Light-dependent quenching of chlorophyll fluorescence in pea chloroplasts induced by adenosine 5′-triphosphate

Addition of ATP to chloroplasts causes a reversible 25–30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by DCMU and electron acceptors and has a half-time of 3 minutes. Electron donors to Photosystem I can not overcome the inhibitory effect of DCMU, suggesting that light activation depends on the reduced state of plastoquinone. Fluorescence emission spectra recorded at ?196°C indicate that ATP treatment increases the amount of excitation energy transferred to Photosystem I. Examination of fluorescence induction curves indicate that ATP treatment decreases both the initial (F_o) and variable (F_v) fluorescence such that the ratio of F_v to the maximum (F_m) yield is unchanged. The initial sigmoidal phase of induction is slowed down by ATP treatment and is quenched 3-fold more than the exponential slow phase, the rate of which is unchanged. A plot of F_v against area above the induction curve was identical plus or minus ATP. Thus ATP treatment can alter quantal distribution between Photosystems II and I without altering Photosystem II-Photosystem II interaction. The effect of ATP strongly resembles in its properties the phosphorylation of the light-harvesting complex by a light activated, ATP-dependent protein kinase found in chloroplast membranes and could be the basis of physiological mechanisms which contribute to slow fluorescence quenching in vivo and regulate excitation energy distribution between Photosystem I and II. It is suggested that the sensor for this regulation is the redox state of plastoquinone.     

Rate of acclimation of the tropical salt-marsh fish Cyprinodon dearborni to temperature changes

The acclimation rates of temperature changes in Cyprinodon dearborni, collected from Laguna Los Patos, Cumana, Venezuela, were determined by the critical thermal maximum method. At an increase in temperature (from 24 to 31°C) fish started to gain acclimation level after 3 hours and took 3 days to fully get up to a higher level of resistance to heat death; however, at a decrease in temperature (from 3 t to 24°C) fish began to lose its acclimation level after 12 days and required 39 days to reach a lower level of resistance to thermal death.     

Implications of Catlin's American Indian population estimates for revision of Mooney's estimate

Catlin's population estimates of 37 American Indian tribes for the period 1832 to 1839 are compared with Mooney's estimates for the same tribes that range from the year 1600 to the year 1780. The remarkably close correspondence between the two totals despite the difference in the time periods indicates considerable inaccuracy on the part of either Mooney or Catlin. If Catlin is given credibility, then the necessity of current upward revisions of Mooney's population estimate is supported.     

Effects of feeding and starvation on growth and swimming activity in an obligatory air-breathing fish

Reared in (tubular) aquaria containing different depths of water, Ophiocephalus striatus (0.7 g, 4.5 cm body length), an obligatory air-breathing tropical fish, swam long or short distances to enable themselves to exchange atmospheric air. In each tested depth (2.5, 5.0, 15.5, 31.0 and 40.0 cm) series, one group was starved, while the other was fed ad libitum twice a day on fish muscle. In the shallowest water (2.5 cm depth), the feeding group surfaced 1,294 times, travelling 64.7 m at an energy cost of 20.4 mg dry fish substance/g live fish/day, against those exposed to the deepest water (40 cm depth), which expended 35.8 mg/g/day, swimming 1,503.4 m on 1,879 visits to the surface. The starving group surfaced only 482 times, travelling 24.1 m at an expense of 5.8 mg/g/day in the shallowest water, while those at 40 cm depth surfaced 504 times, swimming 403.2 m at an energy cost of 7.4 mg/g/day. Owing to the sustained swimming activity and the consequent fatigue, the test individuals belonging to both groups in all the tested series hang to the surface for a definite interval, repaying the O₂ debt. Observations were also made to assess the duration of hanging to precisely estimate the distance travelled. Irrespective of changes in depths of water, the duration of hanging to surface was only 3.0 hr/day for the feeding groups, while it was as much as 15.5 hr/day for the starving groups. The maximum sustained metabolic level of O.striatus reared in 40 cm depth was equivalent to 1.23 ml O₂/g/hr, which is about 2 times higher than the value reported for the active metabolism of swimming Oncorhynchus nerka at 15°C in Brett's (1964) respirometer. O.striatus reared in 2.5 cm depth fed 32.0 mg and converted 6.7 mg dry food/g live fish/day, while those exposed to the deepest water fed 49.1 mg, but converted only 5.5 mg/g/day. Culturing obligatory air-breathing fishes in shallow waters will be advantageous.     

Cost modelling of Pseudomonas fluorescens and Pseudomonas chlororaphis as biocontrol for competitive exclusion of Salmonella enterica on tomatoes

Published research on process-based models for biocontrol of foodborne pathogens on produce is limited. The aim of this research was to develop cost model estimates for competitive exclusion (CE) process using Pseudomonas fluorescens and Pseudomonas chlororaphis (non-plant pathogenic and non-human pathogen) as biocontrol against Salmonella enterica on tomatoes. Cost estimates were based on material inputs, equipment, facilities, and projected processing conditions of post-harvest packaging of tomatoes. The microbiological data for inactivation of S. enterica was based on published papers. The small-scale processing facility was assumed to have a processing capacity of 2000 kg of tomatoes/hour for 16 h per day, operational 6 days a week, and for 3-months /year. The large-scale facility was assumed to have a processing capacity of 100,000 kg of tomatoes/hour. Estimated initial capital investment costs for small and large-scale models (production facility) were US$391,000 and US$2.1 million. Application of CE for biocontrol of S. enterica on tomatoes was estimated at US$0.0058–0.073/kg of tomatoes during commercial processing operations. This exceeds chlorine wash technology estimated at US$0.00046/kg and is competitive with gaseous chlorine dioxide at US$0.02–0.21/kg. For high-value produce, CE may complement existing technologies increase food safety, reduce storage loses, and extend shelf life of produce.     

A Simple Numerical Procedure for Estimating the Prior Probability in the Biomathematical Proof of Paternity

This note gives a simple procedure for finding the maximum likelihood estimate of the prior probabilities in paternity cases. The procedure is based on a fixed point principle.