Double Staining of Plant Materials in Bulk

Ovaries and ovules of Oryza sativa and Zea mays were collected between 9-30 and 10-30 AM, fixed in formalin-acetic-alcohol, stained in Delafield's hematoxylin for 2-4 hr, dehydrated through graded ethanol, counterstained for 3-4 hr either in light green, orange G or fast green (0.05-0.1%) at the 1:1 alcohol-xylene stage and embedded. A few ovaries were hydrolysed in 1 N HCI for 25 min at 60 C, stained in leuco basic fuchsin for 60-90 min, rinsed 3 times with a mixture of: 10% Na₂S₂O₅, 1; N HC1, 1; and distilled water, 18; washed repeatedly in distilled water, dehydrated through graded ethanol, counter-stained for 3-4 hr either with light or fast green (0.05-0.1%) at the 1:1 alcohol-xylene stage and embedded. Microtome sections were cut, ribbons mounted, dried, paraffin removed with xylene, and mounted in balsam. Uniformly stained preparations resulted and the dilute stains gave vivid color contrasts. Large numbers of ovules and ovaries can be processed in a short time, and reliable percentages of viable embryo sacs in normal, sterile and semisterile plants obtained.     

Monitoring of low concentrations of glucose in fermentation broth

A highly sensitive glucose sensor, operating in flow-injection analysis (FIA) mode, was developed for the detection of glucose in fermentation broth. The assay system is based upon the post-column reaction of the peroxide formed in the glucose-oxidase-catalysed reaction and subsequent spectrophotometric detection of the coloured product formed. The sensor system was characterised and calibrated using standard solutions, and later used for quantification of glucose in fermentation media. Two types of enzyme column were used: one operated in packed-bed mode and the other in expanded-bed mode. Both columns were integrated into a FIA system and were found to give good analytical results. Glucose concentrations as low as 0.1 mg/l and 5 mg/l could be detected in packed- and expanded-bed modes respectively. Glucose concentrations were measured during typical fed-batch fermentation conditions in this system, and the results are presented.     

Analysis of micromolar concentrations of glucose by an interference free flow injection based biosensor

A fast, sensitive, interference-free, single enzyme single reagent glucose biosensor, operated in flow injection analysis (FIA) mode, was developed. The method used involved formation of colored complex of titanium sulfate reagent with the peroxide generated by glucose oxidase immobilized in a packed bed reactor. The color developed was detected spectrophotometrically in a flow cuvette. The system could measure down to 0.5 mg glucose l^–1 and the response was reproducible and linear in the range 1 mg l^–1 to 100 mg l^–1. The analysis time for a 500 l sample was 35 s and was free of interference from a number of substances tested. Analysis results using an off-line batch kit were observed to be in agreement with the developed system for determination of glucose in blood plasma samples.     

Fluctuations in circumpolar seabird populations linked to climate oscillations

We found that synchronous fluctuations of two congeneric seabird species across the entire Arctic and sub-Arctic regions were associated with changes in sea surface temperatures (SST) that were linked to two climate shifts, in 1977 and again in 1989. As the SST changes linked to climate shifts were congruent at the scale of ocean basins, fluctuations of these species occurred similarly at continental or basin scale. Changes in colony sizes were examined for a decade following climate shifts. The magnitude of the SST shift was more important than its direction in determining the subsequent rate of population change. Seabirds declined when the SST shift was large and increased when the shift was small, although the effect differed between the Arctic-breeding species and the more temperate-breeding congener. The Arctic species, Thick-billed Murre ( Uria lomvia ) increased most rapidly when SST warmed slightly, while the temperate species, Common Murre ( Uria aalge ) showed most rapid increase with moderate cooling. Both showed negative trends with large temperature shifts in either direction. This pattern was replicated during both climate oscillations. Negative population trends in seabirds presumably indicate the alteration of underlying food webs. Hence, similar widespread fluctuations in response to climate shifts are likely for other ecosystem components (marine mammals, fish, and invertebrates).     

Fast calculation of the quartet distance between trees of arbitrary degrees

Background  

A number of algorithms have been developed for calculating the quartet distance between two evolutionary trees on the same set of species. The quartet distance is the number of quartets – sub-trees induced by four leaves – that differs between the trees. Mostly, these algorithms are restricted to work on binary trees, but recently we have developed algorithms that work on trees of arbitrary degree.