Excretion in the house cricket (Acheta domesticus): ultrastructure of the ampulla and ureter

An ultrastructural analysis of the ampulla and ureter of the cricket, Acheta domesticus, is presented. The excretory system of the cricket is unusual in that the 112 Malpighian tubules do not attach directly to the gut, but fuse to form a bladder-like ampulla which is joined to the colon by a muscular ureter. The ampulla consists of two cell types, primary and regenerative. Primary cells secrete large numbers of membrane-bound vesicles into the lumen and also appear to be involved in fluid reabsorption. Regenerative cells are very small and form a layer just beneath the basal lamina of the ampulla. They are believed to differentiate and replace sloughed off primary cells. The ureter is a muscular tube lined with cuticle which connects the ampulla (endoderm) with the colon (ectoderm). The probable origin and significance of the morphological modifications of the excretory system are discussed.     

Bumetanide inhibition of NaCl transport byNecturus gallbladder

Salt transport by the Necturus gallbladder epithelium is the result of the coupled entry of NaCl into the cells across the apical membrane and the active transport of Na out of the cells across the basolateral membrane. The NaCl entry step was studied by measuring the rate of cell volume increase accompanying ouabain inhibition of the Na--K-ATPase in the basolateral membrane. When bumetanide, a diuretic analog of furosemide, was added to the mucosal bathing solution it reversibly blocked the entry of NaCl into the cells and abolished fluid transport. A dose-response relationship showed half-maximal inhibition of NaCl entry at a bumetanide concentration of 10(-9) M; complete inhibition of coupled NaCl movement occurred with as little as 10(-7) M bumetanide. Partial substitution of Na or Cl in the mucosal solution failed to demonstrate competition between bumetanide and either of the ions. The drug was also effective in blocking NaCl entry in the absence of ouabain; addition of the diuretic to the mucosal bathing solution resulted in prompt cell shrinkage and a decrease in intracellular NaCl. Cell volume decrease followed bumetanide addition to the mucosal bath because NaCl entry was blocked but active Na transport continued for several minutes until the intracellular Na transport pool was depleted.     

Leaf Disc Inoculation, a Fast and Precise Test for the Screening of Metalaxyl Tolerance in Sunflower Downy Mildew

A new method, based on leaf disc inoculation, was developed for the screening of metalaxyl tolerance in field isolates of Plasmopara halstedii . High-pressure liquid chromatography (HPLC) was used to determine the fungicide concentration in the inoculation medium and in the incubated leaf tissue over the test period. These measurements revealed that the fungicide concentration inside the leaf tissue within 24 h had adjusted to the concentration in the outer medium and remained constant for the time of cultivation over a period of more than 11 days. In contrast to whole seedling tests with application of the fungicide via seed dressing, the leaf disc method allows precise quantification of the effective fungicide concentration at the site of infection and is less space and time consuming. Metalaxyl tolerance of P. halstedii isolates was gradually determined according to the sporulation of the pathogen on sunflower leaf discs in the presence of increasing fungicide concentrations. Isolates collected in South Germany showed no tolerance and sporulation was prohibited when tests were carried out at 0.02  μ g (a.i.)/ml of metalaxyl or more. In contrast, a tolerant French isolate developed sporangia on leaf discs incubated in a metalaxyl solution of 100  μ g (a.i.)/ml.     

Alcohol dehydrogenase in the mouse epididymis. Genetic variation and cellular localization

The cellular localization of alcohol dehydrogenase (ADH) in the mouse epididymis was investigated using differential substrate specificities and genetic variation as a means of distinguishing these enzymes histochemically in tissue sections. ADH-C2 exhibited high activity in BALB/c epididymis and was observed as a discrete zone within duct epithelial cells near the nuclei. This isozyme exhibited no detectable activity in C57BL/6J epididymis extracts or histochemical sections.     

Fate of glucose in haemolymph of the American cockroach, Periplaneta americana

The rate of removal of high concentrations of glucose (10 μg/μl haemolymph) from haemolymph of adult male cockroaches, Periplaneta americana, was studied in normal and ligated insects. More than 50% of the injected glucose is removed from the haemolymph of normal insects within 20 min of injection. A period of rapid trehalose synthesis occurs during the initial 10 min following injection of glucose into the haemocoele, and this is succeeded by a period of glycogen synthesis. The results are discussed in terms of earlier observations on ‘stress-induced hypertrehalosemia’ and the possible involvement of a glycogenic agent.