Period and phase control by temperature in the circadian rhythm of carbon dioxide fixation in illuminated leaves of Bryophyllum fedtschenkoi

The rhythm of CO₂ assimilation exhibited by leaves of Bryophyllum fedtschenkoi maintained in light and normal air occurs only at constant ambient temperatures between 10°C and 30°C. Over this range the period increases linearly with increasing temperature from the extremely low value of 15.7 h to 23.3 h, but shows a considerable degree of temperature compensation. Outside the range 10°C–30°C the rhythm is inhibited but re-starts on changing the temperature to 15°C. Prolonged exposure of leaves to high (40°C) and low (2°C) temperature inhibits the rhythm by driving the basic oscillator to fixed phase points in the cycle which differ by 180°, and which have been characterised in terms of the malate status of the leaf cells. At both temperatures loss of the circadian rhythm of CO₂ assimilation is due to the inhibition of phosphoenolpyruvate carboxylase (PEPCase) activity, but the inhibition is apparently achieved in different ways at 40°C and 2°C. High temperature appears to inhibit directly PEPCase activity, but not the activity of the enzymes responsible for the breakdown of malate, with the result that the leaf acquires a low malate status. In contrast, low temperature does not directly inhibit PEPCase activity, but does inhibit enzymes responsible for malate breakdown, so that the malate level in the leaf increases to a high value and PEPCase is eventually allosterically inhibited. The different malate status of leaves held at these two temperatures accounts for the phases of the rhythms being reversed on returning the leaves to 15°C. After exposure to high temperature, CO₂ fixation by PEPCase activity can begin immediately, whereas after exposure to low temperature, the large amount of malate accumulated in the leaves has to be decarboxylated before CO₂ fixation can begin.     

Water relations and growth responses of Uniola paniculata (sea oats) to soil moisture and water-table depth

Summary This study examined the water relations and growth responses of Uniola paniculata (sea oats) to (1) three watering regimes and (2) four controlled water-table depths. Uniola paniculata is frequently the dominant foredune grass along much of the southeastern Atlantic and Gulf coasts of the United States, but its distribution is limited in Louisiana. Throughout most of its range, U. paniculata tends to dominate and be well adapted to the most exposed areas of the dune where soil moisture is low. Dune elevations in Louisiana, however, rarely exceed 2 m, and as a result the depth to the water table is generally shallow. We hypothesized that if U. paniculata grows very near the water-table, as it may in Louisiana, it will display signs of water-logging stress. This study demonstrated that excessive soil moisture resulting from inundation or shallow water-table depth has a greater negative effect on plant growth than do low soil moisture conditions. Uniola paniculata's initial response to either drought or inundation was a reduction of leaf (stomatal) conductance and a concomitant decrease in leaf elongation. However, plants could recover from drought-induced leaf xylem pressures of less than-3.3 MPa, but prolonged inundation killed the plants. Waterlogging stress (manifested in significantly reduced leaf stomatal conductances and reduced biomass production) was observed in plants grown at 0.3 m above the water table. This stress was relieved, however, at an elevation of 0.9 m above the water table. As the elevation was increased from 0.9 to 2.7 m, there were no signs of drought stress nor a stimulation in growth due to lower soil moisture. We concluded that although U. paniculata's moisture-conserving traits adapt it well to the dune environment, this species can grow very well at an elevation of only 0.9 m above the water table. Field measurements of water-table depth in three Louisiana populations averaged about 1.3 m. Therefore, the observed limited distribution of U. paniculata along the Louisiana coast apparently cannot be explained by water-logging stress induced by the low dune elevations and the corresponding shallow water-table depth.     

Effects of visible and ultraviolet radiation on the ultrastructure of zooxanthellae (Symbiodinium sp.) in culture and in situ

Summary Quantitative ultrastructural studies on the effects of visible and ultraviolet radiation on zooxanthellae in culture and in situ showed an inverse relationship between the volume fraction of chloroplast and irridiance. An independent effect of ultraviolet radiation was detected in cultured zooxanthellae only. The volume fraction of chloroplasts in cultured zooxanthellae and zooxanthellae in situ were the same, while the surface density of thylakoid lamellae relative to chloroplast volume in cultured zooxanthellae was less than in zooxanthellae in situ for all irradiances. Additionally, zooxanthellae in situ showed an effect of ultraviolet radiation on surface density of thylakoid lamellae. The response to different irradiances suggests a limit to photoadaptation by means of changing chloroplast volume, and that changes in thylakoid density are responsible for the continued photoadaptive plasticity observed. Flow cytometry and stereological studies show that the volume fraction of accumulation bodies within zooxanthellae increases with irradiance and ultraviolet radiation. Ultrastructurally, accumulation bodies do not resemble plant peroxisomes or glyoxysomes, while other inclusions observed in this stydy are suggestive of peroxisomes. This evidence suggests that accumulation bodies are not peroxisomes, but does support the previous assumptions concerning their role in autophagic processes.     

