Plants and insects in early old-field succession: comparison of an English site and an American site

The plant and insect communities of early, secondary succession beginning with bare ground in an Old World site (southern Britain) and a New World site (Iowa, U.S.A.) shared a number of characteristics. Both sites showed similar temporal patterns of plant species cover and species richness, although overall richness was greater at the Old World site. Annuals dominated at both sites during the first year of succession and were largely replaced by perennials in the second year. Monocotyledons were more abundant at the Old World site, especially in the second year. The two sites differed markedly in the contribution of native and introduced plant species, with the Old World site dominated by natives and the New World site by alien plant species. Insect herbivore load was greater at the Old World site, when expressed in terms of structural complexity of the vegetation, suggesting that there may be major differences in the influence of herbivores on the direction and rate of succession at the two sites.     

Regulation of Electrogenic Pumping in Barley by pH and ATP

The relationship of the electrogenic pump to the ATP concentrationin barley roots was examined. Excision, salt accumulation andchanges in temperature produced changes in the ATP concentrationwhich did not correlate with changes in membrane potential (_m).Illumination of seedlings prior to excision of the root elevatedthe ATP level and caused _m to hyperpolarize. Metabolic inhibitionby sodium azide resulted in a fall in ATP concentration andmembrane depolarization. With treatment in azide for longerthan 10 min there was a linear relationship between ATP concentrationand _m. Time-courses of the effects of azide and carbon monoxideshowed that this relationship did not hold at short treatmenttimes because the ATP concentration fell more rapidly than thedecay of _m. Application of butyrate or fusicoccin produced littleor no change in the ATP concentration but both caused significantchanges in _m. The effects on _m of butyrate, fusicoccin, external pH and metabolicinhibitors were considered to be consistent with regulationof electrogenic pumping by cytoplasmic pH. Key words: Cytoplasmic pH, Electrogenic pumping, Fusicoccin, Butyrate     

Synthesis of Substance P

SUBSTANCE P has been synthesized by the solid-phase procedure of Merrifield^1,2 according to the sequence H-Arg-Pro-LysPro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂ reported in the previous letter.     

Passive Haemagglutination Test for Anti-rhinovirus Antibodies

The use of chromic chloride as a coupling reagent has made it possible to coat red cells with rhinovirus protein. This is shown by immunofluorescence, electron microscopy and immunocolloidal experiments.     

Penultimate Aspartyl unnecessary for Stimulation of Acid Secretion by Gastrin-related Peptide

THE carboxy-terminal tetrapeptide of gastrin, Trp-Met-Asp-Phe-NH₂, has the same biological activity as the parent hormone¹. Morley^2,3 showed that certain substitutions in the Trp, Met and Phe positions gave active analogues and concluded that these positions are concerned only with binding at the site of action. In contrast, the only substitution in aspartic acid that gave activity was tetrazolyl for the β-carboxyl, thereby maintaining a proton donor of similar size at this position. Morley concluded that the aspartyl residue has a functional rather than a binding role and presumably is indispensable. The carboxy-terminal octapeptide of cholecystokinin (OP-CCK) contains the carboxy-terminal tetrapeptide of gastrin and has gastrin-like activity⁴. We report here that the synthetic analogue of OP-CCK, in which alanyl is substituted for aspartyl at the position in question illustration, stimulates gastric acid secretion. In conscious cats with gastric fistulas⁵, dose-response curves were established for gastric acid response to OP-CCK, 7-Ala OP-CCK and pentagastrin⁶. The peptides were given by continuous intravenous infusion and response is taken as peak 10 min output during a 30 min infusion at each dose level (Fig. 1). Assigning a potency of 1 to OP-CCK the relative molar potency of 7-Ala OP-CCK is about 1/110 and of pentagastrin is about 1/4. We also tested the analogue of gastrin tetrapeptide in which alanyl is substituted for aspartyl illustration and found no detectable stimulation of acid secretion at doses as high as 15 mg/kg h, confirming similar negative findings by Morley² in rat. This suggests that the weak action of alanyl substituted analogues cannot readily be detected without the enhancement of potency conferred by the sulphated tyrosyl of OP-CCK⁷. Ondetti et al.⁷ showed that 7-Ala OP-CCK contracts guinea-pig gallbladder with a potency about 1/150th that of OP-CCK, comparable with that reported here for acid secretion. This suggests that the same part or parts of the molecule are required for cholecystokinetic action and for gastric secretory action; the aspartyl residue in the penultimate position is dispensable for both of these actions. On the assumption that gastrin and CCK act at the same site⁸, we propose that the corresponding aspartyl residue of gastrin is similarly dispensable. For a direct test of this hypothesis, studies are needed of the synthetic analogue in which alanyl is substituted for the penultimate aspartyl in gastrin hepta-decapeptide, perferably gastrin II with sulphated tyrosyl because it is more potent than gastrin I in certain species⁹.

Open image in new window

Open image in new window

     

Phytosterols and Other Lipids as Survival Factors for Tetrahymena at 0–5 C

SYNOPSIS. Tetrahymena pyriformis syngen 1, mating type II, (optimal growth temperature ∼ 37 C) ordinarily dies out in 5-14 days at 0-5 C. Dying cells were lumpy, suggesting membrane damage. By supplying crude soy lecithin, survival at 0-5 C was prolonged (after growth in peptone-yeast-dextrin) to at least 22 weeks. Crude soy sterols or sitosterol or stigmasterol, and antioxidant, e.g., Ionox 330 or ascorbylpalmitate, permitted survival of cells in suspension or in growth media for at least 16-22 weeks. These sterols are known to protect against triparanol toxicity, which suggested that triparanol, which blocks cholesterol synthesis in higher animals, might enhance cold-induced injury. Triparanol was more toxic at 0–5 than at 28 C for cell suspensions and cells in growth medium; this toxicity was annulled by crude soy lecithin or β-sitosterol, the only phytosterol tested. The synthetic medium intended as a control on the crude media became toxic at 0–5 C. Protection against cold damage is discussed as a means of elucidating the role of sterols—especially phytosterols—and other lipids in maintaining the integrity of the ciliate cell membrane.