Axis formation and polarity in plants

We have recently gained insight into a number of mechanisms governing the formation of the major axes that define the embryonic and adult plant body plan. Phenotypic analysis and molecular characterization of mutants with aberrant morphogenesis has led to a better understanding of key processes including the generation of the shape of the apical embryo, the establishment and maintenance of the radial pattern of the root, and the placement of lateral organ primordia around the shoot apical meristem.

Cell lineage, cell signaling and the control of plant morphogenesis

It is clear that cell-cell signaling is critical for the development of both root and shoot structures. Recently, several of the key gene products required for intercellular signaling have been defined, and the developmental processes regulated by cell-cell interactions are beginning to be elucidated. Surprisingly, these results suggest that the mechanisms by which plant cells communicate with each other may be quite distinct from those used in animal systems.

Mammalian development: axes in the egg?

An enduring but erroneous belief is that the post-fertilisation period is irrelevant for axis development in mammals. Two recent studies further undermine this belief. Is information for axial developmental encoded in the egg cortex?

[Anatomic and morphological studies on the initiation of somatic embryos obtained from meristematic apexes of Musa sp

The origin of somatic embryos obtained from meristematic apexes of the Musa (AAA) clone "Gran enano" was analyzed through histological and morphological studies during the various development phases of the process. The research point out that somatic embryos developed directly from perivascular parenchyma cells of the leaves. Histological sections of globular embryos showed a radial disposition to cell and the existence of an epidermal layer that surrounds the embryo completely. When citocinine (Z or BA) was added, some embryos remained in globular stage with mild signs of enlargement but with no later development of invagination. Other's embryos reached the invagination stage; and some reached the enlargement stage with active photosynthetic tissues. However there were no to generation of complete plant regardless of additional treatment, such as "osmotic shock" or the additions of GA3--At present do not have an explanations for this results. Therefore, additional experiment should be in early, intermediate and later stages of somatic embryogenesis, in order to understand the mechanisms underlying the lack of development of plants from somatics embryos.

Mechanisms of plant embryo development

1. Evolution in plants has favored both a simpler body plan with fewer cell types and the epigenetic flexibility to regenerate, via growth, dedifferentiation, and redifferentiation, to recover from environmental insults. It has become increasingly apparent that a plant cell uses external signals to differentiate and to maintain or to change the differentiated state. A cell-cell signaling and positional information strategy seems to be the predominant mechanism employed in plant development. 2. An axis can be initiated by physical/chemical forces such as light and ion current, requiring no new gene action. Random chemical fluctuations and physicochemical forces could explain the initiation of differences among cells of equal developmental potential. Amplification of chemical polarizing events may lead to biochemical differences, new gene expression, and finally shoot/root axis establishment. 3. Radial and axial patterning may be governed by a mechanism involving polar auxin transport. 4. Because the meristems and the three fundamental tissues formed during embryogenesis are renewed and extended throughout the life of the plant, with some exceptions, most genes expressed in the embryo are also expressed during postgermination development. 5. Embryogenic competence is acquired during reproductive development. While the zygote is determined for embryogenesis, the developing embryo and often the seedling remain embryogenic. Embryogenic potential declines during vegetative development. The embryogenic strength of a tissue is correlated with its developmental distance from the zygote.

Genomic imprinting and seed development: endosperm formation with and without sex

During seed development, coordinated developmental programs lead to the formation of the embryo, endosperm and seed coat. The maternal effects of the genes affected in the fertilisation-independent seed class of mutants play an important role in seed development. The plant Polycomb proteins MEDEA and FERTILIZATION-INDEPENDENT ENDOSPERM physically interact and form a complex, in a manner similar to that of their counterparts in animals. Maternal-effect phenotypes can result from regulation by genomic imprinting, a phenomenon of critical importance for both sexual and apomictic seed development.

[Study on effect of ABA, PEG4000 and AgNO3 on number of somatic embryos of Larix Principis-Rupprechtii by 311-A regression design]

This paper, the effects of ABA, PEG400 and AgNO3 on the number of somatic embryos of Larix Principis-Rupprechtii were carried out by 311-A regression design. The regression equation was established which expresses the number of somatic embryos of Larix Principis-Rupprechtii as function, and the ABA, PEG400 and AgNO3 on as variable respectively. Using the regression equation, the single factor effect and mutual effect between the number of somatic embryos of Larix Principis-Rupprechtii and ABA, PEG400 and AgNO3 was studied; the optimum concentration recipes can be obtained by computer processing, that are ABA: 18.9138 mg/L, PEG400: 88.8007 g/L and AgNO3: 10.7513 mg/L, the target somatic embryos number is 107.5278 each gram callus. The results of experiment showed that this method is simple, practical and rapid for selecting several hormone category and concentration recipes media of conifer somatic embryogenesis.

