Leaf Form Research Articles

Molecular Phylogenetic Analysis of the Circumboreal Genus Cassiope (Ericaceae) Reveals Trends in Some Morphological and Wood Anatomy Characters and Likely Reticulate Evolution

The genus Cassiope is comprised of 17 species of dwarf alpine shrubs that exhibit a variety of leaf morphologies, yet have very similar flowers and habits. The genus is circumboreally distributed, with species diversity concentrated in northwestern North America and in eastern Asia. This clade has been previously shown to be strongly supported as sister to the subfamily Ericoideae, but relationships within the genus have never been the subject of any phylogenetic study. The goal of this study was to use three molecular markers from the chloroplast and nuclear genomes to generate a phylogeny of Cassiope. Our initial analyses suggested that three species negatively impacted phylogeny reconstruction by introducing conflict between the nuclear and chloroplast genomes. Reanalysis with those three taxa removed generated a very strongly supported phylogeny, suggesting that these three taxa may be of hybrid origin. Some evolutionary trends in morphology and anatomy are apparent based upon analyses using the restricted taxon sampling. Characters with discrete character states, such as leaf form and stomatal distribution, are tightly correlated but appear to be homoplasious within the genus. Continuously varying characters such as habitat elevation and aspects of wood anatomy show compelling phylogenetic trends that may be related to the fact that these species evolved in alpine and subalpine habitats. Cassiope appears to have a complex biogeographical history in the northern hemisphere, which cannot be completely resolved with the current dataset. However, it is likely that the genus has undergone multiple speciation events in the Himalayas with one or more dispersals into northwestern North America, or alternately with origins in the American Northwest followed by dispersal and subsequent divergence in the Himalayas.

Understanding of Leaf Development-the Science of Complexity.

The leaf is the major organ involved in light perception and conversion of solar energy into organic carbon. In order to adapt to different natural habitats, plants have developed a variety of leaf forms, ranging from simple to compound, with various forms of dissection. Due to the enormous cellular complexity of leaves, understanding the mechanisms regulating development of these organs is difficult. In recent years there has been a dramatic increase in the use of technically advanced imaging techniques and computational modeling in studies of leaf development. Additionally, molecular tools for manipulation of morphogenesis were successfully used for in planta verification of developmental models. Results of these interdisciplinary studies show that global growth patterns influencing final leaf form are generated by cooperative action of genetic, biochemical, and biomechanical inputs. This review summarizes recent progress in integrative studies on leaf development and illustrates how intrinsic features of leaves (including their cellular complexity) influence the choice of experimental approach.

Influences of light intensity variations on growth characteristics of Myriophyllum aquaticum

Myriophyllum aquaticum is a heterophyllous plant that is native to South America and has been introduced to the United States. The reallocation of resources to emergent or submersed growth forms likely allows M. aquaticum to overcome changes in light availability and to invade different habitats. Our objective was to determine the effects of light availability on plant length, biomass allocation, and relative growth rate through replicated mesocosm experiments. Myriophyllum aquaticum was grown in full sunlight, 30%, 50%, and 70% shade in replicated treatments. Total plant length, emergent shoot length, submersed shoot length, and the total of number of emergent and submersed shoots were recorded. Plants were harvested and sorted into emergent shoots, submersed shoots, roots, and stolons, then dried and weighed to assess biomass allocation. After 12 weeks, biomass was different among shade treatments. Differences in plant mass were a result of greater plant growth in the 30% shade treatment. Total plant length was greatest in the 50% shade treatment with a reduction in plant length observed in full sunlight. Emergent shoot length was reduced in full sunlight, while an increase in submersed shoot length occurred in 70% shade. Our data suggest that intermediate light availability is optimal for M. aquaticum growth and that the growth of two leaf forms is a physiological response to changes in environmental conditions.

Molecular systematics of Indian Crotalaria (Fabaceae) based on analyses of nuclear ribosomal ITS DNA sequences

