The effects of foliage damage on casebearing moth larvae, Coleophora serratella, feeding on birch

ABSTRACT.

• 1 Mechanical damage to birch (Betula pendula Roth) leaves leads to an increase in the concentration of phenolic compounds, which spreads throughout the leaf within 8 days.
• 2 Coleophora serratella L. (Lepidoptera: Coleophoridae) apparently responds to this chemical change over a similar time scale. Within 24 h of pin-pricking leaves the casebearer moves from the immediate vicinity of the damage, but is just as likely to move to an undamaged portion of the damaged leaf as to vacate the leaf entirely. After 8 days mines on undamaged portions of damaged leaves were significantly smaller than mines on undamaged leaves.
• 3 Furthermore, Coleophora serratella reared on damaged trees took an average of 3 days longer to develop than those reared on undamaged trees.
• 4 It has been suggested that increased movement in response to damage-induced chemical changes causes hyperdispersed damage on plant foliage. Both within and between-leaf casebearer damage patterns were shown to be aggregated on birch.
• 5 Thus although mechanical damage can induce chemical and behavioural changes in the field, these are not reflected in the observed damaged patterns. We speculate on several possible reasons for this.

     

The Effect of Cooling on Photosynthesis, Amounts of Carbohydrate and Assimilate Export in Sunflower

Sunflower plants (Helianthus annuus L.) grown at 30°C werecooled to 13°C in the light in atmospheric CO² or low CO²,or in darkness. Photosynthetic rate at 30°C after coolingwhole plants in atmospheric CO² for 12 h during a photoperiodwas significantly lower than at the start of the photoperiodcompared to plants cooled at low CO², those cooled in the darkand those maintained at 30°C. Amounts of sucrose, hexosesand starch in leaves at 13°C increased throughout a 14 hphotoperiod to levels higher than in leaves at 30°C, whereamounts of sucrose and hexoses were stable or falling after4 h. Carbohydrate accumulation at 13°C during this photoperiodwas more than twice that at 30°C. After three photoperiodsand two dark periods at 13°C carbohydrate levels in leaveswere still as high as at the end of the first photoperiod, butless carbohydrate accumulated during the photoperiods than duringthe first photoperiod, and more was partitioned as starch. Amountsof soluble carbohydrate in roots were greater after 14 h at13°C than in roots of plants at 30°C. Loss of ¹⁴C fromleaves at 30°C as a proportion of ¹⁴CO2 fixed by them at30°C, decreased after exposure of plants to 13°C inthe light for 30 min prior to ¹⁴CO²feeding. Results indicatean effect of cold on the transport process that was light-dependent.It is inferred that the reduction in the proportion of ¹⁴C lostfrom leaves after 10 h cooling was due to reduced sink demand,whereas the rise in the proportion of ¹⁴C lost from leaves after24 h reflects reduced photosynthetic rate. The coincidence ofreduced photosynthetic rate with raised carbohydrate levelsin leaves maintained at 30°C throughout, whilst the restof the plant was cooled to 13°C in the light implies feedbackinhibition of photosynthesis. This may reduce the imbalancebetween source and sink in sunflower during the first days oflong-term cooling. Key words: Temperature, carbon export, carbohydrates, photosynthesis, sunflower     

Genetic variation in natural populations of the aphid Rhopalosiphum padi as revealed by maternally inherited markers