Regulation of lysine catabolism in higher plants

Lysine is an essential amino acid for mammals but its concentration in cereals, one of our main food sources, is low. Research over the past 40 years has unraveled many biochemical and molecular details of the aspartic acid pathway, which is the main route of lysine biosynthesis in plants. However, genetic manipulation of this pathway has not been successful at producing high-lysine seeds. This is because lysine, instead of being accumulated, is degraded via the saccharopine pathway. Recent work has increased our knowledge of this pathway, including both the enzymes involved and their regulation.

Regulation of lysine catabolism in higher plants

Lysine is an essential amino acid for mammals but its concentration in cereals, one of our main food sources, is low. Research over the past 40 years has unraveled many biochemical and molecular details of the aspartic acid pathway, which is the main route of lysine biosynthesis in plants. However, genetic manipulation of this pathway has not been successful at producing high-lysine seeds. This is because lysine, instead of being accumulated, is degraded via the saccharopine pathway. Recent work has increased our knowledge of this pathway, including both the enzymes involved and their regulation.

Microspore culture in Corchorus olitorius: effect of growth regulators, temperature and sucrose on callus formation

Culture of isolated microspores and of anthers on media containing IAA directed free microspore development to an embryogenic pathway in C. olitorius. The first division of microspores on transfer to culture media was symmetrical in contrast to the asymmetrical division seen in normal development in vivo. Initially, 10-30% microspores divided symmetrically, but only 0.2-1% of the dividing microspores continued dividing and produced multicellular microcalli. About 30% of these microcalli produced callus but only on medium with 2.0 mg/L zeatin and 0.1 mg/L IAA. Incubation in the dark at temperatures of 35 degrees C for 1 day and then 25 degrees C was found effective for induction of first embryonic division in Corchorus. The frequency of microspore callus formation was higher on medium containing either 3% or 5% sucrose. Addition of colchicine and addition of activated charcoal to the above medium did not enhance microspore division in Corchorus olitorius. On transfer to different media most calli produced roots but regeneration of shoots and embryos was not induced.

Control of development and motility in the spermatozoids of lower plants

The spermatozoids of lower plants have long been recognized as remarkably complex motile gametes. Spermatozoids differ markedly from the other gametophyte cells that surround or give rise to them. Their differentiation process involves the synthesis and assembly of a complex cytoskeleton and a motile apparatus that can be simple or complex, having as few as two to as many as thousands of ciliary axonemes. An important aspect of spermiogenesis involves the de novo synthesis of basal bodies in a cytoplasmic particle known as the blepharoplast: that is, the cells that produce spermatocytes do not contain centrioles. Thus, these cells provide an ideal system in which to study the formation of basal bodies. The cytoskeletons of spermatozoids from different organisms display a common architecture, with a multilayered structure (MLS) at the anterior end of the cell and a dorsally situated planar ribbon of crosslinked microtubules extending the length of the elongated gamete. The function of the MLS is not known, but it could be involved in cell-body elongation during development and in the control of ciliary motility in the mature gamete, particularly during chemotaxis. The application of modern techniques on these cells can shed light on long-standing problems relating to spermiogenesis and motility.

Somatic embryogenesis of Echinodorus orisis L. and the kinetic changes of the endogenous hormones contents during the embryogenetic process

Somatic embryogenesis was achieved in young Leaf cuttings of Echinodorus orisis L., an aquatic ornamental plant, in a short period (25 days). Among the cytokinins and their combinations tested, 6-BA (1 mg/L) and Zt (1 mg/L) in MS medium induced the highest efficiency (100%) of somatic embryogenesis, with a maximum of 4.87 embryoids per explant. Roots instead of somatic embryos were formed when NAA (0.5 mg/L) was added to MS medium containing Zt (1 mg/L). Matured embryoids were germinated and rooted in MS medium with IAA (1 mg/L) after 5 days cultivation. Seventy-two percent of the rooted plantlets transplanted survived in the aquarium. The endogenous hormone contents in various stages of somatic embryogenetic process were measured by HPLC. The concentrations of all the hormones tested were about 2 times that of the cuttings from the untreated fresh leaves after 10 days incubation. Meanwhile, the concentration of IAA presents two peaks after 10 and 25 days of cultivation, respectively. The cytokinin (Zt and ZR) peak, about 8 times more than CK, appeared in 15 days cultivation when the heart-shaped embryos formed. The fluctuation of the GA3 concentration was very similar to that of cytokinin. The ABA, however, remains stable at quite high concentration after 10 days of cultivation.