Crotalaria L. (Fabaceae) comprises approximately 700 species that are distributed in tropical and subtropical regions of the world. In India, it is the largest legume genus with 92 species. Sequences of the nuclear internal transcribed spacer from species representing all the six recognized sections of Indian Crotalaria were subjected to phylogenetic analyses. Ancestral state reconstructions were done for two morphological characters, corolla keel beak, and leaf form. Analyses reveal five major well-supported clades within a monophyletic Crotalaria. Clade 1 has members with rostrate-spirally twisted keel beaks while the remaining four clades comprise members with keel beaks rostrate-not spirally twisted. Clade 1 further bifurcates into two clades characterized by differences in leaf morphology: (1a) contains species with simple leaves belonging to section Calycinae, section Crotalaria subsection Crotalaria and subsection Bractetae and multifoliolate leaves belonging to section Crotalaria subsection Polyphyllae (1b) contains species with trifoliate leaves belonging to section Dispermae, section Crotalaria subsection Longirostres. Sub-clade iii in Clade 1a contains four species complexes, each forming a monophyletic group. Of these one comprising C. madurensis, C. subperfoliata, C. shevaroyensis, and C. longipes is endemic to a region in southern India. Each of the others contains one endemic species and one widespread species that is sympatric with the endemic one (C. hirta and C.mysorensis; C. epunctata and C. albida; C. clarkei and C. triquetra). The present study suggests that: (1) all members of section Calycinae and most members of section Crotalaria form a clade, (2) members of section Crotalaria subsection Longirostres and section Dispermae form a distinct clade, (3) twisting of the keel beak is an apomorphy within the genus, (4) there is a reversal to keel beak rostrate-not spirally twisted in C. shevaroyensis and an independent origin of a rostrate-spirally twisted keel beak in C. humilis, and (5) the trifoliolate condition is a plesiomorphy in the genus and the simple leaf condition an apomorphy; there is a single reversal to the trifoliolate condition in C. orixensis. The current morphological classification system of Indian Crotalaria species includes six sections, but these circumscriptions are not supported by the molecular data.

Unifoliata-Afila interactions in pea leaf morphogenesis.

Processes of leaf morphogenesis provide the basis for the great diversity of leaf form among higher plants. The common garden pea (Pisum sativum) offers a developmental model system for understanding how gene and hormone interactions impart a large array of mutant leaf phenotypes. • To understand the role of auxin in AF and UNI gene function and their interaction, we compared the range of leaf phenotypes on afila (af) and unifoliata (uni) double mutants, examined the effects of these mutations on auxin levels, auxin transport, auxin response via DR5::GUS, and expression of auxin-regulated genes. • The adult leaves of af uni double mutants have leaflets and tendrils and typically possess two lateral pinna pairs and a terminal leaflet. The af mutants have higher auxin content, stronger auxin response, and higher expression of auxin responsive genes than wildtype. The uni mutant has reduced auxin content and transport, whereas the uni-tac mutant has higher auxin content and transport and reduced auxin response compared to wildtype. • Auxin concentration and response differences characterize the antagonistic relationship between AF and UNI in pea leaf development. The mechanism involves modulation of auxin mediated by one or both genes; UNI is expressed in and promotes high auxin levels, and AF suppresses auxin levels.

Late blight (Phytophthora infestans) occurring on stems - a new problem in potato crops

In recent years changes in the occurrence of the first potato late blight (<i>Phytophthora infestans</i>) symptoms have been noted. Observations of potato crops have showed that occurrence of the blight symptoms is sometimes on the stem instead on the leaves. The aim of the study carried out in 1995-2001 was to determine occurrence and harmfulness of the stem late blight infections. Survey of many potato crops (490 potato fields) made in 1997-2001, around Poland enabled assessment of the incidence of stem blight. Average 69,1% of observed crops were affected with stem blight. The stem blight incidence was not connected with the rate of the leaf form of late blight developing on the foliage. Stem form of the disease has appeared more often in the years with less rainfall during June and July. Its occurrence was influenced by micro climate inside potato canopy. Glasshouse experiments confirmed the importance of stem lesions in decreasing tuber yield (11,2-42,9%) and increasing tuber infections. Results have shown that tubers contaminated with spores were the least probable source of the stem form of late blight.

Abnormal Leaf Morphologies Associated with Primary and Secondary Vein Patterning Defects in Catharanthus roseus: Mid-vein Defect Converts Simple Leaf into Binate Compound Leaf

