Endogenous Hormone Contents During Floral Bud and Vegetative Bud Differentiation in Thin Cell Layer Culture of Cichorium intybus L. Explant

The sectioned thin cell layers (TCL) of flower stalk of Cichorium intybus L. were cultured in MS medium supplemented with NAA and BA or IAA and BA where floral and vegetative buds were developed from the explant. Endogenous IAA, DHZ+DHZR, iPA increased significantly during the floral bud formation, while Z+ZR remained changed. The levels of cytokinins, DHZ +DHZR, iPA, and Z-f-ZR all increased significantly during the vegetative bud formation, however IAA level was reduced during the first 7 days of culture and increased to two-thirds of initial values on the day when the bud primordia were formed. The results suggested that the initiation of floral buds was associated with a high IAA/CTK ratio, whereas the induction of vegetative bud differentiation was related to a low IAA/CTK ratio.     

Statistical and frequency-amplitude characteristics of ultra-weak emissions of loach eggs and embryos under normal conditions and on their optic interactions. II. Changes in characteristics of ultra-weak emissions upon optic interaction of groups of embryos of different ages.

We compared the characteristics of ultraweak emissions from groups of loach embryos of different ages in the presence or absence of optic interaction. The percentage of zero values of emission gradually increased during the first hour of optic interaction. The number and height of rare big pulses estimated by the value of kurtosis increased in parallel. In addition, the correlation between the Fourier spectra of optically interacting samples decreased at a higher rate than in the absence of optical contact. Just after the 1-hour optic interaction was terminated, the number of high pulses decreased in a younger interacting group and increased in the older one and the farther away the partner groups were in developmental stages, the more pronounced these differences were. Measurements of the Fourier spectra after long-term (12-22-hour) optic interactions have shown that an "exchange" of autocorrelation characteristics of the spectra took place among the samples: the sums of autocorrelation coefficients were inverted in the vast majority of cases, often with an "overshoot" or, at least, were smoothed over with reference to the control samples. We conclude that the previously described effects of optic interactions between groups of loach embryos of different ages could be due to changes in the frequency spectra of their ultraweak emissions.     

Ploidy of somatic embryos and the ability to regenerate plantlets in melon (Cucumis melo L.)

Summary The number of chromosomes in cells of callus, somatic embryos and regenerated plantlets during somatic embryogenesis were examined in two cultivars of melon (Cucumis melo L.). Somatic embryos were diploid (50.0%/32.1%), tetraploid (38.5%/57.5%) and octoploid (11.5%/10.4%) whereas in callus cells diploidy (41.9%/43.3%), tetraploidy (27.9%/25.8%), octoploidy (11.6%/15.5%) and a low frequency of other types of ploidy and aneuploidy were observed. Mixoploid somatic embryos were not observed. These results suggest that the somatic embryos were selectively differentiated from diploid, tetraploid and octoploid cells, and that endopolyploidization of cultured cells occurred before the start of cell division leading to somatic embryogenesis. The ratio of diploid to tetraploid (1.30/0.55) in somatic embryos was less than that in callus cells (1.50/1.68) while ratios of diploid to octoploid (4.35/3.09) and tetraploid to octoploid (3.35/5.52) in somatic embryos were greater than those in callus cells (3.61/2.80 and 2.40/1.67). Therefore, it appears that the ability of callus cell to differentiate into somatic embryos increases in the following order: octoploid < diploid < tetraploid. Regenerated plantlets were diploid (65.5%/55.1%) and tetraploid (34.5%/44.9%). No octoploid plantlets were observed. The ratio of diploid to tetraploid in regenerated plantlets (1.72/1.23) was greater than that in somatic embryos. Therefore, it appears that the ability of somatic embryos to develop into plantlets increases in the following order: octoploid < tetraploid < diploid.