Nels R. Lersten

Anatomy and cytology of microsporogenesis in cytoplasmic male sterile angiosperms

ConclusionsThe studies reviewed date from 1925 to 1972 and contain extensive anatomical and cytological information all too often incomplete or vague. The terminology for microsporogenesis used is also often sketchy or inaccurate. An attempt therefore has been made to establish some consistency in microsporogenesis terminology via Fig. 1 and the tables. We have given, in convenient tabular form, CMS taxa, investigators, and the morphological and cytological events reported. By referring to a few keys, the reader can gain further insight into specific CMS taxa and can easily compare studiesThe work of Laser (1972) is only part of a more extensive investigation of the anatomy, cytology, and histochemistry of N and CMSSorghum bicolor (Laser, unpub.). To date, only a small part is published (Christensen, Horner & Lersten, 1972), but when completed it probably will be the most complete study to date of these aspects of CMS. Hoefert (1969a, 1969b, 1971) has investigated only normal microsporogenesis so far, but her intention also is to make a detailed descriptive comparison of N and CMS development. Such comparative electron microscope studies will be needed to help answer questions raised in the Introduction of this review. Concerning the events within microspores at the beginning of abortion, for example, there is complete ignorance of what organelle shows the first sign of disintegration or whether there is a definite sequence or simply a simultaneous collapse. The answer to this question could yield valuable clues to the direct cause of abortionLooking at the existing published studies and taking into account numerous examples of questionable technique and interpretation, we conclude that abortion has been shown to occur at almost every point in development, and that probably more than one mechanism is involved

Calcium oxalate crystal types and trends in their distribution patterns in leaves of Prunus (Rosaceae: Prunoideae)

Calcium oxalate crystal types and distribution within leaves ofPrunus sensu lato (Rosaceae; Prunoideae) were surveyed from mostly herbarium specimens (196 specimens of 131 species of all five subgenera usually recognized). Rehydrated samples were bleached, mounted unstained, and viewed microscopically between crossed polarizers. Six patterns were recognized based on crystal type and relative distribution around veins and in mesophyll. Druses predominate in four subgenera, but prismatics are most common in subgenus Padus. Prunophora and Amygdalus, considered to be the most advanced subgenera, have virtually only druses, which are almost always associated with veins. Cerasus and Laurocerasus, intermediate subgenera, have the greatest diversity of patterns, but few species with prismatics. A trend is evident from mostly mesophyll prismatics in Padus to fewer prismatics and more druses of mixed distribution in Laurocerasus and Cerasus, to mostly druses restricted to veins in Amygdalus and Prunophora.

Oil bodies in leaf mesophyll cells of angiosperms : Overview and a selected survey

Neutral (storage) oil bodies occur in leaf mesophyll cells of many angiosperms, but their literature has been largely forgotten. We review this literature and provide a survey of 302 species and hybrids from mostly north-central US species representing 113 families. Freehand cross sections of fresh leaves stained with Sudan IV verified the presence of oil. In 71 species from 24 families we observed 1-15 oil bodies per mesophyll cell. The eudicot families Asteraceae, Caprifoliaceae, Lamiaceae, and Rosaceae had the highest number of species with oil bodies, whereas few or no species in the Apiaceae, Betulaceae, Fabaceae, and Scrophulariaceae had them. Only three of 19 monocot species sampled had oil bodies. Repeat sampling of a Malus (crabapple) cultivar and a Euonymus species showed conspicuous oil bodies in mid-summer and also in mid-autumn in both attached and recently shed leaves. Oil bodies in leaf mesophyll cells are conspicuous (visible in hand cross sections using moderate magnification in unstained water mounts) in numerous species, and they occur throughout the growing season in at least some species. Neutral oil bodies in leaf mesophyll cells are not mentioned in contemporary textbooks and advanced works, but they deserve recognition as significant cellular components of many taxa, in which they may be significant sources of commercial oils.

