Time course of photosynthetic temperature acclimation in Carex eleocharis Bailey

Abstract Photosynthetic temperature acclimation in Carex eleocharis has been demonstrated in a previous study in which warm grown (35/15°C) plants were shown to have photosynthetic temperature optima approximately 14°C higher than cool grown (20/15°C) plants (Monson, Littlejohn & Williams, 1983). The current study examined the time course of this acclimation by determining photo-synthetic temperature optima as a function of time, of cool grown plants moved to warm growing conditions. Leaves which had developed under cool conditions were capable of an upward adjustment of 6–8°C of their optimum photosynthetic temperature within a time span of 6–14 d. For greatest photosynthetic temperature acclimation it was necessary for leaves to form and develop entirely under warm conditions. These leaves exhibited a 14–15°C upward adjustment of their optimum temperature for photosynthesis within 20–31 d since moving plants from cool to warm growing conditions. Thus, the time course of this acclimation is of short enough duration to be significant during the growing season and presumably contributes toward the ability of this species to maintain active growth during the cool and warm portions of the growing season. It is also noted that the plant with its capacity to form new leaves, has a much wider acclimation capacity than any single leaf.     

Observations on the development and maintenance of the deep sea barnacle,Octolasmis aymonini geryonophila (Pilsbry)

Thirty-two pedunculate barnacles, O. a. geryonophila, were maintained in culture for a period of 2 yr in the laboratory. These barnacles were obtained from the pleopods and mouth parts of the giant marine isopod, Bathynomus giganteus, which had been collected, at a depth of 200 fathoms, in the Gulf of Mexico.

The carina, scutum, mandible and maxilla of adult barnacles were typical of deep water species. However, the tergum and labrum were intermediate between those of shallow and deep water species.

Adults 3.1–4.1 mm in length were cultured in sea water (15–19°C), and fed on benthic copepods such as Tisbe furcata and Laophonte sp. Three broods of nauplii from 8 barnacles were obtained in 2 yr. Larvae were reared on plankton collected from Coney Island waters in which nauplii reached Stage IV in 10–14 days at 16°C. Isochrysis galbana and Thalassiosira pseudonana individually or in combination maintained nauplii to Stage IV, but with very high mortality. The lack of spines on the carapace edge of the nauplii distinguishes this deep water species from the shallow water form, O. mulleri.     

Effect of mosquitofish (Gambusia affinis) and sestonic food abundance on the invertebrate community within a constructed treatment wetland

1. The effect of mosquitofish (Gambusia affinis) predation on the invertebrate community in a hypereutrophic constructed treatment wetland in southern California was investigated at two nutrient levels that influenced sestonic food abundance. 2. Gambusia affinis and insect predators in the wetland had a significant impact on larval mosquito density in the wetland irrespective of nutrient level. At the end of the 5‐month study, cladoceran abundance in predator exclusion enclosures was 2–3 orders of magnitude greater than in the treatments that allowed access by planktivores. Chironomids were the most abundant insect group collected in emergence traps, and midge production from the high nutrient location of the wetland was greater than from the low nutrient location, but was not affected significantly by G. affinis. The presence of abundant alternative prey in this highly enriched wetland may have weakened the predation impact of G. affinis on mosquitoes. 3. The abundances of six invertebrate groups in dipper samples and of four insect groups in emergence trap collections were analysed using a multivariate distance‐based linear model. Fish treatment and location interactions with sampling date explained significant amounts of the variation in the abundance of invertebrate groups. 4. Multivariate multiple regression analysis showed that chlorophyll‐a concentration explained a large portion of the variability in non‐predatory insect and zooplankton abundance at the high nutrient location, whereas bacterial density explained a large portion of the variability in the abundances of these taxa at the low nutrient location. Predatory insects were not directly coupled to the bottom‐up influence of bacterial abundance and chlorophyll‐a.     

The Osmotic Inactivation in situ of Plant Mitochondrial Enzymes

When cauliflower buds are gently disrupted in distilled waterand homogenized immediately thereafter in hypertonic sucrose,the succinoxidase activity of particles prepared from such homogenatesis considerably less than that of particles prepared from tissuehomogenized in sucrose directly. Other enzymatic functions areimpaired as well. When tissue is washed in water for any lengthof time prior to homogenization, the deleterious effect of hypotonicityis exaggerated. The irreversible injury to the mitochondriabrought about by a hypotonic environment may be precluded tosome extent by maintaining the temperature at 0 C. Washinginjury is also minimized by washing tissue in hypertonic solutions. In addition to the irreversible osmotic injury which the mitochondriamay undergo, a reversible inhibition of succinic dehydrogenasemay be effected by a soluble, heat-stable component of cauliflowerjuice. The latter inhibition appears to be competitive in nature. The reduction of ferricyanide has been used as a means of measuringsuccinic dehydrogenase activity anaerobically. The concordanceof manometric and potentiometric measurements of dehydrogenaseactivity suggests that the ferrocyanide ion may move freelyfrom within the cell to the outer solution. There are indicationsas well that certain endogenous cell materials may be removedfrom the tissue during relatively short washing-periods.