Turnover of mitochondrial inner membrane proteins in hepatoma monolayer cultures

The degradation rates of inner mitochondrial membrane proteins were examined in serum-deprived hepatoma cultures. In those nonproliferating cells, the degradation of composite mitochondrial proteins was a first order process with a half-life of 34 h. The half-lives of specific inner mitochondrial membrane polypeptides were determined by examining the 3H/35S of isolated polypeptides from cells given [3H]methionine and [35S]methionine pulses, respectively, before and after a 2-day chase period. The 33 most abundant polypeptides resolved on a bidirectional polyacrylamide gel system showed half-lives ranging from 20 to 100+ h. The 15 polypeptides translated on mitochondrial ribosomes in the presence of inhibitory concentrations of cycloheximide also displayed heterogeneous rates of degradation (t1/2 = 35-100+ h). None of the isolated adenosine triphosphatase (coupling factor F1) or immunoprecipitated cytochrome c oxidase subunits were significantly turned over during the case period. Five of eight cytochrome b-c1 complex subunits, however, were turned over significantly more rapidly (t1/2 = 39-42 h) than the other three (t1/2 = 94+ h). The results demonstrate heterogeneous degradation rates for inner membrane polypeptides, extending in some cases to those within the same respiratory complex.     

Pollinator flight directionality and the assessment of pollen returns

Summary Nectar-foraging pollinators often exhibit a directional pattern of movement between plants when the energetic costs of revisiting previously utilized areas can significantly reduce foraging efficiency. However, bumblebees (Bombus spp.) foraging for pollen on flowers of Aquilegia caerulea rarely moved in a straight line among successively visited plants. Most flights from plants visited were either to closely neighboring plants or were longer and involved bypassing near neighbor plants. Bees biased their flights toward plants with relatively large numbers of flowers yet visited only a small fraction of the flowers on each plant. Such foraging tactics might result when the energetic costs of revisiting plants are minor. Alternatively we suggest that bumblebees foraging for pollen may not perceive revisitations and their associated costs because they do not assess pollen returns on a per plant basis. In this case energetic-efficiency arguments predicting the pattern of foraging movements among plants may be inappropriate. A better level of analysis would be where the bees assess net energy returns, perhaps between bouts of pollen-combing and corbiculae-packing.     

Sugar Composition of Nectars and Fruits Consumed by Birds and Bats in the Tropics and Subtropics1

Several characteristics of flowers and fruits have been suggested as comprising syndromes of characters that indicate particular classes of pollinators and fruit dispersers. Common phylogenetic history among species, however, may also significantly influence these characters and obscure or enhance perceived patterns of plant syndromes. We analyzed the proportions of glucose, fructose, and sucrose by paper chromatography in the nectar and fruit juice of 525 tropical and subtropical plant species to test whether sugar chemistry was correlated with volant vertebrate pollinator or fruit disperser classes. Samples were taken from Old World and New World species and the calculations kept separate. Kruskal-Wallis tests of family means showed significant deviations in the percent sucrose content among pollinatorl disperser classes. Mann-Whitney U-tests showed significant differences among nectars of all pollinator classes but fruit juices differed only due to the high sucrose content of megachiropteran dispersed fruits. In addition, sign tests of samples occurring within families showed significant correlations between percentage sucrose content and pollinator/disperser classes. Passerine nectars had low sucrose content. In striking contrast, the nectar of hummingbird flowers had very high sucrose content. The Microchiroptera nectars showed hexose richness with a sucrose content somewhat greater than that of passerine flowers. Megachiroptera flowers showed sucrose-rich nectars. The results for fruits were comparable to those for nectars. Passerine fruits were hexose dominated, microchiropteran fruits had a sucrose content similar to passerine fruits, and megachiropteran fruits were sucrose-rich. We speculate on the evolutionary sequence of changes in nectar and fruit juice sugar composition and suggest that future investigations consider the chemistry of other food sources such as pollen and leaves. Only with these additions and other ecological studies can the full interplay of such plant-animal interactions be anticipated.     

Efficacy of 1,2-Dibromo-3-chloropropane for Control of Meloidogyne javanica as Influenced by Concentration,Exposure Time and Rate of Degradation

Laboratory experiments were conducted by applying 1,2-dibromo-3-chloropropane (DBCP) to sealed vials of soil infested with Meloidogyne javanica. A minimum initial concentration of 0.25 μg of DBCP/g of oven-dry soil killed all nematodes within 35 days. A concentration of 1.0 μg/g killed all nematodes within 28 days. The rate of degradation of this chemical was determined by treatment of steamed and nonsteamed dry soil in open and sealed vials. Extraction of tile chemical, followed by quantification by gas chromatography, showed approximately 100% of the amount applied recovered after 14 days in sealed vials without soil. With soil present, approximately 10% of the amount of chemical applied was recovered.     

