The Control of Vascular Branching in Coleus 1. The Side Bundle

Xylary branching at the proximal end of a differentiating sidebundle was modified by surgical alteration of the surroundingleaf traces and manipulation of their auxin fluxes. Incisionsthrough one corner trace, with the other pre-existing traceintact, resulting in xylem differentiation in the branch ofthe newly formed side bundle toward only the severed trace.Application of IAA to the cut trace allowed xylem branchingof the new strand in both directions. With sufficient auxinimbalance created by increasing the concentration of the appliedIAA, the new xylem strand branched away from the higher auxinsource. Auxin relations were thus able to regulate the courseof differentiation of vascular strands, but their role in regulatingbranching patterns in intact plants may be questioned. Xylembranched exclusively toward an incised trace only when the auxinflux of the incised trace was virtually eliminated. Phloem andprocambium of the differentiating strand were unaffected bythis treatment. Coleus, vascular differentiation, vascular anatomy, vascular branching, vascular patterns, auxin, auxin balance, node     

Abscission in Coleus: Light and Phytohormone Control

Light control of leaf abscission in Coleus (Coleus blumei Benthcv. Ball 2719 Red) appears to be regulated by the quantity ofendogenous auxin transported from the leaf blade to the abscissionzone. Gas chromatographic—mass spectrophotometric analysisindicated that diffusate collected from leaf tissue treatedwith red light contained significantly higher levels of auxinthan dark and far-red light-treated leaf tissue. In addition,diffusate from red light-treated tissue inhibited abscissionof leafless petioles while diffusate from far-red light-treatedtissue promoted abcission when compared with diffusate fromdark-treated tissue. The effect of red light on abscission couldbe mimicked by IAA, but not by other phytohormones. An auxintransport inhibitor, 2, 3, 5-triiodobenzoic acid (TIBA), appliedeither as a lanolin ring around the petiole or vacuum infiltratedinto tissue, could completely eliminate any red light effecton abscission. The data are consistent with a phytochrome-mediatedlight regulation of endogenous auxin level in the leaf whichthen controls abscission. Key words: Abscission, Coleus, IAA, plant hormones, red (far-red) light, TIBA     

Vascular Regeneration and Long Distance Transport of Indole-3-acetic Acid in Coleus Stems

Excision of all leaves and buds of Coleus blumei Benth. plants reduced xylem cell and sieve tube regeneration a highly significant amount around a wound in internode number 5 when compared with regeneration in intact (wounded) plants. Application of indoleacetic acid (IAA-¹⁴C) to the cut surface of internode number 2 restores regenerative activity around the wound in internode number 5. Radioactivity applied as IAA-¹⁴C reaches the wound area when applied at the cut surface of inter-node number 2 showing a logarithmic decrease with distance from the point of application. Chromatography showed that radioactivity was located close to the R_F of IAA as well as near the solvent front.     

Evolutionary Branching in a Finite Population: Deterministic Branching vs. Stochastic Branching

Adaptive dynamics formalism demonstrates that, in a constant environment, a continuous trait may first converge to a singular point followed by spontaneous transition from a unimodal trait distribution into a bimodal one, which is called “evolutionary branching.” Most previous analyses of evolutionary branching have been conducted in an infinitely large population. Here, we study the effect of stochasticity caused by the finiteness of the population size on evolutionary branching. By analyzing the dynamics of trait variance, we obtain the condition for evolutionary branching as the one under which trait variance explodes. Genetic drift reduces the trait variance and causes stochastic fluctuation. In a very small population, evolutionary branching does not occur. In larger populations, evolutionary branching may occur, but it occurs in two different manners: in deterministic branching, branching occurs quickly when the population reaches the singular point, while in stochastic branching, the population stays at singularity for a period before branching out. The conditions for these cases and the mean branching-out times are calculated in terms of population size, mutational effects, and selection intensity and are confirmed by direct computer simulations of the individual-based model.     

The Mechanism of Apical Dominance in Coleus

The development of lateral buds in isolated stems of Coleus blumei is inhibited by low concentrations of indoleacetic acid or other auxins, just as in other plants. The inhibition can be fully reversed by kinetin, about 3 times as much kinetin as IAA being needed. However, the outgrowth of the same lateral buds on intact Coleus plants is sensitive to environmental conditions, well-nourished plants in full daylight often showing little inhibition by applied auxin. It is shown that (a) the solvent used for IAA, (b) the light intensity and (c) the nitrogen and phosphorus nutrition, all control the sensitivity of the buds to auxin inhibition. Using water instead of lanolin, lowering the light intensity or decreasing the supply of either nitrogen or phosphorus all increase the degree of apical dominance.     

彩叶草的组织培养

1　植物名称　彩叶草 (Coleusblumeivar.ver schaffeltii)。2　材料类别　茎段 (shoots)。3　培养条件　培养基 :( 1 )MS ;( 2 ) 1 /4MS + 6 BA0 .3mg·L- 1 (单位下同 ) ;( 3) 1 /4MS +NAA 0 .0 5 +6 BAl.0 ;( 4 ) 1 /4MS +NAA 0 .1 + 6 BA 2 .0 ;( 5 )1 /2MS + 6 BAl.0 ;( 6) 1 /2MS +NAA 0 .0 5 + 6 BA2 .0 ;( 7) 1 /2MS +NAA 0 .1 + 6 BA 0 .3;( 8)MS +6 BA 2 .0 ;( 9)MS +NAA 0 .0 5 + 6 BA 0 .3;( 1 0 )MS +NAA 0 .1 + 6 BAl.0。上述培养基中加 30 g·L- 1 蔗糖 (sucrose)和 0 .6%的琼脂粉 (agar) ,pH5 .8。…     

