The characteristics of light in floral induction in vitro of Cichorium intybus. The possible role of phytochrome

The action of light in the initiation of floral buds in vitro has been studied using monochromatic light qualities on root explants of a long day plant, Cichorium intybus L. cv. Witloof. Red light (660 nm, 0.30 W m^-2) promotes flowering, while far-red (730 nm, 0.31 W m^-2) and irradiation with combined red + far-red (0.20 + 0.41 W m^-2) have no effect. In short day conditions floral response can be obtained in two ways: 1) by interrupting the dark period with 5 brief irradiations of red light (0.45 W m^-2, 12 min) at regular intervals, although these are counteracted by far-red irradiations of equal intensity and duration; 2) by interrupting the long night with 5 h red light applied during the second third of the night, while at the beginning or at the end it is ineffective. Red light efficiency appears to depend on the photosynthetic activity of the tissues, so that flowering increases with increasing intensity of white light and is suppressed if no white light is supplied. The reproductive development is determined by the coordination of proper irradiation conditions with sufficient sensitivity of the perceiving meristematic cells. The period of highest sensitivity to environmental light conditions in the life cycle of a Cichorium root explant occurs between the 8th and the 16th day after the start of the culture. The data strongly suggest that phytochrome is involved in flower induction of Cichorium in vitro.     

Aspects of the numerical and functional respones of the aphid parasite, Aphidius sonchi, in the laboratory

The fecundity, reproductive rates, and adult survival of Aphidius sonchi Marshall (Hymenoptera: Aphidiidae) parasitizing second and third instar nymphs of the sowthistle aphid, Hyperomyzus lactucae (L.) (Homoptera: Aphididae) were measured at six different host densities under constant laboratory conditions. At host densities of less than 50 aphids per flowering shoot per female per day, oviposition constraints resulting from the lack of hosts reduced the number of eggs laid, enhanced the extent of superparasitization and, as a result, effectively lowered the fecundity and reproductive rates of the parasites. Above this host density the parasites laid on average 220–230 eggs, but the effective fecundity and reproductive rates continued to increase with the host density. By contrast, the survivorship of the parasites seemed unaffected by host density, with an average adult life span of 4–5 days at all densities. Analysis of the data showed that the intrinsic rate of increase (r_m) of the parasite varied with the host density and could reach values higher than that of the host under identical conditions. The response of r_m to changes in host density and parasite sex ratio is illustrated.Overall, A. sonchi showed a typical convex functional response, to host density. However, the response showed obvious changes through the parasite's adult life and, furthermore, the rates of changes were not consistent at all host densities. The frequency distributions of parasite eggs were generally indistinguishable from random, and the number of hosts parasitized were predicted satisfactorily by the random oviposition equation.

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Résumé L'étude a porté sure l'influence de 6 densités différentes d'Hyperomyzus lactucae (L.) (Homoptera: Aphididae), en conditions constantes de laboratoire, sur la fécondité, le taux de reproduction et la survie des adultes d'Aphidius sonchi Marshall (Hym. Aphidiidae, parasite des larves de 2e et 3e stades. A des densités inférieures à 50 pucerons par tige fleurie de Sonchus oleraceus L, par femelle et par jour, la limitation de la ponte due à l'absence d'hôtes a réduit le nombre d'oeufs émis, élevé le taux de superparasitisme et, en conséquence, diminué la fécondité et le taux de reproduction des parasites. Aux densités d'hôtes supérieures, les parasites ont pondu, en moyenne, 220 à 230 oeufs, mais la fécondité réelle et les taux de reproduction ont continué à augmenter avec la densité des pucerons. Par contre, la longévité des parasites n'a pas été affectée par la densité des hôtes, avec une durée moyenne de vie de 4 à 6 jours. L'analyse des données a montré que le taux d'accroissement intrinsèque (r_m) du parasite a changé avec la densité des hôtes, et pourrait atteindre des valeurs supérieures à celles de l'ôte sous des conditions identiques. Les réponses de r_m aux changements de densité des hôtes et au taux sexuel du parasite sont expliquées.Globalement, A. sonchi a présenté une réponse fonctionnelle convexe typique à la densité des hôtes. Cependant, cette réponse a changé au cours de la vie des images et, de plus, les taux de changement ne sont pas logiques à toutes les densités d'hôtes La fréquence de distribution des oeufs n'est généralement pas séparable d'une distribution au hasard, et le nombre d'hôtes parasites peut être prédit d'une façon satisfaisante en utilisant une équation de ponte au hasard.

