Amino acids as determinants of host preference for the xylem feeding leafhopper,Homalodisca coagulata (Homoptera: Cicadellidae)

Summary Homalodisca coagulata is a highly polyphagous xylem feeder with distinct seasonal patterns in it's selection of host plants. These patterns were examined in relation to the amino acid content of the xylem for four common host species; Lagerstroemia indica, Baccharis halimifolia, Prunus persica, and Prunus salicina. Xylem fluid was collected from each host species at times when numbers of feeding leafhoppers were both low and high. In each case, concentrations of amino acids were greatest when numbers were high. Similarly, comparisons between host species at given times showed that concentrations of amino acids were positively correlated with host selection. In a second study, amino acids of xylem were manipulated by budding scions of a non-preferred host (P. persica) on rootstocks of preferred (P. salinica) and non-preferred (P. persica) hosts. Morphology and phenology of the budded trees were similar to that of the scion species yet the xylem composition of amino acids was primarily dependent on the rootstock. Concentrations of amino acids and the preference of leafhoppers were roughly two-fold greater for scions of the preferred than the non-preferred rootstock. In both studies, amides (glutamine plus asparagine) were the amino acids most highly correlated with host selection. These compounds are the predominant amino acids in xylem fluid, have high nitrogen to carbon ratios, and account for a high percentage of the caloric value in xylem fluid. Many of the less abundant amino acids were positively correlated with host preference, but the correlations were less consistent and correlation coefficients were generally lower.Florida Agricultural Experiment Station Journal Series No. 9672     

Evidence that actin reinforces the extensible hyphal apex of the oomyceteSaprolegnia ferax

Summary Filamentous actin in the apices of growing hyphae of the oomyceteSaprolegnia ferax is distributed such that it could compensate for weakness in the expanding apical cell wall and thus play a role in morphogenesis of the tip. The tapered extensible portion of the hyphal tip where the cell wall is plastic contains a cap of actin which differs in organization from the actin in subapical, inextensible regions of the hypha. Rapidly growing hyphae which are expected to have a longer plastic cell wall region contain longer actin caps. Furthermore, the weakest point in the hyphal apex, demonstrated by osmotic shock-induced bursting, was within the taper where the wall is plastic but never in the extreme apex where actin was most densely packed and presumably the strongest. Treatment of hyphae with cytochalasin E/dimethyl sulphoxide induced rapid changes in actin caps. Cap disruption was accompanied by transient growth rate increases, subsequent rounding and swelling of apices and a shift of osmotically induced burst points closer to the apex. These correlated changes are consistent with a role for the actin cap in tip morphogenesis. The association between regions of plasticity in the apical cell wall, the extent of the actin cap, the location of the weakest point in the apex and the effects of damage to the actin cap suggest that the cap functions to support the apex in regions where the cell wall is weak.Abbrevations CE cytochalasin E - DMSO dimethyl sulphoxide - RP rhodamine phalloidin Dedicated to the memory of Professor Oswald Kiermayer     

Effect of gestational sex steroid exposure on limb development and endochondral ossification in the pregnant C57Bl/6J mouse: I. Medroxyprogesterone acetate

Although data supporting the teratogenic potential of intrauterine progestin exposure is lacking, concern persists among some individuals within the scientific community that these drugs have the potential for nongenital teratogenesis, especially with regard to limb reduction defects. Our laboratory has been interested in the ontogeny of steroid receptors in the developing embryo and in the role of steroid-receptor interactions in limb development, particularly the process of endochondral ossification. Since limb reduction defects can be produced from abnormal processes that are operative during organogenesis or during midgestation (vascular disruption) we have designed an animal study whereby embryos were exposed to sex steroids throughout organogenesis and fetal development. The present study assesses the effects of medroxyprogesterone acetate (MPA) on intrauterine endochrondral bone development specifically, as well as overall embryo-fetal development. Primagravid C57Bl/6J mice were treated via subdermal pellets which deliver MPA at dosages of 5.0, 50.0, and 500.0 mg/kg/day on gestational days 7 through 19. These doses were 25-, 250-, and 2,500-fold higher on a mg/kg basis than the human dose equivalent (HDE). No increases in nongenital malformations were noted at any evaluated MPA dosage level. At 25 X the HDE, MPA did not influence endochondral bone development as evidenced by a lack of significant effects on assessed bone growth parameters. In the 250- and 2,500-fold HDE dosage groups, MPA was shown to exert an embryotoxic effect inducing 48 and 100% resorptions respectively. Mean embryo weights/litter were significantly reduced by MPA exposure at 250 X the HDE. Intrauterine exposure to 250 X the MPA HDE induced reductions in humeral and femoral diaphyseal length in proportion to a reduction in overall growth. The data demonstrate that MPA, administered at dosages of up to several orders of magnitude in excess of the HDE and which permitted embryo survival, did not induce increases in the frequency of nongenital teratogenesis at any dose or gestational stage. Importantly, limb reduction defects were not noted even in instances where the dosage of MPA induced an inhibition of endochondral bone growth.     

