CENTROSOMES AND MICROTUBULES DURING MEIOSIS IN THE MUSHROOM BOLETUS RUBINELLUS

The double centrosome in the basidium of Boletus rubinellus has been observed in three planes with the electron microscope at interphase preceding nuclear fusion, at prophase I, and at interphase I. It is composed of two components connected by a band-shaped middle part. At anaphase I a single, enlarged centrosome is found at the spindle pole, which is attached to the cell membrane. Microtubules mainly oriented parallel to the longitudinal axis of the basidium are present at prefusion, prophase I and interphase I. Cytoplasmic microtubules are absent when the spindle is present. The relationship of the centrosome in B. rubinellus to that in other organisms and the role of the cytoplasmic microtubules are discussed.     

BASIDIOSPORE INITIATION AND EARLY DEVELOPMENT IN COPRINUS CINEREUS

Early basidiospore development in Coprinus cinereus has been divided into four stages: 1) inception, 2) asymmetric growth, 3) equal enlargement, 4) elongation, all based on changes in spore size and shape, wall layering, and cytoplasm. The hilar appendix body formed on the adaxial side of the stage 1 basidiospore, persisted through all stages studied, and predicted the site of the hilar appendix. The hilar appendix formed in stage 2 by modification of certain wall layers. A band of peripheral endoplasmic reticulum covered an average of 38 % of the lower spore wall in stage 3 and was oriented around the axis of growth. Stage 4 was initiated by a break in wall layer 3 at the spore apex and the disappearance of the peripheral endoplasmic reticulum. A pore cap formed on the spore apex during spore elongation. The spore wall consisted at first of three layers and became six layered by deposition of layers between two of the initial layers. Cytoplasmic changes associated with spore growth included presence of small vesicles at stage 1 and larger Golgi vesicles later, absence of mitochondria and probable Golgi cisternae from the spore until stage 3, and presence of a zone nearly free of ribosomes and organelles under the spore apex in stage 4. Functions of the hilar appendix body, peripheral endoplasmic reticulum and the different wall layers in control of spore shape are discussed.     

FORMATION OF THE HILAR APPENDIX IN BASIDIOSPORES OF BOLETUS RUBINELLUS

The hilar appendix body is reported in the basidiospore primordium of Boletus rubinellus as well as the subsequent development of the hilar appendix through spore maturation. The hilar appendix body is similar in its morphology and pattern of development to that in Coprinus spp. The evolutionary implications of the results are discussed.     

FLORAL INITIATION AND EARLY DEVELOPMENT IN ERIGERON PHILADELPHICUS (ASTERACEAE)

The order of floral initiation and subsequent organogeny of Erigeron philadelphicus L. (Asteraceae: Astereae) was found to deviate from the acropetal pattern generally reported for the Asteraceae. Light micrographs show periclinal divisions in the first, second, and deeper subsurface layers of cells on the flanks of the inflorescence apex as the earliest evidence of floral initiation. Scanning electron microscope micrographs indicate that the disk flowers appear first and arise as small protuberances approximately one-third of the way up the previously and undifferentiated highly convex inflorescence apex. A succession of disk flowers arises acropetally in a complex anthotaxy characterized by about 21 dextrorse and 12–15 sinistrorse parastichies (although this pattern is obscured at the apex). After one to three disk flowers have been initiated in each parastichy, the first ray flower initials can be seen to initiate in sites proximal to the oldest and largest disk flowers. Additional ray flowers then initiate basipetally following the dextrorse parastichies established by the disk flowers. Overall floral initiation on the inflorescence apex proceeds acropetally for the disk flowers and basipetally for the ray flowers until the available space is filled. Floral development adheres to the same plan—proceeding bidirectionally on the inflorescence meristem with the oldest and most complete flowers of both types located on the equator established at initiation.     

SPORE GERMINATION AND EARLY DEVELOPMENT OF THE GAMETOPHYTE OF SCHIZAEA PUSILLA

During germination of the spore of Schizaea pusilla, the first division of the protoplast was perpendicular to the polar axis and resulted in the formation of the rhizoid. The next division parallel to the polar axis of the spore gave rise to the protonemal initial. Following this “Vittaria”-type germination, the protonema that developed was characterized by an extensive branching to produce uniseriate filaments and rhizoidophores.     

AXILLARY BUD DEVELOPMENT IN POPULUS DELTOIDES. I. ORIGIN AND EARLY ONTOGENY

Origin and early development of axillary buds on the apical shoot of a young Populus deltoides plant were investigated. The ontogenetic sequence of axillary buds extended from LPI –1 (Leaf Plastochron Index) near the apical bud base to LPI –11, the fifth primordium below the bud apex. Two original bud traces diverged from the central (C) trace of the axillant leaf and developed acropetally. During their acropetal traverse the original bud traces gave rise to three pairs of scale traces. All subsequent scale traces, and later the foliar traces, were derived by divergencies from the first two pairs of scale traces. Just before the bud vascular system separated from that of the main axis, a third pair of traces diverged from the original bud traces to vascularize the adaxial scale. Concomitantly, the original bud traces were inflected toward the main vascular cylinder where they developed acropetally and eventually merged with the left lateral trace of the leaf primordium situated three nodes above the axillant leaf; they did not participate in further vascularization of the bud. During early ontogeny a shell zone formed concurrent with initiation of the original bud traces and lay interjacent to them. The shell zone defined the position of the cleavage plane that formed between the axillary bud and the main axis. The axillary bud apex first appeared in the region bounded laterally by the original bud traces and adaxially by the shell zone. Following divergence of the main prophyll traces from the original bud traces, the apex assumed a new position intermediate to the prophyll traces. Ontogenetic development suggested that the axillary bud apex may have been initiated by the acropetally developing original bud traces under the influence of stimuli arising in more mature vegetative organs below.     

