The quantitative ultrastructure of the pea shoot apex in relation to leaf initiation

Summary The ultrastructure of the pea shoot apical meristem was examined quantitatively in longitudinal sections. Photographs were taken at eleven defined positions in the apex, at six developmental stages within a single plastochron. The only change in ultrastructure during the period of a single plastochron was the increase in the proportion of plastids with starch in the central regions of the apex and in the young leaf axils. This increase occurred midway in time between the emergence of successive leaves, at precisely the time that the orientation of growth changes in the region where a new leaf is to emerge. There were quantitative changes in ultrastructure associated with cell differentiation. In the sequence of cell development from the summit of the apex (central zone) to the incipient pith, cell enlargement was accompanied by an increase in the volume of endoplasmic reticulum, dictyosomes, microbodies and vacuoles per cell, an increase in the number of mitochondria, microbodies and vacuoles per cell, and an increase in the volume, but not the number, of plastids per cell. In the sequence of axillary development (before the axillary bud begins to grow) the number of mitochondria per cell decreased as cell volume decreased but the number of plastids per cell remained constant. The number of plastids per cell increased only in the developmental sequence leading to leaf development, in which the number of mitochondria and dictyosomes per cell also increased. There appeared to be no features of ultrastructure, qualitative or quantitative, which could be correlated with the different rates of cell division in different regions of the meristem. The differences in ultrastructure throughout the apex were mainly quantitative and seemed to be associated with cellular differentiation rather than with the plastochronic functioning of the apex during leaf initiation.     

Seasonal changes in leaf lipids of Diapensia lapponica, with special reference to storage lipid bodies

Seasonal fluctuations in storage lipids in the cushion plant Diapensia lapponica , growing in Northern Finland (70°N 27°E), were studied by microscopy and chemical analysis. Lipid bodies in the mesophyll cells were stained with Sudan Black for quantitative observation by light microscope. Electron microscope observations were made using aldehyde prefixed and osmium tetroxide postfixed sections of leaf blades. Thin layer and gas capillary chromatographic techniques were used to analyse total lipids and total fatty acids in green shoots of Diapensia . Free sugars and starch were extracted separately and determined by the anthrone method.
A mesophyll cell was characterized by a large lipid body (storage lipid) in summer but by several small spherules in winter. Total surface area of the cross-sectioned lipid globules was at its lowest from April to September; the maximal value was in March. The amount of total lipids in the leafy tops of D. lapponica was 91–200 mg g^-1 dry weight. Values were lowest at the end of June, when the total carbohydrate level was at its highest. Accordingly, the decrease in the total lipid level in the early growing season, when new leaves were developing, can be attributed primarily to the increase in the level of carbohydrates, particularly starch. The amount of total fatty acids varied from 21 to 30 mg g^-1 dry weight. The level increased in the early growing season and remained elevated throughout the summer. Like the total lipids, the total fatty acids are derived from structurally different parts of the sclerophyllous leaves, including the well-developed cuticle and epicuticular wax layer. The discrepancies in the results obtained from microscopic and chemical analyses are discussed.     

Structure and seasonal study of the shoot apex of two species ofAraucaria

Summary and Conclusions The shoot apices ofAraucaria columnaris andA. bidwillii exhibit a tunica-corpus organization. In the former the tunica is one-layered during spring and summer months and becomes more stratified during winter months. InA. bidwillii it is usually two-layered, with a tendency to further stratification.The corpus is divisible into three zones, the corpus initial zone, the flanking zone and the rib meristem zone. The corpus initial zone is the seat of formation of the rest two. The flanking zone is concerned with the production of leaf primordia, in which the covering tunica layer has no part.The rib meristem zone varies in depth according to the season of the year and the pith cells mature gradually in these species.InA. columnaris, where a seasonal study was undertaken, no period of complete dormancy was observed.     

The ultrastructure of the marine blue green alga,Trichodesmium erythraeum,with special reference to the cell wall,gas vacuoles,and cylindrical bodies

Summary The marine blue green alga, Trichodesmium erythraeum, was studied with electron microscopy in an attempt to elucidate the structural basis for its rapid lysis when removed from its marine environment. In this connection, it was found that a thining of the electron-dense layer of the longitudinal wall at the site adjacent to transverse wall attachment was responsible for lysis. The underlying biochemical basis for this change has not been elucidated because of the extreme difficulties of maintaining and growing the alga in culture under defined conditions. Several other features of considerable interest also were found. Especially interesting is the very regular array of gas vacuoles in the form of a hollow cylinder which shields most of the photosynthetic system. It was suggested that the gas vacuoles might possibly function optically, having adaptive value in protecting the free-floating alga from excessive radiation. In addition, a detailed structure of the cylindrical bodies was presented, and its structure with the photosynthetic lamellae was compared. On the basis of sectoring to form fragments of double lamellar units from the cylindrical body which are identical in structure to the photosynthetic lamellae, it has been postulated that the cylindrical body may be the site of synthesis for the photosynthetic system in Trichodesmium erythraeum.     

