Frost in a future climate: modelling interactive effects of warmer temperatures and rising atmospheric [CO2] on the incidence and severity of frost damage in a temperate evergreen (Eucalyptus pauciflora)

Although plants are more susceptible to frost damage under elevated atmospheric [CO₂], the importance of frost damage under future, warmer climate scenarios is unknown. Accordingly, we used a model to examine the incidence and severity of frost damage to snow gum (Eucalyptus pauciflora) in a sub‐alpine region of Australia for current and future conditions using the A2 IPCC elevated CO₂ and climate change scenario. An existing model for predicting frost effects on E. pauciflora seedlings was adapted to include effects of elevated [CO₂] on acclimation to freezing temperatures, calibrated with field data, and applied to a study region in Victoria using climate scenario data from CSIRO's Global Climate Model C‐CAM for current (1975–2004) and future (2035–2064) 30 years climate sequences. Temperatures below 0 °C were predicted to occur less frequently while the coldest temperatures (i.e. those below ?8 °C) were almost as common in the future as in the current climate. Both elevated [CO₂] and climate warming affected the timing and rates of acclimation and de‐acclimation of snow gum to freezing temperatures, potentially reducing the length of time that plants are fully frost tolerant and increasing the length of the growing season. Despite fewer days when temperatures fall below 0 °C in the future, with consequently fewer damaging frosts with lower average levels of impact, individual weather sequences resulting in widespread plant mortality may still occur. Furthermore, delayed acclimation due to either warming or rising [CO₂] combined with an early severe frost could lead to more frost damage and higher mortality than would occur in current conditions. Effects of elevated [CO₂] on frost damage were greater in autumn, while warming had more effect in spring. Thus, frost damage will continue to be a management issue for plantation and forest management in regions where frosts persist.     

Colonization dynamics of river benthos in response to local changes in bed characteristics

1. The effects of small-scale variation in the nature of a river bed upon the colonization dynamics of benthic invertebrates were explored through a series of microhabitat implants placed in a small river in southern Ontario. The implants presented variations in the levels of four microhabitat features: substrate particle size, current regime, added food and light. The sixteen possible combinations of these variables were replicated five times, for a total of eighty implants.
2. After 14 days of exposure, some of the controlled variables had been modified and a number of other variables (sand, fine (FPOM) and coarse (CPOM) particulate organic matter) had been added by the river.
3. Benthic diversity differed among the implants, with sand and CPOM accounting for 15.5% of the variation. Benthic density was more uniform and was weakly related only to added food. Application of the CANOCO program to the data set suggested that, in general, the environmental variables manipulated in this study were not the key factors influencing colonization, although they may have been important in non-linear combination.
4. A number of important positive associations were evident among colonizing species, some of which are thought to reflect those of predator and prey.
5. Control of colonization appears to be through multiple factors (abiotic, biotic, autochthonous, allochthonous) that differ in nature according to species, and which underline the complexity of selection responses of individual taxa to local variations in bed structure. Researchers must acknowledge this multifactorial organization and dynamic nature if workable models of lotic community structure and development are to be forthcoming.     

FORMATION OF THE FERTILIZATION MEMBRANE BY INSEMINATION OF IMMATURE STARFISH OOCYTES PRETREATED WITH CALCIUM-FREE SEAWATER

When immature oocytes of the starfish, Asterina pectinifera , were treated with calcium-free seawater for 1 hr and then inseminated in normal seawater, they formed several blisters, indicative of polyspermy, and raised fertilization membranes. These oocytes continued to have intact germinal vesicles. Electron microscopic study revealed that the egg surface remained virtually unchanged after the treatment with calcium-free seawater. Upon insemination, however, the cortical granules broke down and the fertilization membrane was formed. These immature oocytes with ferilization membranes underwent maturation (germinal vesicle breakdown) after treatment with 1-methyladenine.
The treatment with calcium-free seawater seems to bring about some physiological change on the surface of immature oocyte, which bestows some attributes of maturation but is insufficient to mature the oocytes completely.     

