Effect of DNA fragment size on transformation frequencies in tobacco (Nicotiana tabacum) and maize (Zea mays)

During eukaryotic cell transformation, the transforming DNA must enter the host cell, traverse the cytoplasm and enter the nucleus before becoming stably integrated into the genome. The limiting step for plant protoplast transformation may lie at the cell membrane, the nuclear membrane, or at the integration step. We show here that the size of the DNA fragment containing the selectable marker used to monitor transformation can directly affect the efficiency of stable transformation. In both tobacco and maize protoplasts, the smallest DNA fragments gave the highest stable transformation frequencies.     

In vivo inhibition of thromboxane synthetase in infarcted canine myocardium

The in vivo effectiveness of the thromboxane synthetase inhibitor OKY-1581 was tested in normal and infarcted canine myocardium. A rapid in vitro assay was developed which permits an accurate assessment of the status of the tissue thromboxane synthetase at the time of sacrifice. Reperfused infarcts were created by two hours of coronary artery occlusion followed by release of occlusion and three days of recovery. OKY-1581 was infused at 100 micrograms/kg/min for 15 minutes, a dose previously found to cause an 85% inhibition of canine platelet thromboxane synthetase in vivo. The heart was rapidly excised and transmural tissue plugs of infarcted and normal areas were obtained. These were incubated for 5 minutes with prostaglandin endoperoxide (PGH2) in phosphate buffer. Thromboxane production was inhibited from 16 +/- 1 ng TxB2 per tissue plug to 5 +/- 1 in normal myocardium and from 27 +/- 5 to 6 +/- 1 in infarcted areas of myocardium. Control incubations showed no further inhibition with the in vitro addition of 20 micrograms/ml OKY-1581, confirming the completeness of in vivo inhibition. Thus significant inhibition of thromboxane synthetase by intravenous OKY-1581 occurs even in a reperfused zone of infarction.     

Effect ofPseudomonas aeruginosa rhamnolipid on human neutrophil migration

The effect ofPseudomonas aeruginosa heat-stable hemolysin (rhamnolipid) on human neutrophil migration has been investigated. Rhamnolipid was prepared from culture filtrate and characterized by thin-layer chromatography. The lytic activity of rhamnolipid was quantitated by titration against neutrophils. Leukocyte migration response was measured using⁵¹Cr-labeled neutrophils with a double-filter technique in modified Boyden chambers. The results suggest rhamnolipid stimulated chemotaxis as well as chemokinesis. Moreover, rhamnolipid impaired a chemotactic response toN-formyl-methionyl-leucyl-phenylalanine. These effects may be important in host-parasite interactions.     

Effect of ultraviolet radiation on the microsporidian Octosporea muscaedomesticae with reference to protectants provided by the host Phormia regina

The effect of ultraviolet light on the microsporidian Octosporea muscaedomesticae in relation to infection in the adult black blowfly, Phormia regina, was investigated. A 30-Watt germicidal lamp, 253.7-nm wavelength, was used as source of uv light in five investigations. In addition, sunlight served as a uv source in two studies. Viable naked dried spores exposed to the uv lamp at a distance of 10 cm were killed after 15 min. Viable naked spores in an aqueous suspension were killed after 30 min of exposure to the uv lamp and after 3 hr of exposure to bright sunlight, respectively. Daily 30-min uv lamp exposures on living hosts harboring all life phases of the parasite did not interfere with the ensuing infection in the blowfly's midgut and the pathogen's developmental cycle. Spores harvested from uv-treated infected hosts were found to be as infective as spores retrieved from hosts not treated with uv. Spores contained in dried fecal droplets and exposed up to 3 hr to the uv lamp, or 12 hr to bright sunlight, respectively, remained infective. Addition of uric acid to a preparation of naked spores prior to 15- and 30-min uv irradiations yielded 100% infection in both host groups. A uv-protective function is ascribed to components provided by the host's tissues and feces.     

Changes in water status during water stress at different stages of development in wheat

The dynamics of stomatal resistance and osmotic adjustment in response to plant water deficits and stage of physiological development was studied in the leaves of spring wheat ( Triticum aestivum L., GWO 1809). Plants were germinated and grown in pots in a growth chamber at the Duke University Phytotron to four physiological stages of development (4th leaf, 7th leaf, anthesis, and soft dough), during which time stomatal resistance, total water potential and osmotic potential were measured on the last fully developed leaf of water stressed and non-stressed plants. Pressure potential was obtained by difference. Stomatal closure of the abaxial and adaxial surfaces were independent of each other, each having a different critical total water potential. The total water potential required to close the stomata on the last fully developed leaf were different at different stages of physiological development, decreasing as the plants grew older. The development of osmoregulation in wheat allows the closure of stomata during the vegetative stage at a high total water potential, but insures that stomata remain open from anthesis through the ear filling period to a lower total water potential.     

Quantum yield and rate of formation of the carotenoid triplet state in photosynthetic structures

The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q⁻) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q⁻ than in the state Q, in nearly the same proportion as chlorophyll a fluorescence. It is concluded that, for excited chlorophyll a, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680⁺ completely saturates, whereas that of carotenoid triplet continues to increase.

The rate of triplet-triplet energy transfer from chlorophyll a to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 · 10⁷ s⁻¹ at 294 K. It is about 2–3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K.     

Central place foraging in the Eastern chipmunk, Tamias striatus

Orians & Pearson (1979) considered the optimal foraging strategies of ‘central place foragers’, animals that repeatedly return with their food to a fixed location. We tested some of their predictions on eastern chipmunks, Tamias striatus. The rate of cheek pouch loading declines as the pouches fill; thus the optimal load size may vary, depending on the time required to travel between the feeding site and burrow. This ‘travel time’ may also affect the choice of feeding site. A method was developed to test this, and preliminary results confirm the hypothesis. Methodological and theoretical implications of these empirical results are discussed.