Simple petiolated leaves are formed on the wild type plants of apocynaceous medicinal-cum-floricultural species Catharanthus roseus. A C. roseus variant line homozygous for two loss-of-function mutations, an induced leafless inflorescence (lli) mutations and a natural bisected leaf (bil) mutation, was isolated on account of its unique leaf bisection phenotype which was characterized. The lli bil phenotype was highly penetrant but poorly expressed. Only about one-fourth of leaves of lli bil plants were bisected. Leaf bisection was correlated with premature termination of midvein. Degree of bisection varied from a nick at the apex of lamina to formation of two complete leaflets. The notch in 43 % of the bisected leaves bore a pin-like apical adventitious growth. The features of bisected leaves showed that midvein was essential for symmetrical development of smooth lamina spans on its either side; although the development of spans was independent. Several lateral veins emerged from proximal midvein and grew acropetally. Lamina development in the proximal region failed in the absence of local lateral veins. Bisected leaves were also formed as bi-lobed simple leaves, each lobe having its own primary (mid) vein arising from proximally bifurcated midvein. Also formed were completely bisected leaves. In these binately compound leaves, each leaflet had its own petiolule attached to the leaf petiole. The lli bil genotype of C. roseus perhaps provides the only example of a compound leaved variant evolving from a simple leaved species. This phenotype of lli bil leaves supports the suggestion that simple leaf form was ancestral in angiosperms.

Insect resistance of a full sib family of tetraploid switchgrass Panicum virgatum L. with varying lignin levels

Little information is available on insect resistance mechanisms and inheritance in biomass grasses. Although reduction of lignin in biomass grasses in order to increase the efficiency of fermentation may result in increased susceptibility to insect feeding, other resistance mechanisms may be more important. Field grown leaves of two tetraploid parent (Kanlow N1, Summer) and 14 progeny switchgrass (Panicum virgatum L.) plant clones selected for a diversity of plant form and ranges in lignin levels were tested for leaf resistance to feeding by the fall armyworm (Spodoptera frugiperda J. E. Smith), a grass feeding insect pest. Although lignin generally appeared important as a resistance mechanism only at early season stages, replicate clones of two low lignin progeny plants generally remained resistant to fall armyworm feeding. Mechanical damaging increased resistance to fall armyworm feeding in several of these plants. Degrees of resistance were sometimes associated with leaf form of progeny. These results indicate there are likely multiple insect resistance mechanisms operating at different stages in switchgrass, and that segregation of some mechanisms appears related to growth form of the plants.

Evolution of leaf form correlates with tropical-temperate transitions in Viburnum (Adoxaceae).

Strong latitudinal patterns in leaf form are well documented in floristic comparisons and palaeobotanical studies. However, there is little agreement about their functional significance; in fact, it is still unknown to what degree these patterns were generated by repeated evolutionary adaptation. We analysed leaf form in the woody angiosperm clade Viburnum (Adoxaceae) and document evolutionarily correlated shifts in leafing habit, leaf margin morphology, leaf shape and climate. Multiple independent shifts between tropical and temperate forest habitats have repeatedly been accompanied by a change between evergreen, elliptical leaves with entire margins and deciduous, more rounded leaves with toothed or lobed margins. These consistent shifts in Viburnum support repeated evolutionary adaptation as a major determinant of the global correlation between leaf form and mean annual temperature. Our results provide a new theoretical grounding for the inference of past climates using fossil leaf assemblages.

Prerequisites for evolution: variation and selection in yellow autumn birch leaves

Prerequisites for evolution: variation and selection in yellow autumn birch leaves

A preliminary study of leaf morphology and flow cytometry in the Vatica diospyroides Symington, endangered medicinal plant of Peninsular Thailand

In modern drug discovery program, Vatica diospyroides Symington consisted of chemical constituents that were found as anticancer in human. V. diospyroides was described as endangered species, and its tree is puzzled by means of leaf forms. Investigating the unique features was very important to support the program. To classify these features, leaf traits and C-DNA values were investigated. Leaf characters of twenty-eight trees of V. diospyroides, including herbarium specimens, were recorded using leaf morphometric study and subsequent analysis by cluster. The results revealed that lamina length, leaflet length and leaflet width were found to be significantly different characters. After being analyzed by cluster, the specimens were evaluated into: 1) small size (SS) and 2) large size (LS) forms using three correlated variables namely lamina length, leaflet length/width and petiole length. The 2C-DNA contents were estimated by using flow cytometric study in each form of seedlings. The results showed that 2C-DNA contents of SS and LS seedlings were 1.83 ± 0.27 and 2.21 ± 0.31 pg; consequently, one haploid genomes (1C-value) were therefore 895 and 1080 Mbp, respectively. It is thus accepted that leaf morphometric and flow cytometric studies were able to distinct V. diospyroides into two specific individuals. It is important to carry out classifications using DNA markers and phytochemical properties in further experiment. Key words: 2C-DNA content, Chan Ka Pho, flow cytometry, genome size, leaf morphology,Vatica diospyroides.

