CHLOROPLAST DNA POLYMORPHISM AND PHYLOGENY IN THE B GENOME OF GLYCINE SUBGENUS GLYCINE (LEGUMINOSAE)

The B genome of Glycine subgenus Glycine comprises three diploid species whose monophyly is supported by morphological, crossing, and chloroplast DNA (cpDNA) data. Previous cpDNA studies indicated low levels of divergence among these taxa and failed to resolve cladistic relationships among them. More intensive studies of cpDNA variation were initiated, using additional restriction endonucleases and accessions. Results from cladistic analyses of over 50 restriction site characters indicate that there is considerable cpDNA polymorphism within this group of species, with a minimum of 27 plastome types occurring among the 74 accessions sampled. Levels of homoplasy observed in this group are relatively high (15%) for closely related congeneric species. There is only limited congruence between plastome type and taxonomic classification based on morphological characters. Explanations for this lack of concordance include: 1) the early state of taxonomic understanding in this group, 2) lack of resolution in the cpDNA tree caused by homoplasy and the small number of synapomorphic characters, 3) introgression among these interfertile, often sympatric taxa, and 4) maintenance of ancestral cpDNA polymorphisms resulting in shared plastomes among species.     

THE GRANULAR INTERSTITIUM IN THE POLLEN OF SUBFAMILY PAPILIONOIDEAE (LEGUMINOSAE)

A wide range of transitional forms of granular interstitia from simple to complex and from random to ordered occur in the pollen of the subfamily Papilionoideae. Three main types are described: 1) large, widely spaced irregular granules (Type A); 2) densely packed groups of columellae and granules (Type B); and 3) a mass of more or less disorganized granules (Type C). In the genus Calopogonium (tribe Phaseoleae) all three types have been found in different species. Two of the types have been found in different species of the genus Psoralea (tribe Psoraleeae). Granular structures so far occur in six tribes: Desmodieae, Indigofereae, Loteae, Phaseoleae, Psoraleeae, and Vicieae. All of the tribes are regarded as being evolutionarily advanced in both macro and micro characters and many, but not all, show specialized pollen characters. It is concluded that the granular interstitium is a derived structure in papilionoid legumes.     

国产狸尾豆属的研究

狸尾豆属(Uraria Desv.)隶属于豆科(Leguminosae)的蝶形花亚科(Subfam. Papilionoideae),岩黄著族(Trlb. Hedysareae),山绿豆亚族(Subtrib. Desmediinae)。     

COMPARATIVE DEVELOPMENT OF SECRETORY CAVITIES IN THE TRIBES AMORPHEAE AND PSORALEEAE (LEGUMINOSAE: PAPILIONOIDEAE)

The tribes Amorpheae and Psoraleeae of the Leguminosae (Papilionoidae) share the characteristics of one-seeded fruits and gland-dotted foliage. Because of this, they traditionally have been considered closely related (either a single tribe or two closely related tribes). However, Barneby (1977) has suggested that the Amorpheae and Psoraleeae are not close but previously had been combined on the basis of a superficial resemblance. This paper describes the structure of the secretory cavities responsible for the gland dots. Approximately 50% of the species of each tribe were surveyed for cavity structure with leaflet clearings. Eight species were then chosen for developmental studies of their glands. Several distinct kinds of secretory cavities are present in these plants. Trabeculate cavities (found only in the Psoraleeae) are traversed by many elongated cells. This type of cavity and nontrabeculate cavities of the Psoraleeae initiate with localized dorsiventral elongation of protodermal cells to form a hemispherical protuberance on the leaf primordium surface. Development proceeds with separation of the cells of a protuberance along their lateral walls facing the protuberance center. As the leaf expands, the protuberance sinks until its apex is flush with the leaf surface. The result is a cavity lined by an epithelium of modified epidermal cells. Trabeculate cavities have more cells in the initial protodermal bump than nontrabeculate “epidermal” cavities, and the central cells of the protuberance are not involved in epithelium formation, but become separated from other cells on all lateral sides, transversing the cavity as trabeculae. Cavities of the Amorpheae are all nontrabeculate and subepidermal. They initiate with periclinal divisions of protodermal cells that result in two cell layers. The exterior layer differentiates into epidermis, while the interior layer divides to produce a small spherical group of cells (“epithelial initials”). Schizogeny occurs in the center of these cells to produce an epithelium-lined cavity. Previous studies of cavity development in the Amorpheae described lysigenous and schizo-lysigenous cavities for most species. These early reports are reviewed, and the possible role of preparation artifacts in producing images of lysigenous development in general is discussed.     

