Formation of Pseudowhorls inPeperomia verticillata(L.) A. Dietr. Shoots Exhibiting Various Phyllotactic Patterns

Pseudowhorls are composed of leaves attached at almost equallevels and separated by single fully elongated internodes. InPeperomiaverticillata, pseudowhorls form regularly in shoots exhibitingboth spiral and truly whorled patterns of phyllotaxis. In spiralsystems, they are composed of successive leaves positioned onthe ontogenetic helix. In whorled phyllotaxis, leaves of twoadjacent whorls occur at almost the same level and this wayform a pseudowhorl. The number of leaves per pseudowhorl dependson the type of phyllotactic pattern and also the system of primordiapacking. In all the shoots, regardless of the type of phyllotaxis,the number of leaves per pseudowhorl equals the number of leafprimordia in physical contact with the apical dome. It is thesame as the higher number in contact parastichy pairs in spiralpatterns or the number of orthostichies in whorled phyllotaxis.The pseudowhorled pattern is already manifested in the arrangementof leaf primordia. In spiral and whorled phyllotaxis the plastochronratio calculated for primordia or whorls belonging to adjacentpseudowhorls is always higher than that calculated for membersof one pseudowhorl. Moreover, angular distances between primordiaof one pseudowhorl in spiral patterns are more uniform thanexpected in Fibonacci phyllotaxis. These observations were madeon plants both growing in pots and culturedin vitro. 6-Benzylaminopurine,a synthetic cytokinin, added to the medium increases the meannumber of leaves per pseudowhorl. It seems that this effectis indirect: phyllotaxis changes first rather than the destinyof a particular internode in a process of selective elongation.Copyright1999 Annals of Botany Company Peperomia verticillata, pseudowhorls, phyllotaxis, shoot apex.     

Branching Principles Governing the Architecture of Cornus kousa (Cornaceae)

The complex structure of the crown of Cornus kousa, generallyfive-forked in vegetative branching and two-forked in reproductivebranching, is analysed quantitatively and described by two basicbranching principles: decussate phyllotaxy and the resettingrule for planes of branching. Most Cornus species have opposite,decussate phyllotaxis. The leaf pair (with axillary buds) definesthe branching plane of a node. Because of regular phyllotaxis,the fundamental branching pattern is that every branching planealong an axis is perpendicular to the preceding one. However,the first node of a lateral horizontal shoot always has a horizontalbranching plane; we term this the resetting rule. We observedthat resetting occurs when the first nodes initiated in thevertical plane are repositioned by a twisting of their firstinternodes. All later nodes alternate directions, i.e. showusual decussate alternation. Foliage leaf nodes usually producethree-forked branchings. When vegetative winter buds are formed,a foliar node and adjacent scale leaf node produce a five-forkedbranching. When reproductive winter buds with a terminal inflorescenceare formed, the last foliar node and two adjacent scale leafnodes can produce a variety of branchings but usually producean equal two-forked branching. To understand better the architecturein C. kousa, we contrast it with C. capitata which does notproduce buds with scale leaves and whose vegetative nodes areclearly separated. Copyright 1999 Annals of Botany Company Branching pattern, Cornaceae, Cornus kousa, decussate branching, dogwood, Japanese strawberry tree, tree architecture, tree geometry.     

The Hierarchical Control of Phyllotaxis

Bolle's phyllotactic theory is enhanced here in the light ofrecent works which underline the importance of vascular organizationin the determination of phyllotactic patterns. It is emphasizedthat non-vascular plants, such as Fucus spiralis, can revealhow normal phyllotaxis originated. These two approaches to phyllotaxis,with others put forward here, present the problem of phyllotaxisas a matter of hierarchical control, which produces the integratedand simple behaviour of the primordia of growing plants. phyllotaxis, hierarchy, brown algae, evolution, vascularity, systems theory, control     