Leaf adaxial-abaxial polarity specification and lamina outgrowth: evolution and development

A key innovation in leaf evolution is the acquisition of a flat lamina with adaxial-abaxial polarity, which optimizes the primary function of photosynthesis. The developmental mechanism behind leaf adaxial-abaxial polarity specification and flat lamina formation has long been of interest to biologists. Surgical and genetic studies proposed a conceptual model wherein a signal derived from the shoot apical meristem is necessary for adaxial-abaxial polarity specification, and subsequent lamina outgrowth is promoted at the juxtaposition of adaxial and abaxial identities. Several distinct regulators involved in leaf adaxial-abaxial polarity specification and lamina outgrowth have been identified. Analyses of these genes demonstrated that the mutual antagonistic interactions between adaxial and abaxial determinants establish polarity and define the boundary between two domains, along which lamina outgrowth regulators function. Evolutionary developmental studies on diverse leaf forms of angiosperms proposed that alteration to the adaxial-abaxial patterning system can be a major driving force in the generation of diverse leaf forms, as represented by 'unifacial leaves', in which leaf blades have only the abaxial identity. Interestingly, unifacial leaf blades become flattened, in spite of the lack of adaxial-abaxial juxtaposition. Modification of the adaxial-abaxial patterning system is also utilized to generate complex organ morphologies, such as stamens. In this review, we summarize recent advances in the genetic mechanisms underlying leaf adaxial-abaxial polarity specification and lamina outgrowth, with emphasis on the genetic basis of the evolution and diversification of leaves.

Oxalate contents in various types of tea drink

Oxalate is one of the major risk factors for kidney stones which become more common in industrialized countries. Tea is a significant source of oxalate. The purpose of the present study was to determine oxalate content in tea samples. One‐hundred and twenty samples of tea (white, green, oolong and black tea) were collected both in leaf and bag forms. The oxalate content was measured by the high performance liquid chromatography (HPLC) method with an anion exchange column using 0.85 mM sodium bicarbonate and 0.9 mM sodium carbonate as a mobile phase. The results showed that the highest of oxalate content was found in black tea (1.36–4.42 mg/g tea), followed by oolong tea (0.74–3.94 mg/g tea), green tea (0.44–2.18 mg/g tea) and the lowest was found in white tea (0.40–1.79 mg/g tea). The oxalate contents in leaf form and bag form were significantly different (p < 0.05). People in a high risk group should avoid drinking high amounts of black tea.

Use of thermal imaging to determine leaf conductance along a canopy gradient in European beech (Fagus sylvatica)

Using an infrared camera, we measured the leaf temperature across different canopy positions of a 23-m-tall deciduous forest tree (Fagus sylvatica L.) including typical sun and shade leaves as well as intermediate leaf forms, which differed significantly in specific leaf area (SLA). We calculated a temperature index (I(G)) and a crop water stress index (CWSI) using the surface temperatures of wet and dry reference leaves. Additional indices were computed using air temperature plus 5 °C (I(G) + 5, CWSI + 5) as dry references. The minimum temperature of the wet leaf and the maximum temperature of the dry leaf proved to be most suitable as reference values. We correlated the temperature indices with leaf area-related conductance to water vapor (g(L)) using porometry at the leaf level and using xylem sap flow at the branch level. At the leaf and at the branch level, I(G) and CWSI were equally well suited as proxies of g(L), whereas the relationships of I(G) + 5 and CWSI + 5 with g(L) were only weak or even insignificant. At the leaf level, the correlations of I(G) and CWSI with g(L) were significant in all parts of the crown. The slopes of g(L) vs. I(G) and CWSI did not differ significantly among the crown parts; this indicates that they were not influenced by SLA or irradiance. At the branch level, close correlations (r > 0.8) were found between temperature indices and g(L) across the crown. These results demonstrate that satisfactory relationships between temperature indices and g(L) can be established in tall trees even in those canopy parts that are exposed to relatively low levels of irradiance and exhibit relatively low values of g(L).

Native environment modulates leaf size and response to simulated foliar shade across wild tomato species.

