Low and High Temperature Limits to PSII : A Survey Using trans-Parinaric Acid, Delayed Light Emission, and F(o) Chlorophyll Fluorescence

Many studies have shown that membrane lipids of chilling-sensitive plants begin lateral phase separation (i.e. a minor component begins freezing) at chilling temperatures and that chilling-sensitive plants are often of tropical origin. We tested the hypothesis that membranes of tropical plants begin lateral phase separation at chilling temperatures, and that plants lower the temperature of lateral phase separation as they invade cooler habitats. To do so we studied plant species in one family confined to the tropics (Piperaceae) and in three families with both tropical and temperate representatives (Fabaceae [Leguminosae], Malvaceae, and Solanaceae). We determined lateral phase separation temperatures by measuring the temperature dependence of fluorescence from trans-parinaric acid inserted into liposomes prepared from isolated membrane phospholipids. In all families we detected lateral phase separations at significantly higher temperatures, on average, in species of tropical origin. To test for associated physiological effects we measured the temperature dependence of delayed light emission (DLE) by discs cut from the same leaves used for lipid analysis. We found that the temperature of maximum DLE upon chilling was strongly correlated with lateral phase separation temperatures, but was on average approximately 4°C lower. We also tested the hypothesis that photosystem II (PSII) (the most thermolabile component of photosynthesis) of tropical plants tolerates higher temperatures than PSII of temperate plants, using DLE and F_o chlorophyll fluorescence upon heating to measure the temperature at which PSII thermally denatured. We found little difference between the two groups in PSII denaturation temperature. We also found that the temperature of maximum DLA upon heating was not significantly different from the critical temperature for F_o fluorescence. Our results indicate that plants lowered their membrane freezing temperatures as they radiated from their tropical origins. One interpretation is that the tendency for membranes to begin freezing at chilling temperatures is the primitive condition, which plants corrected as they invaded colder habitats. An alternative is that membranes which freeze at temperatures only slightly lower than the minimum growth temperature confer an advantage.     

Topography of photosynthetic activity of leaves obtained from video images of chlorophyll fluorescence

The distribution of photosynthetic activity over the area of a leaf and its change with time was determined (at low partial pressure of O₂) by recording images of chlorophyll fluorescence during saturating light flashes. Simultaneously, the gas exchange was being measured. Reductions of local fluorescence intensity quantitatively displayed the extent of nonphotochemical quenching; quench coefficients, q_N, were computed pixel by pixel. Because rates of photosynthetic electron transport are positively correlated with (1 − q_N), computed images of (1 − q_N) represented topographies of photosynthetic activity. Following application of abscisic acid to the heterobaric leaves of Xanthium strumarium L., clearly delineated regions varying in nonphotochemical quenching appeared that coincided with areoles formed by minor veins and indicated stomatal closure in groups.     

The effect of phentolamine on synaptosomal phosphatidylinositol in experimental galactose toxicity

Abnormal myo-[2-³H]inositol incorporation into phosphatidylinositol has been found in phentolamine-treated synaptosomes that were isolated from the cerebral hemispheres of galactose toxic rats and incubated with [³³P]P_i and myo-[2-³H] inositol. In galactose toxic rats phentolamine-stimulated myo-[2-³H]inositol labeling of phosphatidylinositol was 70% greater than in normal animals. This enhanced labeling of synaptosomal phosphatidylinositol in galactose toxic rats during stimulation with phentolamine is in marked contrast to the depressed myo-inositol labeling of phosphatidylinositol reported with acetylcholine stimulation.     

The life history of Sulcascaris sulcata (Nematoda: Ascaridoidea), a parasite of marine molluscs and turtles

Berry G. N. and Cannon L. R. G. 1981. The life history of Sulcascaris sulcata (Nematoda: Ascaridoidea), a parasite of marine molluscs and turtles. International Journal for Parasitoiogy11: 43–54. The morphology, development and hatching of Sulcascaris sulcata eggs are described. Two moults occurred in the egg. Third stage larvae spontaneously hatched and were found to develop in marine bivalves and gastropods. Larvae grew steadily and after three to four months, when about 5 mm long, they moulted to fourth stage larvae characteristic of natural infections in bivalves from commercial catches. Experimentally, when fed to laboratory-reared Caretta caretta, the fourth stage larvae first attached at the oesophago-gastric junction where they moulted to adults in 7–21 days. Subsequent growth to mature adults was obtained by at least 5 months after infection. It is suggested that under natural conditions the life history may take up to 2 years to complete. These findings are discussed in relation to the predatory mode of feeding and the breeding habits of C. caretta and the significance of a possible health hazard to man.     

Genetical variation in three Pacific House mouse (Mus musculus) populations

Studies of allozymic variation at 36 loci in samples of House mouse ( Mus musculus ) populations collected from the island of Hawaii and two islets in the Enewetak Atoll, Marshall Islands are reported. All three populations carried a great deal of inherited variation: the Hawaiian sample had a mean heterozygosity of 16.6% per locus, which is the highest value so far found for a mouse population. The mean heterozygosities for the two atoll populations were 11.4% and 10.9%.
There were no changes in either heterozygosity or allozyme frequencies with age. In this respect, these populations from the tropical Pacific differed from populations living in cold temperate regions where natural selection has been shown to affect allele frequencies in different ways at different stages of the life cycle.     

