Biomedical subjects

L Kunst

Publications and source records attributed to L Kunst.

25 records · Page 2Linked to original sources

PubMed1989

A mutant of Arabidopsis deficient in desaturation of palmitic Acid in leaf lipids.

The overall fatty acid composition of leaf lipids in a mutant of Arabidopsis thaliana was characterized by elevated amounts of palmitic acid and a decreased amount of unsaturated 16-carbon fatty acids as a consequence of a single nuclear mutation. Quantitative analysis of the fatty acid composition of individual lipids suggested that the mutant is deficient in the activity of a chloroplast omega9 fatty acid desaturase which normally introduces a double bond in 16-carbon acyl chains esterified to monogalactosyldiacylglycerol (MGD). The mutant exhibited an increased ratio of 18- to 16-carbon fatty acids in MGD due to a change in the relative contribution of the prokaryotic and eukaryotic pathways of lipid biosynthesis. This appears to be a regulated response to the loss of chloroplast omega9 desaturase and presumably reflects a requirement for polyunsaturated fatty acids for the normal assembly of chloroplast membranes. The reduction in mass of prokaryotic MGD species involved both a reduction in synthesis of MGD by the prokaryotic pathway and increased turnover of MGD molecular species which contain 16:0.

Journal Article↗

PubMed1989

Enhanced thermal tolerance in a mutant of Arabidopsis deficient in palmitic Acid unsaturation.

A mutant of Arabidopsis thaliana, deficient in the activity of a chloroplast omega9 fatty acid desaturase, accumulates high amounts of palmitic acid (16:0), and exhibits an overall reduction in the level of unsaturation of chloroplast lipids. Under standard conditions the altered membrane lipid composition had only minor effects on growth rate of the mutant, net photosynthetic CO(2) fixation, photosynthetic electron transport, or chloroplast ultrastructure. Similarly, fluorescence polarization measurements indicated that the fluidity of the membranes was not significantly different in the mutant and the wild type. However, at temperatures above 28 degrees C, the mutant grew more rapidly than the wild type suggesting that the altered fatty acid composition enhanced the thermal tolerance of the mutant. Similarly, the chloroplast membranes of the mutant were more resistant than wild type to thermal inactivation of photosynthetic electron transport. These observations lend support to previous suggestions that chloroplast membrane lipid composition may be an important component of the thermal acclimation response observed in many plant species which are photosynthetically active during periods of seasonally variable temperature extremes.

Journal Article↗

PubMed1988

Altered regulation of lipid biosynthesis in a mutant of Arabidopsis deficient in chloroplast glycerol-3-phosphate acyltransferase activity.

The leaf membrane lipids of many plant species, including Arabidopsis thaliana (L.) Heynh., are synthesized by two complementary pathways that are associated with the chloroplast and the endoplasmic reticulum. By screening directly for alterations in lipid acyl-group composition, we have identified several mutants of Arabidopsis that lack the plastid pathway because of a deficiency in activity of the first enzyme in the plastid pathway of glycerolipid synthesis, acyl-ACP:sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) (where ACP is acyl carrier protein). The lesion results in an increased synthesis of lipids by the cytoplasmic pathway that largely compensates for the loss of the plastid pathway and provides nearly normal amounts of all the lipids required for chloroplast biogenesis. However, the fatty acid composition of the leaf membrane lipids of the mutants is altered because the acyltransferases associated with the two pathways normally exhibit different substrate specificities. The remarkable flexibility of the system provides an insight into the nature of the regulatory mechanisms that allocate lipids for membrane biogenesis.

Journal Article↗

PubMed1987

The effects of reduced amounts of lipid unsaturation on chloroplast ultrastructure and photosynthesis in a mutant of Arabidopsis.

A mutant of Arabidopsis thaliana with reduced content of C(18:3) and C(16:3) fatty acids in membrane lipids exhibited a 45% reduction in the cross-sectional area of chloroplasts and had a decrease of similar magnitude in the amount of chloroplast lamellar membranes. The reduction in chloroplast size was partially compensated by a 45% increase in the number of chloroplasts per cell in the mutant. When expressed on a chlorophyll basis the rates of CO(2)-fixation and photosynthetic electron transport were not affected by these changes. Fluorescence polarization measurements indicated that the fluidity of the thylakoid membranes was not significantly altered by the mutation. Similarly, on the basis of temperature-induced fluorescence yield enhancement measurements, there was no significant effect on the thermal stability of chlorophyll-protein complexes in the mutant. These observations suggest that the high content of trienoic fatty acids in chloroplast lipids may be an important factor regulating organelle biogenesis but is not required to support normal levels of the photosynthetic activities associated with the thylakoid membranes.

Journal Article↗

PubMed1985

Quantitative correlative proton and electron microprobe analysis of biological specimens.

To investigate the possibility of quantitative correlative proton microprobe (PMP) and electron microprobe (EMP) analysis of biological soft tissue, model specimens were analyzed by both techniques. The specimens consisted of freeze-dried sections of gelatin containing known concentrations of nickel chloride. Both for PMP and for EMP, the signal was expressed as the ratio of the characteristic intensity and the continuum intensity in a peak-free region of the spectrum. With both techniques, calibration curves (signal versus known concentration) obtained, showed a deviation from linearity at high nickel concentrations. However, a linear relation (correlation coefficient 0.996) was obtained in a plot of EMP signal versus PMP signal. This indicates that quantitative correlative PMP and EMP analysis can be carried out by using the same standard for both analytical techniques.

Animals↗

PubMed1984

Formation of Tryptophol Galactoside and an Unknown Tryptophol Ester in Euglena gracilis.

The unicellular alga Euglena gracilis Klebs ;Z' converted exogenous indole-3-ethanol (trytophol) to two major metabolites: tryptophol galactoside and an unknown compound, and to minor amounts of indole-3-acetic acid, tryptophol acetate, and tryptophol glucoside. The unknown was hydrolyzed to tryptophol by methanolic ammonia and should therefore be a tryptophol ester. The galactoside was identified as 2-(indol-3-yl)ethyl-beta-d-galactopyranoside. This structure was established by comparison with an authentic standard involving chromatographic methods, ultraviolet and mass spectroscopy, enzymic and acid hydrolysis, and identification of the galactose in the hydrolysate. By forming tryptophol galactoside, Euglena differs from the higher plants examined so far, for which the corresponding glucoside is the only sugar conjugate of tryptophol detected.

Journal Article↗

PubMed1981

Do pelvic floor exercises really improve orgasmic potential?

Women with orgasmic difficulties are commonly taught pubococcygeal (PC) muscle exercises which, practiced regularly, are said to have both specific and nonspecific beneficial effects on sexual enjoyment. The hypothesis tested was that women practicing these exercises over a 12-week period, would be more likely to become orgasmic than women practicing relaxation exercises, or than women in an attention-control group. Forty-six women were allocated to one of three groups, PC exercise, relaxation or control. PC muscle tone was measured and questionnaires about sexual response were completed over a 12-week period with a 6-month follow-up assessment. Results indicated that there was no difference in orgasmic outcome for the three groups during the experimental period. This was taken to imply that PC exercises are not of specific value for women with normal muscle tone. It remains possible that women with poor muscle tone are helped by the exercises and further research is considered necessary in this area.

Adolescent↗