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Biomedical subjects

J E Pallas

Publications and source records attributed to J E Pallas.

16 recordsLinked to original sources
PubMed1982

Inhibition of photosynthesis by ethylene-a stomatal effect.

Ethylene at hormonally significant levels inhibited net photosynthesis of the cultivated peanut (Arachis hypogaea L.) as measured by gas analysis. Upon the removal of ethylene, the inhibition was naturally overcome at the concentration-exposure duration combinations tested. Increased length of exposure of 1 microliter of ethylene per liter of air up to 6 hours increased the degree of net photosynthesis inhibition (68% reduction after 6-hour exposure). Significantly greater inhibition of photosynthesis by ethylene was detected on peanut genotypes having higher photosynthetic efficiency. In contrast to peanut, hormonal concentrations of ethylene only moderately inhibited sweet potato, Jerusalem artichoke, and sunflower photosynthesis and was without effect on beans, peas, Irish potato, Mimosa pudica, and white clover. No inhibition could be found by ethylene on ribulose 1,5-biphosphate carboxylase activity in vitro. Photosynthesis was lowered at all CO(2) concentrations below ambient at an O(2) concentration of 1.5%, indicating that the action of ethylene was not affected by low O(2); concomitantly, an increase in the CO(2) compensation point occurred. Diffusion resistance measurements of leaf water vapor loss made on ethylene-treated peanut leaves showed a measurable decrease in leaf conductance which correlated with net photosynthesis decrease. Ethylene influenced the conductance of abaxial stomata more so than adaxial.

Journal Article↗
PubMed1980

An apparent anomaly in peanut leaf conductance.

Conductance to gaseous transfer is normally considered to be greater from the abaxial than from the adaxial side of a leaf. Measurements of the conductance to water vapor of peanut leaves (Arachis hypogaea L.) under well watered and stress conditions in a controlled environment, however, indicated a 2-fold higher conductance from the adaxial side of the leaf than from the abaxial. Studies of conductance as light level was varied showed an increase in conductance from either surface with increasing light level, but conductance was always greater from the adaxial surface at any given light level. In contrast, measurements of soybean (Glycine max [L.] Merr.) and snapbean (Phaseolus vulgaris L.) leaf conductance showed an approximate 2-fold greater conductance from the abaxial surface than from the adaxial. Approximately the same number of stomata were present on both peanut leaf surfaces and stomatal size was similar. Electron microscopic examination of peanut leaves did not reveal any major structural differences between stomata on the two surfaces that would account for the differences in conductance. Light microscope studies of leaf sections revealed an extensive network of bundle sheaths with achloraplastic bundle sheath extensions; the lower epidermis was lined with a single layer of large achloraplastic parenchyma cells. Measurements of net photosynthesis made on upper and lower leaf surfaces collectively and individually indicated that two-thirds of the peanut leaf's total net photosynthesis can be attributed to diffusion of CO(2) through the adaxial leaf surface. Possibly the high photosynthetic efficiency of peanut cultivars as compared with certain other C(3) species is associated with the greater conductance of CO(2) through their upper leaf surfaces.

Journal Article↗
PubMed1976

Effects of thermoradiation on bacteria.

A 60Co source was used to determine the effects of thermoradiation on Achromobacter aquamarinus, Staphylococcus aureus, and vegetative and spore cells of Bacillus subtilis var. globigii. The rate of inactivation of these cultures, except vegetative-cell populations of B. subtilis, was exponential and in direct proportion to temperature. The D10 (dose that inactivates 90% of the microbial population) value for A. aquamarinus was 8.0 Krad at 25 degrees C and 4.9 Krad at 35 degrees C. For S. aureus, D10 was 9.8 and 5.3 Krad at 35 and 45 degrees C, respectively. Vegetative cells of B. subtilis demonstrated a rapid initial inactivation followed by a steady but decreased exponential rate. The D10 at 25 degrees C was 10.3 Krad, but at 35 and 45 degrees C this value was 6.2 and 3.8 Krad, respectively. Between 0 and 95 Krad, survival curves for B. subtilis spores at 75 degrees C showed slight inactivation, increasing in rat at and above 85 degrees C. The D10 values for spores at 85 and 90 degrees C were 129 and 92 Krad, respectively. Significant synergism between heat and irradiation was noted at 35 degrees C for A. aquamarinus and 45 degrees C for S. aureus. The presence of 0.1 mM cysteine in suspending media afforded protection to both cultures at these critical temperatures. On the other hand, cysteine sensitized B. subtilis spores at radiation doses greater than 100 Krad. The combined effect of heat and irradiation was more destructive to bacteria than either method alone.

Alcaligenes↗
PubMed1974

Endogenous rhythmic activity of photosynthesis, transpiration, dark respiration, and carbon dioxide compensation point of peanut leaves.

At 14-hour day length, 25 C leaf temperature, 9 mm Hg vapor-pressure deficit, and 1.17 joules cm(-2) min(-1) irradiance, the diurnal change in daily photosynthesis of the cultivated peanut (Arachis hypogaea L.) is a result of an endogenously controlled circadian rhythm in net photosynthesis which peaks near noon and troughs near midnight. By resetting the day-night light regime, the rhythm rephased in continuous light. The free-running rhythm approximates 26 hours. Both transpiration and dark respiration show similar rhythmicity, with transpiration closely in phase with the rhythm in photosynthesis. The rhythm in carbon dioxide compensation point is approximately 12 hours out of phase, peaking at midnight and troughing at midday. Endogenous changes in stomatal aperture seemed to be the major control of the rhythm in photosynthesis. The activity of ribulose-1,5-diphosphate carboxylase increased during the normal photoperiod, leveling off after 12 hours; however, the activity was not correlated with the rhythmic change in photosynthesis.