FOLIAR ONTOGENY AND HISTOGENESIS IN MAGNOLIA GRANDIFLORA L. I. APICAL ORGANIZATION AND EARLY DEVELOPMENT

Foliar ontogeny of Magnolia grandiflora was studied to elucidate possible unique features of evergreen leaves and their development. The apex of Magnolia grandiflora is composed of a biseriate or triseriate tunica overlying a central initial zone, a peripheral zone and a pith rib meristem. Leaf primordia are initiated by periclinal divisions on the apical flank of the tunica in its second layer. This initiation and expansion is seasonal just as in related deciduous magnolias. Following leaf initiation, a foliar buttress is formed and the leaf base gradually extends around the apex. As growth continues, separation of the leaf blade primordium from the stipule proceeds by intensified anticlinal divisions in the surface and subsurface layers near the base. Marginal growth begins in the blade primordium when it reaches approximately 200 μm in height and results in the formation of two wing-like extensions, the lamina. This young blade remains in a conduplicately folded position next to the stipule until bud break.     

EXPERIMENTAL STUDIES OF HAUSTORIUM INITIATION AND EARLY DEVELOPMENT IN AGALINIS PURPUREA (L.) RAF. (SCROPHULARIACEAE)

In parasitic angiosperms the haustorium, an organ specialized for attachment and penetration of host tissue, functions in the transport of water and nutrients from the host to the parasite. In Agalinis purpurea (L.) Raf. (Scrophulariaceae) these organs are initiated laterally along its roots, opposite a primary xylem pole. Analyses of haustoria distribution and cellular root profiles show that the portion of the root which is most sensitive to haustorial elicitor molecules is the area distal to the zone of elongation and near the root meristem. Sectioned material supports this finding and, further, indicates that the cells which are the first to respond to haustorial elicitors are located in the inner cortex. Haustoria develop rapidly in response to a host root or to isolated chemical elicitors (xenognosins) normally contained in host root exudate. By 6 hr, vacuolation and radial cellular enlargement are observed in the cortex, and a lateral swelling along the root is visible. By 12 hr, cells of the epidermis divide anticlinally to establish a group of densely cytoplasmic cells at the apex of the haustorial swelling. Accompanying these divisions is the differentiation of specialized hair cells which elongate from epidermal cells flanking the presumptive haustorial apex. Next, the internal, radially enlarged cortical cells divide periclinally. Periclinal divisions are subsequently initiated in the pericycle as early as 18 hr post-induction. Cellular division and enlargement continue so that by 24–36 hr a mature pre-contact haustorium is formed. There is a reduction in root elongation concomitant with haustorial initiation. Depending upon the number of haustoria produced, elongation typically returns to the preinduction level within 2 or 3 days.     

MORPHOLOGY OF SPORE DEVELOPMENT IN CLOSTRIDIUM PECTINOVORUM.

Fitz-James, Philip C. (University of Western Ontario, London, Ont., Canada). Morphology of spore development in Clostridium pectinovorum. J. Bacteriol. 84:104-114. 1962-The process of spore formation in Clostridium pectinovorum was followed by phase-contrast microscopy and by thin-section electron microscopy employing a polyester plastic for embedding. The development of the forespore membrane was found to be similar to that already described for the genus Bacillus, being, in addition, accompanied by considerable cell enlargement. The cortex, as in the bacilli, was found between the apposed layers of the double forespore membrane. The spore coat was laid down in the narrow zone of cytoplasm peripheral to the outer forespore membrane. As these layers formed, striking changes occurred in the fine structure of the spore nuclear material, mesosomes and ribosomes, reflecting the marked alterations in physical environment known to occur in a developing spore.     

EARLY HISTOGENESIS AND SEMIQUANTITATIVE HISTOCHEMISTRY OF LEAF INITIATION IN TRITICUM AESTIVUM

The shoot apex of Triticum aestivum cv. Ramona 50 was investigated histologically to describe cell lineages and events during leaf initiation. During histogenesis three periclinal divisions occurred in the first apical layer, with one or two divisions in the second apical layer. This sequence of cell divisions initially occurred in one region and spread laterally in both directions to encircle the meristem. Cells of the third apical layer were not involved in leaf histogenesis. Initially, young leaf primordia were produced from daughter cells of periclinal divisions in the two outer apical layers. Nuclear contents of protein, histone, and RNA in the shoot apex were evaluated as ratios to DNA by means of semiquantitative histochemistry. Daughter cells of periclinal divisions in the outer apical layer which produced the leaf primordia had higher histone/DNA ratios than cells of the remaining meristem. However, protein/DNA and RNA/DNA ratios were similar in both regions. Leaf initial cells had a higher ³H-thymidine labeling index, a higher RNA synthesis rate, and smaller nuclear volumes than cells of the residual apical meristem.     

