CLASSIFICATION OF THE ARCHITECTURE OF DICOTYLEDONOUS LEAVES

A classification of the architectural features of dicot leaves—i.e., the placement and form of those elements constituting the outward expression of leaf structure, including shape, marginal configuration, venation, and gland position—has been developed as the result of an extensive survey of both living and fossil leaves. This system partially incorporates modifications of two earlier classifications: that of Turrill for leaf shape and that of Von Ettingshausen for venation pattern. After categorization of such features as shape of the whole leaf and of the apex and base, leaves are separated into a number of classes depending on the course of their principal venation. Identification of order of venation, which is fundamental to the application of the classification, is determined by size of a vein at its point of origin and to a lesser extent by its behavior in relation to that of other orders. The classification concludes by describing features of the areoles, i.e., the smallest areas of leaf tissue surrounded by veins which form a contiguous field over most of the leaf. Because most taxa of dicots possess consistent patterns of leaf architecture, this rigorous method of describing the features of leaves is of immediate usefulness in both modern and fossil taxonomic studies. In addition, as a result of this method, it is anticipated that leaves will play an increasingly important part in phylogenetic and ecological studies.     

PRIMARY STEM VASCULAR PATTERNS IN THREE SUBFAMILIES OF THE CRASSULACEAE

Primary stem vasculature was investigated in seven genera and 69 species of the Cotyledonoideae, Kalanchoideae and Sedoideae. Vascular patterns in whole cleared stems were determined by number of leaf traces per leaf, number of leaf-trace sympodia per stem, and connections between traces and sympodia. Four patterns were found in the Cotyledonoideae, eight in the Kalanchoideae and four in the Sedoideae. Similarities and differences among the patterns are discussed and possible phylogenetic trends are suggested. Changes in vasculature during ontogeny were observed in the Kalanchoideae and related to patterns found in mature stems. Many species in all three subfamilies reveal a relationship between phyllotaxy, number of sympodia per stem, and the intervals at which leaf traces are connected to each sympodium. Patterns of vasculature were found to support many of the intergeneric relationships suggested by other studies of this family.     

Change of shoot architecture during juvenile-to-adult phase transition in soybean

Juvenile-to-adult phase change is an indispensable event which guarantees a successful life cycle. Phase change has been studied in maize, Arabidopsis and rice, but is mostly unknown in other species. Soybean/Fabaceae plants undergo drastic changes of shoot architecture at the early vegetative stage including phyllotactic change and leaf type alteration from simple to compound. These characteristics make soybean/Fabaceae plants an interesting taxon for investigating vegetative phase change. Following the expansion of two cotyledons, two simple leaves simultaneously emerge in opposite phyllotaxy. The phyllotaxy of the third and fourth leaves is not fixed; both opposite and distichous phyllotaxis are observed within the same population. Leaves were compound from the third leaf. But the third leaf was rarely simple. Morphological and quantitative changes in early vegetative phase were recognized in leaf size, leaf shape, number of trichomes, stipule size and shape, and shoot meristem shape. Two microRNA genes, miR156 and miR172, are known to be associated with vegetative phase change. Examination of the expression level revealed that miR156 expression was high in the first two leaves and subsequently down-regulated, and that of miR172 showed the inverse expression pattern. These expression patterns coincided with the case of other species. Taken all data together, the first and second leaves represent juvenile phase, the fifth and upper leaves adult phase, and the third and fourth leaves intermediate stage. Further investigation of soybean phase change would give fruitful understandings on plant development.     

THE EVOLUTION OF PHENOTYPIC CORRELATIONS AND “DEVELOPMENTAL MEMORY”

Development introduces structured correlations among traits that may constrain or bias the distribution of phenotypes produced. Moreover, when suitable heritable variation exists, natural selection may alter such constraints and correlations, affecting the phenotypic variation available to subsequent selection. However, exactly how the distribution of phenotypes produced by complex developmental systems can be shaped by past selective environments is poorly understood. Here we investigate the evolution of a network of recurrent nonlinear ontogenetic interactions, such as a gene regulation network, in various selective scenarios. We find that evolved networks of this type can exhibit several phenomena that are familiar in cognitive learning systems. These include formation of a distributed associative memory that can “store” and “recall” multiple phenotypes that have been selected in the past, recreate complete adult phenotypic patterns accurately from partial or corrupted embryonic phenotypes, and “generalize” (by exploiting evolved developmental modules) to produce new combinations of phenotypic features. We show that these surprising behaviors follow from an equivalence between the action of natural selection on phenotypic correlations and associative learning, well‐understood in the context of neural networks. This helps to explain how development facilitates the evolution of high‐fitness phenotypes and how this ability changes over evolutionary time.     