The laminae of leaves optimize photosynthetic rates by serving as a platform for both light capture and gas exchange, while minimizing water losses associated with thermoregulation and transpiration. Many have speculated that plants maximize photosynthetic output and minimize associated costs through leaf size, complexity, and shape, but a unifying theory linking the plethora of observed leaf forms with the environment remains elusive. Additionally, the leaf itself is a plastic structure, responsive to its surroundings, further complicating the relationship. Despite extensive knowledge of the genetic mechanisms underlying angiosperm leaf development, little is known about how phenotypic plasticity and selective pressures converge to create the diversity of leaf shapes and sizes across lineages. Here, we use wild tomato accessions, collected from locales with diverse levels of foliar shade, temperature, and precipitation, as a model to assay the extent of shade avoidance in leaf traits and the degree to which these leaf traits correlate with environmental factors. We find that leaf size is correlated with measures of foliar shade across the wild tomato species sampled and that leaf size and serration correlate in a species-dependent fashion with temperature and precipitation. We use far-red induced changes in leaf length as a proxy measure of the shade avoidance response, and find that shade avoidance in leaves negatively correlates with the level of foliar shade recorded at the point of origin of an accession. The direction and magnitude of these correlations varies across the leaf series, suggesting that heterochronic and/or ontogenic programs are a mechanism by which selective pressures can alter leaf size and form. This study highlights the value of wild tomato accessions for studies of both morphological and light-regulated development of compound leaves, and promises to be useful in the future identification of genes regulating potentially adaptive plastic leaf traits.

Toward elucidating the mechanisms that regulate heterophylly

Introduction The leaves of plants show tremendous variation in size and shape, despite all leaf primordia initially developing as simple protrusions from the flanks of the shoot apical meristem (Tsukaya 2006). Aside from variation among species, some species show abrupt changes in leaf form in response to surrounding environmental conditions. This phenomenon is termed heterophylly, and it is generally defined as the variation in leaf form in a single plant in response to environmental conditions (Zotz et al. 2011). Heterophylly allows us to study not only the environmental plasticity of plant development but also leaf development and regulation of leaf form. However, there is limited information on the mechanisms that regulate heterophylly, probably due to the lack of an adequate model, despite numerous morphological studies that have been conducted on this subject (Arber 1920, Bell 2008, Fassett 1957). A thorough understanding of leaf development is required to understand heterophylly. Many recent studies have contributed toward improving our knowledge of leaf development. In addition to understanding the structure and development of leaves, many genes involved in leaf morphogenesis have been isolated, and their networks have been studied in several model species (Blein et al. 2009, Ichihashi et al. 2011, Moon and Hake 2011, Szakonyi et al. 2010, Tsukaya 2006). Moreover, research on the morphological diversification of leaves during the course of evolution is also in progress. In particular, molecular mechanisms, such as those responsible for the difference between simple and compound leaves and the difference in the complexity of leaf form among related species, have been examined in several model plants and their close relatives (Hay and Tsiantis 2006, Kimura et al. 2008, Piazza et al. 2010). Furthermore, the links between phytohormones and leaf development have been examined in detail (Bilsborough et al. 2011, Braybrook and Kuhlemeier 2010, Koenig et al. 2009, Shani et al. 2010, Umehara et al. 2008). Indeed, phytohormones, particularly abscisic acid (ABA) and ethylene, are critical for heterophyllous transformation in various species (Anderson 1978, Hsu et al. 2001, Kane and Albert 1987, Kuwabara et al. 2003). Thus, it appears that the foundation has been laid toward elucidating the mechanisms of heterophylly To facilitate our investigation on heterophylly, we selected Neobeckia aquatica (Eaton) Greene as the model system. N. aquatica is an aquatic member of Brassicaceae and is closely related to the genera Rorippa and Cardamine (Les 1994). N. aquatica exhibits distinct leaf morphology, depending on the environmental conditions; it exhibits simple leaves in terrestrial environments and Plant Morphology vol. 24 pp. 57-63

Soil water potential does not affect leaf morphology or cuticular characters important for palaeo-environmental reconstructions in southern beech, Nothofagus cunninghamii (Nothofagaceae)

Leaf form is closely related to local prevailing abiotic conditions and thus the morphology of fossil and sub-fossil leaves is often used to reconstruct both historical and palaeo-environmental conditions. However, palaeo-environmental reconstruction is difficult because leaf form is controlled potentially by many interacting environmental factors such as temperature, CO2 concentration, light and water availability. We used a glasshouse trial to investigate the impact of water availability on the leaf and cuticle morphology of a species important for palaeo-environmental reconstruction, the southern beech, Nothofagus cunninghamii. We found that reducing soil water potential to –0.2 or –0.5 MPa had no impact on leaf form or cuticular characters, despite reducing leaf carbon assimilation and severely restricting plant growth. Although plant accession affected many leaf characters, there were few significant impacts of altitude of origin and no substantial interactions between altitude of origin and soil water potential. Thus, both cuticular and gross leaf morphology seem to be stable across a range of soil water potentials in this species, meaning that palaeo-environmental signals from this species are unlikely to be affected by changes in water availability.