The Control of the Differentiation of Vascular Networks

A polar control of vascular differentiation by stimuli movingfrom the shoot to the root has been demonstrated many timesand accounts for some traits of the pattern of vascular strands.The problem dealt with here is whether this polar mechanismcontrols the formation of the vascular networks which are commonin leaves. Networks generally, though not invariably, includestrands which do not connect the shoot to the root, and thereforecannot be considered as polar. A small transverse vascular strandin Phaseolus stems includes neighbouring vessels which haveopposite shoot to root directions. A developmental study indicatedthat vessels with opposite polarities do not mature at the sametime, and suggested that there are repeated changes in the directionof the flow of the polar stimuli which control vessel formation.Experiments with Pisum show that auxin can induce the formationof a non-polar strand of xylem when the location of the sourceof auxin, and the resulting direction of auxin flow, are changedrepeatedly. It is concluded that in the first stages of vasculardifferentiation there is a determination of the axis, but notof the direction, of the movement of differentiation-inducingstimuli. When the rate of development and of the productionof stimuli is not synchronous throughout the organ, this earlydetermination of an axis of movement leads to the differentiationof vascular networks.     

Neuronal Control of Metabolism through Nutrient-Dependent Modulation of Tracheal Branching

1. Download : Download high-res image (189KB)
2. Download : Download full-size image

     

A Comparison of the Flowering and Branching Control Systems in Lathyrus odoratus L. and Pisum sativum L.

In the sweet pea (Lathyrus odoratus L.) the difference in floweringbehaviourbetween photoperiodic (long-day) and day-neutral cultivars appearsto be due to a difference in their ability to produce a graft-transmissiblefloral inhibitor. The flowering control systems in the sweetpea and the garden pea (Pisum sativum L.) appear to be verysimilar on the basis of inter-generic graft results. It is suggestedthat the major flowering genes Dn* in L. odoratus and Sn andDne in P. sativum control steps in a biochemical pathway commonto these two species (which are related at the tribal level)and that the product of this pathway inhibits flowering andpromotes outgrowth of basal laterals in both species.     

The biosynthesis of rosmarinic acid in suspension cultures of Coleus blumei

Suspension cultures of Coleus blumei accumulate very high amounts of rosmarinic acid, an ester of caffeic acid and 3,4-dihydroxyphenyllactate, in medium with elevated sucrose concentrations. Since the synthesis of this high level of rosmarinic acid occurs in only five days of the culture period, the activities of the enzymes involved in the biosynthesis are very high. Therefore all the enzymes necessary for the formation of rosmarinic acid from the precursors phenylalanine and tyrosine could be isolated from cell cultures of Coleus blumei: phenylalanine ammonia-lyase, cinnamic acid 4-hydroxylase, hydroxycinnamoyl:CoA ligase, tyrosine aminotransferase, hydroxyphenylpyruvate reductase, rosmarinic acid synthase and two microsomal 3- and 3-hydroxylases. The main characteristics of these enzymes of the proposed biosynthetic pathway of rosmarinic acid will be described.Abbreviations DHPL 3,4-dihydroxyphenyllactate - DHPP 3,4-dihydroxyphenylpyruvate - pHPL 4-hydroxyphenyllactate - pHPP 4-hydroxyphenylpyruvate - RA rosmarinic acid     

The Characterization of Modified Starch Branching Enzymes: Toward the Control of Starch Chain-Length Distributions

Starch is a complex branched glucose polymer whose branch molecular weight distribution (the chain-length distribution, CLD) influences nutritionally important properties such as digestion rate. Chain-stopping in starch biosynthesis is by starch branching enzyme (SBE). Site-directed mutagenesis was used to modify SBEIIa from Zea mays (mSBEIIa) to produce mutants, each differing in a single conserved amino-acid residue. Products at different times from in vitro branching were debranched and the time evolution of the CLD measured by size-exclusion chromatography. The results confirm that Tyr352, Glu513, and Ser349 are important for mSBEIIa activity while Arg456 is important for determining the position at which the linear glucan is cut. The mutant mSBEIIa enzymes have different activities and suggest the length of the transferred chain can be varied by mutation. The work shows analysis of the molecular weight distribution can yield information regarding the enzyme branching sites useful for development of plants yielding starch with improved functionality.     

The Reaction of the Medium in Relation to Root Formation in Coleus

Background: As seed dispersal can vary among years and individuals, studies that focus on a single year or on a few individuals may lead to erroneous conclusions.

Aims: To study temporal and spatial intraspecific variation of seed dispersal in Scrophularia canina, a widespread species with capsule-type fruit.

Methods: Primary seed dispersal was quantified by placing traps in each cardinal direction around 10 individuals during two consecutive years. We correlated several seed shadow parameters (modal dispersal distance, kurtosis, skewness, percentiles, slope, and seed percentage beneath the plant canopy) with three plant features (maximum height, lateral spread and seed production).

Results: Scrophularia canina dispersed their seeds by boleochory, giving rise to a typical leptokurtic curve, but behaving as a barochorous species, because about 90% of seeds landed beneath the plant canopy. Temporal dispersal in S. canina included several seed waves associated with maximum wind speeds. Plant lateral spread was significantly positively correlated with seed percentiles and percentage of seeds beneath the plant canopy regardless of year. A seed production effect was only evident when both years were considered together.

Conclusions: Although time-consuming, investigation of the dispersal process for more than 1 year provides more realistic information on seed dispersal. Lateral spread is the main plant feature determining seed shadow.     

Branching out for detection of type 2 diabetes

Type 2 diabetes is an epidemic disease worldwide, but it is difficult to predict its appearance in the general population. A recent study demonstrates that circulating concentrations of a small group of essential amino acids predict risk for diabetes, contributing to a recent resurgence of interest in these common analytes.