Flower Development in Silene: Morphology and Sequence of Initiation of Primordia

The initiation and development of the flower of Silene coeli-rosawas followed by examining apices by scanning electron microscopy.The sepals, stamens and carpets are initiated in a spiral sequence,the direction of the spiral king the opposite of the acropetalhelix of unequal axillary buds at the nodes below the flower.The petals are initiated almost simultaneously and at the sametime as the first few stamens. The change in phyllotaxis fromopposite and decussate in the vegetative shoot to spiral inthe flower occurs with the displacement of the first two sepalsaway from the mid-line of the apex and towards the axillarybud at the node below the flower. The sizes of the sepals andstamens are a function of their age since initiation but thepetals grow more slowly. The Silene flower can be interpretedas a shoot bearing primordia with associated axillary primordia,some of the latter being precocious in their development. Silent weli-rosa, flower initiation, flower development, phyllotaxis, primordia     

Anisophylly of Lateral Shoots

The inequality shown by anisophyllous leaves in plants withdecussate phyllotaxis can be measured as the difference in sizebetween the two leaves at a node, expressed as a percentageof their mean size. This is referred to as the degree of anisophylly. In Acer anisophylly of two types with different causation occurs.

1. 1. Primary anisophylly which is shown only by first year shootsdeveloped from axillary buds and which is due to the inequalityof the leaf primordia. Primary anisophylly is thus determinedby events occurring during the formation of the bud and is irreversible.
2. 2. Secondary amsophylly which is shown chiefly by the second(and subsequent) year's extension growth of lateral shoots frombuds which are isophyllous and which is due to the positionin which the shoot develops. This type of anisophylly is reversibleif the position of the developing shoot be changed.

Effects of secondary anisophylly may be superimposed on thoseof primary anisophylly. The recognition of these two causally distinct types of anisophyllyoccurring in one plant does much to resolve the apparently conflictinginformation available relating to lateral anisophylly.     

Experimental and Analytical Studies of Pteridophytes: XXIX. The Effect of Progressive Starvation on the Growth and Organization of the Shoot Apex of Dryopteris aristata Druce

Observations on shoot apices of Dryopteris aristata maintainedunder conditions of progressive starvation for periods of upto a year are recorded. Changes in the size of the shoot apexand leaf primordia, in the rates of inception and developmentof leaf primordia, and in phyllotaxis, are described and discussed.     

Validation of the Principal Axis Model (PAM) and its Application to Genotype Selection in Field Pea (Pisum sativum L.) Crops

The principal axis model (PAM) uses a principal axis and anellipse to characterize the variation in the relationship betweenthe seed (SWT) and plant (PWT) weights of individual plantswithin a crop. The theoretical linkage between the magnitudeand variability of plant harvest index (PHI), and thereforeseed yield per unit area, and changes in the components of thePAM was examined using data from four field pea (Pisum sativumL.) genotypes sown at 9, 49, 100, 225 and 400 plants m^-2. Astrong linear relationship (R ²>93.8%) between SWT and PWTand a negative SWT-axis intercept were confirmed for all crops.Analyses indicated that decreased variability of PHI withina crop would result from selection to: (a ) increase the SWT-axisintercept of the PAM; (b ) increase the slope of the PAM; (c) optimize the ellipse location; and (d ) minimize the deviationaround the principal axis. The first three methods were usedto explain yield differences (P <0.05) among genotypes ofdifferent populations. A potential strategy for single plant selection based on thePAM is proposed. This may enable early generation (F₄) selectionof small, high performing plants that may be ideal crop ideotypes.A theoretical example of the strategy is presented, with differencesamong selections based on the PAM, SWT or harvest index highlighted. Field pea(Pisum sativum L.); genetic harvest index; minimum plant weight; plant harvest index; principal axis model; plant population; seed weight; selection criteria     

Phyllotaxis in the Oil Palm: Application in the Evaluation of pisiferas

Yield differences between and within four segregating familiesof Oil Palm are shown to be highly correlated with differencesin the phyllotaxis index, E.P.I., of the female inflorescences.This association should facilitate prediction of the yield potentialof an effectively sterile segregant palm type known as pisifera,which is used as a male parent in hybrid seed production.     