油松树脂道的发生和发育研究

关于松科植物的树脂道,以往都认为是以裂生方式发生。本文通过对油松各类器官的发育解剖学研究,发现其各类器官中树脂道的结构,发生和发育方式并不完全一致,并对产生这些差异的原因进行了分析和讨论。     

FLORAL DEVELOPMENT IN SAURURUS CERNUUS (SAURURACEAE): 1. FLORAL INITIATION AND STAMEN DEVELOPMENT

The inflorescence of Saururus cernuus L. produces lateral “common” primordia in acropetal succession on the flanks of the inflorescence meristem; curiously, the “subtending” bract is initiated upon the lateral primordium rather than subtending it. On the basis of mature floral structure, flowers of S. cernuus have previously been described as having spiral initiation of parts. The current ontogenetic investigation contradicts this interpretation. Stamens arise in three successive pairs; the carpels also are initiated in pairs. Floral symmetry is shown to be bilateral from the onset of organ initiation, a rare feature among primitive angiosperms. On the basis of symmetry and paired initiation of organs, the possibility of close relationships between Saururaceae and Magnolialian or Ranalian lines appears remote.     

Physiology of Flowering in Saccharum: I. DAYLENGTH CONTROL OF FLORAL INITIATION AND DEVELOPMENT IN S. SPONTANEUM L.

Flowering in two clones of Saccharum spontaneum L. is controlledby photoperiod. The earliest stages of development, ‘induction’and ‘initiation of the inflorescence axis primordium’(IAP) were optimally promoted under intermediate days of 12h 30 min, while the subsequent stage ‘initiation of inflorescencebranch primordia’ (IBP) was inhibited by days longer than13 h. The following stage ‘initiation of spikelet primordia’(ISP) showed a quantitatively intermediate response with anoptimum photoperiod of 9 h to 11 h. The elongation of the differentiatedinflorescence was found to be only slightly sensitive to photoperiodsof 13 h or longer in one of the clones. Unfavourable photoperiodsat stages following induction resulted in the arrest or delayof inflorescence development and when these were given duringthe IAP and IBP stages, reversion to the vegetative conditioncommonly occurred.     

MOLECULAR HETEROCHRONIES AND HETEROTOPIES IN EARLY ECHINOID DEVELOPMENT

By comparing the spatial and temporal distribution of three proteins during early development in seven echinoid species, we demonstrate that both heterochronies and heterotopies in gene-product expression have accompanied the radiation of post-Paleozoic echinoids. All three proteins examined showed significant alterations in time of expression, site of expression, or both. These molecular heterochronies and heterotopies indicate that early development is not necessarily as evolutionarily conservative as morphology of embryos alone would suggest. Evolutionary alterations in early development may be more common than is generally assumed.     

INITIATION AND EARLY DEVELOPMENT OF THE INFLORESCENCE IN PINEAPPLE (ANANAS COMOSUS, ‘SMOOTH CAYENNE') TREATED WITH ACETYLENE

Pineapple plants ‘Smooth Cayenne’ were made to flower by treatment with acetylene. The organization of the vegetative shoot apex is similar to that of many investigated angiosperms in that it shows a zonate pattern, viz., apical zone, peripheral zone, and central-core rib meristem. The latter zone is weakly developed. Cytological changes at the shoot apex occur as early as 3 days after treatment; these involve nuclear changes and an increase in ribonucleic acid (RNA) in the cytoplasm of cells of the apical zone. A marked increase in the height of the apex occurs by the 9th day; this is preceded by rib meristem activity in the central core. All component parts of the inflorescence are present and in various stages of development by the 21st day at which time vegetative scales and “crown” leaves are initiated.     

SPORE DEVELOPMENT IN THE LIVERWORT RICCARDIA PINGUIS

The ontogeny of spores of the liverwort Riccardia pinguis was studied at the light and electron microscope levels. Three stages of development were arbitrarily defined: spore mother cell (SMC); early tetrad with nonpigmented and unsculptured walls; and mature tetrad with pigmented and sculptured spore walls. The SMC is quadrilobed with a two-layered SMC wall, containing a central nucleus, many chloroplasts, spherosomes, and other organelles. During and following meiosis cell plates form from coalescing Golgi vesicles. These plates by continued coalescence eventually form a septum, completing the tetrad. This septum comprises middle lamella and primexine; within the latter the exine forms. By continued addition of vesicle contents to the septum and dorsal surfaces of the tetrad, the exine (sexine and nexine) and intine layers of the spore wall are laid down. The contents of the vesicles change successively during wall formation, corresponding to the different wall layers being formed. It is concluded that wall formation is under the exclusive control of the spore protoplast, and that the pattern of the mature exine is determined by the primexine. Rearrangement of organelles and other cellular components during sporogenesis is described.