Effect of aphidicolin on de novo DNA synthesis,DNA repair and cytotoxicity in γ-irradiated human fibroblasts. Implications for the enhanced radiosensitivity in ataxia telangiectasia

The antibiotic, aphidicolin, is a potent inhibitor of DNA polymerase α and consequently of de novo DNA synthesis in human cells. We report here that in γ-irradiated normal human cells, aphidicolin (at 5 μg/ml and less) had no significant effect on the rate of the rejoining of DNA single strand breaks or rate of removal of DNA lesions assayed as sites sensitive to incising activities present in crude protein extracts of Micrococcus luteus cells. γ-irradiated human ataxia telangiectasia cells are known to demonstrate enhanced cell killing and exhibit resistance to the inhibiting effects of radiation on DNA synthesis. Under conditions of minimal aphidicolin cytotoxicity but extensive inhibition of de novo DNA synthesis, the radiation responses of neither normal nor ataxia telangiectasia cells were significantly modified by aphidicolin. Firstly, we conclude that human DNA polymerase α is not primarily involved in the repair of the two classes of radiogenic DNA lesions examined. Secondly, the radiation hypersensitivity of ataxia telangiectasia cells cannot be explained on the basis of premature replication of damaged cellular DNA resulting from the resistance of de novo DNA synthesis to inhibition by ionizing radiation.     

Observations on the ecology and breeding biology of the genus Chiromantis (Amphibia: Rhacophoridae)

The construction of foam nests by the Anura seems to be a habit that has evolved separately in all the main zoogeographical regions. Chiromantis is a large tree frog weighing up to 5.5 g which is restricted to the Ethiopian region. This genus comprises three species which are found in the three main African biomes from rain forest ( C. rufescens ), through woodland ( C. xerampelina ) to semi-arid savannah ( C. petersii ). The female of C. rufescens is shown in this study to construct her nest with the assistance of three males, and like the other two species, the nests are always fastened to objects over temporary water sources.
Although the rain forest and savannah species are the same size the latter lays twice as many eggs as the former. Additionally it is shown that the eggs of C. petersii are only half the size of C. rufescens. These facts can be correlated with the degree of permanence of the water source over which the nest is constructed.
Features of the water economy and ecology are also described.     

CELL POPULATION GROWTH IN THE CASTRATE MOUSE PROSTATE COMPLEX: EXPERIMENTAL VERIFICATION OF COMPUTER SIMULATION

The stimulatory action of androgen on cell proliferation in the castrate mouse seminal vesicle and coagulating gland has been studied by DNA measurements in mice 14 days after castration. 100 hr after continuous androgen treatment the level of DNA had increased 2.5-fold in the seminal vesicle and coagulating gland compared with 14 days castrated controls. A mathematical model predicted this new experimental data when the parameters employed in the simulation were constrained by the results of previous experiments.     

STRUCTURE AND FUNCTION OF THE ALGAL PYRENOID. I. ULTRASTRUCTURE AND CYTOCHEMISTRY DURING ZOOSPOROGENESIS OF TETRACYSTIS EXCENTRICA1

The fine structure of the pyrenoid in the mature vegetative cell of Tetracystis excentrica Brown and Bold is described. During zoosporogenesis, the pyrenoid undergoes regression, and the ultrastructure of this process is described in detail. The ground substance undergoes dissolution, and reticulate fibrillar structures appear as well as intruding chloroplast thylakoids. Pyrenoid-associated starch plates diminish, and quantities of starch not associated with the pyrenoid are produced. New pyrenoids appear late in the division cycle after all other major organelles associated with the motile cell have been formed. Zoospore pyrenoids develop in thylakoid-free spaces of the chloroplast which are similar to the DNA-containing regions. The new pyrenoid ground substance, which is loosely fibrillar, arises in close proximity to starch grains which may be formed in the stroma. Then the zoospore pyrenoid produces 2 hemispherical starch plates identical to those in the mature vegetative cell. Zoospore pyrenoids lack the 2 convoluted thylakoids between the starch plates and the ground substance characteristic of those in the mature vegetative cell. Instead, the thylakoids are identical to those of the chloroplast at first, and then develop into a convoluted state in the vegetative cell. Cytochemical tests for DNA, RNA, and protein were made for the cytoplasm, nucleus, nucleolus, and pyrenoid. Conclusive evidence is presented for the presence of RNA in the cytoplasm and nucleolus, DNA in the nucleus, and protein in the pyrenoid. The tests did not conclusively demonstrate the presence or absence of DNA and RNA in the pyrenoid; however, they suggested that small amounts of both DNA and RNA may be present.     

Novelties in Hedeoma (Labiatae)

Hedeoma pilosum andH. microphyllum are described as new. The former, an endemic of western Texas, is closely related toH. pusillum andH. apiculatum; the latter is intermediate betweenH. costatum andH. nanum. H. oblongifolium var.mexicanum andH. drummondii var.crenulatum are presented as two new varieties, both of which may have originated as hybrids.Hedeoma crenulatum is proposed as a new name to replaceH. montanum (Brade) Epling & Játiva. Three new combinations are made in the genusHesperozygis, and new status is accorded to two species.