A mathematical basis for plant patterning derived from physico‐chemical phenomena

The position of leaves and flowers along the stem axis generates a specific pattern, known as phyllotaxis. A growing body of evidence emerging from recent computational modeling and experimental studies suggests that regulators controlling phyllotaxis are chemical, e.g. the plant growth hormone auxin and its dynamic accumulation pattern by polar auxin transport, and physical, e.g. mechanical properties of the cell. Here we present comprehensive views on how chemical and physical properties of cells regulate the pattern of leaf initiation. We further compare different computational modeling studies to understand their scope in reproducing the observed patterns. Despite a plethora of experimental studies on phyllotaxis, understanding of molecular mechanisms of pattern initiation in plants remains fragmentary. Live imaging of growth dynamics and physicochemical properties at the shoot apex of mutants displaying stable changes from one pattern to another should provide mechanistic insights into organ initiation patterns. Editor's suggested further reading in BioEssays Computer simulation: The imaginary friend of auxin transport biology Abstract     

Theoretical Analysis of Yield of Field Pea (Pisum sativum L.) Crops using Frequency Distributions for Individual Plant Performance

Variability among individual plants causes low seed yields infield pea (Pisum sativum L.) crops. To quantify this variability,an empirical principal axis model (PAM) was developed whichhas two components: (a ) a principal axis, representing therelationship between the seed weight (SWT) produced and plantweight (PWT) of individual plants; and (b ) an ellipse, whichcharacterizes the scatter of individual values around the axis.To develop the model, plant-to-plant variability was simulatedby systematically changing the mean and standard deviation (s.d.)of frequency distributions for SWT and PWT. Changes in the interceptand slope of the principal axis and the location and shape ofthe associated ellipse were used to describe the plant-to-plantvariability. Differences in the mean SWT or PWT altered the location of theellipse. When changes in the s.d. values were equal for SWTand PWT, the dimensions of the ellipse changed, but the axesratio was constant. Non-proportionate changes in the s.d. valuescaused rotation of the principal axis and altered the shapeof the ellipse. The effect of differences in the PAM on plant harvest index(PHI) was also examined. When the intercept of the principalaxis passed through the origin, PHI was independent of PWT,and equal to the gradient of the axis. However, when the SWT-axisintercept was negative, indicating that a minimum plant weightwas required for seed production, the relationship between PHIand PWT was asymptotic. This relationship is of major importancefor interpreting differences in PHI distributions, and thuscrop harvest index and seed yield among crops. Field peas (Pisum sativum L.) individual plants; plant harvest index; plant weight; principal axis model; seed weight; simulation     

Application of Two Mathematical Models to the Araceae, a Family of Plants with Enigmatic Phyllotaxis

In this paper we show that two mathematical models can be ofgreat help in the analysis of observational data, in this casethe difficult and little studied phyllotactic phenomena thatoccur in the Araceae family. We apply the Fundamental Theoremof Phyllotaxis, together with an explanatory model of phyllotaxis,to plant specimens of this family, to obtain phyllotactic parametersand information that cannot be otherwise obtained. Most significantis the fact that the two models show evidence of regularitiesin the overwhelming diversity of the patterns observed in theAraceae (essentiallyDracontium and Anthurium) characterizedby discontinuous transitions. In particular, this work revealsthe regularity of the behaviour of the divergence angle in thespecimens analysed. Features of the inflorescences ofDracontium, especially the presence of whorls, are compared to those observedin inflorescences ofAnthurium (characterized by the absenceof whorls), and in the capitulae of Compositae (characterizedby continuous transition). We question the possible meaningat the genetic level of the diversity of patterns observed atthe macroscopic level. Copyright 2001 Annals of Botany Company Phyllotaxis, Araceae, mathematical models, inflorescence, development     

