The significance of alkaline phosphatase activity in Lough Neagh

SUMMARY. A study of the eutrophic Lough Neagh was undertaken to ascertain the use of alkaline phosphatase activity as an indicator of phosphorus-limited algal growth. Lough Neagh and its surrounding rivers were monitored during 1974 and 1975. Alkaline phosphatase activity increased in the lough when the algal crop increased and depleted orthophosphate to a growth-limiting concentration. Enzyme activity was appreciable, however, at all other times of the year and may on occasions have been associated with zooplankton. The enzyme activity in the inflowing rivers was much greater than in the lough itself. Depending on enzyme stability the enzyme inputs from rivers could contribute significantly to the lough activity. Sewage disposal works effluent appeared to be a major source of enzyme activity in river water. As the alkaline phosphate activity in Lough Neagh resulted from several sources, increased activity could not be used as a reliable indicator of phosphorus limited algal growth.     

Anatomical variation in some perennial Triticeae

JARVIE, J. K. & BARKWORTH, M. E., 1992. Anatomical variation in some perennial Triticeae. Cross-sectional anatomy of glumes and leaf blades was examined in 22 taxa of the perennial Triticeae. The taxa included diploids and polyploids based largely on various combinations of the E, J and S genomes. The objective was to determine how much correlation exists between anatomical characteristics and genomic constitution. The data were analysed by principal co-ordinate and cluster analyses. The results showed that monogenomic species based on different genomes were readily distinguishable on glume and leaf blade features. Most heterogenomic taxa exhibited some aspects of each genome present except in the case of JE allotetraploids, which exhibited no E genome characteristics.     

Morphological variation and genome constitution in some perennial Triticeae

JARVIE, J. K. & BARKWORTH, M. E., 1992. Morphological variation and genome constitution in some perennial Triticeae. A numerical analysis of species of five genomically defined genera of the Triticeae was undertaken, based on 42 morphological characters and 142 operational taxonomic units (OTUs). The primary goal was to determine the degree of congruence between morphological variation and genomic constitution. The second goal was to determine which existing supraspecific classification, if any, best reflected the morphological variation encountered. The five genera investigated were Thinopyrum (J genome), Lophopyrum (E genome), Pseudoroegneria (S genome), Trichopyrum (EES genome) and Elytrigia (SJE/SSX genome). Both principal co-ordinate and cluster analysis of the data placed the OTUs in supraspecific groups that reflected their genomic constitution. Monogenomic taxa were clearly separated. Allotetraploids between the E and S genomes were situated between E and S monogenomic taxa. Allotetraploids between the J and E genomes were situated closest to J genome taxa. The EES taxa of Trichopyrum were placed closest to Lophopyrum. OTUs of Elytrigia overlapped those of Pseudoroegneria , but not those of Lophopyrum or Thinopyrum.     

Direct Measurements of Turgor Pressure Potentials of Guard Cells: II. THE MECHANICAL ADVANTAGE OF SUBSIDIARY CELLS, THE SPANNUNQSPHASE, AND THE OPTIMUM LEAF WATER DEFICIT

Evidence of the mechanical advantage of subsidiary cells wasobtained by simultaneous measurements of turgor pressure potentialsin adjacent subsidiary and guard cells using injection circuitswith two separate needles. In Tradescantia virginiana the mechanicaladvantage approaches two. Using the same technique evidencewas obtained that the Spannungsphase is, in the first place,a turgor relations phenomenon due to the mechanical advantageof epidermal or subsidiary cells. In addition, the evidenceindicated that the elastic properties of guard cell walls mayundergo changes during the Spannungsphase when potassium iontransport commences. During these measurements it was confirmedthat the optimum leaf water deficit for maximum stomatal openingoccurs when the epidermal turgor is near zero. Under these conditionsthe width of the stomatal pore is a function of the turgor pressureof the guard cells, since at zero turgor of the subsidiary cellstheir mechanical advantage has disappeared.     