TRACHEID BAR AND VESTURED PITS IN LEGUME SEEDS (LEGUMINOSAE: PAPILIONOIDEAE)

The tracheid bar, a strip composed of vertically oriented large tracheid-like cells (tracheoids), occurs only in the hilum of seeds of papilionoid legumes. An anatomical survey of the bar was made from seeds representing 232 species of 97 genera from 29 of the 31 tribes recognized by Polhill. Seeds were sectioned freehand, coated, then viewed by SEM. The tracheid bar is quite uniform in its general features throughout the subfamily, although differences in size and shape of both the bar and the tracheoids were found. Eight species from tribes considered to be among the primitive elements of the subfamily exhibited three variant forms: horizontal tracheary elements instead of the usual bar (2 species), tracheid bar with subtending but separate vascular bundle (1 species), and the tracheid bar with fused horizontal tracheary elements (5 species). Bordered pits of individual cells in the tracheid bar virtually always lacked a membrane and had smooth, warty, or variously elaborate vestures on the border. This appears to be the first report of vestured pits other than in secondary xylem. With some exceptions, bordered pits tended to be vestured in primitive tribes, warty in intermediate tribes, and smooth or only slightly warty in the most advanced tribes.     

LOSS OF FLORAL ORGANS IN ATELEIA (LEGUMINOSAE: PAPILIONOIDEAE: SOPHOREAE)

Ateleia herbert-smithii is unique among legumes in being a wind-pollinated tree; carpellate and staminate flowers are restricted to different trees. Development of the two floral morphs, however, is essentially the same except for smaller carpels in functionally staminate flowers and failure of pollen formation in the anthers of functionally carpellate flowers. The floral development of Ateleia herbert-smithii is highly atypical among papilionoids and the tribe Sophoreae. Order of organ initiation is: sepals, solitary petal, carpel, and lastly all stamens in erratic order. Sepal order is unidirectional from the abaxial side, the normal pattern for papilionoids. Only one petal, the vexillum or standard, is initiated. Subsequent initiation is completely different from the usual unidirectional pattern of most papilionoids. A meristem ring forms, delimiting the solitary carpel centrally. Ten stamen primordia are initiated on the meristem ring, first laterally, then adaxially, and lastly abaxially. There is a tendency for antesepalous stamens to form before the antepetalous ones. The loss of four of the five petals is thought to alter drastically the subsequent organogeny as to position of organs and their order of initiation. Carpel initiation in Ateleia is precocious, but not uniquely so among legumes.     

A REAPPRAISAL OF THE SUBGENUS GLYCINE

The genus Glycine Willd. is divided into three subgenera, Glycine Willd., Soja (Moench) F. J. Herm., and Bracteata Verdc. Six species are currently recognized in the subgenus Glycine: G. canescens F. J. Herm., G. clandestina Willd., G. falcata Benth., G. latrobeana (Meissn.) Benth., G. tabacina (Labill.) Benth., and G. tomentella Hayata. Distribution of the subgenus extends from south China to Tasmania and includes several Pacific islands. A collection of these species was examined cytologically and morphologically in an attempt to evaluate existing variability between and within taxa. Chromosome counts confirmed G. canescens, G. clandestina and G. falcata to be diploid with 2n = 40. Both tetraploids (2n = 80) and diploids were found in G. tabacina, the latter restricted to Australia. Glycine tomentella accessions were primarily tetraploid, but several collections from New South Wales, Australia, were found to be aneuploid with 78 chromosomes. One collection was aneuploid at the diploid level with 38 chromosomes. Meiosis appeared normal in the aneuploids with regular bivalent formation. Several accessions previously identified as G. tomentella were diploid. Seed of G. latrobeana was not available for analysis. Numerical techniques in the form of cluster analysis and principal components analysis were applied to morphological data on vegetative and inflorescence characters obtained from each collection. Numerical analysis grouped the accessions essentially according to current species delimitations with some exceptions. Glycine tabacina specimens from Taiwan approached G. clandestina in several characteristics. The diploid G. tomentella specimens formed a separate cluster and appeared morphologically distinct from the remaining taxa.     

POLLEN AND TAPETUM DEVELOPMENT IN DESMODIUM GLUTINOSUM AND D. ILLINOENSE (PAPILIONOIDEAE; LEGUMINOSAE)

Each of the four microsporangia has three or four wall layers, a uninucleate tapetum of various cell shapes with nuclei that remain in prophase, and 12-24 pollen mother cells (PMCs). A sterile transverse septum sometimes bisects the microsporangium. PMCs secrete callose but not uniformly, and contact among them continues through meiosis. Simultaneous cytokinesis by furrowing isolates each microspore in callose, which later disperses. The separated microspores become vacuolate, undergo mitosis to become pollen, and later become filled with food reserves. Endothecial wall thickening and tapetal dissolution occur after pollen engorgement. Calcium oxalate crystals form in tapetal cells during the sporogenous stage, reach maximum size during early meiosis, and remain prominent until tapetal dissolution.     

