Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). II. Pollen transport in flow fields and capture by stigmas

Flow chamber observations of the filamentous pollen of Zostera marina L. (Potamogetonales) revealed that pollen rotated and moved toward inflorescences where they were captured by stigmas. The mechanics of this abiotic pollination process were examined and found to be related to the flow environment around emergent flowers. The translational movement of pollen was imparted by the advection of the fluid (e.g., pollen kinetic energy, K, ranged from 0.8 x 10-14 to 2.4 x 10-14 J, and the average K of the fluid was _ 0.7 x 10-14 J), while the rotational motion was imparted by the fluid shear stress (tau) within the velocity gradient (e.g., pollen shear stress, sigmat = omegamu where omega is the rotational velocity and mu is the dynamic viscosity, ranged from 3.4 x 10-4 to 26 x 10-4 Pa, and the average fluid shear stress was tau _ 10 x 10-4 Pa; Ackerman, 1997, American Journal of Botany 84: 1099-1109). These results indicate that there is a greater potential for pollination by filamentous pollen relative to spherical pollen. Functionally, while spherical pollen needs to be directly upstream from stigmas to be captured, filamentous pollen need only be in the vicinity of inflorescences and flowers to be captured by stigmas. Thus, in addition to direct interception on stigmas, filamentous pollen can be captured while they rotate past flowers or when they are redirected through the velocity gradient towards flowers. Filamentous pollen is an adaptation to submarine pollination in seagrasses.     

Nutrient limitation restricts growth and reproductive output in a tropical montane cloud forest bromeliad: findings from a long-term forest fertilization experiment

From studies in seasonal lowland tropical forests, bromeliad epiphytes appear to be limited mainly by water, and to a lesser extent by nutrient supply, especially phosphorous. Less is understood about the mineral nutrition of tropical montane cloud forest (TMCF) epiphytes, even though their highest diversity is in this habitat. Nutrient limitation is known to be a key factor restricting forest productivity in TMCF, and if epiphytes are nutritionally linked to their host trees, as has been suggested, we would expect that they are also nutrient limited. We studied the effect of a higher nutrient input on reproduction and growth of the tank bromeliad Werauhia sintenisii in experimental plots located in a TMCF in Puerto Rico, where all macro- and micronutrients had been added quarterly starting in 1989 and continuing throughout the duration of this study. We found that bromeliads growing in fertilized plots were receiving litterfall with higher concentrations of N, P, and Zn and had higher concentrations of P, Zn, Fe, Al, and Na in their vegetative body. The N:P ratios found (fertilized = 27.5 and non-fertilized = 33.8) suggest that W. sintenisii may also be phosphorous limited as are lowland epiphytes. Fertilized plants had slightly longer inflorescences, and more flowers per inflorescence, than non-fertilized plants, but their flowers produced nectar in similar concentrations and quantities. Fertilized plants produced more seeds per fruit and per plant. Frequency of flowering in two consecutive years was higher for fertilized plants than for controls, suggesting that fertilized plants overcome the cost of reproduction more readily than non-fertilized plants. These results provide evidence that TMCF epiphytic bromeliads are nutrient limited like their lowland counterparts.     

Comparison of methods to diagnose an epizootic of Corynebacterium kutscheri pneumonia in rats

An outbreak of Corynebacterium kutscheri pneumonia occurred in a colony of laboratory rats. Diagnostic methods compared on a prospective basis included (1) an enzyme-linked immunosorbent assay (ELISA) for serum antibody to C. kutscheri; (2) C. kutscheri isolation from retrograde nasal wash, cervical lymph nodes, tracheal wash, lung homogenate; and (3) histopathology. C. kutscheri was isolated from one or more of the cultured sites from suspected cases, but no individual rat yielded C. kutscheri from all of the sites. The presence of histological lung lesions was the most frequent indicator of infection (8 of 9 suspected cases), followed by isolation of C. kutscheri from lung homogenate (5 of 6), ELISA for serum antibody (6 of 8), and isolation of C. kutscheri from cervical lymph node (4 of 8). Isolation of C. kutscheri from nasal wash (1 of 9) was the least sensitive indicator of infection. ELISA antibody was not detected in rats which had normal lungs and did not harbor C. kutscheri. It was concluded that ELISA provides noninvasive means for detecting infection and cervical lymph node culture increase the potential for successful isolation of the agent in C. kutscheri infected rats.     

