Electrical Polarity and Cellular Differentiation in Meroistic Ovaries

SYNOPSIS. In the oocyte-nurse cell syncytium of meroistic insectovaries a gradient in electrical potential is shown to drivea micro-injected basic protein (fluorescein-labeled lysozyme)and its methylcarboxylated, acidic derivative in opposite directions.In the polytrophic Cecropia ovary the electrophoretic effectis greatest in the intercellular bridges, while in the telotrophicRhodnius ovary it is greatest within the nurse chamber. We speculatethat in both systems the potential gradient prevents the freediffusion of cell cycle and differentiative control proteins,while at the same time reinforcing the transport of acidic precursorstoward the ooplasm. Because of its apparent ability to affectthe distribution of polyions that govern nuclear function, electricalpolarity can also be envisioned to have a more general rolein the control of differentiation. The possibility is consideredthat it serves as a relay mechanism for the non-diffusing determinantthat is already known to govern the differentiation of oocytesfrom nurse cells.     

The Correlation of Digestive Vacuole pH and Size with the Digestive Cycle in Paramecium caudatum1

ABSTRACT. The temporal changes in the size and pH of digestive vacuoles (DV) in Paramecium caudatum were reevaluated. Cells were pulsed briefly with polystyrene latex spheres or heat-killed yeast stained with three sulfonphthalein indicator dyes. Within 5 min of formation the intravacuolar pH declined from ～7 to 3. With the exception of a transient and early increase in vacuolar size, vacuole condensation occurred rapidly and paralleled the acidification so that vacuoles reached their lowest pH and minimal size simultaneously. Neutralization and expansion of vacuole size began when vacuoles were GT8 min old. No labeled vacuoles were defecated prior to 21 min after formation but almost all DV were defecated within 1 h so that the digestive cycle of individual vacuoles ranged from 21 to 60 min. Based on these size and pH changes, the presence of acid phosphatase activity, and membrane morphology, digestive vacuoles can be grouped into four stages of digestion. The DV-I are GT6 min old and undergo rapid condensation and acidification. The DV-II are between 4 to 10 min old and are the most condensed and acidic vacuoles. The DV-III range in age from 8 to ～20 min and include the expanding or expanded vacuoles that result from lysosomes fusing with DV-II. The DV-IV are GD21 min old, and since digestion is presumably completed, they can be defecated. The rise in intravacuolar pH that accompanies vacuole expansion suggests that lysosomes play a role in vacuole neutralization in addition to their degradative functions. The acidification and condensation processes in DV-I appear to be unrelated to lysosomal function, as no acid phosphaiase activity has been detected at this stage, but may be related to phagosomal functions important in killing food organisms, denaturing proteins prior to digestion, and preparing vacuole membrane for fusion with lysosomes.     

The Onset of Germination Ability in Developing Wheat

The ability of primary wheat grains (cv. Sappo) to germinatewas determined at different times from anthesis. Fresh, prematurelyharvested grains germinated best at low temperatures (<10°C). The temperature range over which appreciable germinationtook place broadened and the maximum percentage germinationachieved increased with lengthening time between anthesis andharvest. Chilling and exogenous applications of GA₃ each affectedthe rate of germination and the maximum percentage germinationof grains in their own ways. The results are discussed in relationto the identification of ‘dormancy’ in wheat grains.     

Detection and validation of EST‐derived SNPs for poplar leaf rust Melampsora medusae f. sp. deltoidae

We report the discovery, characterization and validation of 118 single nucleotide polymorphisms (SNPs) for poplar leaf rust Melampsora medusae f. sp. deltoidae identified using a gene‐targeted approach in an expressed sequence tag (EST) library. We developed a genotyping assay using the iPLEX? primer extension method for two multiplex assays of 28 and 22 SNPs.     

The Effects of One-Off Ivory Sales on Elephant Mortality

ABSTRACT We revisited the debate about whether the 1999 one-off sale of ivory promoted elephant (Loxodonta africana) poaching in Africa. Complementing earlier work based on ivory seizure data, we considered data on elephant mortality in Zimbabwe and Kenya. Our findings present a mixed picture. At the local level there was some evidence that the one-off sale resulted in extra elephant killing, but this effect was relatively small (and probably short-lived). Although the data were too scanty to draw strong conclusions, decision-making about elephant management and the ivory trade has to continue and will necessarily be based on imperfect information for a long time to come. Our findings suggest that further experimenting with one-off sales may be beneficial from a conservation and development perspective.