Observations on the ultrastructure of nerve cells in the brain of the earthworm,Eisenia foetida,with special reference to neurosecretion

Summary The submicroscopic structure of nerve cells in the brain of the earthworm Eisenia was studied. Six types of neurons containing morphologically different inclusions are identified. Types 1, 2 and 3 contain vesicles filled with homogeneous materials of high electron density. These are essentially similar to elementary granules in neurosecretory systems of vertebrates and invertebrates. Type 4 shows dense-cored vesicles which resemble in size catechol-containing granules as described, for example, in chromaffin cells of the adrenal gland. Type 5 has clear vesicles with a mean diameter of 400 Å. Some of these vesicles have a dense osmium deposit. Type 6 contains electron lucent vesicles with diameters of 500–800 Å. Occasionally these have osmiophilic cores. Clear vesicles of types 5 and 6 are similar to classical synaptic vesicles, while granulated vesicles resemble in size and appearance those described in adrenergic nerve endings. All six vesicle types have the same mode of origin from Golgi membranes. All of these vesicles are considered to be discharged from the perikarya into the axons entering the neuropil.     

A study of karyotypes and heterochromatic associations in Artemia,with special reference to two N. Greek populations

The chromosomes of three stains of Artemia were studied, a bisexual diploid (A. franciscana, strain GSL), and two parthenogenetic tetraploids from Northern Greece. Routine karyotypes were constructed for the diploid and tetraploid forms, as well as a Giemsa C-banding karyotype of the bisexual form; some data are also presented on the chromosomal C-banding patterns of the parthenogenetic populations. The possible significance of various chromosomal configurations that have been observed, and their relationships to heterochromatin, are discussed.This paper is dedicated to Professor C. Barigozzi for introducing us to Artemia research.Supported by a grant from the Greek Ministry of Agriculture, Request offprints from: Th. Abatzopoulos, Lab. of General Biology, School of Sciences, Aristotelian University, Thessaloniki, 54006, Greece.     

Deep simple epicotyl morphophysiological dormancy in seeds of two Viburnum species, with special reference to shoot growth and development inside the seed

Background and Aims

In seeds with deep simple epicotyl morphophysiological dormancy, warm and cold stratification are required to break dormancy of the radicle and shoot, respectively. Although the shoot remains inside the seed all winter, little is known about its growth and morphological development prior to emergence in spring. The aims of the present study were to determine the temperature requirements for radicle and shoot emergence in seeds of Viburnum betulifolium and V. parvifolium and to monitor growth of the epicotyl, plumule and cotyledons in root-emerged seeds.

Methods

Fresh and pre-treated seeds of V. betulifolium and V. parvifolium were incubated under various temperature regimes and monitored for radicle and shoot emergence. Growth of the epicotyl and cotyledons at different stages was observed with dissecting and scanning electron microscopes.

Key Results

The optimum temperature for radicle emergence of seeds of both species, either kept continuously at a single regime or exposed to a sequence of regimes, was 20/10 °C. GA₃ had no effect on radicle emergence. Cold stratification (5 °C) was required for shoot emergence. The shoot apical meristem in fresh seeds did not form a bulge until the embryo had grown to the critical length for radicle emergence. After radicle emergence, the epicotyl–plumule and cotyledons grew slowly at 5 and 20/10 °C, and the first pair of true leaves was initiated. However, the shoot emerged only from seeds that received cold stratification.

Conclusions

Seeds of V. betulifolium and V. parvifolium have deep simple epicotyl morphophysiological dormancy, C_1bB (root)–C₃ (epicotyl). Warm stratification was required to break the first part of physiological dormancy (PD), thereby allowing embryo growth and subsequently radicle emergence. Although cold stratification was not required for differentiation of the epicotyl–plumule, it was required to break the second part of PD, thereby allowing the shoot to emerge in spring.     

A new method for the developmental study of the shoot apex

A method of observing and photographing an intact shoot apex prior to killing and fixing for anatomical study is deseribed. By the use of a newly devised instrument, the external shape, cell pattern in its protoderm, and the internal structure of the same shoot apex can be studied. Supported by the Grant in Aid for Scientific Research, Ministry of Education, Project No. 148017.     

Nuclear bodies in human prostate with special reference to appearance rate

The Nuclear Body Appearance Rate in seventeen human prostatic cases was statistically analyzed according to three lesion areas--the hyperplastic nodule, non-nodule and atrophic--in the secretory epithelium and basal cells. It was meaningfully high in the secretory epithelium of the hyperplastic nodule, but not in the other two lesion areas. There was no meaningful result in basal cells. Though there is a wide variety of reported data on the human prostate, particular care must be taken in analysis at the electron microscopic level, keeping in mind that even in a single specimen this organ has a notable variety of tissue changes. The Nuclear Body Appearance Rate reflects cellular hyperactivity although it does not have a specific known function at present.