Ribozymes correctly cleave a model substrate and endogenous RNA in vivo

The alpha-sarcin domain of 28 S RNA in Xenopus oocytes is attacked by several catalytic toxins (e.g. alpha-sarcin and ricin) that abolish protein synthesis. We synthesized 6 ribozymes targeted to the alpha-sarcin domain and to an oligoribonucleotide (34-mer) that mimics this domain. Sarcin ribozyme 5 (SR5) efficiently cleaved after the CUC site in the synthetic 34-mer in vitro at 50 degrees C. SR5 also cut the same site when both substrate and ribozyme were coinjected or injected separately into oocytes at 18 degrees C. Correct cleavage in vivo was shown by isolating and sequencing the large cleavage fragment. The cleavage reaction appeared to function equally well in the oocyte nucleus and cytoplasm. SR5 also correctly cleaved endogenous 28 S RNA in oocytes, although cutting was much less efficient than with alpha-sarcin. We therefore demonstrated that a ribozyme specifically cuts both a model substrate and a cellular RNA in vivo. Earlier work showed that certain injected deoxyoligonucleotides complementary to the alpha-sarcin region abolish protein synthesis. Oocyte protein synthesis was also abolished by an SR5 containing a single G----U substitution that inactivates RNA catalysis, indicating that SR5's translational suppression was perhaps due to antisense function rather than ribozyme cleavage.     

Auditory stimulus intensity gradients and response to methylphenidate in ADD children

Using an auditory stimulus intensity paradigm, we obtained both event related potentials (ERPs) and press and release reaction times (RT) from a large sample of children with Attention Deficit Disorder (ADD). The ERP gradients to three tone intensities were used to classify the children as augmenters (steep gradients), moderates, or reducers (shallow or negative gradients). The RT data were used to classify the children as strong or sensitive, following neo-Pavlovian guidelines. The children were then cross-classified on these two dimensions and compared on cognitive, behavioral, and performance measures. The groups were also compared in response to two dosage levels of methylphenidate. Based on prior studies, we hypothesized that: 1. ERP augmenters would respond as well to the low as high dose but that reducers would respond better to high than low dose; and II. sensitive types (RT measure) would do better on the higher dose and strong types on the low dose. The first hypothesis was confirmed on a performance task but not on behavioral ratings. At the lower dose, augmenters improved most and reducers least on a 10-minute coding task presumed to require sustained attention. There was no support for the second hypothesis either in ratings or performance. The ERP augmentation measure was significantly related to teacher rated attentiveness; i.e., reducers and moderates were rated more adversely. The RT sensitivity measure tended to be related to achievement; i.e., strong types had lower reading and spelling scores. The ERP and RT sensitivity measures were not significantly correlated.     

The effect of incubation media on the water exchange of snapping turtle (Chelydra serpentina) eggs and hatchlings

