The rôle of ecdysone in pupation of Manduca sexta

Slow infusions of β-ecdysone are more effective in eliciting a normal physiological response than are discrete injections of the hormone. Infusion of β-ecdysone into final instar larvae in the presence of juvenile hormone (JH) induces apolysis and the deposition of a normal larval cuticle. In the absence of JH larvae display the prodromal symptoms of pupation (exposure of the heart, purging of the gut, etc.) in response to a β-ecdysone infusion. The occurrence of certain covert physiological events that accompany the exposure of the heart are evidently necessary to prepare a larva for pupation. An infusion of β-ecdysone can induce apolysis and pupal cuticle deposition only after the prodromal signs of pupation have become evident. Of the two pulses of ecdysone that normally precede pupation in Manduca, the first is apparently responsible for the genetic switchover from larval to pupal development whereas the second one triggers apolysis and the subsequent events that lead to pupation. Results obtained from infusion experiments in which the dose and exposure time were varied independently are consistent with the idea that ecdysone has to be present for a certain minimum time above a threshold concentration to induce a physiological response. The requisite exposure time is apparently not dose-dependent.     

The röle of the head coelom in proboscis eversion in Arenicola marina (I.)

The dependence of proboscis eversion on the behaviour of the trunk coelom and the effect of increasing the external resistance to eversion have been investigated in Arenicola marina (L.).Two types of proboscis eversion are distinguished; Type I, in which there is an increase of 50–100% in the volume of the head region and where the high pressures recorded in the trunk coelom are needed, it is suggested, to force fluid into the head coelom; Type II, in which the volume change in the head region is small and where simultaneous recordings of head and trunk coelomic pressures indicate that the head coelom can be isolated from the rest of the coelom.Pressures in the trunk are only related to the extent of proboscis eversion when there is a high external resistance to eversion.     

The rôle of the plastome in evolution of the genusOenothera

In the subgenusEuoenothera, five plastid types can be identified. The same major groups of genome complexes as established byCleland, stand out when attention is focused on the co-operation between genomes and plastomes.Experiments on plastid competition and plastid-genotype compatibility lead to an unambiguous interpretation of phylogenetic relations within the subgenus.Based on a paper read at the XI International Congress of Genetics, The Hague, of which an abstract has been published in theProceedings, Vol. I, p. 131–132 (1963).     

The rôle of vitamins in plant development

The Botanical Review -     

Rôle of the midgut,crop, and maxillae of Bombyx mori in the production of cocoon-digesting enzyme

The rôle of the midgut, crop, and maxillae in the production and utilization of the cocoon-digesting enzyme was investigated in the silkworm, Bombyx mori.About a sixtyfold purified preparation of midgut protease was obtained by ammonium sulphate precipitation and column chromatography.Immunological studies by the agar diffusion method of Ouchterlony revealed that the crop and midgut proteases of the pharate adult are antigenically identical whereas that of the maxillary protease is different.From the results of extirpation experiments and previous studies it was shown that the midgut, crop, and maxillae play important rôles in the escape of moths from their cocoons.     

The rôle of amino acids in diet intake and selection and the utilization of dipeptides by Aphis fabae

Eight amino acids considered essential for the growth of Aphis fabae were investigated in relation to their rôle in protein synthesis and phagostimulation. When either alanine, histidine, methionine, proline, or serine were omitted from synthetic diets, intake was lower than that of the complete diet over a 4 day period. The omission of cysteine, phenylalanine, or tyrosine failed to reduce diet intake. Histidine and methionine were considered essential for protein synthesis and did not act as phagostimulants; alanine and proline, however, appeared to act primarily as phagostimulants. When subjected to choice chamber tests aphid larvae had a severely limited ability to select between complete diets and ones deficient in a single amino acid. If methionine and glycine were replaced by either glycyl l-methionine or l-methionyl glycine the size attained by larvae during growth was less than that of aphids reared on a complete diet but greater than that of aphids reared on diets deficient in both dipeptides and methionine.     

The nonallosteric mechanism of enzyme activity regulation. Is it the only true mechanism?

The nonallosteric regulation mechanism of enzyme reaction velocity assumes that the substrate and enzyme interact via a metal cation and form simple and mixed, mono- and multi-nuclear complexes. A solution of equations for individual cases gives a function of initial reaction velocity at any given substrate or modifier concentration. This function can describe kinetic effects that are considered allosteric, as well as phenomena omitted by commonly-accepted models.