A survey on 148 clones of the aphid Rhopalosiphum padi from 11 widespread localities has been carried out to study the genetic structure of populations of this species as revealed by mitochondrial DNA restriction site and length polymorphisms as well as by restriction site analysis of a maternally inherited plasmid carried by the aphid eubacterial endosymbiont Buchnera aphidicola. Our results support the existence in the area under study of two main aphid maternal lineages strikingly coincidental with the two main reproductive categories displayed by this species. Those aphid clones possessing an incomplete life cycle that lacks the sexual phase (anholocyclic or androcyclic clones) show mitochondrial DNA (mtDNA) haplotype I and plasmid haplotype I, whereas those clones displaying the complete life cycle (holocyclic clones) posses some other distinct mtDNA haplotypes closely related to each other and plasmid haplotype II. While restriction-site analysis of maternally inherited markers points to a relatively ancient origin of anholocycly/androcycly (between 460 000 and 1 400 000 years) followed by interrupted gene flow with respect to the ancestral holocyclic population, mtDNA size variation also suggests that historical stochastic processes have a different effect on the evolution of both main aphid lineages. Evidence of occasional nuclear gene flow between lineages and its consequences on the correspondence between maternally inherited haplotypes and life cycle are also presented and discussed.     

Dissociation of Lipid Components and Reconstitution at – 75° C of Mg<Superscript>2+</Superscript> Dependent,Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> Stimulated,Adenosine Triphosphatase in Rat Brain

MEMBRANE enzymes, because of their lipid content, are insoluble in water and usually solubilized as micelles in aqueous solution by detergents for biochemical study. Direct study of lipid components by means of organic liquids in which they dissolve leads at once to the denaturation of the enzyme. At temperatures appreciably colder than 0° C, however, organic solvents may leave enzymatic activity intact^1–3, making it possible to study enzyme reactions.     

Interferon Induction: DNA–RNA Hybrid or Double Stranded RNA?

Interferon inducing capacity resides solely with double stranded RNA.     