Summary The effect of two different incubation media, sand and vermiculite, on the water exchange of eggs and the mass of hatchlings of snapping turtles (Chelydra serpentina) was assessed. The eggs were incubated fully buried in either sand or vermiculite at 30 °C and egg mass was measured periodically throughout incubation. The wet and dry masses of each hatchling and its residual yolk were measured at the end of incubation. The media had similar water potentials () but their thermal conductivities differed 2.8-fold. The eggs experienced a net water gain during incubation. The rates of water uptake between treatments were not statistically different throught the first 36 days of incubation but were statistically different thereafter, with eggs incubating in sand taking up water at about twice the rate of eggs incubating in vermiculite. Hatchling masses were similar to both media but hatchling water contents were significantly different. Hatchlings incubated in sand had lower water contents than hatchlings incubated in vermiculite even though the eggs in sand took up more water. Hatchling mass was correlated with egg water exchange for eggs incubated in vermiculite but not for eggs incubated in sand. The difference in egg water exchange in the two media appears to be attributable to differences in the thermal conductivity of the media. The presence of such a thermal effect supports the hypothesis that the eggs exchanged water with the media as water vapor. Egg water exchange was limited by the shell and shell membranes and not by the media. The shell and shell membranes appear to present an effective barrier to water uptake.Abbreviations M _{H 2 O} water flux (cm³·day^-1) - L _p hydraulic conductivity (cm·day^-1·kPa^-1) - A shell area (cm²) - A _p pore area (cm²) - l shell thickness (cm) - r pore radius (cm) - viscosity (kPa·day) - P _{EH 2 O} egg water potential (kPa) - P _{AH 2 O} medium water potential (kPa) - G _{H 2 O} water vapor conductance (cm³·day^-1·kPa^-1) - D _{H 2 O} diffusion coefficient (cm²·day^-1) - R gas constant (cm³·kPa·K^-1·cm^-3) - T temperature (K) - P _{EH 2 O} egg water vapor pressure (kPa) - P _{AH 2 O} medium water vapor pressure (kPa) - d egg diameter - K soil hydraulic conductivity (cm²·day^-1·kPa^-1) - DHM hatchling dry mass - WHM hatchiling wet mass - WU water uptake - IM initial egg mass     

Calcium ionophore A23187 calcium-dependent cytolytic degranulation in human eosinophils

The divalent cation ionophore A23187 is frequently used for studies of eosinophil degranulation. Nonetheless, the mechanism whereby A23187 induces degranulation in human eosinophils is still unclear. In the present experiments, A23187 caused human eosinophils to release a granule protein, eosinophil-derived neurotoxin (EDN) and a membrane-associated protein, Charcot-Leyden crystal (CLC) protein in a calcium and a concentration-dependent manner. However, A23187 at a concentration (1 microgram/ml) that caused 15% EDN release and 30% CLC protein release also produced release of the cytoplasmic enzyme lactic dehydrogenase (LDH) and loss of cell viability, both of which were calcium dependent. CLC protein release preceded EDN release and was detectable even at 15 min after the addition of 1 microgram/ml A23187, whereas EDN release occurred after a lag period of 30 min, and coincided with LDH release. At 1 microgram/ml A23187, neither the release of LDH nor the loss of viability occurred with purified neutrophils obtained in the same blood sample as a by-product of eosinophil purification. Electron microscopic examination demonstrated that exposure to A23187 for 15 min resulted in an increase and elongation of microridges on the cell surface, and exposure for 45 min caused cell disruption followed by extrusion of membrane-bound granules through breaks in the plasma membrane. Only once was granule exocytosis observed. These results indicate that A23187 treatment of eosinophils causes an initial release of membrane-associated CLC protein by a noncytolytic mechanism, and causes degranulation as a result of eosinophil lysis.     

Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). I. The influence of floral morphology on fluid flow

An understanding of the process of submarine pollination should provide insight into the evolutionary and reproductive ecology of the marine angiosperms (seagrasses). The flow around the reproductive organs of the seagrass Zostera marina L. (Potamogetonales) was, therefore, examined in a flow chamber. The phenological emergence of flowers during (1) pollen capture and (2) pollen release, and by fruit during (3) seed release, led to a reduction in flow rate toward the inflorescence. This change in flow due to floral emergence was associated with a 50% increase in the fluid shear stress [tau = (2.2 _ 0.3) x 10-3 Pa for an immature flower vs. tau = (3.1 _ 0.5) x 10-3 Pa for a receptive flower]. The Reynolds number (Re) and fluid shear stress around inflorescences and infructescences were comparable, indicating a dynamic similarity in the processes of pollen capture and fruit dehiscence [Re = 47 _ 5, tau = (1.6 _ 0.3) x 10-3 Pa for inflorescences; Re = 38 _ 5, tau = (1.3 _ 0.1) x 10-3 Pa for infructescences]. These results indicate that the emergence of reproductive organs leads to changes in fluid shear stress, which will affect the release, transport, and capture of particles including pollen. Theoretical considerations of these observations using aerosol-filtration theory suggest that pollen capture in Z. marina occurs through direct interception of pollen by stigmas.