Embryonic Shoot Research Articles

Bud Content and its Relation to Shoot Size and Structure in Nothofagus pumilio(Poepp. et Endl.) Krasser (Nothofagaceae)

Buds of shoots from the trunk, main branches, secondary branches and short branches of 10–21 year-old Nothofagus pumilio trees were dissected and their contents recorded. The number of differentiated nodes in buds was compared with the number of nodes of sibling shoots developed at equivalent positions during the following growing season. Axillary buds generally had four cataphylls, irrespective of bud position in the tree, whereas terminal buds had up to two cataphylls. There were more nodes in terminal buds, and the most distal axillary buds, of trunk shoots than in more proximal buds of trunk shoots, and in all buds of shoots at all other positions. The highest number of nodes in the embryonic shoot of a bud varied between 15 and 20. All shoots had proximal lateral buds containing an embryonic shoot with seven nodes, four with cataphylls and three with green leaf primordia. The largest trunk, and main branch, shoots were made up of a preformed portion and a neoformed portion; all other shoots were entirely preformed. In N. pumilio, the acropetally-increasing size of the sibling shoots derived from a particular parent shoot resulted from differences in: (1) the number of differentiated organs in the buds; (2) the probability of differentiation of additional organs during sibling shoot extension; (3) sibling shoot length; (4) sibling shoot diameter; and (5) the death of the apex and the most distal leaves of each sibling shoot.

Aluminium triggers genotoxic adaptation to methyl mercuric chloride and ethyl methane sulfonate, but not to maleic hydrazide in plant cells in vivo

Non-toxic, conditioning doses of aluminium chloride were tested for induction of adaptive response to the genotoxic challenge doses of methyl mercuric chloride (MMCl), maleic hydrazide (MH) and ethyl methane sulfonate (EMS). Embryonic shoot cells of Hordeum vulgare and root meristem cells of Allium cepa were employed as the assay systems. Plant tissues fixed at different recovery hours following the challenge treatments with or without prior Al-conditioning were analyzed for cells with genotoxicity markers that include spindle and/or chromosome aberrations and micronuclei (MNC). The results provided evidence that Al 3+ triggered adaptive response that protected the plant cells from the genotoxicity of MMCl and EMS. Al 3+, however, failed to induce adaptive response against the genotoxicity of MH. A comparison of Al-induced adaptive response with that induced by heavy metals: Cd 2+, Cu 2+, Hg 2+, Ni 2+, Pb 2+, Zn 2+ and oxidative agents: hydrogen peroxide (H 2O 2) and paraquat (PQ) pointed to the similarity of Al-adaptive response to that of PQ rather than to other heavy metals or H 2O 2. Al-induced adaptive response demonstrated in the present study to MMCl and EMS possibly involved antioxidant defense and DNA repair systems, respectively.

Präformierte Und neoformierte Syllepsis sowie Prolepsis bei der Buche (Fagus sylvatica L.)

The different annual shoots and shoot systems forming from regularly induced buds, bud primordia and bud meristems are analysed and described in dependence upon the development and morphology of the bud of European Beech ( Fagus sylvatica L.). Thereby the following buds and shoot systems can be distinguished b1) the regular (winter) bud, b2) the big winter bud, b3) the embryonic bud or lammas shoot bud, s1) the unbranched regular long shoot from the normal winter bud, s2) the preformed sylleptically branched long shoot from the "big winter bud" (hidden or preformed syllepsis), s3) the unbranched “early- and late proleptic shoot” from the bud primordium or the embryonic bud, s4) the neoformed sylleptically branched early and late proleptic shoot from the bud meristem. Within syllepsis there must be distinguished three types, first the meso-/basitonous preformed or hidden syllepsis of the regular shoot (syllepsis developing from embryonic shoots), second the acrotonous neoformed syllepsis of the regular shoot (syllepsis developing from bud primordia) and third the mesotonous neoformed syllepsis of the proleptic shoots (syllepsis developing from bud meristems) In regard to regular and precocious shoot formation and branching a simple helpful temporal and morphologic term system is suggested. The term prolepsis is subdivided in suitable subterms, by which all precocious shoot formations can be described appropriately and clearly understandable. Possible relationships between the different shoot forms and growth conditions are discussed.

