Biomedical subjects

D Appleman

Publications and source records attributed to D Appleman.

11 recordsLinked to original sources

PubMed1990

Younger and older adolescents' thinking about commitments.

One hundred and sixty-three adolescents listed factors they consider or would consider when choosing a career and a romantic partner, and defined "commitment" in an open-ended essay. Male and female ninth graders, twelfth graders, and college juniors, from public and private schools served as subjects. Gender, grade, and type of school differences were found in the types and number of different types of factors listed for the above commitments, but not in the number of factors listed. Conceptions of the nature of commitment became more complex with grade, and differed as a function of gender and of type of school. Females listed more "internal" factors than did males for romantic commitments. Males described commitment more contractually, women more affectively. Older students focused more upon long-term and internal concerns, and defined "commitment" more in terms of cognitive processing and emotional attachment than younger students. Implications for related areas of work are discussed.

Adolescent↗

PubMed1971

Chlorophyll synthesis in chlorella: regulation by degree of light limitation of growth.

The degree of light limitation of growth is the primary controlling factor of chlorophyll synthesis during photoautotrophic growth of Chlorella. The chlorophyll content of the cells increases when light is limiting for growth as occurs in dense cultures, or in cultures under low incident light, or when the light is used less efficiently through partial inhibition of photosynthesis by 3-(p-chlorophenyl)-1, 1-dimethylurea. The chlorophyll content decreases when light is not limiting for growth, as occurs in cells in high light intensity and in dilute suspensions. The initial lag in rate of chlorophyll synthesis in a freshly inoculated culture can be attributed to light at first not being growth limiting, and then becoming growth limiting as the cell suspension becomes denser. Continuous culture experiments support the above conclusions by showing that under steady state conditions the chlorophyll content is inversely related to the relative available light.

Journal Article↗

PubMed1966

Correlation of alpha-Linolenate to Photosynthetic O(2) Production in Chlorella.

Photosynthetic oxygen evolution per milligram of chlorophyll in Chlorella vulgaris varies with the age of the culture. The rate of oxygen evolution is low in the starting cells, it rises to a maximum after 24 hours of growth and then declines to the initial low value after 72 to 90 hours. These changes in photosynthetic competence of chlorophyll in Chlorella are paralleled by changes in alpha-linolenate per milligram of chlorophyll. In general the magnitude of the photosynthetic competence of chlorophyll is directly proportional to the magnitude of the ratio of alpha-linolenate to chlorophyll, regardless of whether high ratios are due to high alpha-linolenates or low chlorophyll values. This relationship holds when the cultures are grown either under continuous or intermittent illumination.

Journal Article↗

PubMed1966

Chlorophyll synthesis in chlorella I. Occurrence of a lag phase on initiation of a dilute culture.

A culture of Chlorella established by 30-fold dilution of a culture already grown to a level of 15 ml packed cell volume per liter produces little chlorophyll for approximately 12 hours. Investigation of other characteristics such as nitrogen incorporation, increase in packed cell volume and dry weight as well as RNA level show all of these to increase without any significant lag. alpha-Linolenate, which can be considered as a chloroplast marker, increased markedly. Photosynthetic oxygen evolution and respiration as well as the heme enzyme, catalase, increase also, indicating that the lag in chlorophyll synthesis is not due to a general inability to produce the porphyrin moiety.The lag period was demonstrated not to be related to a deficiency of culture elements nor to inhibitors produced. Neither was there a need for a conditioning period of the medium.It is concluded that the lag in chlorophyll synthesis is unique and that the reasons for it are related to the response of the cells to environmental conditions following dilution.

Journal Article↗

PubMed1966

Chlorophyll Synthesis in Chlorella II. Effect of Glucose and Light Intensity on the Lag Phase.

Dense cultures of Chlorella grown under our conditions contain large amounts of chlorophyll on a packed cell basis. Upon dilution the cells are, in effect, put into an environment in which light is not limiting and chlorophyll seemingly in excess (at least temporarily). Thus it is not economical for the cell to produce more chlorophyll until it is the limiting factor. It is our contention that the cell may sense this situation by the piling up of products such as glucose or starch. The observed light intensity effect which causes a stimulation of chlorophyll production at lowered intensities is analogous to that previously reported by others and is felt to be related to the rate of photosynthate production.Chlorophyll synthesis commences after a period of about 12 hours. Once it has become established, added substrate or light have a smaller effect. At 36 hours addition of glucose stimulates growth markedly but chlorophyll production continues at the control rate. This suggests that the effect of substrate is not upon the action of an enzyme involved in the actual synthesis of the chlorophyll molecule. Glucose has been known to influence production of certain enzymes involved usually in substrate catabolism. It is quite possible that the role of glucose here is quite similar. The data are consistent with such an explanation. The substrate would have to influence the production of an enzyme in the magnesium branch of the biosynthetic pathway of porphyrin compounds and not in the portion common to both iron and magnesium porphyrins. Accordingly the lag period is viewed as both an inhibitory period as well as a preparatory period for subsequent chlorophyll synthesis.

Journal Article↗

PubMed1965