William P. Wergin

Changes in microbial populations on fresh cut spinach

The microbial populations found on fresh-cut spinach leaves that were stored in gas permeable bags at 10 degrees C for 12 days were examined and identified. The microorganisms consisted of mesophilic aerobic bacteria, psychrotrophic bacteria, Pseudomonadaceae, Enterobacteriaceae, Micrococcaceae, lactic acid bacteria and yeasts. Populations of mesophiles, psychrotrophs, Pseudomonadaceae and Enterobacteriaceae increased sharply during the storage period. The initial populations were 10(7), 10(6), 10(6) and 10(4) CFU.g-1 respectively. Populations reached 10(10) for the mesophiles, psychrotrophs and Pseudomonadaceae and 10(7) CFU.g-1 for Enterobacteriaceae after 12 days of storage. Micrococcaceae, lactic acid bacteria and yeasts remained constant (10(3)-10(4) CFU.g-1. The majority of the bacterial isolates were identified as Pseudomonas fluorescens, Aeromonas caviae and Staphylococcus xylosus. The yeasts, which were most frequently isolated, were classified in the genus Cryptococcus. No pathogens such as Listeria monocytogenes and Salmonella were detected. Observations with low temperature scanning electron microscopy (LTSEM) indicated that the microorganisms were not present on the surface of healthy unbroken leaves. Alternatively, they were found in areas where the cuticle was broken and could be seen infecting the internal palisade parenchyma.

Development of woronin bodies from microbodies inFusarium oxysporum f. sp.lycopersici

SummaryWoronin bodies are cytoplasmic organelles which commonly lie near the septa in ascomycetous fungi. Although these organelles were observed nearly 100 years ago, little is known about their origin and development. The present ultrastructural investigation describes the ontogeny of Woronin bodies inFusarium oxysporum f. sp.lycopersici [Sacc.] Snyd. and Hans. In this fungus, Woronin bodies are produced by microbodies. Development of the Woronin body begins with the appearance of electron dense material within the microbody. This material aggregates adjacent to the membrane of the microbody and condenses into a single paracrystalline inclusion. Following its formation, the inclusion is gradually extruded and is eventually separated from the parent organelle by an exocytotic mechanism. After the separation, the paracrystalline inclusion is found at the septal pore. Although many recent electron microscopic studies have used various terms to designate these membrane bound organelles, inFusarium these inclusions are believed to correspond to the Woronin bodies initially described by light microscopists.

Structure and distribution of antennal sensilla of the red imported fire ant.

The morphology of the antenna of the red imported fire ant, Solenopsis invicta, was examined by light microscopy, scanning electron microscopy, and transmission electron microscopy. The antennae are sexually dimorphic: the worker antenna has porous sensilla on the two distal segments (the antennal club), whereas the clubless male antenna has porous sensilla on all segments past the pedicel. The major type of porous sensilla on both male and female is sensilla tricodea curvata. However, the male s. tricodea curvata are rather uniform in size, whereas the female s. tricodea curvata vary considerably in thickness. The number of sensilla on the distal segment of the worker antenna increases with segment length. This suggests a possible mechanism by which task assignments in S. invicta could be determined by the presence or absence of sensilla sensitive to specific task-related odor or pheromone cues. The sensilla basiconica have an invariant spatial pattern on worker and queen antennae.

Olfaction in a hemimetabolous insect: Antennal-specific protein in adult Lygus lineolaris (Heteroptera: Miridae)

Abstract Antennal sensilla, electrophysiological responses to an insect and a plant odorant, and polypeptide profiles were investigated in fifth instar nymphs and adults of the tarnished plant bug, Lygus lineolaris . Sensilla with surface pits characteristic of porous olfactory sensilla develop on the second and third antennal segments during the final molt from fifth instar nymph to adult. Concurrent with development of these sensilla in the adult, neural responses to a component of green odor (1-hexanol) and an insect-produced volatile [( E )-2-hexenyl butyrate] increase dramatically. Antennal extirpation experiments indicated that sensilla responsive to these odorants are housed principally on the second and third antennal segments. A protein with a molecular weight of 17,000 present in the soluble fraction of adult antennae was absent in nymphs. Localization of this protein to the antenna, the coincidence of its expression with development of olfactory sensilla and its molecular weight were characteristic of odorant-binding proteins in moths. However, antisera raised against pheromone-binding protein of the gypsy moth, Lymantria dispar , did not react with the Lygus protein. The N-terminal sequence for our antennal-specific protein was determined, and showed no significant homology with other known insect protein sequences. This lack of homology with other insect proteins including odorant binding proteins indicates that if it is an odorant binding protein as we suspect, it is either widely divergent or independently derived. This is the first report of an antennal-specific protein in a hemimetabolous insect and the only report of such a protein in an insect other than moths or Drosophila melanogaster .