Journal Article↗
PubMed1973

Organic Acid Changes in the Epidermis of Vicia faba and Their Implication in Stomatal Movement.

Considerable evidence indicates that the increase in guard cell turgor resulting in stomatal opening is brought about by active K(+) uptake into guard cells. Only a small increase in inorganic anions appears to accompany the increase in K(+). A plausible explanation is that organic acids are produced within guard cells and act as counterions, whereas the H(+) produced are exchanged for K(+).This hypothesis was tested by using different levels of ambient CO(2) in light to control stomatal aperture and at the same time measure changes in organic acid production in the epidermis of Vicia faba. Epidermal strips were used, quickly frozen in liquid nitrogen, and later extracted.A positive correlation was found between stomatal resistance (r(s), indirect measure of stomatal aperture) and CO(2) level. With decreases in r(s), total titratable acidity increased. The organic acids, glyceric, malic, and citric, in the epidermis, as measured by gas chromatography of trimethylsilyl derivatives, increased. Changes in glucose or sucrose were not found. These analyses provided evidence that organic acid production in the epidermis is associated with stomatal opening.

Journal Article↗
PubMed1973

Carbon dioxide metabolism in leaf epidermal tissue.

A number of plant species were surveyed to obtain pure leaf epidermal tissue in quantity. Commelina communis L. and Tulipa gesnariana L. (tulip) were chosen for further work. Chlorophyll a/b ratios of epidermal tissues were 2.41 and 2.45 for C. communis and tulip, respectively. Phosphoenolpyruvate carboxylase, ribulose-1,5-diphosphate carboxylase, malic enzyme, and NAD(+) and NADP(+) malate dehydrogenases were assayed with epidermal tissue and leaf tissue minus epidermal tissue. In both species, there was less ribulose 1,5-diphosphate than phosphoenolpyruvate carboxylase activity in epidermal tissue whether expressed on a protein or chlorophyll basis whereas the reverse was true for leaf tissue minus epidermal tissue. In both species, malic enzyme activities were higher in epidermal tissue than in the remaining leaf tissue when expressed on a protein or chlorophyll basis. In both species, NAD(+) and NADP(+) malate dehydrogenase activities were higher in the epidermal tissue when expressed on a chlorophyll basis; however, on a protein basis, the converse was true. Microautoradiography of C. communis epidermis and histochemical tests for keto acids suggested that CO(2) fixation occurred predominantly in the guard cells. The significance and possible location of the enzymes are discussed in relation to guard cell metabolism.

Journal Article↗
PubMed1972

A Re-evaluation of Soybean Leaf Photorespiration.

Recalculations of soybean photorespiration indicate that mean rates are closer to 16.1 than 5.6 milligrams of CO(2) per square decimeter per hour as previously reported. Photorespiration of soybean thus amounts to at least a 30% carbon turnover of light-saturated photosynthesis. Photorespiration showed no significant relationship to net photosynthesis. Negative correlations were found between CO(2) efflux and stomatal resistance as well as between corrected photorespiration and residual intracellular resistance of the leaf to CO(2) uptake.

Journal Article↗
PubMed1967

Photosynthesis, Transpiration, Leaf Temperature, and Stomatal Activity of Cotton Plants under Varying Water Potentials.

Cotton plants, Gossypium hirsutum L. were grown in a growth room under incident radiation levels of 65, 35, and 17 Langleys per hour to determine the effects of vapor pressure deficits (VPD's) of 2, 9, and 17 mm Hg at high soil water potential, and the effects of decreasing soil water potential and reirrigation on transpiration, leaf temperature, stomatal activity, photosynthesis, and respiration at a VPD of 9 mm Hg.Transpiration was positively correlated with radiation level, air VPD and soil water potential. Reirrigation following stress led to slow recovery, which may be related to root damage occurring during stress. Leaf water potential decreased with, but not as fast as, soil water potential.Leaf temperature was usually positively correlated with light intensity and negatively correlated with transpiration, air VPD, and soil water. At high soil water, leaf temperatures ranged from a fraction of 1 to a few degrees above ambient, except at medium and low light and a VPD of 19 mm Hg when they were slightly below ambient, probably because of increased transpirational cooling. During low soil water leaf temperatures as high as 3.4 degrees above ambient were recorded. Reirrigation reduced leaf temperature before appreciably increasing transpiration. The upper leaf surface tended to be warmer than the lower at the beginning of the day and when soil water was adequate; otherwise there was little difference or the lower surface was warmer. This pattern seemed to reflect transpiration cooling and leaf position effects.Although stomata were more numerous in the lower than the upper epidermis, most of the time a greater percentage of the upper were open. With sufficient soil water present, stomata opened with light and closed with darkness. Fewer stomata opened under low than high light intensity and under even moderate, as compared with high soil water. It required several days following reirrigation for stomata to regain original activity levels.Apparent photosynthesis of cotton leaves occasionally oscillated with variable amplitude and frequency. When soil water was adequate, photosynthesis was nearly proportional to light intensity, with some indication of higher rates at higher VPD's. As soil water decreased, photosynthesis first increased and then markedly decreased. Following reirrigation, photosynthesis rapidly recovered.Respiration was slowed moderately by decreasing soil water but increased before watering. Respiration slowed with increasing leaf age only on leaves that were previously under high light intensity.

Journal Article↗