Inhibition of a Discrete Bacterial DNA Polymerase by 6-(<Emphasis Type="Italic">p</Emphasis>-Hydroxyphenylazo)-uracil and 6-(<Emphasis Type="Italic">p</Emphasis>-Hydroxyphenylazo-)-isocytosine

6-(p-HYDROXYPHENYLAZO)-URACIL (HPUra) specifically inhibits the semi-conservative replication of DNA in Gram-positive bacteria^1–3. We have reported that HPUra inhibits ATP-dependent polymerization of deoxyribonucleotides in vitro in toluene-treated B. subtilis⁴. Further studies of the effect of HPUra and its amino analogue, HPIsocytosine (6-(p-hydroxyphenylazo)-2-amino, 4-keto pyrimidine), in toluene-treated B. subtilis have provided considerable information on the mechanism of arylazopyrimidine action. First, HPUra and HPIsocytosine do not inhibit DNA synthesis unless they first are reduced to their colourless, hydrazo forms (refs. 4 and 5 and Mackenzie, Wright and Brown, unpublished results). Second, the inhibitory action of reduced HPUra and that of reduced HPIsocytosine are completely antagonized, respectively, by dGTP and dATP⁵. Third, drug-resistant mutants have been isolated which catalyse drug-resistant DNA synthesis following their permeabilization with toluene. These observations suggest that reduced HPUra and HPIsocytosine inhibit DNA replication by interfering competitively with the enzymatic polymerization of specific purine deoxyribonucleotides. We examined, therefore, cell free preparations of ^{B. subtilis} in an effort to identify a discrete DNA polymerase as the site of drug action. We report here experiments with crude and partially fractionated extracts of DNA polymerase I-deficient mutants which indicate the existence of at least one drug sensitive polymerase. Bazill and Gross⁶ have independently isolated chromatographically discrete HPUra-sensitive polymerases from extracts of B. subtilis.     

Effects of Colchicine and Light on Cell Form in Fern Gametophytes. Implications for a Mechanism of Light-induced Cell Elongation

Spores of the fern, Onoclea sensihilis L., suffer a disruption of normal development when they are cultured on media containing colchicine. Cell division is inhibited, and the spores develop into giant spherical cells under continuous white fluorescent light. In darkness only slight cell expansion occurs. Spherical cell expansion in the light requires continuous irradiation. Photosynthesis does not seem to be involved, since variations in light intensity do not affect the final cell diameter; the addition of sucrose to the medium does not permit cell expansion in darkness; and the inhibitor DCMU does not block the light-induced cell expansion. Continuous irradiation of colchicine-treated spores with blue, red or far-red light produces different patterns of cell expansion. Blue light permits spherical growth, similar to that found under white light, whereas red and far-red light promote the reestablishment of polarized filamentous growth. Although ethylene is unable to induce polarized cell expansion in colchicine-treated spores in darkness or white and blue light, it enhances filamentous growth which already is established by red or far-red irradiation. Both red and far-red light increase the elongation of normal filaments (untreated with colchicine) above that of dark-grown plants, but under all 3 conditions the rates of volume growth are identical. Light, however, does cause a decrease in the cell diameters of irradiated filaments. These data are used to construct an hypothesis to explain the promotion of cell elongation in fern protonemata by red and far-red light. The model proposes light-mediated changes in microtubular orientation and cell wall structure which lead to restriction of lateral cell expansion and enhanced elongation growth.     

Chlorophyll formation and the development of photosynthesis in dark grown seedlings of Picea abies

Abstract Seeds of Picea abies were germinated and grown in either darkness or constant light. The chlorophyll content and photosynthetic carbon dioxide uptake of developing seedlings of different ages was determined. Ten-day-old dark grown seedlings showed an instant ability for photosynthetic carbon dioxide uptake and also formed further chlorophyll most rapidly upon subsequent illumination. These activities progressively diminished when the dark growth period was extended. Light grown seedlings reached a maximum chlorophyll level after 15 days growth, and this preceded maximal photosynthetic development.     

A comparative study of the effects of NaCl salinity on respiration, photosynthesis, and leaf extension growth in Beta vulgaris L. (sugar beet)

Abstract. Three parameters influencing the capacity for carbon accumulation, i.e. photosynthesis, respiration, and leaf extension growth, were studied in Beta vulgaris L. (sugar beet) cultured in nutrient solution containing 0.5 to 500 mol m⁻³ NaCl. Leaf extension growth was the parameter most sensitive to salinity: the initial rate of leaf extension and final leaf length each declined linearly with increase in external NaCl concentration. Photosynthetic O₂ evolution of thin leaf slices did not decline until salinity levels reached 350 to 500 mol m⁻³ NaCl, while respiratory O₂ consumption was not affected by salinity throughout the range. The results suggest that the influence of salinity on the capacity for carbon accumulation in B. vulgaris occurs primarily through reduction in the area of photosynthetic surface.