Occurrence of endodermis with a casparian strip in stem and leaf

It is well known that an endodermis with casparian strip always occurs in roots, but few people are aware that it also occurs in stems and leaves of some vascular plants. The rather sparse literature on endodermis in aerial organs was last included in a review in 1943. The present compilation, which does not consider hydathodes, nectaries, or other secretory structures, emphasizes distribution of cauline and foliar endodermis with casparian strip. It occurs unevenly among major taxa: quite common in rhizomes and leaves among pteridophyte groups, with exceptions; absent in gymnosperm stems but found in leaves at least among some conifers; in stems of at least 30 mostly herbaceous angiosperm families, but far less common in leaves, where it is mostly reported from petioles. Etiolation can induce casparian strips in stems and petioles of some herbaceous plants, but results from leaf blades are questionable. There are recent reports of an endodermis with casparian strip in leaves of both woody and herbaceous taxa. The physiological function, if any, of a casparian strip in aerial organs remains unknown.

Leaf anatomy inCaesalpinia andHoffmannseggia (Leguminosae, Caesalpinioideae) with emphasis on secretory structures

Leaflets of 65 species ofCaesalpinia s.l. and seven species ofHoffmannseggia were studied in clearings supplemented by resin sections and scanning electron microscopy. Three types of secretory structure occurred among 46 species; in 43 species they were distributed mutually exclusively (external glands: 8 species; internal cavities: 5 species; idioblastic cells: 30 species); three other species each had two types. Species with secretory structures conform mostly to proposed subgenera and informal “groups.” Other unusual features were external glands with internal spaces, thickened walls or conspicuous localized wall thickenings in epidermal cells or mesophyll cells of certain species, and differentially stained epidermal cells surrounding stomata. Prismatic crystals predominate but druse crystals also occur.

Suspensors in Leguminosae

Published descriptions of suspensors from Mimosoideae (12 genera, 21 species), Caesalpinioideae (7 genera, 9 species), and Papilionoideae (about 65 genera, 150 species) were collated and compared with the most recent classification scheme of the Leguminosae. The first two subfamilies have mostly suspensorless embryos. Suspensors of various forms are usually present in the Papilionoideae (20 of the 32 tribes have been sampled). The putatively primitive and intermediately placed tribes have mostly inconspicuous suspensors. This is also true in some advanced tribes, but some or all members of other tribes have conspicuous suspensors of differing morphology: Phaseoleae, Loteae/Coronilleae, Vicieae/Cicereae/ Trifolieae, Crotalarieae, and Genisteae. There is no discernible correlation between suspensor development with amount of endosperm produced or amount present at maturity, or with habit, although elaborate suspensors are more common in derived herbaceous groups. Suspensor morphology helps to outline broad evolutionary trends in the family and to place studies on individual species in perspective.ResúmenDescripciones publicadas de suspensores en Mimosoideae (12 géneros, 21 especies), Caesalpinioideae (7 géneros, 9 especies) y Papilionoideae (cerca de 65 géneros, 150 especies) fueron revisadas y comparadas con el sistema de clasificación mas reciente de las Leguminosas. En las dos primeras subfamilias, el embrión—en su mayoría—carece de suspensor. Suspensores de variadas formas están comúnmente presente en Papilionoideae (20 de las 32 tribus han sido examinadas). Las tribus comúnmente consideradas como más primitivas presentan, en su mayoría, suspensores inconspicuos. Esta característica es también encontrada en algunas tribus avanzadas, pero en general algunos o todos los miembros de otras tribus tienen suspensores conspicuos de diferente morfología: Phaseoleae, Loteae/Coronilleae, Vicieae/Cicereae/Trifolieae, Crotalarieae, y Genisteae. No hay una clara correlación entre el desarrollo del suspensor con la cantidad de endospermo producido, la cantidad presente cuando la madurez es alcanzada o con el hábito. Sin embargo, suspensores complejos son mas comunes en grupos herbáceos derivados. La morfología del suspensor es útil para delinear líneas evolutivas en la familia y dirigir estudios sobre especies individuales en su propio contexto.