CAESALPINIA SUBGENUS MEZONEURON (LEGUMINOSAE,CAESALPINIOIDEAE) FROM THE TERTIARY OF NORTH AMERICA

Legume fruits from the Eocene of Tennessee and Wyoming and the Miocene of Idaho are described and assigned to Caesalpinia subgenus Mezoneuron (Caesalpinioideae), an extant Paleotropical taxon that does not occur in North or South America today. Morphological and anatomical details of the fruits are used in evaluating their systematic relationships. The features of the fossil fruits are accommodated only within this extant subgenus. These fossils represent the only reliable known occurrence of C. subgenus Mezoneuron in the paleobotanical record. These fossils suggest that subgenus Mezoneuron was distinct from subgenus Caesalpinia by the Middle Eocene. Further, they document the widespread occurrence of this currently Paleotropical group for at least 30 million years in North America.     

FLORAL DEVELOPMENT IN OTTAWA AND FLOREX RED CLOVER TRIFOLIUM PRATENSE (PAPILIONOIDEAE: LEGUMINOSAE)

Floral development in Florex and Ottawa cultivars of red clover (Trifolium pratense L.: Leguminosae) was examined by scanning electron microscopy. No differences between the two cultivars were found. The terminal inflorescence is initiated in the axil of the penultimate bract before the final bract is initiated. After initiation of the final bract, the remnant apical dome is transformed to become the least mature part of the inflorescence dome. Subsequent inflorescences are initiated laterally in basipetal sequence. Inflorescence development is zygomorphic. This leads to an unusual pattern of floret initiation, the oldest florets resting basally and proximal to the penultimate bract. Florets develop with zygomorphic symmetry, each whorl of floral organs developing unidirectionally from the abaxial side. Initiation of the adaxial organ of each whorl is delayed until the abaxial organ of the succeeding whorl has been initiated. Thus there is overlapping development of the whorls of organs. The antepetalous stamens arise in close association with their respective petal primordia. As development proceeds, the corolla tube and the staminal tube exhibit basal zonal growth. In the mature flower, above the distal zone of fusion of the keel petals, marginal cells project and interlock, producing a pollination mechanism that can be sprung by the pollinator.     

EVOLUTIONARY SIGNIFICANCE OF THE LOSS OF THE CHLOROPLAST-DNA INVERTED REPEAT IN THE LEGUMINOSAE SUBFAMILY PAPILIONOIDEAE

The distribution of a rare chloroplast-DNA structural mutation, the loss of a large inverted repeat, has been determined for 95 species representing 77 genera and 25 of the 31 tribes in the legume subfamily Papilionoideae. This mutation, which is regarded as a derived feature of singular origin within the subfamily, marks a group comprising six temperate tribes, the Galegeae, Hedysareae, Carmichaelieae, Vicieae, Cicereae, and Trifolieae, an assemblage traditionally considered to be monophyletic. This mutation also occurs in the chloroplast genome of Wisteria, a member of the tropical tribe Millettieae whose other members so far surveyed lack the mutation. These new DNA data, together with traditional evidence, support the hypothesis that Wisteria is an unspecialized member of a lineage that gave rise to the temperate tribes marked by the chloroplast-DNA mutation; the probable paraphylesis of Millettieae is revealed. Two other tribes, Loteae and Coronilleae (traditionally regarded as a derived element of the aforesaid temperate tribes) do not possess this chloroplast-DNA structural mutation and, therefore, presumably represent a distinct temperate lineage. This hypothesis is supported by additional evidence from pollen, inflorescence, and root-nodule morphology that suggests that the Loteae and Coronilleae share a more recent ancestry with tropical tribes such as Phaseoleae and Millettieae than with other temperate tribes.     

OVERLAPPING ORGAN INITIATION AND COMMON PRIMORDIA IN FLOWERS OF PISUM SATIVUM (LEGUMINOSAE: PAPILIONOIDEAE)

The floral ontogeny of Pisum sativum shows a vertical order of succession of sepals, petals plus carpel, antesepalous stamens, and antepetalous stamens. Within each whorl, unidirectional order is followed among the organs, beginning on the abaxial side of the flower, as in most papilionoids. Unusual features include the four common primordia which precede initiation of discrete petal and antesepalous stamen primordia, and the marked overlap of organ initiations between whorls which are usually separately initiated. The stamens arise in free condition, then become diadelphous by intercalary growth at the base of nine stamens, and finally become pseudomonadelphous by surface fusion between the vexillary stamen filament and the adjacent edges of the filament tube. The early initiation of the carpel is not unique among papilionoids, but is somewhat unusual.     