     

Relative efficiency of two mating systems and selection procedures for yield improvement in wheat (Triticum aestivum L.)

Summary The relative efficiences of the biparental mating systems and selfing series in connection with phenotypic and geno-phenotypic selection procedures were evaluated for yield improvement in a cross HP1102 X CPAN 1681 of wheat. Two selection cycles having a 4 per cent selection intensity for grain yield were carried out following both selection procedures under the two mating systems. Following these selection procedures, a greater improvement for grain yield could be achieved with the biparental mating system than with the selfing series. During the first selection cycle, the geno-phenotypic selection procedure had an edge over phenotypic selection procedure. The realized response due to the second cycle of selection and the predicted response for the third selection cycle indicated that the phenotypic selection procedure is more efficient than the geno-phenotypic selection procedure. It is suggested that selection following intermating in early segregating generations is able to overcome several inherent limitations of the simple pedigree method as it is possible to increase genetic variation and to concentrate favourable genes and gene combinations for grain yield. An increase in grain yield was, in general, accompanied by an increase in plant height, peduncle length, 100 grain weight, tiller number and biological yield. Therefore, it is suggested that an index comprised of grain yield, plant height, tiller number, grain weight and biological yield could be used for selecting high yielding genotypes of suitable height.     

Effects of random and non-random errors on phenotypic selection in autotetraploids

Summary A theoretical investigation was made to ascertain the effects of random and non-random deviations, called errors, of phenotypic from genotypic values on population means and on the response to phenotypic recurrent selection. The study was motivated as a selection experiment for disease resistance where there was either variability in the inoculation or environment (the random errors) or where the inoculation was above or below the the optimum rate where genetic differences in resistance are maximized (the non-random errors). The study was limited to the genetics at a diallelic locus (alleles B and b) in an autotetraploid population in random mating equilibrium. The response to selection was measured as the covariance of selection and compared to the exact covariance which was the covariance of selection without errors in phenotype. The random errors were modeled by assuming that a given percentage () of the population was uniformly distributed among the five possible genotype classes independent of their true genotypes. This model was analyzed numerically for a theoretical population with the frequency of the B allele (p) ranging from 0.0 to 1.0 and assumed errors of=0.1 and 0.5 for the following six types of genic action of the B allele: additive, monoplex dominance, partial monoplex dominance, duplex dominance, partial duplex dominance, and recessive. The effect of random error was to consistently reduce the response to selection by a percentage independent of the type of genic action at the locus. The effect on the population mean was an upward bias when p was low and a downward bias when p approached unity. In the non-random error model below optimum inoculations altered the phenotypes by systematically including percentage of susceptible genotypes into one or more other genotype classes with more genetic resistance (a positive shift). With above optimum inoculations, some resistant genotypes are classed with the non-resistant genotypes (a negative shift). The effects on the covariance of selection were found by numerical analysis for the same types of genic action and's as investigated for random error. With a negative shift and a low p, the covariance of selection was always reduced, but for an increasing p the covariance approached and exceeded the exact covariance for all types of genic action except additive. With a positive shift and a low p, response to selection was greatly improved for three types of genic action: duplex dominance, partial duplex dominance, and recessive. The effect of a non-random error on population means was to greatly bias the means upwards for a low p and positive shift, but with increasing p the bias decreased. A relatively slight decrease in the mean occurred with a negative shift. This study indicated check varieties commonly used to monitor selection pressures in screening programs are very responsive to positive non-random shifts, but are relatively unresponsive to negative shifts. The interaction of selection pressure, types of genic action, and genotypes in the class shift models was suggested as a partial explanation for the lack of response to increasing selection pressures observed in some breeding programs.Cooperative investigations of the Alfalfa Production Research Unit, United States Department of Agriculture, Agricultural Research Service, and the Nevada Agricultural Experiment Station, Reno, Nevada. Paper No. 404 Scientific Journal Series. Nevada Agricultural Experiment Station     