Cloning of the y1 Locus of Maize,a Gene Involved in the Biosynthesis of Carotenoids

The y1 gene is one of the genes responsible for the production of [beta]-carotene in the endosperm and leaves of maize. We have cloned a Robertson's Mutator-tagged allele of the y1 gene (y1-mum) by using a Mu3 element as a hybridization probe. We substantiate that the cloned sequence is a portion of the y1 gene by molecular analyses of a revertant of a putative Mutator-induced y1 allele and the incidence of insertions within the cloned y1 sequence from several independently derived Mutator-induced y1 mutant stocks. The y1-mum sequence was used to isolate the standard Y1 allele, which conditions the presence of [beta]-carotene in the endosperm of the maize kernel.     

The sigma compounds 1,3-di-o-tolylguanidine and N-allylnormetazocine inhibit agonist-stimulated inositol phospholipid metabolism in bovine adrenal medullary cells

Muscarine stimulated a concentration-dependent accumulation of [³H]inositol phosphates in bovine adrenal medullary cells preloaded with [³H]inositol. This muscarinic activation of inositol phospholipid metabolism was fully inhibited by the -ligand 1,3-di-o-tolylguanidine (DTG) with an IC₅₀ of approximately 45 M. Higher concentrations (100 M) of (+) N-allylnormetazocine (SKF-10047) also partially inhibited this response. A concentration of DTG sufficient to fully inhibit the muscarinic response also produced a significant partial inhibition of [³H]inositol phosphate accumulation in response to histamine but not to angiotensin II. These data demonstrate that -compounds inhibit agonist-stimulated inositol phospholipid metabolism in bovine adrenal medullary cells, with a degree of selectivity towards the muscarinic response.     

A SURVEY OF SIZES AND WEIGHTS OF BEMISIA TABACI (HOMOPTERA:ALEYRODIDAE)B BIOTYPE LIFE STAGES FROM FIELD GROWN COTTON AND CANTALOUPES

Abstract Size and weight measurements were made for all the life stages of Bemisia tabaci (Gennadius) B biotype from field grown cotton ( Gossypium hirsutum L.) and cantaloupe ( Cucumis melo L., var. cantalupensis ) in Phoenix, AZ and Fargo, ND, USA in 2000 and 2001. Nymphal volumes were derived from the measurements. The average nymphal volume increase for settled 1 st to the late 4th instar was exponential. The greatest increase in body volume occurred during development from the 3rd to early 4th instar. Nymphs on cotton leaves were wider, but not longer compared with those on cantaloupe. Ventral and dorsal depth ratios of nymphal bodies from 1 st to late 4th instars from cantaloupe leaves were significantly greater compared with those from cotton leaves. During nymphal development from 1st to 4th instar, the average (from the two host species) ventral body half volume increased by nearly 51 times compared with an increase of 28 times for the dorsal body half volume. Adult female and male average lengths, from heads to wing tips, were 1 126 μm and 953 μm, respectively. Average adult female and male weights were 39 and 17 μg, respectively. Average widths, lengths, and weights of eggs from cotton and cantaloupe were, 99 μm, 197 μm, and 0.8 μg, respectively. Average widths, lengths, and weights for exuviae of non-parasitized nymphs from both cotton and cantaloupe were 492 μm, 673 μm, and 1.20 μg, respectively; and widths, lengths, and weights of parasitized nymph exuviae were 452 μm, 665 μm, and 3.62 μg, respectively. Both exuviae from non-parasitized and parasitized nymphs from cotton leaves were wider, longer, and heavier than those from cantaloupe leaves.     