FLORAL DEVELOPMENT OF A FLOWER-STRUCTURE MUTANT IN SOYBEANS,GLYCINE MAX (L.) MERR. (LEGUMINOSAE)

A flower-structure mutant with cleistogamous flowers (but often with an exposed style and stigma) and very low seed set was found in soybeans (Glycine max (L.) Merr.). The mutant, assigned Genetic Type Collection Number T269, is controlled genetically by duplicate recessive genes, fs₁ and fs₂. A study of flower development in T269 plants was undertaken to determine the cause of the low seed set. Both normal and mutant flower buds were observed with a light microscope by using paraffin serial sections and with a scanning electron microscope. Measurements of various floral structures were taken to verify differences observed between mutant and normal flowers. Young mutant flower buds had longer carpels and larger receptacles than did normal flower buds. These two factors caused the sepals to be positioned abnormally, which, in turn, prevented normal development of the petals. The abnormal petal development prevented staminal tube elongation, and a spatial separation between the anthers and stigma existed at anthesis, preventing self-pollination. Observations of the gynoecium of mutant flowers revealed that megasporogenesis and megagametogenesis were normal but that other features of ovule ontogeny were abnormal. In all ovules examined, the outer integuments failed to form micropyles. In addition, many ovules were positioned abnormally. The degree of aberration varied even within a carpel, but we estimated that at least 75% of the ovules were too aberrant to be functional. Therefore, the low seed set on T269 plants was due both to a lack of self-pollination and to partial female sterility. It is the only naturally occurring structural sterile reported in soybeans to date.     

FLORAL ONTOGENY IN SOPHOREAE (LEGUMINOSAE: PAPILIONOIDEAE). I. MYROXYLON (MYROXYLON GROUP) AND CASTANOSPERMUM (ANGYLOCALYX GROUP)

Floral ontogeny is described and documented using scanning electron microscopy in Myroxylon balsamum and Castanospermum australe, representatives respectively of Polhill's Myroxylon and Angylocalyx groups (Leguminosae: Papilionoideae), groups exhibiting relatively unspecialized flower structure for the tribe Sophoreae. Both are woody tropical trees with axillary or terminal racemes or panicles. Bracteoles are present in both Myroxylon and Castanospermum. Flowers are initiated singly in bract axils, which are produced in acropetal order by the inflorescence apical meristem. The flower structure of both includes a broad calyx tube, five petals lacking any fusion (only the vexillary distinctive), ten free homogeneous stamens in two whorls, and a long-stipitate carpel. The two taxa are alike in early organogenetic stages with essentially acropetal order of initiation: sepals, petals, outer stamens plus carpel, inner stamens. Within each whorl the order is unidirectional from the abaxial side. They are alike through middevelopment with one exception. There is accelerated vexillar enlargement in Castanospermum by middevelopment, not found in Myroxylon. Both have a hypanthium, which forms late in development. In both, large flower size, exserted stamens, and hypanthium are adaptations to bird-pollination. Differences between the two that are manifested in late development include strongly zygomorphic calyx and petal color change over time (Castanospermum), stamens sagittate and apiculate with some basal filament fusion (Myroxylon), stigma form differences, and fruit form.     

EFFECT OF OVULE POSITION IN THE POD ON PATTERNS OF SEED FORMATION IN TWO SPECIES OF LATHYRUS (LEGUMINOSAE: PAPILIONOIDEAE)

Using a combination of observations of fate of ovules in matured fruits and of fluorescence techniques to study pollen tube growth and fertilization of ovules, we examined patterns of seed formation within pods in natural populations of two species of Lathyrus, L. sylvestris and L. latifolius. We also examined variation in these patterns within and among populations and between two consecutive years. In both species, only a portion of the ovules were fertilized. Fertilization occurs over a period of several days and ovules at the stigmatic end of the fruit are the first to be fertilized. Fertilized ovules farthest from the stigma are closest to the maternal nutrition. The pattern of embryo abortion is interpreted as a balance between the early start and genetic quality of embryos near the stigma, on the one hand, and the nutritional advantage of proximity to maternal nutrients, on the other. Differences between the two species in patterns of seed maturation are postulated to be related to differences in breeding system. In L. sylvestris, a higher frequency of selling leads to less genetic diversity of pollen deposited on the stigma, lower competition among potential sires, and a more nearly random pattern of ovule fertilization and maturation within the pod.     

STIGMA,STYLE, AND OBTURATOR OF SOYBEAN,GLYCINE MAX (L.) MERR. (LEGUMINOSAE) AND THEIR FUNCTION IN THE REPRODUCTIVE PROCESS

Soybeans have a wet stigma overtopped by a pellicle that originates from the cuticle. There are numerous exudate-filled, axially oriented channels between cells of the transmitting tissue in the stigma and style. Pollen tubes grow in these channels and receive nutrition and mechanical guidance. Transmitting-tissue cells of the obturator are secretory also, but the obturator in soybean does not appear to control direction of pollen tube growth mechanically. The significant function of transmitting tissue in soybeans is to provide nutrition and to control direction of pollen tube growth.