Juvenile hormone and ovarian growth in Manduca sexta

In Manduca sexta the major size increase of ovarian follicles is accomplished by two processes: (1) vitellogenesis in which follicular volume and dry weight increase simultaneously, and (2) hydration in which absorption of water by the oocyte accounts for an 80% increase in volume prior to chorion formation. Vitellogenic growth occurs in both a slow and rapid phase. Rapid vitellogenic growth is initiated only by follicles of a threshold size (1 mm) and is a juvenile hormone (JH)-dependent event. In the absence of JH follicles grow to 1 mm and then degenerate.     

Evidence for matrotrophy in the viviparous sea cucumber Leptosynapta clarki: A role for the genital haemal sinus?

Summary

Viviparity, where the embryos develop in the female reproductive system, is a rare form of reproduction in marine invertebrates, being described in only 14 species of echinoderm. In the intraovarian brooding sea cucumber, Leptosynapta clarki Heding 1928 (cf., Sewell et al. 1995), we used direct evidence (changes in energetic content) to show that significant additional nutrients are provided to the embryos during viviparous development (matrotrophy). In the transition from a structure used to produce gametes to a long-term brooding structure there are visual, histological and transmission electron microscopy (TEM) changes in the structure of the ovarian wall. Changes occur primarily in the cells of the visceral peritoneum and involve an increase in size of the connective tissue/genital haemal sinus (CT/GHS). In the latter part of the brooding period the visceral peritoneum returns to a flattened form, and new oocytes develop along the tubule wall. Similar changes in the intraovarian brooding sea cucumber Oneirophanta mutabilis affinis lead us to suggest that there is a role for the genital haemal sinus in providing nutrition during the brooding period in viviparous echinoderms. Future research is suggested to focus on changes in the ovarian wall structure during the different phases of reproduction (gamete production/brooding) in these species.     

Mutual mate choice by mountain pine beetles: size‐dependence but not size‐assortative mating

1. Mutual mate choice may be rare, occurring when both sexes invest heavily in reproduction, mating opportunities are abundant, and individuals differ in quality. 2. Mountain pine beetles, Dendroctonus ponderosae (Curculionidae: Scolytinae) appear to meet the conditions for mutual mate choice. We introduced males to females in breeding sites and observed the occurrence and speed of a male entering a female's gallery. We tested for consequences of mutual mate choice, namely condition‐dependent choosiness and assortative mating. 3. Males were more likely to enter a female's gallery when the gallery was in a smaller tree with less resin production and when the gallery was larger. Female body size and condition did not influence the probability of entry. Larger males were less likely to enter a gallery than were smaller males, probably because of size‐dependent choosiness rather than physical limitations. 4. Small males took longer to enter galleries of large females than of small females, whereas large males entered as quickly into galleries of large females as small females. This suggests size‐dependent choosiness by females. 5. No assortative mating by body size was detected, probably because males appeared to choose on the basis of female‐associated resources rather than on female traits.     

Methane production by microbial mats under low sulphate concentrations

Cyanobacterial mats collected in hypersaline salterns were incubated in a greenhouse under low sulphate concentrations ([]) and examined for their primary productivity and emissions of methane and other major carbon species. Atmospheric greenhouse warming by gases such as carbon dioxide and methane must have been greater during the Archean than today in order to account for a record of moderate to warm palaeoclimates, despite a less luminous early sun. It has been suggested that decreased levels of oxygen and sulphate in Archean oceans could have significantly stimulated microbial methanogenesis relative to present marine rates, with a resultant increase in the relative importance of methane in maintaining the early greenhouse. We maintained modern microbial mats, models of ancient coastal marine communities, in artificial brine mixtures containing both modern [] (c. 70 mm ) and ‘Archean’[] (<0.2 mm ). At low [], primary production in the mats was essentially unaffected, while rates of sulphate reduction decreased by a factor of three, and methane fluxes increased by up to 10‐fold. However, remineralization by methanogenesis still amounted to less than 0.4% of the total carbon released by the mats. The relatively low efficiency of conversion of photosynthate to methane is suggested to reflect the particular geometry and chemical microenvironment of hypersaline cyanobacterial mats. Therefore, such mats were probably relatively weak net sources of methane throughout their 3.5 Ga history, even during periods of low environmental levels oxygen and sulphate.