Use of additive models to represent trends in a barley field trial

Even when a field experiment has been designed with care, subsequent examination of the plot values may reveal additional unforeseen trends. In this paper we examine data from a barley pathology field trial and show that additive models provide a flexible representation of environmental trends, in one or two dimensions. Such models smooth out noise in the observed data, rather than fit an equation specified in advance. This approach tends to increase the precision of treatment comparisons relative to a classical analysis of variance. We recommend the use of residual plots to explore experimental data for underlying trends, and additive models to display these trends and estimate treatment effects.     

Catalytic RNA and RNA Splicing

The capacity of Watson-Crick base-pair complementarity to directinformational transactions basic to gene expression has longbeen appreciated. Among RNA molecules, it mediates mRNA-tRNAcodon-anticodon pairing and the 16S rRNA-mRNA Shine-Dalgarnointeraction. More recently, we have come to realize that therole of RNA may transcend that of intermolecular recognition,per se, to include catalysis. Following the tour-de-force studiesof the self-splicing Tetrahymena rRNA precursor, the stage isnow set for the primary role of RNA to be revealed in nuclearpre-RNA splicing, which is catalyzed by a large ribonucleoprotein(RNP) complex in the cell nucleus, called the spliceosome. Theremoval of introns from nuclear pre-messenger RNA (pre-mRNA)shares fundamental properties with certain RNA self-splicingreactions. It therefore seems likely that the major catalyticstrategies in nuclear pre-mRNA splicing are carried out by thesmall nuclear RNAs (snRNAs), which are major constituents ofthe spliceosome.     

Chemical Composition of the Epidermal, Hypodermal, Endodermal and Intervening Cortical Cell Walls of Various Plant Roots

A survey of chemical modifications in the cells of the epidermis,hypodermis, cortical parenchyma and endodermis in roots of 27plant species was performed. Cortical parenchyma walls weregenerally free of modifying substances whereas the walls ofthe epidermis, hypodermis and endodermis were usually modifiedby the presence of lipids, phenols, suberin or lignin. In mostcases, wall-modifying components could be detected within 5mm of the root apex. lipids, phenols, suberin, lignin, ferulic acid, root, epidermis, hypodermis, cortex, endodermis, cell wall     

Synthesis of Acetylcholine in the Absence of Exogenous Choline

THE breakdown of acetyl-CoA during incubation with rat brain homogenate or sections of rat nervous tissue in the absence of choline has been reported by Kasa, Mann and Hebb¹. They found that the conversion of ¹⁴C-acetyl-CoA to ¹⁴C-acetate thus incubated was considerably depressed by 10^?4 eserine or 10^?5 M di-isopropylfluorophosphate (DFP) but further depressed by 10^?3 M DFP. Experiments in our laboratories lead us to offer an explanation for that part of the breakdown inhibited by eserine or low concentrations of DFP.     

Aerobic Metabolism of Brochothrix thermosphacta Growing on Meat Surfaces and in Laboratory Media

Acetoin and acetic, isobutyric and isovaleric acids are major end-products, and important components of the spoilage odours, of Brochothrix thermosphacta growing aerobically on meat surfaces or in tryptone-based medium containing glucose, ribose or glycerol. Acetoin and acetic acid are probably derived entirely from the carbohydrates and isobutyric and isovaleric acids from valine and leucine respectively. Glucose and pH are both important factors in controlling the relative amounts of end-products, low glucose and near neutral pH favouring fatty acid formation, high glucose and lower pH values favouring acetoin formation.     

Influence of Photoperiod, Daylength, and Feeding Schedule on Tadpole Growth and Development

The metamorphic rate of Rana pipiens tadpoles was studied under different photoperiods, daylengths, and feeding schedules. Tail resorption and hindlimb growth and development induced by immersion in 30 μg/l thyroxine (T₄) were accelerated under longer photoperiods and continuous light when 6L: 18D, 12L: 12D, 18L: 6D, and 24L regimes were compared. Constant light exposure did not produce faster development than an 18 hr photoperiod, and initially was less effective. The rate of spontaneous and T₄-induced metamorphosis was greater the shorter the day on 9L:9D, 12L: 12D, or 15L: 15D cycles, although all groups received the same overall amount of light, but in different dosages. When feeding schedule but not the LD cycle was varied, groups of tadpoles fed on 18, 24, or 30 hr regimes showed no differences in growth and development rate on 19L: 5D, and only random variations under continuous light. Differences in metamorphic rate on 18, 24, or 30 hr days are not due to the feeding schedules, but to the LD cycles. From these experiments we conclude that illumination, particularly the length and frequency of the photoperiod, affects the utilization of T₄. Development rates independent of the total amount of illumination, but related to daylength and light schedule, suggest interaction of light with an endogenous timing mechanism.     

In vitro screening of coffee genotypes for resistance to coffee berry disease (Colletotrichum kahawae)

An in vitro protocol was developed to screen Coffea arabica genotypes for resistance to coffee berry disease caused by Colletotrichum kahawae. Initially, cultural conditions which influenced the growth of isolates of C. kahawae on agar media suitable for callus growth were determined. The growth of the fungus on the callus derived from susceptible and resistant genotypes was then assessed. This ensured that no detrimental competition for nutrients between the pathogen and the calli occurred. Optimisation of the concentration of the phytohormones added to the media, the temperature and incubation period were found to be important in the expression of differential responses of calli to inoculation with the pathogen as detected by measurement of hyphal growth. The screening of calli of nine C. arabica genotypes showed that this method identified genotypes highly resistant or susceptible to the disease and was sufficiently sensitive to distinguish those genotypes with moderate or low resistance.     

Bud-eating by bullfinches, Pyrrhulapyrrhula in relation to the chemical constituents of two pear cultivars

Damage to pear trees of the cultivars Conference and Doyenne du Cornice caused by Bullfinches feeding on the flower buds was measured during January-April 1981. Bud-eating was concentrated on trees near woodland, and occurred at a steady rate within each row, though progressively more rows were attacked. Levels of total soluble protein, free amino acids, starch, glyeeride-glycerol, fructose, glucose and phosphorus were low until mid March, when the amounts per bud (and concentrations of starch and total soluble protein) rose sharply, coinciding with an increase in the size of buds. Sucrose did not occur at detectable levels. Conference buds contained significantly higher concentrations of fructose and free amino acids than Cornice. The implications for understanding bullfinches' bud-feeding habits are discussed.