The Development of the Enzyme Complement in Growing Root Cells

Fifteen serial sections, each 1.0 mm. in length, have been takenfrom the tip towards the base of the bean root. On correspondinggroups of sections determinations have been made of water content,protein content, and of dipeptidase, glycine oxidase, phosphatase,and invertase activities. The number of cells in each sectionof the series has also been determined. From these data unitcell values have been calculated which show how each of thequantities involved changes as the cell grows. It has been shown that four phases are involved in the earlydevelopment of the cell. In the first, which is traversed inthe meristematic zone of the root, the volume increases slightly,the protein content decreases, and the activities of three ofthe enzymes studied also decrease. In the second, volume, proteincontent, and all enzyme activities increase considerably. Inthe third, while the volume enlarges by increase in breadthonly, protein content and enzyme activities decrease. In thefourth, growth has ceased and protein content, and enzyme activitiescontinue to decrease. The significance of these changes in discussed.     

A PROPERTY OF OX MUSCLE AFFECTING BACTERIAL GROWTH AT 0°

SUMMARY: Increases occurring in bacterial populations at 0° were followed on minced preparations of two selected muscles of beef cattle which had been exposed to various treatments before death. In one muscle ( Psoas ), bacterial growth increased with increase in pH while in the other ( Longissimus dorsi ) it decreased with increase in the time elapsing prior to onset of rigor mortis. This second relationship could not be observed in the Longissimus dorsi of cows. The nature of the property responsible for the effects of rigor delay time in the Longissimus dorsi of steers has not yet been established.     

Carbon stored in human settlements: the conterminous United States

Urban areas are home to more than half of the world's people, responsible for >70% of anthropogenic release of carbon dioxide and 76% of wood used for industrial purposes. By 2050 the proportion of the urban population is expected to increase to 70% worldwide. Despite fast rates of change and potential value for mitigation of carbon dioxide emissions, the organic carbon storage in human settlements has not been well quantified. Here, we show that human settlements can store as much carbon per unit area (23–42 kg C m⁻² urban areas and 7–16 kg C m⁻²exurban areas) as tropical forests, which have the highest carbon density of natural ecosystems (4–25 kg C m⁻²). By the year 2000 carbon storage attributed to human settlements of the conterminous United States was 18 Pg of carbon or 10% of its total land carbon storage. Sixty-four percent of this carbon was attributed to soil, 20% to vegetation, 11% to landfills, and 5% to buildings. To offset rising urban emissions of carbon, regional and national governments should consider how to protect or even to increase carbon storage of human-dominated landscapes. Rigorous studies addressing carbon budgets of human settlements and vulnerability of their carbon storage are needed.     

The effects on Arbutus unedo L. of long-term exposure to elevated CO2

Arbutus unedo is a sclerophyllous evergreen, characteristic of Mediterranean coastal scrub vegetation. In Italy, trees of A. unedo have been found close to natural CO₂ vents where the mean atmospheric carbon dioxide concentration is about 2200 μmol mol^?1. Comparisons were made between trees growing in elevated and ambient CO₂ concentrations to test for evidence of adaptation to long-term exposure to elevated CO₂. Leaves formed at elevated CO₂ have a lower stomatal density and stomatal index and higher specific leaf area than those formed at ambient CO₂, but there was no change in carbon to nitrogen ratios of the leaf tissue. Stomatal conductance was lower at elevated CO₂ during rapid growth in the spring. In mid-summer, under drought stress, stomatal closure of all leaves occurred and in the autumn, when stress was relieved, the conductance of leaves at both elevated and ambient CO₂ increased. In the spring, the stomatal conductance of the new flush of leaves at ambient CO₂ was higher than the leaves at elevated CO₂, increasing instantaneous water use efficiency at elevated CO₂. Chlorophyll fluorescence measurements suggested that elevated CO₂ provided some protection against photoinhibition in mid-summer. Analysis of A/C_i curves showed that there was no evidence of either upward or downward regulation of photosynthesis at elevated CO₂. It is therefore anticipated that A. unedo will have higher growth rates as the ambient CO₂ concentrations increase.