Bacterial leaf nodule symbiosis in angiosperms with emphasis on Rubiaceae and Myrsinaceae

Over 400 species of three genera of Rubiaceae and one genus of Myrsinaceae reportedly have bacterial leaf nodules. Light and/or electron microscope studies of a few species have shown that bacteria exist in spaces within buds filled with mucilage secreted by glands. These bacteria enter substomatal chambers (Rubiaceae) or marginal hydathodes (Myrsinaceae) and establish short-lived colonies, in intercellular spaces, that die out almost before full leaf expansion. Bacteria occur in seeds between endosperm and embryo, but only two studies have followed bacteria into flowers and ovules. Previous work on the physical relations of bacteria and host plants is discussed critically. Reviewing work done on isolation and identification of presumed endophytes leads to the conclusion that there is no agreement whether one or several bacterial taxa are the endophyte, and no unambiguous identifications, although four genera are suggested as possibilities. Nitrogen fixation was considered as the bacterial contribution until quite recently, but a review of such studies reveals that fixation has been detected almost exclusively in isolated presumed endophytes, whereas almost all studies involving the bacterium in intact leaves have failed to detect nitrogen fixation. Studies of particular substances (besides combined nitrogen) contributed by the endophyte have been inconclusive, although the most recent works suggest that cytokinins are involved. Host plants lacking the endophyte have been reportedly produced many times, either spontaneously or by seed treatment. Such “cripples”, used for several aspects of symbiosis study, frequently revert to a nodulated condition, and a more reliable method of producing them is needed. Tissue culture may offer the best potential, but this approach has not yet produced whole bacteria-free plants. A proposed scheme for the evolution of the symbiosis suggests that a variety of bacteria entered buds first, and only in rare instances were compatible with the host bud mucilage. In a few of these cases, specific bacteria, compatible with the microenvironment, contributed a useful substance to the host, and bud mucilage and those bacteria co-evolved until large numbers of bacteria thrived in the buds. Nodules may have resulted from accidental entry of bacteria into leaves, with the possibility that some host plant nodules are merely pathogenic responses, whereas in others the bacteria are beneficial and further selection has resulted in numerous, regularly produced nodules. This review deals with taxonomy of host plants and endophytes, morphology of the symbiosis, its physiology, and speculation on the evolution of the symbiosis.AuszugÜber 400 Arten der drei Gattungen von Rubiaceae und eine Gattung von Myrsinaceae haben, wie berichtet ist, bakterielle Blatt-Knötchen. Licht und/ oder elektron-mikroskopische Studien von einigen Arten haben gezeigt, dass Bakterien existieren in Räumen innerhalb von Knospen, die von Pflanzenschleim ausegefüllt sind, von Drüsen erzeugt. Diese Bakterien dringen in unteren-Spaltöffnungs-Räume ein (Rubiaceae) oder Rand-Wasser-Poren (Myrsinaceae) und bilden kurzlebende Kolonien, in Räumen zwischen den Zellen, welche aussterben, fast bevor der völligen Blattentfaltung. Bakterien finden sich in Samen zwischen dem Endosperm und dem Embryo, aber nur zwei Untersuchungen konnten den Bakterien nachfolgen in die Blüten und die Eier. Frühere Arbeit über die physikalischen Beziehungen zwischen Bakterien und Wirtspflanzen ist kritisch besprochen. Nachprüfende Arbeit ist unternommen an der Isolierung und Identifizierung an vermutlichen Endophyten und führt zu dem Ergebnis, dass da keine Einigung besteht, ob eine oder mehrere bakterielle Gruppen die Endophyten sind, und keine unzweideutige Identifikationen, trotzdem 4 Gattungen als Möglichkeiten vorgeschlagen sind. Bis ziemlich kürzlich wurde Stickstoff-Fixierung als Bakteriellen-Beitrag angesehen, aber ein Überblick über solche Untersuchungen ergiebt, dass Fixierung wurde festgestellt nahezu ausschliesslich in isolierten, vermutlichen Endophyten, wogegen fast alle Untersuchungen, die sich auf Bakterien in unverletzten Blattern bezogen, versagt haben, Stickstoff-Fixierung festzustellen. Untersuchugen von besonderen Substanzen (ausser kombiniertem Stickstoff), von den Endophyten beigetragen, sind nicht entscheidend gewesen, wenn auch die aller-jüngsten Arbeiten andeuten, dass cytokinins verwickelt sind. Wirtspflanzen, die das Endophyte entbehren, sind, wie berichtet ist, fielfach erzeugt worden, entweder spontan oder durch Behandlung der