Shoot organization genes regulate shoot apical meristem organization and the pattern of leaf primordium initiation in rice

The mechanism regulating the pattern of leaf initiation was analyzed by using shoot organization (sho) mutants derived from three loci (SHO1, SHO2, and SHO3). In the early vegetative phase, sho mutants show an increased rate of leaf production with random phyllotaxy. The resulting leaves are malformed, threadlike, or short and narrow. Their shoot apical meristems are relatively low and wide, that is, flat shaped, although their shape and size are highly variable among plants of the same genotype. Statistical analysis reveals that the shape of the shoot meristem rather than its size is closely correlated with the variations of plastochron and phyllotaxy. Rapid and random leaf production in sho mutants is correlated with the frequent and disorganized cell divisions in the shoot meristem and with a reduction of expression domain of a rice homeobox gene, OSH1. These changes in the organization and behavior of the shoot apical meristems suggest that sho mutants have fewer indeterminate cells and more determinate cells than wild type, with many cells acting as leaf founder cells. Thus, the SHO genes have an important role in maintaining the proper organization of the shoot apical meristem, which is essential for the normal initiation pattern of leaf primordia.     

Studies of aberrant phyllotaxy1 Mutants of Maize Indicate Complex Interactions between Auxin and Cytokinin Signaling in the Shoot Apical Meristem

One of the most fascinating aspects of plant morphology is the regular geometric arrangement of leaves and flowers, called phyllotaxy. The shoot apical meristem (SAM) determines these patterns, which vary depending on species and developmental stage. Auxin acts as an instructive signal in leaf initiation, and its transport has been implicated in phyllotaxy regulation in Arabidopsis (Arabidopsis thaliana). Altered phyllotactic patterns are observed in a maize (Zea mays) mutant, aberrant phyllotaxy1 (abph1, also known as abphyl1), and ABPH1 encodes a cytokinin-inducible type A response regulator, suggesting that cytokinin signals are also involved in the mechanism by which phyllotactic patterns are established. Therefore, we investigated the interaction between auxin and cytokinin signaling in phyllotaxy. Treatment of maize shoots with a polar auxin transport inhibitor, 1-naphthylphthalamic acid, strongly reduced ABPH1 expression, suggesting that auxin or its polar transport is required for ABPH1 expression. Immunolocalization of the PINFORMED1 (PIN1) polar auxin transporter revealed that PIN1 expression marks leaf primordia in maize, similarly to Arabidopsis. Interestingly, maize PIN1 expression at the incipient leaf primordium was greatly reduced in abph1 mutants. Consistently, auxin levels were reduced in abph1, and the maize PIN1 homolog was induced not only by auxin but also by cytokinin treatments. Our results indicate distinct roles for ABPH1 as a negative regulator of SAM size and a positive regulator of PIN1 expression. These studies highlight a complex interaction between auxin and cytokinin signaling in the specification of phyllotactic patterns and suggest an alternative model for the generation of altered phyllotactic patterns in abph1 mutants. We propose that reduced auxin levels and PIN1 expression in abph1 mutant SAMs delay leaf initiation, contributing to the enlarged SAM and altered phyllotaxy of these mutants.     