Somatic embryogenesis in Arabidopsis thaliana is facilitated by mutations in genes repressing meristematic cell divisions.

Embryogenesis in plants can commence from cells other than the fertilized egg cell. Embryogenesis initiated from somatic cells in vitro is an attractive system for studying early embryonic stages when they are accessible to experimental manipulation. Somatic embryogenesis in Arabidopsis offers the additional advantage that many zygotic embryo mutants can be studied under in vitro conditions. Two systems are available. The first employs immature zygotic embryos as starting material, yielding continuously growing embryogenic cultures in liquid medium. This is possible in at least 11 ecotypes. A second, more efficient and reproducible system, employing the primordia timing mutant (pt allelic to hpt, cop2, and amp1), was established. A significant advantage of the pt mutant is that intact seeds, germinated in 2,4-dichlorophenoxyacetic acid (2, 4-D) containing liquid medium, give rise to stable embryonic cell cultures, circumventing tedious hand dissection of immature zygotic embryos. pt zygotic embryos are first distinguishable from wild type at early heart stage by a broader embryonic shoot apical meristem (SAM). In culture, embryogenic clusters originate from the enlarged SAMs. pt somatic embryos had all characteristic embryo pattern elements seen in zygotic embryos, but with higher and more variable numbers of cells. Embryogenic cell cultures were also established from seedling, of other mutants with enlarged SAMs, such as clavata (clv). pt clv double mutants showed additive effects on SAM size and an even higher frequency of seedlings producing embryogenic cell lines. pt clv double mutant plants had very short fasciated inflorescence stems and additive effects on the number of rosette leaves. This suggests that the PT and CLV genes act in independent pathways that control SAM size. An increased population of noncommitted SAM cells may be responsible for facilitated establishment of somatic embryogenesis in Arabidopsis.

Differential induction of adaptive responses by paraquat and hydrogen peroxide against the genotoxicity of methyl mercuric chloride, maleic hydrazide and ethyl methane sulfonate in plant cells in vivo

Induction of adaptive response by conditioning doses of paraquat (PQ) and hydrogen peroxide (H 2O 2) in embryonic shoot cells of Hordeum vulgare and root meristem cells of Allium cepa was tested against the genotoxicity of challenge doses of methyl mercuric chloride (MMCl), maleic hydrazide (MH) or ethylmethane sulfonate (EMS). Plant tissue fixed at different recovery hours following the challenge treatments was analysed for cells with genotoxicity markers that include spindle or chromosome aberrations and micronuclei. The results provided clear-cut evidence that whereas H 2O 2 induced adaptive response for the chromosome damage caused by MMCl and MH, PQ induced the same for MMCl and EMS, but not for damage caused by MH. The findings pointed to the differences in the underlying mechanisms of oxidative responses induced by H 2O 2 and O 2 − · .

The development of embryo and endosperm inRanalisma rostratum

The embryo and endosperm development inRanalisma rostratum was studied in this paper. The zygote divides by a transverse wall to form basal and apical cells. The larger basal cell undergoes no further division and becomes the basal suspensor cell. The embryo development conforms to the Caryophyllad type. In the mature seed, the embryo is U-shaped and forms the embryonic shoot apex accompanied by one intraseminal leaf. The endosperm development belongs to the Hebolial type. The primary endosperm nucleus (invariably lying in the chalazal part of the embryo sac) divides and forms a large micropylar chamber and a small chalazal chamber. The chalazal endosperm chamber remains uninucleate, and free nuclear divisions occur in the micropylar chamber. Cellularization of the endosperm begins simultaneously from the micropylar and the chalazal ends. The cellularization is related to phragmoplast and cell plate, and does not arise from the free growth wall. Accompanying the embryo development, the endosperm degrades and does not exist in the mature seed. In the proembryo developing stages, the basal suspensor cell and chalazal endosperm cell grow to a considerable size. The nucleus and cytoplasm stain densely. Sometimes, binucleate or trinucleate was observed in both of the two cells. In the laterally concave embryo stage, they begin to degenerate which coincides with the cellularization of the endosperm. They are presumed to participate in the nourishment of the embryo proper in the early stages of embryo development.