Analysis of chlorophyll fluorescence quenching by DBMIB as a means of investigating the consequences of thylakoid membrane phosphorylation

The effect of Mg²⁺ concentration and phosphorylation of the light harvesting chlorophyll $\text{a}\text{b}$ protein on the ability of DBMIB to quench chlorophyll fluorescence of isolated pea thylakoids has been studied. Over a wide range of Mg²⁺ concentrations (5?0.33 mM), the observed changes in fluorescence yield are mirrored by similar changes in the quenching ability of DBMIB, indicating that the cation-induced phenomenon involves alterations in radiative lifetimes. In contrast, phosphorylation at 10 mM Mg²⁺ brings about a lowering of the chlorophyll fluorescence yield, while having no effect on the quenching capacity of DBMIB. This result can be interpreted as a phosphorylation-induced decrease in PS II absorption cross-section. At Mg²⁺ levels between 5 and 1 mM, phosphorylation leads to a change in the quenching of fluorescence by DBMIB, when compared with non-phosphorylated thylakoids. At these cation levels, the degree of DBMIB-induced quenching cannot wholly account for the observed changes in chlorophyll fluorescence due to phosphorylation. It is concluded that the phosphorylation- and Mg²⁺-induced changes in fluorescence yield are independent but inter-related processes which involve surface charge screening as emphasised by the change in cation sensitivity of the DBMIB quenching before and after phosphorylation.     

Monitoring ovarian function in marmosets and tamarins by the measurement of urinary estrogen metabolites

Practical aspects of urinary estrogen analysis were considered with regard to establishing simple and reliable methods for monitoring ovarian function in marmosets and tamarins. Changes in the hormone:creatinine ratio in small volumes of urine from the common marmoset were significantly correlated with changes in 24-h excretion. Comparison of the metabolism and excretion of estrogens during the ovarian cycle in the common marmoset and cottontop tamarin revealed interesting species differences. High concentrations of conjugated estrone were measured in marmoset plasma, but estradiol 17β was the predominant estrogen in urine. In contrast, estrone was the most abundant estrogen measured in tamarin urine. Both species excreted very little estriol. Sulfates and glucuronides were present in urine in similar proportions before ovulation in the marmoset, although after ovulation sulfates were the more abundant. Conversely, most of the estrogens in tamarin urine appeared to be conjugated as glucuronides. Direct assay for estrone sulfate was applied to the measurement of urinary estrogen excretion during the ovarian cycle in a marmoset. The results compared well with those for total estradiol 17β after hydrolysis and ether extraction. The use of direct assays for conjugated estrogens in small volumes of urine is suggested as a practical method for monitoring ovarian function in marmosets and tamarins.     

Reversible,long-term inhibition of ovulation with a gonadotropin-releasing hormone antagonist in the marmoset monkey (Callithrix jacchus)

The effects of weekly injections of a gonadotropin-releasing hormone (GnRH) antagonist (GnRHa) ([N-acetyl-DβNal1-D-pCl-Phe2-D-Phe3-D-Arg6-Phe7-Arg8D-Ala10] NH2 GnRH) on pituitary and ovarian function were examined in the marmoset monkey, Callithrix jacchus. In experiment 1, five cyclic females were given weekly injections of vehicle (50% propylene glycol in saline) for 6 weeks followed by GnRHa for 20 weeks, animals receiving either 200 μg GnRHa/injection (n = 2) or 67 μg GnRHa/injection (n = 3) for 10 weeks, after which the treatment was reversed. Bioactive luteinizing hormone (LH) and progesterone (Po) were measured in blood samples (0.2–0.4 ml) collected twice weekly until at least 8 weeks after the last GnRHa injection. GnRHa treatment, timed to begin in the midluteal phase, caused a rapid decline in LH and Po and luteal regression after a single injection (both doses). Po levels were consistently low (<10 ng/ml), and ovulation was inhibited throughout 200 μg treatment in all animals. Short periods of elevated Po (>10 ng/ml) were, however, occasionally seen during 67 μg treatment, indicating incomplete ovarian suppression. Mean LH levels were significantly lower during GnRHa treatment compared with the period of vehicle injection (all animals 200 μg; three animals 67 μg), and there were significant differences in LH levels between GnRHa treatments (200 μg vs. 67 μg) in four animals. Four animals resumed normal ovarian cycles after the end of GnRHa treatment (15/16 days, three animals; 59 days, one animal); the fifth animal died of unknown causes 32 days after the last GnRHa injection. In a second experiment, pituitary responsiveness to exogenous GnRH was tested 1 day after a single injection of vehicle or antagonist (200 or 67 μg). Measurement of bioactive LH indicated that pituitary response to 200 ng native GnRH was significantly suppressed in animals receiving the antagonist, the degree of suppression being dose related. A third experiment examined the effect of four weekly injections of 200 μg GnRHa on follicular size and granulosa cell responsiveness to human follicle-stimulating hormone (hFSH) in vitro. Follicular development beyond 1 mm was inhibited by GnRHa treatment (preovulatory follicles normally 2-4 mm) although granulosa cell responsiveness to FSH during 48 hr of culture was not impaired. These results suggest that the GnRHa-induced suppression of follicular development and ovulation was mediated primarily by an inhibition of pituitary gonadotropin secretion and not by a direct action at the level of the ovary.