α-Mannosidase-1 mutants of Dictyostelium dkoideum: Early aggregation-essential genes regulate enzyme precursor synthesis, modification, and processing

The lysosomal enzyme alpha-mannosidase-1 is one of the earliest developmentally controlled gene products in Dictyostelium discoideum. Although this enzyme is synthesized throughout the first 20 h of development, it is not required for complete morphogenesis, since structural gene (manA) mutants lacking activity develop normally. We isolated six strains deficient in alpha-mannosidase-1 activity which, unlike structural gene mutants, fail to aggregate. Fruiting revertants of these strains accumulate wild-type levels of alpha-mannosidase-1 activity, suggesting that both the enzymatic and morphological defects are caused by single mutations in nonstructural genes essential for early development. Direct genetic evidence for mutations outside of the structural gene was obtained by complementation analysis. We used alpha-mannosidase-1-specific monoclonal antibodies to analyze the biochemical defects in these mad (alpha-mannosidase-1-deficient) mutants. All mad mutants show a significantly reduced relative rate of enzyme precursor biosynthesis. The mad-404 mutation results in a complete lack of precursor biosynthesis, as well as a lack of functional alpha-mannosidase-1 mRNA. In some cases, however, the enzymatic defect results from improper post-translational modification which affects precursor processing. We conclude that a small number of aggregation-essential genes are involved in regulating the synthesis, modification, and processing of alpha-mannosidase-1 during development.     

Response and fertility of dairy heifers following injection with prostaglandin F(2alpha) during early, middle or late diestrus

After an observed estrus, 250 dairy heifers were injected once with 25 mg of PGF(2alpha) either on cycle days 5 through 7 (E), 8 through 11 (M) or 12 through 15 (L). For five days after the PGF(2alpha) injection, heifers were inseminated at about 12 h after estrus was first observed. Observed estrual response rates were 43.0%, 83.6% and 100% for E, M and L, respectively. Average time from PGF(2alpha) to observation of estrus for E, M and L was 59, 70 and 72 h. Conception rates for heifers responding to PGF(2alpha) were 56.8%, 62.1% and 78.3% for E, M and L, respectively. Based on blood samples drawn at the time of PGF(2alpha) injection, progesterone concentration was significantly correlated with response rate but not with conception rate. When compared with M and L, E had a significantly lower response rate and conception rate as well as a shorter period between injection of PGF(2alpha) and observation of estrus.     

小鼠肝脏免疫抑制蛋白质(LISP)的分离纯化和鉴定

用硫酸铵分段盐析及DEAE-Sephadex A-50、羟磷灰石和CM纤维素等多种柱层析方法,从正常小鼠肝浸液中分离纯化出一种免疫抑制蛋白质(LISP)。在体外用微量该蛋白质就能强烈抑制小鼠T、B淋巴细胞对促有丝分裂原和同种异型抗原的增生反应。纯化的蛋白质在聚丙烯酰胺凝胶电泳(PACE)和等电聚焦(IEF)鉴定时均显示为一条区带,其等电点(pI)值在7.5—7.8范围。沉降系数利S_(20),w为5.39。Sephadex G-100凝胶层析测得LISP的分子量为78,000道尔顿。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)提示LISP是由二个相同的亚基组成,亚基分子量为38,500道尔顿。LISP是一种既非糖蛋白又非脂蛋白的碱性蛋白质,对它的氨基酸组成也作了分析。     

Effects of UV-B on motility and photobehavior in the green flagellate,Euglena gracilis

UV-B inhibits the motility of the green flagellate, Euglena gracilis, at fluences rates higher than those expected to occur in the natural sunlight even when the stratospheric ozone layer is partially reduced by manmade pollutants. The phototactic orientation of the cells, however, is drastically impaired by only slightly enhanced levels of UV-B irradiation. Since only negative phototaxis (movement away from a strong light source) is impaired while positive phototaxis (movement toward a weak light source) is not, the delicate balance by which the organisms adjust their position in their habitat is disturbed. Under these conditions the cells are unable to retreat from hazardous levels of radiation and are eventually killed not by the UV-B irradiation but by photobleaching of their photosynthetic pigments in the strong daylight at the surface.