Division frequency of pea protoplasts in relation to starch accumulation

Division frequency of alginate-embedded pea (Pisum sativum var. Belman) protoplasts derived from embryonic shoot tips was studied quantitatively by image analysis in relation to starch accumulation and protoplast size. Protoplast divisions were observed from day 4 on and the number of protoplasts undergoing division increased in a stepwise manner to 70% the following days. The starch content increased rapidly during the first 3 days of culture prior to the onset of division and resulted a 4.2-fold increase in the intracellular starch area and a 3.0-fold increase (from 27% to 80%) in the number of protoplasts containing starch. Subsequent periods with rapid increases the number of dividing protoplasts were preceded by further starch accumulation. Dividing protoplasts were 33–60% smaller and contained 8–42% less starch than non-dividing protoplasts. However, calculations showed that, in the dividing protoplasts, the relative area covered by starch was 6–12% higher than in non-dividing protoplasts. These data suggest that starch accumulation precedes division of pea protoplasts.

Epidermal Fate Map of theArabidopsisShoot Meristem

The shoot meristem generates all of the aerial structures of an adult plant. It is organized in three layers which produce the epidermis (L1 layer) and the subepidermal layers (L2 and L3). The origin of adult structures has previously been fate mapped to the primary meristem for L2 and L3 tissues. In this work we constructed a fate map of L1 cells in the embryonic shoot meristem. Using the trichome mutationstichelas an epidermal marker, we analyzed 153 plants that included 178 sectors. Sectors on early leaves were found to be smaller and occurred more frequently than those on late leaves. Sectors on late leaves also appeared often to affect more than one leaf. In general, the width and extent of sectors were found to be variable rather than cell lineage-restricted. Our analysis allowed us to assign the most likely fates of L1 precursor cells within the embryonic shoot meristem. The results suggest that the meristem integrates growth dynamics and patterning of all three tissues. In contrast to this coordinated growth behavior of meristematic cells, we found a difference in the lineage restrictions between the L1 and the L2 for the formation of axillary buds.

The CLAVATA and SHOOT MERISTEMLESS loci competitively regulate meristem activity in Arabidopsis

The CLAVATA (CLV1 and CLV3) and SHOOT MERISTEMLESS (STM) genes specifically regulate shoot meristem development in Arabidopsis. CLV and STH appear to have opposite functions: c1v1 and Clv3 mutants accumulate excess undifferentiated cells in the shoot and floral meristem, while stm mutants fail to form the undifferentiated cells of the shoot meristem during embryonic development. We have identified a weak allele of stm (stm-2) that reveals STM is not only required for the establish- ment of the shoot meristem, but is also required for the continued maintenance of undifferentiated cells in the shoot meristem and for proper proliferation of cells in the floral meristem. We have found evidence of genetic interactions between the CLV and STM loci. clv1 and c1v3 mutations partially suppressed the stm-1 and stm-2 phenotypes, and were capable of suppression in a dominant fashion. clv stm double mutants and plants homozygous for stm but heterozygous for clv, while still lacking an embryonic shoot meristem, exhibited greatly enhanced postembryonic shoot and floral meristem development. Although stm phenotypes are recessive, stm mutations dominantly suppressed clv homozygous and heterozygous phenotypes. These results indicate that the stm phenotype is sensitive to the levels of CLV activity, while the clv phenotype is sensitive to the level of STM activity. We propose that these genes play related but opposing roles in the regulation of cell division and/or cell differentiation in shoot and floral meristems.