Nutrition and Physical Activity Program to Attenuate Obesity and Promote Physical and Metabolic Fitness in Elementary School Children

Obesity and low levels of physical and metabolic fitness are risk factors for cardiovascular disease and diabetes. The purpose of this investigation was to attenuate obesity and improve physical and metabolic fitness in elementary school children. Schools have the opportunity, mechanisms, and personnel in place to deliver nutrition education, fitness activities, and a school food service that is nutritious and healthy. Cohorts from grades 3 to 5 in two school districts in rural Nebraska (Intervention/Control) participated in a 2-year study of physical activity and modified school lunch program. Data collection for aerobic capacity, body composition, blood chemistry, nutrition knowledge, energy intake, and physical activity was at the beginning and end of each year. Int received enhanced physical activity, grade specific nutrition education, and a lower fat and sodium school lunch program. Con continued with a regular school lunch and team sports activity program. At year 2, Int lunches had significantly less energy (9%), fat (25%), sodium (21%), and more fiber (17%). However, measures of 24-hour energy intake for Int and Con showed significant differences for sodium only. Physical activity in the classroom was 6% greater for Int compared to Con (p < 0.05) but physical activity outside of school was ?16 % less for Int compared to Con (p < 0.05). Body weight and body fat were not different between schools for normal weight or obese children. No differences were found for cholesterol, insulin, and glucose; however, HDL cholesterol was significantly greater and cholesterol/HDL was significantly less for Int compared to Con (p < 0.05). It appears that compensation in both energy intake and physical activity outside of school may be responsible for the lack of differences between Int and Con.     

Critical evaluation of the VSC model for tip growth

The vesicle supply centre (VSC) model (Bartnicki-Garcia et al., 1989) for hyphal tip growth is powerful because it can model diverse developmental morphologies and predicts cellular organization based in current cell biology. It predicts that tip growth results from the random distribution of cell surface synthesizing vesicles from a point in the tip, the VSC, which determines their pattern of impact and fusion at the plasma membrane. We derive equations for tip-high gradients of vesicle fusions, generated by mechanisms not related to a supply centre, which create typical hyphal morphologies. These equations direct the conceptual basis for tip growth to vesicle fusion gradients, presumably mediated by a putative membrane skeleton associated with the plasma membrane. We also show that the organization and behaviour of motile organelles in growing hyphal tips of the oomycete,Saprolegnia ferax, argue against the presence of an apparatus capable of generating the distribution of vesicles postulated by the VSC model. We conclude that the VSC model is unlikely to describe the mechanistic basis of tip growth inS. ferax, and therefore, at best, it is not universally applicable.     

Correlation of two-hybrid affinity data with in vitro measurements.

Since their introduction, the interaction trap and other two-hybrid systems have been used to study protein-protein interactions. Despite their general use, little is known about the extent to which the degree of protein interaction determined by two-hybrid approaches parallels the degree of interaction determined by biochemical techniques. In this study, we used a set of lexAop-LEU2 and lexAop-lacZ reporters to calibrate the interaction trap. For the calibration, we used two sets of proteins, the Myc-Max-Mxi1 helix-loop-helix proteins, and wild-type and dimerization-defective versions of the lambda cI repressor. Our results indicate that the strength of interaction as predicted by the two-hybrid approach generally correlates with that determined in vitro, permitting discrimination of high-, intermediate-, and low-affinity interactions, but there was no single reporter for which the amount of gene expression linearly reflected affinity measured in vitro. However, some reporters showed thresholds and only responded to stronger interactions. Finally, some interactions were subject to directionality, and their apparent strength depended on the reporter used. Taken together, our results provide a cautionary framework for interpreting affinities from two-hybrid experiments.