Spatio-temporal accumulation and activity of calcium-dependent protein kinases during embryogenesis, seed development, and germination in sandalwood

Western-blot analysis and protein kinase assays identified two Ca(2+)-dependent protein kinases (CDPKs) of 55 to 60 kD in soluble protein extracts of embryogenic cultures of sandalwood (Santalum album L.). However, these sandalwood CDPKs (swCDPKs) were absent in plantlets regenerated from somatic embryos. swCDPKs exhibited differential expression (monitored at the level of the protein) and activity in different developmental stages. Zygotic embryos, seedlings, and endosperm showed high accumulation of swCDPK, but the enzyme was not detected in the soluble proteins of shoots and flowers. swCDPK exhibited a temporal pattern of expression in endosperm, showing high accumulation and activity in mature fruit and germinating stages; the enzyme was localized strongly in the storage bodies of the endosperm cells. The study also reports for the first time to our knowledge a post-translational inhibition/inactivation of swCDPK in zygotic embryos during seed dormancy and early stages of germination. The temporal expression of swCDPK during somatic/zygotic embryogenesis, seed maturation, and germination suggests involvement of the enzyme in these developmental processes.

Is there a role for oligosaccharides in seed longevity? An assessment of intracellular glass stability

We examined whether oligosaccharides extend seed longevity by increasing the intracellular glass stability. For that purpose, we used a spin probe technique to measure the molecular mobility and glass transition temperature of the cytoplasm of impatiens (Impatiens walleriana) and bell pepper (Capsicum annuum) seeds that were osmo-primed to change oligosaccharide content and longevity. Using saturation transfer electron paramagnetic resonance spectroscopy, we found that the rotational correlation time of the polar spin probe 3-carboxy-proxyl in the cytoplasm decreased, together with longevity, as a function of increasing seed water content, suggesting that longevity may indeed be regulated by cytoplasmic mobility. Osmo-priming of the seeds resulted in considerable decreases in longevity and oligosaccharide content, while the sucrose content increased. No difference in the glass transition temperature was found between control and primed impatiens seeds at the same temperature and water content. Similarly, there was no difference in the rotational motion of the spin probe in the cytoplasm between control and primed impatiens and bell pepper seeds. We therefore conclude that oligosaccharides in seeds do not affect the stability of the intracellular glassy state, and that the reduced longevity after priming is not the result of increased molecular mobility in the cytoplasm.

Biochemical and functional characterization of the Tn-specific lectin from Salvia sclarea seeds

SSL, the lectin isolated from Salvia sclarea seeds, recognizes the Tn antigen (GalNAcalpha-O-Ser/Thr), a specific marker of many human carcinomas. Two-dimensional electrophoresis, amino-acid and amino-sugar analysis, and MALDI-TOF MS showed that SSL is an acidic (pI 5.5), 60-61-kDa dimeric glycoprotein composed of apparently identical subunits linked by a single disulfide bond. The apparent molecular mass of SSL in solution determined by equilibrium sedimentation analytical ultracentrifugation was 59 +/- 9 kDa. This value did not change in the pH range 2.5-8.5, indicating that SSL does not associate into higher order structures. Tandem mass spectrometry and methylation analysis of N-glycans released from SSL by hydrazinolysis indicated that SSL possesses 2-3 glycosylation sites occupied with the typical plant glycans Manalpha1-6[(Manalpha1-3)(Xylbeta1-2)]Manbeta1-4 -GlcNAcbeta1-4(Fucalp ha1-3)GlcNAc and [(Manalpha1-3/6)(Xylbeta1-2)]Manbeta1-4-GlcNAcbeta1 -4(Fucalpha1-3)Glc NAc. The influence of adjacent Tn structures on the binding of two Tn-specific lectins (SSL and the isolectin B4 from Vicia villosa) and an anti-Tn monoclonal antibody (mAb 83D4) was evaluated using synthetic Tn glycopeptides. The binding of both lectins to the synthetic Tn glycopeptides was independent of the density of Tn structures. On the other hand, mAb 83D4 only reacted with glycopeptides displaying two or three consecutive Tn structures.

[Studies on kinetics of somatic embryo suspension culture in Picea meyeri Rehd. et Wils]

Embryogenic calli were produced from mature zygotic embryos of Picea meyeri Rehd. et Wils. which were cultured on modified LP medium containing 30 g/L sucrose, 2 mg/L 2,4-D and 1 mg/L 6-BA. The growth rate of embryogenic calli could be improved by way of suspension culture in medium MS containing 20 g/L sucrose, 1 mg/L 2,4-D and 1 mg/L KT. The optimum values of initial cell density and shake rate of flask in suspension culture were 3.0% (fresh weight) and 150 r/min respectively. Several parameters which might be correlated with growth were determined over a 10 day period. Maximum growth in terms of fresh weight, dry weight and number of ESM occurred during 6-10 day. pH and conductivity attained the lowest point during 6-8 day. A lot of somatic embryos were obtained following transfer of the suspension cultures to medium MS containing 5 mg/L ABA. Mature somatic embryos grew into plantlets with well developed cotyledons after being cultured on 1/2 MS medium supplemented with 0.5% activated charcoal but without hormone.