Ultrastructure of a neurosensory organ in a root-knot nematode

Second stage larvae of the root-knot nematode, Meloidogyne incognita [(Kofoid and White) Chitwood], were examined to elucidate the ultrastructure of the amphids, which are paired lateral organs believed to function in chemosensory perception. The amphids were found to consist of supportive, nervous, and secretory tissues. The support tissue forms two cuticular canals and encircling “supporting cells,” which extend from the external anterior region of the nematode posteriorly into the body of the larva. Each amphid is innervated by a group of axons that become modified into cilia. Generally, seven of these cilia enter the amphidial canal and terminate near the external pore; whereas, three to five “accessory” cilia remain external to the canal and terminate beneath the cuticle at the cephalic region. The secretory structures of the amphid consist of an amphidial “gland,” a large irregularly shaped cell containing mitochondria, and a duct, an intercellular area having a granular content. The physical associations and the functional significance of these structures are discussed.

Characterization of the Cell Wall Microdomain Surrounding Plasmodesmata in Apple Fruit

In fleshy fruits ripening is generally associated with a loss in tissue firmness resulting from depolymerization of wall components and separation of adjacent cells. In the regions of the wall that contain plasmodesmata, the usual sequences of ripening events, i.e. depolymerization of the middle lamellae and splitting of the walls, are not observed. In the present study we attempted to characterize in apple (Malus domestica Borkh.) fruit the structural microdomain of the cell wall that surrounds the plasmodesmata by in muro visualization of the cell wall components. Anionic sites of galacturonic acids were labeled with cationic gold. Low-esterified homogalacturonans were labeled with the monoclonal antibody JIM 5. In addition, a polyclonal antibody directed toward [beta](1->3)-glucopyranose was used to target callose in situ. The results indicated that the plasmodesmata-wall complexes were surrounded by a pectic microdomain. This domain was composed of low-esterified homogalacturonans that were not involved in calcium cross-bridging but were probably surrounded by a cationic environment. These structural features may result in the prevention of normal cell wall separation in regions containing plasmodesmata. However, observations by low-temperature scanning electron microscopy suggested that splitting of these walls ruptured the plasmodesmata and ultimately resulted in the spatial separation of adjacent cells.

Effects of snow crystal shape on the scattering of passive microwave radiation

A discrete dipole scattering model is used to measure the passive microwave radiation scattered by snow particles having different shapes and sizes. The model results demonstrate that the shape of the snow crystal is insignificant in scattering microwave energy in the 37-GHz region of the spectrum.

Structural organization of the sex pheromone gland in Helicoverpa zea in relation to pheromone production and release

Morphological location of the sex pheromone producing area in the ovipositor of the female corn earworm Helicoverpa zea, was correlated with gas chromatographic analysis of the extracted pheromone. Histological studies showed that the pheromone gland occupied an almost complete ring of specialized columnar cells between the 8th and 9th abdominal segments. Ultrastructure of the pheromone gland cells revealed distinct features such as microvilli, pockets of granular material, intercellular canals with abundant desmosomes. Apparent changes in some of these features are associated with phases of pheromone production and non-production. Examination of the tissue with low temperature scanning electron microscopy showed the presence of excreted droplets at the tips of cuticular hairs in the glandular area during the period of pheromone production.

Distribution of the anionic sites in the cell wall of apple fruit after calcium treatment: Quantitation and visualization by a cationic colloidal gold probe

SummaryThe ripening and softening of fleshy fruits involves biochemical changes in the cell wall. These changes reduce cell wall strength and lead to cell separation and the formation of intercellular spaces. Calcium, a constituent of the cell wall, plays an important role in interacting with pectic acid polymers to form cross-bridges that influence cell wall strength. In the present study, cationic colloidal gold was used for light and electron microscopic examinations to determine whether the frequency and distribution of anionic binding sites in the walls of parenchyma cells in the apple were influenced by calcium, which was pressure infiltrated into mature fruits. Controls were designed to determine the specificity of this method for in muro labelling of the anionic sites on the pectin polymers. The results indicate that two areas of the cell wall were transformed by the calcium treatment: the primary cell walls on either side of the middle lamella and the middle lamella intersects that delineate the intercellular spaces. The data suggest that calcium ions reduce fruit softening by strengthening the cell walls, thereby preventing cell separation that results in formation of intercellular spaces.

Ultrastructural investigation of clover roots during early stages of infection by the root-knot nematode,Meloidogyne incognita

SummaryMigration of root-knot larvae (Meloidogyne incognita) into the primary root tissues of red clover (Trifolium pratense, cult. “Kenland”) was accompanied by separation and subsequent compression of cells in front of and along the path of the penetrating nematode. The protoplasts of the parenchymatous cortical cells did not respond to the presence of the penetrating larvae. However, as the nematode approached the differentiating vascular tissue, the cytoplasmic density of the pericyclic and meristematic cells increased. This increased density was accompanied by an alteration in the morphological features of the nucleus. In addition to these changes, two different types of extracellular material were observed during penetration. A homogeneous substance appeared in and around the external opening of the amphid; and an electron dense material was found along the middle lamellae of the separating plant cells and between the cuticle of the nematode and the cell walls of the host.