Spatial variations in the water quality of Lough Erne, Northern Ireland, on the basis of surface sediment diatom analysis

SUMMARY. 1. Constrained cluster analysis of thirty-five surface sediment diatom assemblages shows that Lough Erne, a complex multi-basin lake in Northern Ireland, can be sub-divided into four main zones.
2. All areas of the lake system have planktonic diatoms typical of eutrophic lakes but the lack of small Stephanodiscus species in zone 4 suggests that this area of the system is least productive.
3. Surface sediment diatom assemblages can be used to assess spatial variations in complex lake systems and can thereby be used as a guide to the choice of sites for water quality monitoring and sediment coring.     

THE ORIGIN OF ECHINOID HATCHING ENZYME MESSENGER RNA*

To determine if echinoid hatching enzyme messenger RNA is newly synthesized from embryonic chromatin or is a maternal mRNA stored in the unfertilized egg, hybrid andromerogones have been constructed containing a sea urchin (Strongylocentrotus purpuratus) genome in sand dollar (Dendraster excentricus) cytoplasm. Such hybrid andromerogones developed at a normal rate to the blastula stage but failed to hatch. Diploid hybrids or merogones containing at least one complement of sand dollar genome hatched on the normal maternal schedule. Since the sea urchin hatching enzyme is not able to digest the sand dollar fertilization membrane, this failure to hatch is evidence that new mRNA synthesis from embryonic chromatin is required before hatching enzyme can be synthesized.     

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.     

Regulation of Internodal Extension in Avena Shoots by the Inflorescence, Nodes, Leaves, and Intercalary Meristem

It has been found in recent studies that the inflorescence and nodes (node-pulvini) are the primary sources for native gibberellins in the Avena shoot, and that GA₃ is the predominant gibberellin in the inflorescence. In the present work, linear growth of next-to-last internode is drastically reduced by removal of the inflorescence and last leaf. This growth is completely abolished when the nodes are also excised. It is restored fully by the addition of GA₃ when the nodes are present, and restored only partially when the nodes are deleted. Internodal growth in Avena stem segments with basal node present is also restored by native GA₃-like substances extracted from Avena inflorescences and partially purified by silica gel partition column chromatography. Evidence from these studies, taken in toto, indicates that the inflorescence, nodes, and leaves supply gibberellins, leaves supply substrate, and nodes modulate the gibberellin growth response in next-to-last Avena internodes.     

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.