A new plant with novel leaves from the Upper Devonian of Zhejiang Province,China

The evolution of vascular plants during the Devonian Period has had great impacts on terrestrial ecosystems through innovations of key characters such as leaves, heterospory, seed reproduction, and woods. Here we report a new plant, Qianshouia mira n. gen. n. sp., from the Upper Devonian Wutong (Wutung) Formation of Fanwan section, Changxing County, Zhejiang Province, China. This plant has slender axes which seldom branch. Its leaves are arranged in pseudowhorls, departing from axes with an acute angle. The leaves are strap-shaped and each can be subdivided into proximal, middle and distal portions. At the proximal portion, a middle ridge develops, and at the middle portion this ridge divides at least three times forming four to six daughter ridges, and in between are grooves. The distal portion of leaves (leaf apex) is suggested to be adaxially curved, with no ridges but with forked tips. Qianshouia probably represents a small plant with a shrubby or herbaceous habit. Due to the unique leaf morphology and the lack of fertile structures and anatomy, the exact phylogenetic position of Qianshouia is uncertain. Qianshouia might be a lycopsid in light of the pseudowhorled phyllotaxis, or alternatively, could be a sphenopsid if the dichotomous ridge system of the leaf could be demonstrated to be leaf veins. Nevertheless, Qianshouia adds to the diversity of leaf morphologies among the Late Devonian vascular plants.     

Transport of 14C-labelled Assimilates and 32P-labelled Phosphate in Salix viminalis in Relation to Phyllotaxis and Leaf Age

Autoradiographic techniques have been used to investigate thetransport of ¹⁴C-assimilates and ³²P-phosphate in relation tophyllotaxis and age of leaves in Salix viminalis. The leavesborne on the young shoots of S. viminalis are arranged in fiveorthostichies. Three of these orthostichies share one main transportchannel, a second channel being shared by the leaves on theremaining two orthostichies. Where two orthostichies are separatedby an angular distance of 72°, transport may occur betweenleaves on these orthostichies. In addition to the phyllotaxis of the leafy shoot, it has beendemonstrated that the age of the leaf is a factor which determinesthe distribution of materials between leaves.     

Sectorial Patterns in Leaves on Fruit Tree Shoots Produced by Radioactive Assimilates and Solutions

In vigorously growing shoots of apple and plum ¹⁴C-assimilateswere translocated from a ‘fed’ leaf to particularsectors of other leaves in a distribution pattern associatedwith the phyllotaxis; the same sectorial and distribution patternswere produced by ³²P phosphate solution taken into the shootthrough a cut petiole. The frequency with which a given sectorialpattern occurred at a particular position on the phyllotacticspiral was ascertained. Such patterns were not observed abovethe third rolled leaf in the apple shoot apex. Killing the phloem in the petiole prevented egress of labelledassimilate but not of ³²P solution. Barkringing above the sourceleaf reduced, but did not completely prevent, assimilate movementup the stem, suggesting some translocation in the xylem. Distribution of label from ⁴⁵CaCl₂, ⁸⁶RbCl and [³H]asparagine,incorporated through cut petioles, did not follow the same patternas label from ³²P solutions. Malus pumila Mill., apple, Prunus domestica L., Prunus insititia. L., leaf plum, patterns, transport of radioisotopes, vascular phyllotaxis     

Effect of 2-Thiouracil on Cell Differentiation and Leaf Morphogenesis in Cannabis sativa

When supplied through the leaf at low dosage levels, the pyrimidineanalogue, 2-thiouracil, progressively arrests apical growthand organogenesis in young plants of Cannabis sativa. Duringthe treatment period, a generation of leaves arises in whichcell differentiation is inhibited without a parallel reductionin laminal expansion. With the withdrawal of treatment, apicalgrowth is resumed, but severe morphogenetic defects later becomeevident in leaves developing from primordia initiated duringthe treatment period or shortly afterwards, and there is simultaneouslya loss of apical dominance and of the control of phyllotaxis.Growth of a more normal pattern is, however, gradually restoredat stem apices, although local anomalies in the anatomy of thelamina recur throughout the life of the plant, and otherwisenormal leaves continue to show sporadic flecks or streakingsof abnormal pigmentation. The latter phenomenon suggests thatthe analogue induces a persistent state of instability in someof the proplastids of meristematic tissues.     