CHOLERA TOXIN

1. Death in several infectious diseases is caused by protein toxins secreted by invading bacteria. Cholera toxin is a simple protein secreted by Vibrio cholerae colonizing the gut; it is responsible for the massive diarrhoea that is cholera. 2. The primary action of cholera toxin is an activation of adenylate cyclase, an enzyme found on the inner membrane of eukaryotic cells that catalyses the conversion of ATP to cyclic AMP. Consequent increases in the intracellular concentration of cyclic AMP are responsible for other manifestations of cholera toxin including the diarrhoea. The toxin is active on almost all eukaryotic cells. 3. The toxin can be purified from culture filtrates of V. cholera. It has a molecular weight of 82000; and is composed of one subunit A (itself two polypeptide chains joined by a disulphide bond: AI (22000) and A2 (5000)) and five subunits B (11500). These can be separated in dissociating solvents such as detergents or 6 M guanidine hydrochloride. An amino-acid sequence of subunit B has been published. The five B subunits (sometimes found by themselves in the filtrate and known as ‘choleragenoid’) are probably arranged in a ring with the subunit A in the middle joined to them non-covalently by peptide A2. 4. The first action of cholera toxin on a cell is to bind to the membrane strongly and irreversibly. Several thousand molecules of toxin bind to each cell and the binding constants are of the order of 10^-10 M. The binding is rapid, but is followed by a lag phase of about an hour before the intracellular cyclic AMP concentration begins to increase. 5. Ganglioside G_M1, a complex amphiphilic lipid found in cell membranes, binds tightly to the toxin which shows an enzyme-like specificity for this particular ganglioside. Toxin that has already bound ganglioside can no longer bind to cells and is therefore inactive. This and other experiments using cells depleted of endogenous ganglioside suggest that ganglioside G_M1 is the natural receptor of the toxin on the cell surface. The binding is followed by a lateral movement of the toxin-ganglioside complex in the cell surface forming a ‘cap’ at one pole of the cell. 6. The binding of ganglioside by toxin is a function exclusively of subunit B; Subunit A does not bind and can be eluted with 8 M urea from an insolubilized toxin-ganglioside complex. Subunit B is not by itself active, and so preincubation with B can protect cells or even whole gut from the action of toxin by occupying all the ganglioside binding sites. 7. Subunit A is responsible for activation of adenylate cyclase. Purified subunit A or just peptide AI is active by itself and this activity is not inhibited by ganglioside or by antisera to subunit B. In intact cells the activity is low and shows the characteristic lag phase but in lysed cells the subunit (or the whole toxin) is much more active and there is no lag phase. This suggests that the lag phase represents the time that subunit A takes to cross the cell membrane and get to its target. 8. Several cofactors are needed for toxin activity in lysed cells: NAD+, ATP, sulphydryl compounds and another unidentified cytoplasmic component. The activity of the cyclase is altered in a complex way generally rather similarly to the action of hormones such as adrenalin, but it is difficult to draw any general conclusions. 9. There are two chief theories of how cholera toxin acts. The first is that subunit A (or just peptide AI) enters the cell and there catalyses some reaction leading to activation of the cyclase. The cleavage of NAD+ into nicotinamide and adenosine diphosphoribose could be such a reaction; it is catalysed by high concentrations of cholera toxin. 10. The other theory is that part of the toxin binds directly to the adenylate cyclase or to some other molecule that can then interact with the cyclase, perhaps after the lateral movement of the toxin-ganglioside complex in the cell surface. This binding may be related to the known action of guanyl nucleotides on the cell surface. 11. The entry of peptide AI into the cell and its transport through the membrane is mediated by the binding of subunits B to the cell surface, perhaps just because the binding increases the local concentration of subunit A, or perhaps following specific conformational changes in the subunits and the formation of a tunnel of B subunits through the membrane. An experiment showing that the toxin remains active when the subunits are covalently bonded together suggests that peptide AI does not separate completely from the rest of the molecule. 12. There are several other proteins that resemble cholera toxin in structure and function. For example, glycoprotein hormones such as thyrotrophin also activate adenylate cyclase and have an apparently similar subunit structure with one type of subunit that binds to a ganglioside. There may also be analogies between the amino-acid sequences of toxin and hormones. 13. The enterotoxin made by some strains of Escherichia coli produces a similar diarrhoea to that of cholera. Several different toxic proteins have been prepared but they all seem to activate adenylate cyclase in the same sort of way as cholera toxin does and also to cross-react immunologically with it. The E. coli toxin also reacts with ganglioside G, but the reaction is weak and probably physiologically insignificant. Salmonella typhimurium secretes a similar toxin. 14. Tetanus toxin also reacts with a ganglioside receptor. This protein has two polypeptide chains of which only one reacts with the ganglioside; but the molecular activity is not yet known. 15. Diphtheria toxin has an A fragment that is directly responsible for the toxicity (by catalysing an NAD+ cleavage reaction leading to the total inhibition of protein synthesis) and a B fragment that gets the A fragment into the cells. This structure of active and binding components therefore seems to be common to many toxins. 16. The ability to produce toxin may confer some selective advantage on V. cholerae. The toxin may originate from accidental incorporation of DNA from an eukaryotic host, or alternatively from some material involved with the cyclic AMP metabolism of the bacterium.     

The Unique Position of the Degenerating Macronucleus in Tetrahymena tropicalis1

In contrast to the situation in 13 other species of the Tetrahymena pyriformis complex, in which the condensed degenerating old macronucleus lies in the posterior end of the cell during the late stages of conjugation, in Tetrahymena tropicalis that nucleus is found in the anterior portion. This developmental characteristic may be useful for taxonomic purposes as well as being of value in investigations on nucleocytoplasmic interaction.     

Late Pleistocene and Holocene equid remains from Israel

Equid remains–mostly isolated teeth–from archaeological sites in Israel are described. Particular attention is paid to dental enamel fold morphology and criteria are established tor separating several Old World Quaternary equid species. Eauus hydruntinus , which is here considered a zebra rather than an ass, was present until 12,000 bp in northern Israel, while at the same time E-asinus/hemionus inhabited the arid regions in the south. Inirequent remains of E. caballus are also described. By 4000 years ago ass, probably the domestic form, was present in northern Israel.