Amino Acid Transport into Cultured Tobacco Cells: II. EFFECT OF CALCIUM

The effects of calcium ions on lysine transport into cultured Wisconsin-38 tobacco cells were examined. In the presence of calcium, lysine was transported at a relatively low rate for 30 to 40 minutes followed by a period of increasing rates and subsequent stabilization at a higher rate after 2 to 3 hours. In the absence of calcium, transport was uniformly low.     

Mechanism of action of porphobilinogen deaminase. The participation of stable enzyme substrate covalent intermediates between porphobilinogen and the porphobilinogen deaminase from Rhodopseudomonas spheroides.

Highly stable labelled complexes are formed between porphobilinogen deaminase and stoicheiometric amounts of [14C]porphobilinogen. On completion of the catalytic cycle by the addition of excess of substrate, the complexes yield labelled product and display all the properties expected from covalently bound enzyme intermediates involved in the deaminase catalytic sequence.     

Colorado potato beetle control by application of the entomopathogenic nematode Heterorhabditis marelata and potato plant alkaloid manipulation

Control of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), with the entomopathogenic nematode Heterorhabditis marelata Liu and Berry (Nematoda: Heterorhabditidae) was examined in the laboratory and in potato fields in north central Oregon. This research tested the hypothesis that varying nitrogen fertilizer levels would affect foliar alkaloid levels, which would stress the host, and allow increased nematode reproduction and long‐term control of the CPB. Laboratory results indicated that nematodes tended to reproduce more readily in CPB fed on potato plants with high levels of fertilizer. Field trials tested CPB population responses to four treatments: application of nematodes vs. no nematodes, with application of low vs. high rates of nitrogen fertilizer. The higher nitrogen application rate increased field foliar levels of the alkaloids solanine by 35%, and chaconine by 41% over the season. Nematodes were applied twice during the season, causing a 50% reduction in adult CPB populations, and producing six times as many dead prepupae in nematode‐treated soil samples as in the untreated samples. However, no reproducing nematodes were found in the 303 dead prepupae and pupae collected from nematode‐treated plots. Nitrogen fertilizer levels, and their related alkaloid levels, did not affect nematode infection rates or reproduction in the field. Foliar alkaloid levels of plants from the growth chamber were 3–6‐fold as high as those in the field, which may explain the variation in nematode response to nitrogen applications to host plants of the CPB. Heterorhabditis marelata is effective for controlling CPB in the field, and does not have negative non‐target effects on one of the most common endemic CPB control agents, Myiopharus doryphorae (Riley) (Diptera: Tachinidae), but the low rate of nematode reproduction cannot be manipulated through alkaloid stress to the beetle. Until H. marelata can be mass‐produced in an inexpensive manner, it will not be a commercially viable control for CPB.     

FINE STRUCTURE OF CELLS ISOLATED FROM ADULT MOUSE LIVER

Suspensions of isolated cells in various media were prepared from mouse liver which had been perfused via the portal vein with a buffered medium containing 0.40 M sucrose, and the cells were fixed with osmium tetroxide. Their fine structure was compared with that of cells from perfused and unperfused intact liver. Perfusion brought about some separation of the cells with little or no damage to cell membranes. When cells were dispersed in 0.40 M sucrose medium the plasma membranes partially broke down, and this disintegration was increased by transfer of the cells to media of lower osmolarity. This is presumed to account for the loss of permeability barriers which occurs in isolated liver cells. The mitochondria in cells of perfused liver and in isolated cells remained elongated, but the layers of many mitochondrial cristae became separated by clear spaces. When cells were transferred to a medium containing 0.20 M sucrose, the mitochondria swelled and became spherical, often with displacement of the swollen cristae to the periphery. In a medium containing 0.06 M sucrose and 0.08 M potassium chloride the outer chamber of many mitochondria became swollen with displacement of the mitochondrial body to one side to give a crescent-shaped appearance. These changes in mitochondrial morphology are discussed in relation to the metabolic activity of isolated liver cells.     

Initiating a crystallographic study of a class II fructose-1,6-bisphosphate aldolase.

We have reproducibly crystallized the metal-dependent Class II fructose-1,6-bisphosphate aldolase from Escherichia coli. Crystals in the shape of truncated hexagonal bipyramids have unit cell dimensions of a = b = 78.4 A, c = 290.6 A and are suitable for a detailed structural analysis. The space group has been identified as P6(1)22 or enantiomorph. Data sets to approximately 2.9 A resolution have been recorded using both the Rigaku R-AXIS IIc image plate area detector coupled to a copper target rotating anode X-ray source and using the MAR image plate systems with synchrotron radiation at the EMBL outstation DESY in Hamburg, and at S.R.S. Daresbury. Diffraction beyond 2.5 A has been observed when large freshly grown crystals are used with the synchrotron beam. A data set to this resolution has been collected. Several putative heavy-atom derivative data sets have also been measured using synchrotron radiation facilities and analysis of these data sets is in progress.