Aquatic Primary Production

The ecosystem concept has been particularly useful and extensivelyemployed in the study of aquatic primary productivity. The flowof energy through the system is an attractive area of investigationwhen it involves some process, but has a more restricted valuewhen units of biomass are simply converted to calories. Althoughwe are able to measure primary productivity in terms of thecarbon fixed, we are not yet able to measure the actual changein the oxidative state of the newly fixed carbon. The fate ofphotosynthate as food for higher trophic levels is thereforedependent upon a considerable array of biological and environmentalvariables. Primary productivity is considered in terms of itsevolution from measures of standing crop and yield, which havebeen gradually replaced by measures of rate of carbon uptakeor oxygen production, or by measure of nutrient loss, or bychange of CO₂ in the environment. Data from five lakes are usedto illustrate the evolutionary thread of eutrophication andthe great range in primary productivity to be expected on thebasis of either unit volume or unit surface area at differenttrophic states. Light and nutrients are important in limitingprimary productivity, and are contributing factors to the greatvariability which one may encounter within a given lake. Onlywith a sounder understanding of productivity at the base ofthe food-chain can we have any real hope of controlling theproductivity of aquatic environments for the benefit of man.     

Hyperpigmentation of Chinchilla Stria Vascularis Following Acoustic Trauma

This report describes morphological alterations of the chinchilla stria vascularis seen 30 days after exposure to impulse noise. The observed changes included a dramatic increase in strial melanin content which occurred in 7 of 36 animals exposed to electronically synthesized impulses presented in various temporal patterns at either 135 or 150 dB peak SPL. In these animals, densely pigmented areas of stria 1.5 to 3 mm in length were found in the basal cochlear turn. Light and electron microscopic study revealed that these areas contained large numbers of melanin granules situated primarily in pale-staining cells of the middle layer of the stria. Unlike the pigment granules present in normal chinchilla stria, the melanosomes found in the noise-exposed material clearly showed ultrastructural features characteristic of eumelanin. Melanin granules were also observed in marginal and basal cells of the noise-exposed stria. In some cases, pigment granules which had apparently been expelled from the marginal cells were present in the endolymphatic space beneath Reissner's membrane and on the strial surface. These findings support the view that the melanin-bearing cells of the inner ear are capable of markedly increased activity in response to stressful conditions.     

Comparative morphology of the venom gland and reservoir in opiine and alysiine braconid wasps (Insecta, Hymenoptera, Braconidae)

Detailed venom reservoir and venom gland intima morphology was investigated in representatives of 178 species and 76 genera of Braconidae belonging to the subfamilies Opiinae (23 genera and 69 species) and Alysiinae (36 genera and 67 species of Alysiini, and 17 genera and 42 species of Dacnusini). The presence of an unsculptured sack–like expansion of the anterior end of the reservoir suggests a relationship between some members of the alysiine tribe Dacnusini, viz. Exotela and Chorebus , and the genera Oenonogaster and Glyphogaster , both of which are currently placed in the Alysiini. The same feature also suggests that Exotela, Chorebus, Oenonogaster and Glyphogaster may be derived from the Opiinae separately from other Alysiinae. Other dacnusines examined are indicated as forming a monophyletic taxon on the basis of their reduced and narrow reservoirs. An anterior insertion of the venom glands on to the reservoir generally supports the Phaenocarpa group of alysiine genera, with some modification, whereas the presence of a discrete, narrow posterior extension of the reservoir represents a synapomorphy for members of the Aspilota group of alysiine genera. The phylogenetic inferences from this venom apparatus study are discussed in the light of the biology of the taxa concerned. Twenty-one new combinations are made in the Opiinae and seven in the Alysiinae.     

Methane flux from Missippi River deltaic plain wetlands

Methane emissions from three wetland habitats in the MississippiRiver deltaic plain were measured over a three year period. Fluxdata collected indicate that each habitat was a net source of methane to the atmosphere throughout the year. Average emissionfrom a Taxodium distichum / Nyssa aquatica (bald cypress / watertupelo) swamp forest was 146 ± 199 mgCH₄ m^-2d^-1 whileemissions from a Sagittaria lancifolia (bulltongue) freshwatermarsh averaged 251 ± 188 mg CH₄m^-2d^-1. Methane flux from a Spartina patens / Sagittaria lancifolia intermediate marsh was significantlyhigher, 912 ± 923 mg CH₄m^-2d^-1. Seasonal variation wassignificant with emissions being higher in the late summer andearly fall. Significant diurnal emissions were observed fromthe Sagittaria lancifolia marsh site. Soil temperature (5 and 10 cm depths) was found to be significantly correlated with methaneemission from the three sites.     