Characterization of global molecular shape transitions between “open” and “closed” protein conformations

Induced-fit configurational transitions in proteins can take many forms. In cases, we find small “closures” of a loop onto the substrate. In other cases, the structural changes triggered by a ligand involve large rearrangements that affect entire domains. The nature of these transitions is normally assessed by a visual analysis or in terms of simple local geometrical parameters, such as interresidue distances, backbone dihedral angles, and relative displacements between domains. This approach is limited and rather undiscriminating. In this work, we apply recently introduced ideas from macromolecular shape analysis to characterize the global shape changes accompanying “open closed” transitions in proteins. Here, we monitor two distinct properties simultaneously: molecular size and self-entanglements. The method is applied to some proteins exhibiting pairs of structurally different conformations (adenylate kinase, hexokinase, citrate synthase, alcohol dehydrogenase, triosephosphate isomerase, thioredoxin, and aspartate amino-transferase). The conformational change associated with these proteins is classified according to an order parameter that considers various molecular shape features. The results allow one to recognize, in a nonvisual fashion, the likely occurrence of local or global structural rearrangements. In addition, the technique provides an insight into folding features that may remain invariant during the configurational transitions. © 1996 John Wiley & Sons, Inc.     

THE ROLES OF HETEROCHRONY AND HETEROBLASTY IN THE DIVERSIFICATION OF LEAF SHAPES IN BEGONIA DREGEI (BEGONIACEAE)

The relationship between shape variation in the transitional series of leaves and in adult leaves was examined in seedlings of seven morphs of Begonia dregei using several quantitative methods of shape analysis. There is variation in the shape of adult leaves among individuals as well as in juvenile leaves within individuals in B. dregei. As an individual grows, there is a gradual transition in leaf shape from the symmetrical, oval, smooth-margined leaves through a series of more than ten transitional leaves to a stable adult leaf shape. There appear to be two basic patterns to the acquisition of adult traits. Traits that differ among morphs are acquired gradually throughout the entire transitional series while those that are similar among morphs are acquired by about leaf 5 and remain stable through the later juvenile leaves. There is no identity of leaf shape between the earlier leaves of some morphs and the later leaves of others. Evolutionary diversification in adult leaf morphology in this species is not related to simple changes in ontogeny of the whole plant.     

CHANGE IN EPILOBIUM PHYLLOTAXY DURING REPRODUCTIVE TRANSITION

The ontogeny of Epilobium hirsutum grown under natural summer photoperiod in a glasshouse was divided into vegetative, early transitional, transitional, and floral stages. Bijugate phyllotaxy, common to both the vegetative and early transitional stages, is transformed into spiral phyllotaxy during the transitional stage by an initial change in the divergence angle of a single primordium inserted at a unique level on the shoot. Leaf primordia subsequently are inserted in a spiral arrangement in the indeterminate floral shoot apex. The early transitional shoot apical meristem is about 1.5 times the volume of the vegetative meristem but expands at about two-thirds the relative plastochron rate of volume increment of the vegetative meristem. There are progressive decreases in the plastochron and relative plastochron rates of radial and vertical shoot growth through ontogeny. Relative chronological rates of shoot growth, however, are not altered during ontogeny. Spiral transformation results from changes in the relative points of insertion of leaf primordia on the shoot meristem. These changes are accompanied by an increased rate of primordia initiation on a more circular shoot meristem. The change in phyllotaxy during ontogeny is similar to that which was artificially induced by chemical modification of auxin concentration gradients in the shoot apex, with the additional feature that there is an initial increase in the volume of the shoot meristem prior to the natural spiral transformation. Size of the shoot apical meristem, however, appears to have little influence on Epilobium phyllotaxy; but the geometric shape of the meristem is well correlated with bijugate to spiral transformations. This suggests that geometric parameters of the shoot meristem should be considered in theoretical models of phyllotaxy.     

ESTABLISHMENT OF THE VASCULAR SYSTEM IN SEEDLINGS OF POPULUS DELTOIDES BARTR.

Seven seedlings ranging from 1 to 25 days old were embedded in Spurr's resin and serially sectioned at 1–2 μm. Sectioning extended from well above the apex downward to the hypocotyl base in the 1–day seedlings and to varying levels in the hypocotyl in the older seedlings. Procambial development was analyzed in its entirety for each seedling, and a composite two-dimensional diagram representing the procambial system of a 25-day-old seedling was prepared. Each cotyledon was served by a double-trace, one-half of which was derived from each of two embryonic bundles. The central traces serving the four primary leaves were in turn derived from the four cotyledonary bundles comprising the double traces. The procambial system serving the cotyledons and the four primary leaves approximated a decussate phyllotaxy. The central traces serving the secondary leaves were arranged in a helix that conformed at first to a 1/3 and then to a 2/5 phyllotaxy. Transitions to higher phyllotactic orders were systematic and reproducible, and they occurred in an orderly sequence in both the central and lateral leaf traces. The manner in which leaf traces diverged from parent traces to serve new leaf primordia provided for vascular redundancy. Thus, the entire vascular system was integrated into a highly functional whole.     