The role ofEMF1in regulating the vegetative and reproductive transition inArabidopsis thaliana (Brassicaceae)

To understand the genetic regulation of vegetative to reproductive transition in higher plants, further characterization of the Arabidopsis mutant embryonic flower1, emf1, was conducted. Using three flowering symptoms, we showed that emf1 mutants could only grow reproductive and not rosette shoots under five different growth conditions. The mutant embryos did not produce the typical tunica–corpus shoot apical structures at the heart‐, torpedo‐, and mature stages. The divergent shoot apical development during mutant and wild‐type embryogenesis indicated that the wild‐type EMF1 gene was expressed in early embryogenesis. Mutations in the EMF1 gene affected the embryonic shoot apical development and caused the germinating embryo and regenerating callus to grow inflorescence, instead of rosette, shoots. Our results support the hypothesis that the EMF1 gene regulates the switch between vegetative and reproductive growth in Arabidopsis.

Cycloheximide and buthionine sulfoximine prevent induction of genotoxic adaptation by cadmium salt against methyl mercuric chloride in embryonic shoot cells of Hordium vulgare L

Presoaked seeds of barley Hordeum vulgare L. pretreated with cycloheximide (CH), 10 −6 M or bythionine sulfoximine (BSO), 10 −4 M, were exposed to methyl mercuric chloride (MMCl), 10 −4 M, with or without prior conditioning with cadmium sulfate (CdSO 4), 10 −4 M. Subsequently as the seeds germinated the endpoints measured were mitotic index, cells with mitotic aberrations and micronuclei (MNC) in embryonic shoot cells fixed at 40, 44, 48 and 52 h of recovery. Indicated by the significance reduction (p ≤ 0.05) of the yield of cells with aberrations or MNC, the results confirmed that CdSO 4-conditioning triggered an adaptive response to MMCl-challenge. Pretreatments of CH and BSO, whereas they potentiated the genotoxicity of MMCl, significantly prevented ( p ≤ 0.05) the Cd-induced genotoxic adaptation. That underscores a possible involvement of proteins in addition to phytochelatins in the underlaying mechanisms.

Gibberellin A4/7Enhanced Flowering in Tsuga Heterophylla. II. Apical Development and Shoot Formation

In studying the early anatomical events of bud differentiation we found that the production of pollen cones and seed cones in 7-8-yr-old ramets of cloned Tsuga heterophylla was promoted by weekly foliar sprays of gibberellin A4/7. Vegetative bud phenology and the differentiation of reproductive buds exhibited a 2-wk delay compared with earlier studies of larger mature trees. Further subtle delays in the spring resumption of mitotic activity and early bud development appeared related to increasing ortet latitude and low fecundity. Although an inverse relationship between the final expanded shoot length and the preformed embryonic shoot axis length appeared by the end of the treatment season, GA4/7 had no consistent effect on either. No early indicators of reproductive bud-type differentiation could be identified.

Formation of the shoot apical meristem in Arabidopsis thaliana: an analysis of development in the wild type and in the shoot meristemless mutant

ABSTRACT The primary shoot apical meristem of Arabidopsis is initiated late in embryogenesis, after the initiation of the cotyledons. We have identified a gene, called SHOOT MERISTEMLESS, which is critical for this process. shoot meristemless mutant seedlings lack a shoot apical meristem but are otherwise healthy and viable. The anatomy of mutant embryos demonstrates that the shoot meristemless-1 mutation completely blocks the initiation of the shoot apical meristem, but has no other obvious effects on embryo development. The failure of shoot meristemless tissue to regenerate shoots in tissue culture suggests that this gene regulates adventitious shoot meristem formation, as well as embryonic shoot meristem formation.