Samen. Solche “Krüppel, ” welche in verschiedener Hinsicht für das Studium von Symbiose verwendet wurden, schlagen häufig zu einer Knötchen-Beschaffenheit zurück, und eine besser zuverlässige Methode, sie zu erzeugen, ist notwendig. GewebeKulturen mögen eine bessere Möglichkeit bitten, aber diese Annäherung hat bislang noch nicht gänzliche bakteriumfreie Pflanzen erzeugt. Eine vorgeschlagene Methode für die Evolution der Symbiose nimmt an, dass eine Art von Bakterien zuerst in die Knospen eindringen, und nur in seltenen Fällen verträglich waren mit dem Pflanzenschleim der Wirts-Knospen. In einigen wenigen dieser Fälle haben besondere Bakterien, verträglich mit der Mikro-Umbebung, dem Wirt eine nützliche Substanz beigetragen, und Knospenschleim, und die Bakterien sind zusammen aufgetreten, bis eine grosse Zahl von Bakterien in den Knospen gediehen. Knötchen können sich ergeben haben vom zufälligen Eintritt von Bakterien in Blätter, mit der Möglichkeit, dass einige Wirtspflanzen-Knötchen lediglich pathologische Rückwirkungen sind, wogegen in anderen die Bakterien nützlich sind, und weitere Selektion resultierte in zahlreichen, normalerweise erzeugten Knötchen.Dieser Überblick handelt sich mit der Taxonomie von Wirtspflanzen und Endophyten, Morphologie der Symbiose, ihrer Physiologie, und Spekulation über die Evolution der Symbiose.RésuméPlus de quatre cents espèces de trois genres de Rubiacées et un genre de Myrsinacées possèdent des nodules bactériens dans les feuilles. Les études des microscopes lumineux et/ou des microscopes électroniques ont révélé que les bactéria se trouvent dans les espaces à l’intérieur des bourgeons qui sont remplis mucilage sécreté par les glandes. Ces bactéria entrent dans les chambres substomatales (Rubiacées) ou dans les hydathodes périphériques (Myrsinacées) et elles establissent dans les espaces intercellulaire des colonies de courte durée qui meurent presque avant l’expansion complète de la feuille. Les bactéria se trouvent dans les graines entre l’endosperm et l’embryon mais seulement deux études ont trouvé les bactéria dans les fleurs et les ovules. Les travaux précédents au sujet des rapports physiques des bactéria avec des hôtes sont discutés d’une manière critique. L’examination du travail fait au sujet de l’isolation et de l’identification des endophytes presumés mène à la conclusion qu’il n’y a pas d’accord soit une taxum bactérienne soit plusieurs taxa bactériennes sont l’endophyte et il n’y a pas d’identification certaine, bien que quatre genres soient suggérés comme possibilities. La fixation du nitrogène était considerée comme la contribution bactérienne jusqu’a ces derniers temps, mais une revue de telles études révèle que la fixation était decouverte presque exclusivement dans des endophytes presumés isoles, tandis qu’au contraire presque toutes les études ou les bactéria sont dans les feuilles intactes n’ont pas reussi a decouvrir la fixation du nitogène. Des études des matières particulières (en plus de nitrogène combinè) qui sont contribuées par l’endophyte avaient été peu concluant, bien que les travaux les plus récents suggèrent que les cytokinins soient engagés. On a dit que les hôtes qui manquent l’endophyte étaient produits plusieurs fois, soit spontanément soit par le traitement des graines. Ces “estropies”, utilizés pour l’étude de quelques aspects de symbiose, frequemment reviennent à une condition nodulaire et on a besoin d’une meilleure méthode pour les produire. La culture de tissus peut offrir le meilleure possibilité mais cet abord n’a pas encore produit de plantes entières qui sont sans bactéria. Un plan proposé pour l’évolution de la symbiose suggere qu’une variété de bactéria est entrée premièrement dans les bourgeons et seulement dans des cas rares les bacteria étaient compatible avec le mucilage des bourgeons de l’hôte. Dans quelquesuns de ces cas des bactéria spécifiques qui étaient compatible avec le micromilieu ont contribués une substance utile a l’hôte. Aussi le mucilage des bourgeons et ces bactéria ont dévelopé ensemble jusqu’a ce qu’un grand nombre de bactéria se developpaient bien dans les bourgeons. Les nodules pouvaient résulter de l’entrée accidentel de bactéria dans les feuilles avec la possibilité que les nodules de quelques hôtes sont tout simplement des réponses pathogéniques, tandis qu’au contraire dans quelques autres hôtes les bactéria sont avantageux pour les hôtes et le résultat de sélection additionnelle est de nombreux nodules produits regulièrements. Cette revue traite de la taxonomie des hôtes et des endophytes; la morphologie de la symbiose; la physiologie de la symbiose; et la speculation sur l’évolution de la symbiose.