Observations on the Occurrence of Prickles on the Leaves of Ilex aquifolium

The number of prickles upon the edge of a leaf is related bycomplex laws to the size of the leaf, the number of prickleson the other edge, the number of prickles on other leaves ofthe shoot, the phyllotaxy of the shoot, and the intrinsic asymmetryof the leaf. The available evidence indicates that pricklesarise by the interaction of not less than five recognizablephysiological systems. The physical nature of these systemsis unknown but their mathematical properties have been partlyelucidated. Some of them are found to involve the transmissionof morphogenetic impulses while others may be purely local intheir action. As one of the consequences of this physiologicalsituation it is found that shoots having opposite directionsof phyllotaxy differ quantitatively as well as qualitatively.     

ITOPSIDEMA,A NEW GENUS OF THE OSMUNDACEAE FROM THE TRIASSIC OF ARIZONA

Daugherty , Lyman H. (San Jose State College, San Jose, Calif.) Itopsidema, a new genus of the Osmundaceae from the Triassic of Arizona. Amer. Jour. Bot 47(9): 771–777. Illus. 1960.—Itopsidema vancleavei, a new genus and species of the family Osmundaceae, is described. The specimen consists of several segments of an arborescent stem obtained from the Upper Triassic of the Petrified Forest National Monument near Holbrook, Arizona. The surfaces on 2 of the segments are covered by adventitious roots and the remaining segments are covered by leaf bases. The fronds are spirally arranged and have an 8/21 phyllotaxy. The cortex of the stem, which contains numerous leaf traces and adventitious roots, consists of parenchyma with cell walls of medium thickness. The leaf traces are oblong to crescent-shaped in the inner cortex and horseshoe-shaped in the outer cortex. The base of the petiole contains a single, large vascular bundle and is covered by multicelled, glandular spines. The adventitious roots originate on the abaxial side of the leaf traces in the region of the inner cortex. The center of the stem is occupied by an ectophloic, mesarch siphonostele without leaf gaps. The pith is composed of firm-walled parenchyma cells which have isolated tracheids with reticulate pitting scattered among them. These tracheids are so rare the pith cannot be considered a “mixed pith.” The relationship and morphological significance of Itopsidema with respect to other members of the Osmundaceae are briefly discussed.     

THE RELATION OF AGE AND BUD BREAK TO THE DETERMINATION OF PHYLLOTAXY IN CATALPA SPECIOSA

Catalpa speciosa is interesting in that the phyllotaxy of the lateral shoots can be either decussate or whorled. The pattern appears to be correlated with the number of buds which emerge. The arrangement is not related to dormancy; nor does the stage of development of the bud at the time of bud break influence the phyllotaxy. The control of bud break appears to be related to the position of the bud on the stem. Possible mechanisms controlling the lateral shoot pattern are discussed.     

ANOMALOUS SECONDARY GROWTH IN LIANAS OF THE BIGNONIACEAE IS CORRELATED WITH THE VASCULAR PATTERN

Vascular pattern and anomalous secondary growth were studied in shoots of Clytostoma callistegoides, a liana having two types of phyllotaxy, one decussate and the other whorled. In shoots with decussate phyllotaxy, typical of bignoniaceous lianas, the vascular pattern has four major vascular strands that extend continuously from internode to internode, whereas in shoots having a whorled phyllotaxy the pattern has six major vascular strands. The first unidirectional cambium segments which result in the anomalous secondary growth were initiated precisely opposite each of the major vascular strands in both types of shoots. It is concluded that positioning of unidirectional cambium segments responsible for anomalous growth is correlated morphogenetically with the vascular pattern.     