Phyllotaxis. I. A Mechanistic Model

A quantitative two-dimensional model for phyllotaxis is described.The model is based on the production, diffusion and degradationof a morphogen, and it is assumed that primordial initiationcan only take place in competent tissue when the morphogen concentrationdrops to a certain critical level. The model predicts the anglesbetween successive primordia; under appropriate conditions asteady state is achieved where the divergence angle is constant;and for limiting values of the parameters, the predicted steady-statedivergence angle approaches the Fibonacci angle. To accountfor non-spiral phyllotaxis, an additional hypothesis, calledspatial competence, is introduced. As well as a morphogen levelbelow the threshold level, and for competence in the usual sense,this assumes that particular spatial demands must be satisfiedbefore primordial initiation can proceed.     

Observations on the Aphlebiae and Megasporangia of Stauropteris burntislandica P. Bertrand

The aphlebiae of Stauropteris burntislandica are shown to bemore complex than the simple forked processes indicated by Surange.They are variable structures and consist of a protuberance orridge bearing 5–7 appendages probably arising by dichotomousbranching; the vascular system is also branched and supplieseach large lobe of the aphlebiae with a small strand of tissueof tracheidal character. A megasporangium is described containing more than four megaspores,possibly as many as seven or eight, indicating that two tetradsmay sometimes be involved in megaspore formation.     

Ultrastructure and Development of the Laticifers of Ficus carica L

Laticifers of Ficus caricaL. are of the branched, non-articulatedtype. They occur in the cortex and pith of the plant axis andpenetrate leaves and inflorescences. Observations were madeon laticifers located in shoot apices. Growing regions of laticifers undergo a sequence of ultrastructuralchanges. These are: (a) a pronounced increase in the vacuolarspace which divides the cytoplasm into separated masses; (b)a development of numerous vesicular structures in the cytoplasm.The vesicular structures are released into the vacuolar space.The whole process is accompanied by disintegration of cytoplasm.Apparently isolated masses of cytoplasm occur in the luminaof laticifer tips in sections taken from dormant apices. Itis assumed that these masses have a role in the initiation ofnew laticifer regions in the next growing season. Ficus caricaL., laticifers, ultrastructure, development differentiation     

A Modification of Flowering and Phyllotaxis in Silene

Modified proliferous flowers arose spontaneously in a smallproportion of plants of Silene coeli-rosa growing in gardenplots. The modified flowers consisted of leaves, arranged spirallywith a mean divergence angle of 138.4° instead of the pentamerousarrangement of the normal flower, and sometimes also carpelswhich ranged from open structures with exposed ovules to follicle-likestructures, free or fused, to fully fused carpels with free-centralplacentation. In the modified flowers petals and stamens werenot formed. The primordia at initiation were intermediate insize (relative to the apical dome) between normal leaf and normalsepal primordia but were the same absolute size as the latter.The structure of these anomalous flowers is discussed in relationto the normal flowering process. Silene coeli-rosa, flowering, phyllotaxis     

Experimental and Analytical Studies of Pteridophytes: XXXVIII. Some Observations on Spiral and Bijugate Phyllotaxis in Dryopteris aristata Druce

In an attempt to assess some of the factors which determineleaf arrangement at the shoot apex, a study has been made ofphyllotaxis in the fern Dryopteris aristata. It is shown thatclockwise and counter-clockwise spirals occur with equal frequencyboth in field collections and in adventitious and experimentallyinduced buds which arise on the rhizomes and apices of plantsgrown in the laboratory. In addition to the two common spiralarrangements, a form with bijugate phyllotaxis has been noted.It is concluded that the three types of leaf arrangement arenot under direct genetic control, but rather are dependent oncircumstances of growth at the apex.