The dual role of oxygen in avocado fruit respiration: Kinetic analysis and computer modelling of diffusion-affected respiratory oxygen isotherms

Abstract. Oxygen plays a dual role in affecting the rate of respiration of avocado fruit ( Persea americana Mill, cv. Hass). The respiration rate v. oxygen concentration curve for steady state avocado fruit respiration is biphasic. The curve becomes monophasic, however, when measured under conditions of rapidly changing oxygen concentration in a closed circulating system. The results are interpreted as indicating that oxygen at relatively high concentrations modulates respiration independent of its interaction with the terminal oxidase—presumably cytochrome oxidase.
A computer model is presented which takes into account the effect of diffusion barriers on the kinetics of oxygen utilization as a function of concentration in avocado fruit. The model is used to make predictions concerning the apparent K _m of the terminal oxidase or oxidases in avocado fruit. It is concluded that the apparent K _m of the terminal oxidase of uninhibited avocado fruit is that of cytochrome oxidase, and that the alternative, cyanide-resistant oxidase of avocado fruit does not contribute appreciably to the uninhibited respiration of preclimacteric or climacteric avocado fruit.     

Large mobile versus small sedentary herbivores and their resistance to seaweed chemical defenses

Summary Small, relatively sedentary herbivores like amphipods and polychaetes (mesograzers) often live on the plants they consume and should therefore view plants as both foods and living sites. Large, relatively mobile herbivores like fishes commonly move among, and feed from, many plants; they should view plants primarily as foods and rarely as potential living sites. In marine communities, fishes that consume plants are also important predators on mesograzers. Since seaweeds avoided by fishes should represent safer living sites for small herbivores, mesograzers living on and consuming seaweeds that are not eaten by fishes should have higher fitness than mesograzers living on plants preferred by fishes. In previous work, we demonstrated that seaweed secondary metabolites that deterred feeding by a fish and sea urchin had no effect on feeding by a common amphipod (Hay et al. 1987a). We then hypothesized that mesograzers would, in general, be less affected by seaweed chemical defenses than larger, more mobile herbivores like fishes. In this investigation, we evaluate the generality of this hypothesis by comparing the feeding of an omnivorous fish (Lagodon rhomboides) with that of an omnivorous, tube-building polychaete (Platynereis dumerilii) to see if the mesograzer prefers seaweeds avoided by the fish and if it is less affected by seaweed chemical defense. Platynereis dumerilii fed almost exclusively on Dictyota dichotoma, the seaweed eaten least by Lagodon rhomboides. The diterpene alcohols (dictyol-E and pachydictyol-A) produced by Dictyota significantly deterred feeding by Lagodon but did not affect, or at one concentration stimulated, feeding by Platynereis. Our data support the hypothesis that small, relatively sedentary herbivores that live on plants are more resistant to chemical defenses than are large, relatively mobile herbivores that move among many plants.     

Temporal relationships of rubbing behavior with foraging and petiole enlargement inParapolybia indica (Hymenoptera: Vespidae)

Summary The frequency of application of ant repellent secreted from the metasomal sternum VI gland to the nest petiole (=rubbing behavior) inParapolybia indica colonies decreased significantly from the preemergence, single-foundress stage to the post-emergence stage. In the pre-emergence stage, rubbing occurred in close temporal association with the departure from the nest, which may maximize the antrepelling effect of the rubbing substance during the period when the nest is not attended by any wasps. On the other hand, only a small proportion of the departures was associated with rubbing in the post-emergence stage.Unlike in other independent-founding polistine wasps, rubbing inP. indica was not associated with petiole enlargement. Among independent-founding polistines,P. indica is unusual in that females enlarge the nest petiole with a large amount of plant fibers instead of strict use of adult saliva, and in that the petiole surface is rough, and may be much more absorbent than that of the secretion petiole. On the other hand, in the species showing a temporal association between petiole enlargement and rubbing, females typically rub immediately after petiole licking (application of oral secretion). This fact, and the lack of such a temporal association inP. indica, may suggest a possibility that the mixture of oral secretion and rubbing substance on the smooth surface of the secretion petiole makes the chemical barrier last longer.     

Embryology of Chaoborus-induced spines in Daphnia pulex

Daphnia pulex (Crustacea: Cladocera) embryos were found to be sensitive to a chemical cue (kairomone) in an extract of the predator Chaoborus americanus (Insecta:Diptera). Sensitivity of embryos to the kairomone remains throughout embryonic development. Apparently declining sensitivity as development proceeds may be due to the amount of time the embryos are exposed to the kairomone. Male embryos were also found to be sensitive to the kairomone. The smallest eggs within a brood produced small offspring, which showed the antipredator morphology to a significantly lower degree than largest eggs. The production of the neckteeth is described, at the developmental stage in the maturation of the Daphnia coinciding approximately with the escape of the embryos from the brood chamber.     

花生幼苗下胚轴质膜氧化还原系统

花生幼苗下胚轴细胞膜制剂具有氧化NAD(P)H,还原Fe(CN)_6~(3-)与EDTA-Fe~(3 )的能力,当Fe(CN)_6~(3-)浓度为1mmol/L时,膜制剂氧化NADH和NAD(P)H的K_m分别为100和110μmol/L;V_(max)为1400和710nmol mg~(-1) proteinmin~(-1),最适pH为8.0。NADH 0.25 mmol/L浓度下,膜制剂还原Fe(CN)_6~(3-)的K_m为40,V_(max)为1300;还原EDTA-Fe~(3 )的K_m为125,V_(max)为180,最适pH分别为8.0与7.0。氧为该系统天然受体,鱼藤酮、抗霉素A与CN~-对其活性无影响,10μmol/L的DCCD抑制其活性约20％,10μmol/L的SHAM抑制近50％活性。     

Chemische Verteidigung der Lupinen: Zur biologischen Bedeutung der Chinolizidinalkaloide

Quinolizidine alkaloids deter the feeding of herbivores (mammals, insects, molluscs), inhibit the growth and the development of bacteria and fungi and inhibit the germination of grass seeds and lettuce. Half-maximal inhibitor concentrations fall in the range between 0.5 and 15mM (= 0.01–0.3%). The actual concentrations of lupin alkaloids in the plant are between 5–200mmol/kg, i.e. much higher than the inhibitory concentrations. Since alkaloid-free lupins have a higher incidence of herbivory and disease, we assume that the biological function of lupin alkaloids is chemical defense besides minor roles as nitrogen transport and nitrogen storage compounds.

Teil der Habilitationsschrift (Wink 1984c). — Vorgetragen auf der Tagung der Deutschen Botanischen Gesellschaft, Wien, September 1984.