UDP-Glucose: Sterol Glucosyltransferase and a Steryl Glucoside Acyltransferase Activity in Amyloplast Membranes from Potato Tubers

Envelope membranes were isolated from potato tuber amyloplastby a discontinuous sucrose density gradient and high speed centrifugation.These membranes catalyzed the transfer of [¹⁴C]glucose fromUDP-[¹⁴C]glucose to endogenous sterol acceptors and, in turn,catalyzed the esterification of steryl glucosides with fattyacids from an endogenous acyl donor. The synthesis of sterylglucosides was stimulated in the presence of Triton. X-100,while formation of acyl steryl glucosides was inhibited by thedetergent. However, in the presence of an added sterol acceptorand Triton X-100, the inhibition of acyl steryl glucoside synthesiswas overcome by the addition of phosphatidylethanolamine. Theenzyme involved in steryl glucoside formation was solubilizedby treatment of the envelope membranes with 0.3% Triton X-100.The solubilized enzyme had an almost absolute requirement forsterol acceptors. Key words: Solanum tuberosum, Sterol glucosylation, Steryl glucoside acylation, Amyloplast membrane     

Latitudinal and ecological correlates of morphological variation in Galaxias platei (Pisces, Galaxiidae) in Patagonia

We examined the morphological variability (23 morphometric traits) among individual Galaxias platei ( N  = 380) collected from 20 postglacial lakes in the southern Andes. The lakes were chosen to cover the latitudinal range of the species in Patagonia. Diet examined for a subset of these fish ( N  = 261) collected during the summer months (January through March), differed among river basins but there were no clear latitudinal trends in the consumption of any prey type. Diet may, however, have partially shaped morphology, as pelvic measures were negatively correlated with consumption of amphipods. Substantial differentiation among populations was observed, primarily in the shape and dimensions of the head, in caudal morphology and in fin length. Our results indicate that the morphology of G. platei varies with latitude, and may be related to risk of predation and diet.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 69–82.     

INFLUENCE OF ENVIRONMENTAL PARAMETERS ON REPRODUCTION OF THE EUROPEAN FLAT OYSTER (OSTREA EDULIS L.) IN A COASTAL LAGOON (MAR MENOR, SOUTHEASTERN SPAIN)

The influence of environmental parameters (temperature, dissolvedoxygen, suspended matter, chlorophyll a) on the condition indicesand gametogenic cycle of the European flat oyster (Ostrea edulisL.) was analyzed in the Mar Menor (Murcia, Spain) between January1990 and December 1992. The highest condition index values wererecorded during the prespawning season at temperatures between11–12°C. Condition index values gradually decreasedfrom 14°C, coinciding with the appearance of the first larvaein the plankton. Condition index values were lowest in summer.Multiple regression analysis revealed that the condition indiceswere correlated mainly with temperature and to a lesser extent,with dissolved oxygen, chlorophyll a and suspended matter. Absolutechlorophyll concentrations were low and presented a negativecorrelation with the condition index values, though this correlationwas less pronounced than that of temperature. Gametogenesiswas continuous all year round, but spawning took place onlyat temperatures of 14°C or higher, and larvae were presentin the plankton to 28°C. The low absolute values of chlorophylla and suspended matter found in the oligotrophic Mar Menor didnot seem to affect the gametogenesis, spawning or the larvaldevelopment of the oysters, which feed on picoplankton, principallycomposed of dinoflagellates and bacteria. (Received 29 April 1996; accepted 18 October 1996)