The effect of environmental aneuploidy-inducing agents on the microtubule architecture of mitotic meristematic root cells in Hordeum vulgare.

Microtubules are the prime components involved in chromosomal segregation, their functional accuracy ensuring maintenance of the normal karyotype in the progeny. Chemically-induced disruption of microtubules during mitosis can lead to aneuploidy. In this study, seven environmental chemicals, i.e. cadmium chloride (CD), econazole nitrate (EZ), benomyl (BM), thiabendazole (TB), griseofulvin (GF), thimerosal (TM) and hydroquinone (HQ), were tested for their ability to induce microtubule disruption in mitotic meristematic root cells of the higher plant Hordeum vulgare, with the use of anti-tubulin indirect immunofluorescence microscopy. All chemicals tested in this study, with the exception of TB and HQ, produced modifications in the morphology of microtubule organization and reduced the fidelity of the spindle apparatus in Hordeum vulgare.

The eggshell of the almond wasp Eurytoma amygdali (Hymenoptera, Eurytomidae) - 2. The micropylar appendage.

Micropylar apparatuses in insects are specialized regions of the eggshell through which sperm enters the oocyte. This work is an ultrastructural study and deals with the structure and morphogenesis of the micropylar appendage in the hymenopteran Eurytoma amygdali. The micropylar appendage is a 130 microm long cylindrical protrusion located at the posterior pole of the egg, unlike other insects i.e. Diptera. in which the micropylar apparatus is located at the anterior pole. In mature eggs there is a 0.4 microm wide pore (micropyle) at the tip of the appendage leading to a 6 microm wide micropylar canal. The canal contains an electron-lucent substance, it travels along the whole appendage and finally reaches the vitelline membrane of the oocyte. The vitelline membrane is covered by a wax layer and an electron-lucent layer, whereas the chorion surrounding the canal consists of a granular layer (fine and rough) and a columnar layer. The morphogenesis of the appendage starts in immature follicles: four central cells located at the posterior tip of the oocyte near the vitelline membrane, differing morphologically from the adjacent follicle cells. These central cells degenerate during early chorionic stages, thus assisting in the formation of the micropylar canal. The adjacent, peripherally located cells secrete the electron-lucent substance which fills the canal and at the same time, the fine granular layer is formed starting from the base towards the tip of the appendage. The secretion persists at late chorionic stages and results in the formation of the chorion around the micropylar canal. The extremely long (compared to other insects) micropylar appendage seems to facilitate the egg passage through the very thin and long ovipositor. The structure and morphogenesis of this appendage differs significantly from the micropylar apparatuses studied so far in other insects i.e. Diptera, and may reflect adaptational and evolutionary relationships.

Structure and morphogenesis of the eggshell and micropylar apparatus in the olive fly, Dacus oleae (Diptera: Tephritidae).

The egg of the olive fly, Dacus oleae (Diptera, Tephritidae), is laid inside olives and the larva eventually destroys the fruit. The oocyte is surrounded by several distinct layers which are produced during choriogenesis. The chorion covering the main body of the egg outside of the vitelline membrane includes a "wax" layer, an innermost chorionic layer, an endochorion consisting of inner and outer layers separated by pillars and cavities similar to their counterparts in Drosophila melanogaster, as well as inner and outer exochorionic layers. The anterior pole is shaped like an inverted cup, which is chiefly hollow around its base and has very large openings communicating with the environment. Holes through the surface of the endochorion result from deposition of endochorionic substance around follicular cell microvilli. An opening at the apex of the cup provides an entrance for sperm entering the micropylar canal, which traverses the endochorion and continues into a "pocket" in a thickened vitelline protrusion. The micropylar canal is formed by deposition of endochorion and vitelline membrane around an elongated pair of follicular cell extensions. These extensions later degenerate and leave an empty canal about 5 microns in diameter and the narrower pocket about 1 micron in diameter. Respiration is thought to be facilitated by openings at the base of the anterior pole as well as by openings through the "plastron" around the main body of the shell.