Biophysical and Biochemical Regulation of Cytoplasmic pH in Chara corallina during Acid Loads

The contribution of membrane transport to regulation of cytoplasmicpH in Chara corallina has been measured during proton-loadingby uptake of butyric acid. In the short-term (i.e. up to 20min) uptake of butyric acid is not affected by removal of externalK⁺, Na⁺ or Cl^– but over longer periods uptake is decreased(by 20–50% in different experiments) in the absence ofexternal Na⁺ or, sometimes, K⁺. Influxes of both Na⁺ and K⁺increase temporarily after addition of butyrate, Na⁺ immediatelyand K⁺ after a lag. Effects on Cl^– influx are small butCl^– efflux increases enormously after a short lag. Anapproximate comparison of internal butyrate with changes inthe concentration of K⁺, Na⁺, and Cl^– suggests that initially(i.e. for a few min) cytoplasmic pH is determined by bufferingand possibly by some decarboxylation of organic acids (biochemicalpH regulation), and that biophysical pH regulation involvingefflux of H⁺ balanced by influxes of K⁺, Na⁺ and especiallyefflux of Cl^– progressively becomes dominant. When butyric acid is washed out of the cells, cytoplasmic pHis restored completely or partially (depending on the butyrateconcentration used) and this is independent of the presenceor absence of external Cl^–. Where Cl^– is present,its influx is relatively small. It is suggested that cytoplasmicpH is then controlled biochemically, involving the synthesisof an (unidentified) organic acid and the accumulation of acidicanions in place of butyurate lost from the cell. During thesecond application of butyrate, net Cl^– efflux is small:it is suggested that control of cytoplasmic pH then involvesdecarboxylation of the organic acid anions. The questions of the source of Cl^– lost from the cell(cytoplasm or vacuole) and of possible cytoplasmic swellingassociated with the accumulation of butyrate are discussed. Key words: Chara corallina, butyric acid, cytoplasmic pH, membrane transport     

A critical analysis of the causes of boron toxicity in plants

This study investigated the main factors contributing to boron toxicity in plants. Growth was rapidly inhibited by internal B concentrations in the range 1–5 m m across a range of plant types that included monocot, dicot and algal species. In contrast, mature cells were able to withstand up to 60 m m B for several days. In wheat, rapid inhibition of root growth occurred if high B was applied to the root tip, but not if high B was applied to mature sections of the root. In leaves, there were gradations in B concentrations that correlated with visible symptoms of toxicity. However, there was no evidence to support the hypothesis that toxicity in leaves is due to osmotic stress induced by the accumulation of B. Analysis of the sensitivity to B of a range of metabolic processes including photosynthesis, respiration and protein synthesis leads to the conclusion that growth is not restricted by effects of B on energy supply and not directly by inhibition of protein synthesis. At higher B concentrations, many cellular activities were found to be partially inhibited and the toxicity to mature tissues was therefore considered not to arise from the disruption of a single process, but from the accumulated retardation of many cellular processes, exacerbated in light by photo‐oxidative stress.     

Responses of house mice to the removal of mammalian predators and competitors

Efforts to eradicate multiple mammal pests from offshore islands and fenced mainland ‘habitat islands’ often fail to remove mice, and such failures can result in a dramatic change in the food‐web whereby the removal of larger mammal pests facilitates a population explosion of mice through predator and competitor release. We investigated the ecological responses of house mice to the removal of mammalian predators from a 500‐ha fenced sanctuary at Tawharanui, northern New Zealand. Data on population structure and body condition of mice trapped in 2007, in four habitat types within the sanctuary, were compared with baseline data collected in 2001, before mammal control operations commenced. We hypothesized that: (i) in the absence of mammalian predators mouse densities would increase in all habitat types that provide vegetation cover, and (ii) in the absence of mammalian competitors mice would become heavier due to greater access to food resources. Mouse densities were significantly higher in 2007 than in 2001 in three habitat types. The high density of mice in forest – where none were trapped prior to control – suggests a competitive release, in which mice profited from the removal of ship rats. No mice were caught in the presence of ship rats on a forest trap‐line at a control site outside the sanctuary. Mice trapped in 2007 were significantly heavier than those trapped in 2001, and significantly heavier than mice trapped at the control site. Greater access to food in the absence of competing and predatory mammals probably explains the heavier body weight of Tawharanui mice. There has been a significant change in the mammalian food‐web at Tawharanui, such that the house mouse is now the primary pest. A rapid and dramatic increase in mouse numbers is likely to adversely impact invertebrates and seedling recruitment, which in turn could affect ecosystem functions.     

Endogenous Gibberellins and Growth of Tobacco Callus Cultures

Tobacco callus grown under a range of conditions for different lengths of time contained various levels of gibberellin-like substances. Culture conditions, viz: light versus darkness and the quantity of cytokinin in the medium, affected the amount of gibberellins found in the tissue. These culture conditions were also important in controlling growth rate of the callus and modified the ability of the tissue to respond to exogenous gibberellins. Furthermore, substances which are known to inhibit gibberellin biosynthesis and also thought to block gibberellin action in some cases, were found to reduce the rate of growth. These data support the idea that endogenous gibberellins may be important in the control of the normal growth of tobacco cells in culture.     

A biological consequence of reducing Arctic ice cover: arrival of the Pacific diatom Neodenticula seminae in the North Atlantic for the first time in 800 000 years

The Continuous Plankton Recorder survey has monitored plankton in the Northwest Atlantic at monthly intervals since 1962, with an interegnum between 1978 and 1990. In May 1999, large numbers of the Pacific diatom Neodenticula seminae were found in Continuous Plankton Recorder (CPR) samples in the Labrador Sea as the first record in the North Atlantic for more than 800 000 years. The event coincided with modifications in Arctic hydrography and circulation, increased flows of Pacific water into the Northwest Atlantic and in the previous year the exceptional occurrence of extensive ice‐free water to the North of Canada. These observations indicate that N. seminae was carried in a pulse of Pacific water in 1998/early 1999 via the Canadian Arctic Archipelago and/or Fram Strait. The species occurred previously in the North Atlantic during the Pleistocene from∼1.2 to∼0.8 Ma as recorded in deep sea sediment cores. The reappearance of N. seminae in the North Atlantic is an indicator of the scale and speed of changes that are taking place in the Arctic and North Atlantic oceans as a consequence of regional climate warming. Because of the unusual nature of the event it appears that a threshold has been passed, marking a change in the circulation between the North Pacific and North Atlantic Oceans via the Arctic. Trans‐Arctic migrations from the Pacific into the Atlantic are likely to occur increasingly over the next 100 years as Arctic ice continues to melt affecting Atlantic biodiversity and the biological pump with consequent feedbacks to the carbon cycle.