Survey of leaf anatomy, especially secretory structures, of tribeCaesalpinieae (Leguminosae, Caesalpinioideae)

We studied leaflet anatomy, emphasizing secretory structures, from herbarium specimens of 128 species of 44 genera of tribeCaesalpinieae, using clearings, resin sections, and scanning electron microscopy. These observations, combined with those from our three earlier papers, provide a survey of 210 species representing all genera. Seventy-three species had secretory structures: 21 had glands or gland-like trichomes, 40 had living mesophyll idioblasts, and nine had cavities (three species each had two different types). Five additional species, all inCercidium (Caesalpinia group), had paired or clustered large spheroidal, thick-walled, empty cells (veinlet idioblasts) interconnected by perforation plate-like gaps. Secretory structures have systematic significance at various taxonomic levels.

Transfer aleurone cells inSetaria lutescens (Gramineae)

SummaryTypical aleurone cells occur around the periphery of the caryopsis. These cells are tabular with moderately thick walls and lack cell wall ingrowths. Transfer aleurone cells only occur adjacent to the placental vascular bundle, which supplies the developing embryo and endosperm. These specialized aleurone cells are approximately columnar, with thick walls bearing ingrowths on the outer radial and outer tangential walls. The wall ingrowths of transfer aleurone cells appear similar to those of transfer cells previously described and quite likely also function in short-distance transport of substances.

Foliar anatomy ofPolygonum (Polygonaceae): Survey of epidermal and selected internal structures

Several anatomical characters in leaves were described, and their distribution determined, for 153 species ofPolygonum, mostly from herbarium specimens. Structures surveyed were epidermal (glandular and nonglandular trichomes, nodules, specialized parenchyma, stomatal apparatus) and internal (cavities, crystals, laticifer-like cells, nodules, subepidermal fibers). Cleared leaves were supplemented by resin-embedded sections and SEM preparations of selected species. No feature defines any taxonomic section, but some features occur only within one section. Laticifer-like cells, epidermal and internal nodules, resin cups, and unique epidermal and subepidermal cavities seem to be unknown elsewhere; other features (invaginated epidermal cells; enlarged crystal cells confined to paraveinal layer) are rare among angiosperms.