Residual mercury in seed of barley ( Hordeum vulgare L.) confers genotoxic adaptation to ethyl methanesulfonate, maleic hydrazide, methyl mercuric chloride and mercury-contaminated soil

Seeds of barley, Hordeum vulgare L., with or without residual mercury were exposed to concentrations of ethyl methanesulfonate (EMS), maleic hydrazide (MH), methyl mercuric chloride (MMCl) and mercury-contaminated soil. Subsequently the endpoints measured were germination, seedling height, mitotic index, mitotic chromosome or spindle aberrations in embryonic shoot cells and meiotic chromosome aberration in pollen mother cells. The results unequivocally demonstrated that the seed-residual mercury conferred protection against the genotoxicity of EMS, MH, MMCl as well as mercury-contaminated soil in barley. The genotoxic adaptation to MH and MMCl was significantly prevented by pre-exposing the Hg-seeds to buthionine sulfoximine, an inhibitor of phytochelatin synthesis. Furthermore, compared to normal seedlings, the seedlings grown from Hg-seeds exhibited a higher amount of non-protein SH. The findings indicated a possible involvement of phytochelatins in the mercury-induced adaptive response.

The susceptibility of pea cultivars to pea seed‐borne mosaic virus infection and virus seed transmission in the UK

The reaction of 25 UK pea cultivars to pea seedborne mosaic virus (PSbMV) was studied in the glasshouse. All cultivars proved to be susceptible. When leaf or tendril samples from inoculated plants were analysed, it was found that most combining cultivars had a lower virus content, as measured by A‐405 values in ELISA, than garden and vining cultivars, and that garden and vining cultivars had a similar virus content. Seed transmission of PSbMV in 20 cultivars ranged from 0% in cvs Maro, Princess and Progreta to 74% in cv. Vedette. There was no obvious relationship between virus content and the efficiency of seed transmission in different cultivars. Wide variation in percentage seed transmission between individuals of single cultivars was observed; for seven cvs (ST 2–49%) tested, all showed some plants escaping seed transmission altogether Seedlings infected through the seed showed symptoms similar to those in the infected parent plants. Virus particles were readily detectable by immunosorbent electron microscopy in infected seedlings, and in elongated infected embryonic shoots produced 3 days after seed germination, by ELISA. An ELISA test of seed samples from cv. Wavercx showed that virus was as readily detected 3 days after germination as after growth to symptomatic seedlings (4 weeks), and probably provides the most sensitive, accurate and time‐saving assay for seed transmission of PSbMV.

In Vitro Embryo Culture and Induction of Multiple Shoots in Lychee (Litchi chinensis Sonn.)

Immature embryos of different sizes and ages from commercial varieties of lychee (Litchi chinensis Sonn.) were cultured in a range of different media. Embryos as small as 3 mm could be cultured using in vitro techniques and subsequently grown into plants. MS solid medium with 2% sucrose supplemented with 150 ml l -1 coconut water was most effective in stimulating the germination of immature lychee embryos. Embryos of lychee were treated to induce adventitious buds from embryonic shoots as a means of achieving multiplication

A fate map of the Arabidopsis embryonic shoot apical meristem

ABSTRACT We have mapped the fate of cells in the Arabidopsis embryonic shoot apical meristem by irradiating seed and scoring the resulting clonally derived sectors. 176 white, yellow, pale green or variegated sectors were identified and scored for their position and extent in the resulting plants. Most sectors were confined to a fraction of a leaf, and only occasionally extended into the inflorescence. Sectors that extended into the inflorescence were larger, and usually encompassed about a third to a half of the inflorescence circumference. We also find that axillary buds in Arabidopsis are clonally related to the subtending leaf. Sections through the dry seed embryo indicate that the embryonic shoot apical meristem contains approximately 110 cells in the three meristematic layers prior to the formation of the first two leaf primordia. The histological analysis of cell number in the shoot apical meristem, in combination with the sector analysis have been used to construct a map of the probable fate of cells in the embryonic shoot apical meristem.