STUDY OF THE ESSENTIAL LEAF OILS OF THE GENUS MONARDA (LABIATAE)

Vapor-phase chromatographic patterns obtained from the distilled essential oils of 20 taxa in the genus Monarda (Labiatae) are discussed. The influence of leaf tissue maturity, plant habitat, and oil storage upon the composition of the essential oils was investigated, as well as similarities of leaf and flower oils in the same plant. The taxa of the subgenus Cheilyctis have very similar chromatographic “fingerprints” which confirm their homogeneity. On the other hand, the polyploid subgenus Monarda has heterogeneous patterns of essential oil composition among its species. A population of M. fistulosa gave evidence of being a chemical race.     

MORPHOLOGY OF THE CURD OF CAULIFLOWER

Sadik , Sidki . (U. California, Davis.) Morphology of the curd of cauliflower. Amer. Jour. Bot. 49(3): 290–297. Illus. 1962.—The development of the curd and inflorescence of cauliflower, Brassica oleracea Linn., var. botrytis D.C., is described. The cultivars ‘Snowball M’ and ‘February-Early-March’ were studied. The curd has a nonfasciated and monopodial type of branching. Curd initiation of ‘Snowball M’ is not dependent on vernalization, but the curd of ‘February-Early-March’ and the floral primordia of both cultivars are initiated only after vernalization. Associated with flowering is the disruption of the curd by the elongation of some of the inflorescence branches. The initiation of leaves, branches, and floral primordia follows a 5 + 8 phyllotaxy throughout all stages of development. This system of phyllotaxy changes at the time of initiation of floral parts.     

Control of Plant Architecture: The Role of Phyllotaxy and Plastochron

Plants display a wide variety of three dimensional forms, or architectures, that are critical for their survival in competitive environments or, in the case of crops, for their productivity. Architecture is generated after embryogenesis through the activities of shoot apical meristems and root apical meristems. Leaves are the principal lateral organ that determines the plant shoot morphology, and they normally develop in very regular patterns in time and space. The spatial pattern of leaf arrangement is called phyllotaxy, and the temporal pattern is determined by the plastochron, which is the time between successive leaf initiation events. Both programs involve many gene activities as well as the hormones auxin and cytokinin. Apparently, the mechanisms controlling phyllotaxy and plastochron share some regulatory components. In this review, the molecular mechanisms for both patterning programs will be discussed.     

DEVELOPMENT OF FLORAL ORGANS IN THE SITES OF LEAF PRIMORDIA IN PINGUICULA VULGARIS

Plants of Pinguicula vulgaris L. have either clockwise or counterclockwise spiral phyllotaxy. The inception of floral primordia occurs in leaf sites as a normal sequence of development. Only two leaf primordia initiated late in the season develop into floral primordia in the following year. They do not represent a direct modification of the apical meristem nor of the detached meristem. The apical meristem continues to produce leaves in the vegetative phase and flowers in the reproductive phase, and thus the plants show a monopodial growth. Axillary buds are not developed in this perennial species and instead additional buds of adventitious ontogeny appear. Such buds are produced on the older leaves of larger plants, and they are extremely useful in the vegetative propagation of the species.     

The influence of size on body shape diversification across Indo‐Pacific shore fishes*

Understanding the causes of body shape variability across the tree of life is one of the central issues surrounding the origins of biodiversity. One potential mechanism driving observed patterns of shape disparity is a strongly conserved relationship between size and shape. Conserved allometry has been shown to account for as much as 80% of shape variation in some vertebrate groups. Here, we quantify the amount of body shape disparity attributable to changes in body size across nearly 800 species of Indo‐Pacific shore fishes using a phylogenetic framework to analyze 17 geometric landmarks positioned to capture general body shape and functionally significant features. In marked contrast to other vertebrate lineages, we find that changes in body size only explain 2.9% of the body shape variation across fishes, ranging from 3% to 50% within our 11 sampled families. We also find a slight but significant trend of decreasing rates of shape evolution with increasing size. Our results suggest that the influence of size on fish shape has largely been overwhelmed by lineage‐specific patterns of diversification that have produced the modern landscape of highly diverse forms that we currently observe in nature.