Temporal Markers in Plant Morphogenesis

In plants as well as in animals, time may be registered in permanent structures at all organization levels. In this brief review, some examples of spatial rhythmic patterns related to plant morphogenesis and as far as possible the underlying mechanisms will be described. In conclusion, the practical interest of these structures will be emphazised.     

Temporal Markers in Plant Morphogenesis

In plants as well as in animals, time may be registered in permanent structures at all organization levels. In this brief review, some examples of spatial rhythmic patterns related to plant morphogenesis and as far as possible the underlying mechanisms will be described. In conclusion, the practical interest of these structures will be emphazised.     

Arabinogalactan Proteins: Involvement in Plant Growth and Morphogenesis

Arabinogalactan proteins (AGPs) are highly glycosylated hydroxyproline-containing variously located proteoglycans dynamically regulated in the course of plant ontogenesis. Special functions of AGPs are still unclear, but their involvement in vegetative growth and reproduction of plants is well established. This review considers data on the structure, biosynthesis, and metabolism of AGPs. Special attention is given to involvement of AGPs in growth and morphogenesis, and possible mechanisms of their regulatory action are considered. AGPs are also compared with animal proteoglycans.     

Mechanisms of Side Branching and Tip Splitting in a Model of Branching Morphogenesis

Recent experimental work in lung morphogenesis has described an elegant pattern of branching phenomena. Two primary forms of branching have been identified: side branching and tip splitting. In our previous study of lung branching morphogenesis, we used a 4 variable partial differential equation (PDE), due to Meinhardt, as our mathematical model to describe the reaction and diffusion of morphogens creating those branched patterns. By altering key parameters in the model, we were able to reproduce all the branching styles and the switch between branching modes. Here, we attempt to explain the branching phenomena described above, as growing out of two fundamental instabilities, one in the longitudinal (growth) direction and the other in the transverse direction. We begin by decoupling the original branching process into two semi-independent sub-processes, 1) a classic activator/inhibitor system along the growing stalk, and 2) the spatial growth of the stalk. We then reduced the full branching model into an activator/inhibitor model that embeds growth of the stalk as a controllable parameter, to explore the mechanisms that determine different branching patterns. We found that, in this model, 1) side branching results from a pattern-formation instability of the activator/inhibitor subsystem in the longitudinal direction. This instability is far from equilibrium, requiring a large inhomogeneity in the initial conditions. It successively creates periodic activator peaks along the growing stalk, each of which later on migrates out and forms a side branch; 2) tip splitting is due to a Turing-style instability along the transversal direction, that creates the spatial splitting of the activator peak into 2 simultaneously-formed peaks at the growing tip, the occurrence of which requires the widening of the growing stalk. Tip splitting is abolished when transversal stalk widening is prevented; 3) when both instabilities are satisfied, tip bifurcation occurs together with side branching.     

Plant utilization: Patterns and prospects

Concern for the future of mankind, in a world of expanding human population and increasing demands on the biota, has intensified interest in the greater use of less well-known plants that are presumed to have potential to ameliorate current and predicted shortages of food and other products derived from organic sources. The premise that a wide range of plants is underutilized is examined. Consideration of plant use in hunting-gathering societies and through the development of agriculture places utilization in a different perspective and indicates that man selects from the biota plants that reflect and support his needs in any given cultural context and at any level of technological achievement. The future of agricultural systems and practices is considered. The potential of plants is discussed as an outgrowth of historical trends and predicted changes in the earth’s plant resource base and its genetic diversity, modifications in primary, secondary, and tertiary pools of utilized plants, and advances in biotechnology. The evidence indicates continued humanization of the world, greater management of biotic resources, and increased applications of technology to agriculture, accompanied by a general decline worldwide in species and genetic diversity and increasing simplification and internationalization of the primary and secondary pools of cultivated plants. The direct utilization of wild plants by man will become more limited. Increased use of plants thought to be underutilized is likely to develop largely in relation to new needs and imperatives of mankind.     

Tomato Spotted Wilt Virus Particle Morphogenesis in Plant Cells

A model for the maturation of tomato spotted wilt virus (TSWV) particles is proposed, mainly based on results with a protoplast infection system, in which the chronology of different maturation events could be determined. By using specific monoclonal and polyclonal antisera in immunofluorescence and electron microscopy, the site of TSWV particle morphogenesis was determined to be the Golgi system. The viral glycoproteins G1 and G2 accumulate in the Golgi prior to a process of wrapping, by which the viral nucleocapsids obtain a double membrane. In a later stage of the maturation, these doubly enveloped particles fuse to each other and to the endoplasmic reticulum to form singly enveloped particles clustered in membranes. Similarities and differences between the maturation of animal-infecting (bunya)viruses and plant-infecting tospoviruses are discussed.     