An Electron Microscope-Cytochemical Method for Differentiating Membranes of Host Red Cells and Malaria Parasites*

Limiting membranes of malaria parasites and host red cells stain differently when exposed to positively charged iron colloid. Negatively charged red cell membranes avidly bind colloid, whereas parasite membranes do not. This selectivity in colloidal iron uptake by the 2 types of membranes can be utilized as an aid in discerning the amounts of contaminating host cell membranes in “free” malaria parasite preparations and in related cell-free membrane extracts.     

A Comparative Study of Gametocyte Ultrastructure in Avian Haemosporidia*

The fine structure of gametocytes of 3 avian haemosporidian parasites Plasmodium gallinaceum, Haemoproteus columbae, and Leucocytozoon simondi has been studied and compared by electron microscopy. The gametocytes of all 3 species are bounded by a 3-layered limiting membrane system, possess a cytostome during some portion of their residence within host cells, and their sex can be distinguished by both nuclear and cytoplasmic characteristics. L. simondi differs most significantly from P. gallinaceum and H. columbae in possessing large intranuclear granules, mitochondria associated with pocket infoldings of the nuclear envelope near the atypical centriole complex and compartmentalization of the cytoplasm by segments of closely aligned unit membranes. Further, the cytostome of L. simondi does not appear to be a persistent structure as in the other 2 species and pigment is not present within food vacuoles. L. simondi also is capable of infecting a wider variety of host cells and within leukocytes produces striations of the host nucleus and an apparent spiral banding of the host cell surface. The comparison of P. gallinaceum, H. columbae, and L. simondi gametocytes by electron microscopy leads to the conclusion that Plasmodium and Haemoproteus are more closely related to each other than either of them is on Leucocytozoon. The terminology used to describe certain organelles within the gametocyte's cytoplasm has been reexamined and the relationship of the nucleolus to parasite maturation also is described.     

Effects of elevated CO2, nitrogen deposition, and decreased species diversity on foliar fungal plant disease

Three components of global change, elevated CO₂, nitrogen addition, and decreased plant species richness (‘diversity’), increased the percent leaf area infected by fungi (pathogen load) for much to all of the plant community in one year of a factorial grassland experiment. Decreased plant diversity had the broadest effect, increasing pathogen load across the plant community. Decreased diversity increased pathogen load primarily by allowing remaining plant species to increase in abundance, facilitating spread of foliar fungal pathogens specific to each plant species. Changes in plant species composition also strongly influenced community pathogen load, with communities that lost less disease prone plant species increasing more in pathogen load. Elevated CO₂ increased pathogen load of C₃ grasses, perhaps by decreasing water stress, increasing leaf longevity, and increasing photosynthetic rate, all of which can promote foliar fungal disease. Decreased plant diversity further magnified the increase in C₃ grass pathogen load under elevated CO₂. Nitrogen addition increased pathogen load of C₄ grasses by increasing foliar nitrogen concentration, which can enhance pathogen infection, growth, and reproduction. Because changes in foliar fungal pathogen load can strongly influence grassland ecosystem processes, our study suggests that increased pathogen load can be an important mechanism by which global change affects grassland ecosystems.     

Membrane water permeability and aquaporin expression increase during growth of maize suspension cultured cells

Aquaporins (AQPs) are water channels that allow cells to rapidly alter their membrane water permeability. A convenient model for studying AQP expression and activity regulation is Black Mexican Sweet (BMS) maize cultured cells. In an attempt to correlate membrane osmotic water permeability coefficient (P_f) with AQP gene expression, we first examined the expression pattern of 33 AQP genes using macro-array hybridization. We detected the expression of 18 different isoforms representing the four AQP subfamilies, i.e. eight plasma membrane (PIP), five tonoplast (TIP), three small basic (SIP) and two NOD26-like (NIP) AQPs. While the expression of most of these genes was constant throughout all growth phases, mRNA levels of ZmPIP1;3 , ZmPIP2;1 , ZmPIP2;2, ZmPIP2;4 and ZmPIP2;6 increased significantly during the logarithmic growth phase and the beginning of the stationary phase. The use of specific anti-ZmPIP antisera showed that the protein expression pattern correlated well with mRNA levels. Cell pressure probe and protoplast swelling measurements were then performed to determine the P_f. Interestingly, we found that the P_f were significantly increased at the end of the logarithmic growth phase and during the steady-state phase compared to the lag phase, demonstrating a positive correlation between AQP abundance in the plasma membrane and the cell P_f.