Relative humidity has dramatic impacts on leaf morphology but little effect on stomatal index or density in Nothofagus cunninghamii (Nothofagaceae)

Reconstructing past environmental conditions using proxies based on fossil and subfossil leaves is difficult because leaf form is influenced by many interacting environmental factors such as temperature, CO2 concentration, light, soil water availability and, potentially, atmospheric relative humidity (RH). We used a species important for palaeo-environmental reconstruction, the southern beech, Nothofagus cunninghamii, to test for the effects of a 50% difference in RH on leaf morphology and epidermal anatomy in a glasshouse experiment. Leaf size, shape and thickness were all strongly affected by RH with leaves from high humidity being larger, narrower and thicker than those from low humidity regardless of plant accession. RH impacts on epidermal characters were generally slight and dependent upon accession. In particular, epidermal cell size was remarkably consistent across accessions and RH levels. Thus, gross leaf morphology of N. cunninghamii was sensitive to changes in RH but, on average, epidermal characters were not. Thus, palaeoenvironmental signals from the epidermis of this species are unlikely to be affected by variation in RH, provided sufficient numbers of leaves are investigated. Gross leaf morphology, however, was strongly related to RH and should not be used for palaeo-climatic reconstruction if changes in RH are likely.

Reducing size to increase number: a hypothesis for compound leaves

Adaptive advantages of the compound leaf form in flowering plants have so far remained elusive.  A novel idea—proposed here—is that there are no direct advantages; the compound leaf evolved instead as a trade-off of selection in favour of something else: greater leafing intensity.  Producing more leaves per unit of supporting shoot or plant body size generates a larger ‘bud bank’— an aggregate of axillary meristems available for optimal deployment in strategies for growth, survival, and reproduction, and also facilitating capacity (through DNA replication errors) for generating novel adaptive mutations that can be transmitted through the germ line.  But higher leafing intensity requires that individual leaf mass be smaller.  Transition from a simple leaf (the ancestral form in angiosperms) to a compound leaf, therefore, may represent one mechanism whereby individual leaf mass was reduced within some angiosperm lineages.  Compound leaves however are rare in angiosperms, I suggest, because more parsimonious mechanisms for mass reduction in a simple leaf are likely to involve straightforward reductions in overall dimensions (length, width), or increased lobing.

A role for PHANTASTICA in medio-lateral regulation of adaxial domain development in tomato and tobacco leaves

Diverse leaf forms in nature can be categorized into two groups: simple and compound. A simple leaf has a single blade unit, whilst a compound leaf is dissected into leaflets. For both simple and compound leaves, a MYB domain transcription factor PHANTASTICA (PHAN) plays an important role in establishing the adaxial domain in the leaf. Absence of PHAN in arabidopsis and antirrhinum leaves supresses blade development, and in tomato suppresses leaflet development. However, in the rachis and petiole regions of tomato leaves where PHAN and the adaxial domain coexist, it has been unclear why leaf blade and leaflets are not formed. We hypothesized that PHAN regulates the medio-lateral extent of the adaxial domain, thereby determining compound leaf architecture. To test this hypothesis, we generated and analysed transgenic tomato plants expressing tomato PHAN (SlPHAN) under the Cauliflower mosaic virus (CaMV) 35S promoter in both sense and antisense orientations, and tobacco plants that over-express tomato SlPHAN. Modulations in SlPHAN resulted in a variety of leaf morphologies such as simple, ternate and compound in either a peltate or non-peltate arrangement. Measurements of the extent of the adaxial domain along the wild-type tomato leaf axis showed that the adaxial domain is narrowed in the rachis and petiole in comparison with regions where laminar tissue arises. In antiSlPHAN transgenic leaves, no blade or leaflet was formed where the adaxial domain was medio-laterally narrowed, and KNOX gene expression was correlatively upregulated. CaMV35S::SlPHAN expression led to widening of the adaxial domain and ectopic blade outgrowth in the rachis of tomato and in the petiole of tobacco. Taken together, these results suggest that SlPHAN plays a role in medio-lateral extension of the adaxial domain and contributes to final leaf morphology in tomato. This study provides a novel insight into leaf architecture in tomato and highlights how changes in the expression domain of a master regulator gene such as SlPHAN can be translated into diverse final leaf morphologies.