The Effects of Varying Chromosome Arm Dosage on Maize Plant Morphogenesis

Maize is an especially well-suited species for studying the effects of aneuploidy on plant development. We used B-A translocations and testers that were crossed seven times into inbred W22 to generate a dosage series for 14 chromosome arms. This is the first report of dosage effects on maize morphogenesis using inbred B-A stocks and inbred tester stocks. We compared plants containing one dose or three doses of each of the 14 chromosome arms with plants containing two doses for seven measured traits. These were leaf width, leaf length, plant height, ear height, internode length, ear node circumference, and tassel branch number. We observed the typical maize aneuploid syndrome wherein one dose was more widespread and more severe in its effects than three doses. All but two of the one-dose effects were negative, and all of the three-dose effects were negative. The occurrence of positive responses by hyperploid plants in our earlier B-A-A study and the absence of any positive responses among the hyperploids reported for the 14 simple B-A translocations tested for dosage effects in the present study and previously may reflect gene dosage interaction between the two chromosome arm segments present in the B-A-A translocations. The overall congruence of our results with those of previous studies suggests that the traits measured are quantitative traits controlled by multiple genes whose activities provide a balanced regulation that transcends individual inbred lines or diverse genetic backgrounds and that such genes may be especially abundant in chromosome arm 1L.     

Morphogenesis in Relation to Chromosomal Constitution in Long-term Plant Tissue Cultures

A number of strains of callus tissues derived from 1-mm root tips of the garden pea, Pisum sativum L., cultivated on a complex medium containing yeast extract and 2, 4-D for eight years, were tested periodically for their capacity to initiate roots. Chromosomal cytological analyses accompanied each test. It was found that during the prolonged period of subculture there was a progressive loss of organ-forming Capacity in all tissue strains. At the outset all callus tissues could be stimulated to form normal diploid roots. After several years of continuous subculture, some callus tissues formed normal tetraploid roots. Still later, these callus tissues lost completely the capacity to initiate roots. This loss was paralleled by increasing abnormalities in the chromosomal constitution, including higher chromosome numbers and greater frequency of aneuploidy. Early in subculture normal diploid and tetraploid divisions were present in the callus tissues. Later, higher polyploids at 8n and 16n were more frequent, as well as aneuploids around these numbers. Some tissue strains after prolonged cultivation showed a wide range of chromosome numbers at the higher ploidy levels but completely lacked diploid divisions. It is suggested that the loss in organ-forming capacity is correlated with the increase in abnormality of chromosomal constitution. Differentiation of certain characteristic cell types was unaffected by these changes.     

Signals,Motors, Morphogenesis -the Cytoskeleton in Plant Development1

Abstract: Plant shape can adapt to a changing environment. This requires a structure that (1) must be highly dynamic, (2) can respond to a range of signals, and (3) can control cellular morphogenesis. The cytoskeleton, microtubules, actin microfi-laments, and cytoskeletal motors meets these requirements, and plants have evolved specific cytoskeletal arrays consisting of both microtubules and microfilaments that can link signal transduction to cellular morphogenesis: cortical microtubules, preprophase band, phragmoplast on the microtubular side, transvacuolar microfilament bundles, and phragmosome on the actin side. These cytoskeletal arrays are reviewed with special focus on the signal responses of higher plants. The signal-triggered dynamic response of the cytoskeleton must be based on spatial cues that organize assembly and disassembly of tu-bulin and actin. In this context the great morphogenetic potential of cytoskeletal motors is discussed. The review closes with an outlook on new methodological approaches to the problem of signal-triggered morphogenesis.     

Plant Growth and Morphogenesis in vitroIs Promoted by Associative Methylotrophic Bacteria

The effects of aerobic methylotrophic bacteria Methylovorus mayson growth and morphogenesis were studied in in vitropropagated tobacco, potato, and flax. Colonization of plant explants with the methylo-trophic bacteria led to the stable association of bacteria and plants and enhanced the growth and the capacity of the latter for regeneration and root formation. When colonized by the methylotrophic bacteria, the rootless transgenic tobacco plants carrying the agrobacterial cytokinin gene iptrestored their ability to form roots. These data indicate the possibility to employ methylotrophic bacteria as a tool in experimental biology and plant biotechnology.     

Efficient Plant Regeneration via Shoot Tip Explant in Jatropha curcas L

An efficient regeneration method via shoot tip explant has been developed for Jatropha curcas, which is a medicinally as well as economically important plant. Shoot tips were proliferated on MS medium incorporated with BAP (2.0 mg l^?1) and IAA (0.5 mg l^?1) along with adenine sulphate, glutamine and activated charcoal. In vitro produced shoots were induced to root on IBA (0.5–5.0 mg l^?1) added to half strength MS medium. The highest frequency of root induction was on the medium with 3.0 mg l^?1 IBA. Regenerated plantlets were successfully transferred to field after initial acclimatization.     

Morphogenesis in lentil: Plant regeneration from callus cultures of Lens culinaris medik. Via somatic embryogenesis

Plants were regenerated by the process of somatic embryogenesis from embryo-derived callus cultures of Lens culinaris Medik. cv. Laird. The callus originated from embryonal axes cultured on Murashige and Skoog (MS) (Physiol. Plant., 15 (1962) 473) medium or on a modified B5 (Gamborg et al. Exp. Cell Res., 50 (1968) 151) medium (containing 500 mg · 1⁻¹ ammonium nitrate, designated B5A) supplemented with 1–10 mg · 1⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D). The callus was pale white, friable, organized and slow growing. On transfer to B5A medium without hormones or with benzyladenine (BA) and indoleacetic acid (IAA), certain peripheral areas of the callus turned green. Such green patches later differentiated into several embryoid-like structures. Further subculture of the embryoid-like structures (or embryoids) on a glutathione-supplemented medium produced well organized embryos having cotyledons, shoots and roots which were able to develop into whole plants.