Monitoring and assessment of mercury pollution in the vicinity of a chloralkali plant. II Plant-availability, tissue-concentration and genotoxicity of mercury from agricultural soil contaminated with solid waste assessed in barley ( Hordeum vulgare L.)

Barley ( Hordeum vulgare L.) was used to assess plant-availability, tissue-concentration and genotoxicity of mercury from the solid waste deposits of a chloralkali plant. Seeds of H. vulgare, presoaked in distilled water, were allowed to germinate and grow on agricultural soil mixed with solid waste containing 2550 ± 339 mg Hg kg −1 at different proportions (0·75, 1·5, 2·5 and 5%). Plants raised from germinating seeds on uncontaminated agricultural soil served as controls. On day 7, germination counts and seedling heights were recorded. The concentration of mercury in soil, and plant tissue (dry weight) were determined at different stages of plant growth from day 7 till maturity and harvest. The availability of mercury from the soil was assessed by extracting mercury at a range of pH values (2–6) and by chemical methods. The embryonic shoots excised at 36 h of germination were subjected to cytological analysis to determine mitotic index and frequency of mitoses with chromosomal aberrations. The pollen mother cells from anthers of young M 1-spikes were analysed to score meiotic aberrations. Subsequently, the pollen fertility and seed set were determined. Furthermore, M 2-seedlings were analysed for chlorophyll-deficient mutations. The cytogenetic analysis revealed the effects of mercury on the mitotic and meiotic chromosomes which were significantly correlated with soil-mercury. The bioconcentration of mercury in aerial tissues decreased with the age of the plant. Roots, in particular, were found to concentrate most of the mercury taken up by the plant. At the time of harvest, the bioconcentration of mercury in straw was at a minimum. The accumulation of mercury in grain, which was significant, did not increase with the increase in concentration of mercury in soil but maintained a plateau, indicating a restriction of transport of mercury through the phloem. The unique advantage with the use of Hordeum assay is that, besides assessing the germline toxicity, the assay takes into account the possible contamination of the agricultural food-chain.

Seed biology of Potamogeton nodosus Poir

In Potamogeton nodosus Poir., the zygote divides by a transverse wall to form basal and terminal cells. The basal cell wall subjacent to the nucellus stains intensely for the periodic acid-Schiff (PAS) reaction and the cell shows a higher concentration of proteins and RNA than the organogenetic portion of the embryo derived from the terminal cell. Proteins and RNA are uniformly distributed in the embryonic shoot apex, the intraseminal leaves and the procambium, whereas the cotyledonary and hypocotyledonary cells have a low profile for RNA, but are well provided with starch grains and protein bodies. The basal cell persists in the mature seed. During seed development, both the integuments are compressed and lyse, and the seed is protected by the pericarp which comprises a one-layered epicarp, a parenchymatous mesocarp with air spaces and a sclerenchymatous endocarp.

An unusual case of winter bud damage in British Columbia interior conifers

A widespread and unusual form of damage was suffered by most buds above the putative 1988–1989 winter snow line on Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), Engelmann and white spruces (Piceaengelmannii Parry and P. glauca (Moench) Voss, respectively) and their hybrids, and subalpine and amabilis firs (Abieslasiocarpa (Hook.) Nutt. and A. amabilis (Dougl.) Forbes, respectively). By mid-June, on trees less than 30 years old, all tissues above the innermost bud scales, including the dome of the apical meristem, were dead, and a whorl of embryonic shoots arising from bud scale axils was developing. These shoots either produced a bud or developed into short stem segments during the 1989 growing season. The probable cause of the phenomenon was a warmer (1.0 to 3.6 °C above normal) October to December, and a very warm (2.9 to 4.7 °C above normal) January followed by a sudden cold snap with temperatures falling to −30 °C in early February.