everal myxosporean parasites are of importance in fisheries and aquaculture in British Columbia. The PKX organism and Ceratomyxa shasta Noble, 1950 cause disease and mortality, Kudoa thyrsiles (Gilchrist, 1924) and Henneguya salminicola Ward, 1919 are of importance because they infect somatic muscle, cause unsightly cysts and soft flesh, and thus reduce the market value of the fish. Myxobolus arcticus Pugachev et Khokhlov, 1979, an apparently non-pathogenic species, along with H. salminicola, is used as a biological tag in fishery management. Myxobolus arcticus has also been used in our laboratory as a model for the study of myxosporean life cycles. Other myxosporeans that have been found in salmonids in British Columbia include Myxobolus squamalis (Iverson, 1954), Myxobolus insidiosus Wyatt et Pratt, 1963, Myxidium truitae Léger, 1930, Myxidium salvelini Shuhnan et Konovalov, 1966, Chloromyxum sp., ľarvicapsula sp., and Sphaerospora sp.
Morphology of adult parasitic hermaphrodites, free-living males and females, rhabditoid and infective larvae of Rhabdias agkistrodonis Sharpilo, 1976 is described. Adult parasites of the species differ from corresponding stage of other Rhabdias species from snakes in the presence of short cuticular needle on the tip of the tail. Free-living generation stages of R. agkistrodonis have typical rhabditoid morphology. Homogonic infective larvae differ from heterogonic ones in the shape of stoma and oesophagus. Three new hosts: Halys viper (Agkistrodon halys) (Pallas) from Altaiskii Krai (Russia), Okinawa habu (Trimeresurus flavoviridis) (Ilallowell)' and T, elegans (Gray) from Okinawa Island (Japan) are added to the host range of R. agkistrodonis known previously exclusively from short-tailed viper (Agkistrodon blomhoffi) from the Russian Far East.
A new nematode, Rhabdochona mexicana sp. n., is described based on specimens recovered from the intestine of two species of fishes, Astyanax mexicanus (De Filippi) (type host) and Astyanax J'asciatus (Cuvier) (Characidae: Characiformes) in central Mexico. This species is characterised by the following characters: 10 anteriorly directed teeth in the prostom, a larger (left) spicule which is slender in form with a small bifurcation at its distal tip covered by a culicular membrane, a smaller (right) spicule without a barb at its distal tip, eggs bearing an irregular flock-like coaling, and a conical tail without a cuticular spike (in both sexes).
During the growth cycle of micropropagated Juglans regia plantlets, phosphoenolpyruvate carboxylase (PEPC) activity was aiways higher than initial ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity. The ratio of PEPC/RuBPCO activities was higher during the first part of the exponential phase of growth and lower during the second part. The variations of PEPC activity were parallel to the soluble protein content and the variations of initial and total RuBPCO activities were parallel to the chlorophyll accumulation.
Two cultivars of bean, Tacarigua and VUL 73-401 were subjected to two levels of water stress followed by rewatering. During the water deficit period, water potential (Ψ№), osmotic potential (Ψ5) and relative water content (rwc) decreased with an associated decrease of ribulose-l,5-bisphosphate carboxylase activity (RuBPC), protein and chlorophyll (Chi) contents. In cv. Tacarigua, the % decrease of RuBPC was less marked than that of protein content. There was a significant correlation among the components of leaf water status and the measured photosynthetic parameters. Groups of water stressed plants were rewatered, when reached -1.25 to -1.60 MPa. During the recovering period all components of leaf water status increased and reached the control values on the 6th day after rewatering. Chi content increased above the control values. Protein content and RuBPC activity also increased during the rewatering period, but the % increases in protein content and RuBPCase activity were not parallel.