Effects of prostacyclin on cardiovascular reflexes from the ventricular epicardium of the dog: Comparision with the effects of prostaglandin E2

Application of bradykinin to the exposed ventricular surface of the dog's heart produced reflex pressor effects and tachycardia, whereas application of nicotine evoked reflex hypotensin and bradycardia. Prostacyclin (PGI₂) or prostaglandin E₂ (PGE₂), when applied epicardially, had no effects by themselves but potentiated the reflex pressor changes to bradykinin; the depressor responses to nicotine were not changed. The potentiating effect of PGI₂ was prompt but short-lived, whereas that of PGE₂ was slow in onset but prolonged. The results suggest that PGI₂, which is present in the pericardial fluid, may contribute to signalling of pain and reflex circulatory changes when kinin formation occurs during myocardial ischaemia or pericardial inflammation.     

Körpergrösse,Körperzeiten und Energiebilanz

Ohne Zusammenfassung     

The interaction of abscisic acid with growth stimulators in germination of partially after-ripened apple embryos

The effect of abscisic acid (ABA), gibberellin A₄₊₇ and benzyladenine on germination of apple embryos which had been stratified for different periods of time was investigated. The growth stimulators accelerated the germination of non-stratified embryos or those stratified for a short time. After a longer period of stratification, the effect of growth stimulators was visible only when germination of the embryos was artificially inhibited by simultaneous application of synthetic ABA. The sensitivity of stratified apple embryos to the exogenous ABA diminished with the number of hours elapsed between the imbibiting by the embryos of the water or gibberellin and the application of the ABA. This was similar to the change in the sensitivity of apple embryos during stratification due to the increasing concentrations of ABA.     

Influence d'un choc osmotique sur la composition des feuilles de cotonnier en acides amines libres

The effect of water stress on the free amino acids in cotton leaves has been investigated. The water deficit, obtained by lowering of osmotic potential through the use of polyethylene glycol (PEG-600) as the osmotic agent, induces an accumulation of free amino acids.Significant modifications in the composition of this fraction are observed. The major differences from treated and untreated leaves are in the levels of γ-aminobutyric acid, asparagine, proline, and glutamic acid and its amide.     

The influence of leaf traits and deficit irrigation on insect communities in mature green tomato production

1. Drought affects many agriculturally important areas, hampering the cultivation of water intensive crops such as tomatoes.
2. Unlike processing tomatoes, deficit irrigation of fresh market tomatoes is not currently practiced. Deficit irrigation could have negative trade‐offs for yield and pest populations by changing plant nutritional values and the microenvironment.
3. The present study compared crop response and insect populations at two field locations: an on‐farm trial with 0%, 15% and 30% water deficit treatments, and a research station trial with 0%, 10%, 20% and 30% water deficit treatments.
4. At the on‐farm trial, water deficits of 30% affected fruit yield, leaf relative water content (RWC) and leaf δ¹³C, whereas, in the research station trial, water deficits only affected leaf RWC. Treatments did not change the abundance of any insect groups.
5. Sap‐feeding insects such as silverleaf whitefly (Bemisia tabaci) increased with plant traits indicating hydration such as canopy temperature depression (CTD) and RWC. Furthermore, CTD influenced the composition of insect communities.
6. Sap‐feeding insect abundance may vary with traits indicating hydration because of turgor pressure required for feeding, as well as a more suitable microenvironment.

     

The molecular nature of damage by oxygen to freeze-dried Escherichia coli

The damage occurring in freeze-dried bacteria exposed to oxygen is mainly in the bacterial membrane and involves the DNA-initiation complex. This injury occurs in two stages: The primary damage is due to the freeze-drying itself, and is repaired upon reconstitution of bacteria and their subsequent incubation in nutrient broth. The repair process requires protein synthesis. In the next step, the exposure of freezedried bacteria to oxygen, the injury becomes irreversible and the bacteria “die.” The lethal effects of oxygen can be counteracted by either engaging the initiation sites on the membrane (e.g., by colicin E₁), or by arresting the activity of the initiation complex. Such arrest occurs in ts-mutants at nonpermissive temperature, or when appropriate mutants are starved of amino acids or thymine.After freeze drying and storage in vacuo, the reconstituted bacteria grow in filaments and synthetize DNA multifocally; they do not form septa and do not divide. After exposure to oxygen of the freeze-dried bacteria the ability to initiate DNA synthesis is lost.It is assumed therefore that oxygen specifically acts on the initiation complex in the bacterial membrane of the freeze-dried bacteria. When an external DNA synthesis control is provided, e.g., by infection with phage the productivity of the freeze-dried bacteria exposed to oxygen is the same as of the lyophilized controls held in vacuo.