Control of C4 photosynthesis: effects of reduced activities of phosphoenolpyruvate carboxylase on CO2 assimilation in Amaranthus edulis L.

Heterozygous mutants of Amaranthus edulis deficient in PEP carboxylase (PEPC) have been used to study the control of photosynthetic carbon assimilation. A reduction in PEPC activity led to a decrease in the initial slope of the relationship between the CO2 assimilation rate and the intercellular CO2 concentration and to a decrease in photosynthesis at high light intensities, consistent with a decrease in the capacity of the C4 cycle in high light. PEPC exerted appreciable control on photosynthetic flux in the wild-type, with a relatively high flux control coefficient of 0.35 in saturating light and ambient CO2. The flux control coefficient was decreased in low light or increased in low CO2 or in plants containing lower PEPC activity. However, the rate of CO2 assimilation decreased down to about 55% PEPC, followed by an up-turn in the light-saturated photosynthetic rate as PEPC was further reduced, suggesting the existence of a mechanism that compensates for the loss of PEPC activity. The amounts of photosynthetic metabolites, including glycine and serine, also showed a biphasic response to decreasing PEPC. There was a linear relationship between the activity of PEPC and the activation state of the enzyme. A possible mechanism of compensation involving photorespiratory intermediates is discussed.

Intrapartum prediction of birth weight: clinical versus sonographic estimation based on femur length alone.

OBJECTIVE: To determine the relative accuracy of predicting birth weight by clinical estimate versus sonographic mensuration of femur length (FL) alone. METHODS: Two hundred pregnant women at term and in early labor had the weight of their fetuses estimated by clinical and sonographic methods. RESULTS: Clinical assessment of birth weight had a significantly lower mean standardized absolute error (90.6 g/kg) than sonographic estimate based on FL alone (106.7 g/kg) (P < .05). Clinical estimates were significantly more often within 5% (35%) of actual birth weight than were those derived sonographically (29%) (P = .005). CONCLUSION: Using FL alone to predict birth weight has no advantage over a clinical estimate among term patients in labor.

Intrapartum clinical, sonographic, and parous patients' estimates of newborn birth weight.

The accuracy of estimating birth weight clinically, sonographically (using femur length and abdominal circumference), and by maternal prediction was studied prospectively in 106 term parous women who were in active labor. Estimates of birth weight by these women had lower standardized error (86.8 +/- 78.0 g/kg) than either clinical estimates (90.2 +/- 84.8 g/kg) or sonographically derived estimates (155.8 +/- 118.0 g/kg) of birth weight (P = not significant). Maternal estimates of birth weight were within +/- 10% of the actual weight in 69.8%, compared with 66.1% for clinical estimates and 42.4% for sonography. A term parous woman in labor can predict the birth weight with accuracy comparable to a clinical estimation by a physician or a sonographic estimate based on infant measurements.

Changes in fluorescence quenching brought about by feeding dithiothreitol to illuminated leaves.

When CO(2) is abruptly removed from the atmosphere surrounding an illuminated leaf, the primary electron-accepting plastoquinone of photosystem II (Q(A)) (as measured by photochemical quenching, q(p)) is rapidly reduced and then, after some seconds, becomes more oxidized. The reoxidation of Q(A) (-) is accompanied by an increase in DeltapH (as measured by nonphotochemical quenching, q(N)) with kinetics consistent with a causal relationship. The fact that, in such circumstances, Q(A) can become more oxidized in the absence of CO(2) than in its presence indicates a diminished rate of reduction of Q(A), consequent upon impaired photosystem II efficacy. Dithiothreitol (DTT) feeding, which does not affect quantum yield or the maximum rate of photosynthesis, inhibits the reoxidation of Q(A) (-) but not the increase in the proton gradient. When leaves are reilluminated in high light following a dark interval of several minutes, DTT also abolishes the separation in time between the first maximum in q(P) and the first maximum in the rate of O(2) evolution. It also diminishes subsequent oscillations. These results are held to demonstrate DeltapH control of photosystem II and are consistent with DTT inhibition of the xanthophyll cycle and hydrogen peroxide reduction. They support the concept that oxygen and hydrogen peroxide are involved, as Hill oxidants, in a pH-related manner, during oscillatory behavior.

Diurnal progesterone rhythms in the female mouse.

The patterns of peripheral progesterone concentrations were investigated in a number of murine models on a 13 h light: 11 h darkness lighting regime. The pattern in the intact mouse at dioestrus was compared with that in the ovariectomized mouse. A diurnal pattern was recorded in both, maxima occurring around the end of the light period; no conspicuous nadir was recorded, levels of progesterone remaining relatively constant over a 14-h period. Adrenalectomized mice displayed no such rhythm, indicating that the adrenal is responsible for any diurnal rhythm in peripheral plasma progesterone concentrations at dioestrus. At pro-oestrus in intact animals a similar rhythm was observed, but the maximum levels of progesterone were approximately five times greater than at dioestrus and, moreover, persisted in adrenalectomized mice, indicating that the rhythm of adrenal secretion of progesterone is masked by ovarian secretion. Ovariectomized mice with implants of oestradiol-17 beta displayed a similar rhythm to that of intact mice at dioestrus, but had significantly higher plasma progesterone levels around the time of the maxima although not over the total 24-h period. An s.c. injection of oestradiol benzoate superimposed on oestrogen levels produced by implants had no significant effect on plasma progesterone levels. Also at pro-oestrus the pattern of peripheral LH concentration was investigated in both the intact and the adrenalectomized mouse. For both, maxima were recorded just before darkness, at 19.00 h, in advance of the progesterone surge. In adrenalectomized mice this surge at 19.00 h was attenuated. The possible role of adrenal progesterone in ovulation and the mechanisms by which endogenous oestrogens might enhance adrenal progesterone output are considered.

Observations on the effects of vibration and noise on plasma ACTH and zinc levels, pregnancy and respiration rate in the guineapig.

The responses of female guineapigs to vibration and noise were examined with the use of an apparatus designed to simulate transport. Peak levels of plasma ACTH and zinc concentrations were attained after 4 min of exposure to vibration and 80-90 dB of noise. The respiration rate, normally around 90/min, was increased to 103/min when the animals were moved (while still in their cages) to the experimental area; it rose to 129/min when the apparatus was switched on to expose the animals to vibration and noise. Those left adjacent to the apparatus and exposed to noise alone elevated their respiration rates to 115/min. Respiration rates returned to normal within 2.5 h. There was no apparent effect on the maintenance of pregnancy, gestation length, litter size or post-partum growth of the young born to guineapigs exposed to this vibration and noise for a period of 1 h at mid-term.

An analysis of some behavioural effects of the vibration and noise components of transport in pigs.

The reactions of pigs to the vibration and noise components of transport were examined with the use of an apparatus which simulated these factors. The pigs were trained to switch off the apparatus by pressing a switch panel with their snouts. It was found that vibration was aversive but that noise was not. The pigs switched off the apparatus more frequently when the vibration was fast and when they had been fed a large meal before the test. Although the sedative tranquillizing drug azaperone decreased the number of times the apparatus was switched off, the effect appeared to be non-specific because azaperone also reduced the number of responses that pigs would make in order to receive food.