Responses to Water Stress in Adapted and Unadapted Carrot Cell Suspension Cultures

The responses of suspension-cultured cells of carrot to polyethyleneglycol (PEG)-induced water stress were studied after transferto culture medium containing PEG at concentrations between 0%and 25%. Growth characteristics, cellular osmotic potentialand organic solute concentration changes were followed in unadaptedcells and in cell lines adapted to growth in various PEG concentrations.A decline in fresh and dry weight increase occurred in unadaptedcells with decreasing water potential, while dry weight gainwas unaffected in adapted lines. Substantial osmotic adjustmentwas observed in adapted lines, due mainly to increased glucose,fructose and sucrose. Proline concentration increased up to40-fold in adapted and 12-fold in unadapted cells and otheramino acids including alanine, histidine and arginine showedsimilar, though smaller, responses. Polyamines and glycinebetainedid not increase significantly in either adapted or unadaptedcells. Changes leading to long-term adaptation to water stressare discussed in relation to short-term stress—shock responses. Key words: Water stress, cell culture, Daucus carota, osmotic adaptation, solute accumulation     

Genotype by environment interaction in the assessment of tolerance of partially resistant potato clones to potato cyst nematodes

Genotype by environment interactions in a number of field trials in different years are examined in relation to tolerance of potato cyst nematodes and the subsequent yield losses. A biplot technique is used to display the interaction effects graphically and facilitate identification of any patterns in the data. The results are assessed and discussed in relation to breeding strategies and the variation found between different nematode populations.     

Effects of Gibberellic Acid on the Activation, Synthesis, and Release of Acid Phosphatase in Barley Seed

Acid phosphatase activity was present in unimbibed barley seed,but rose during incubation of embryoless half-seeds and isolatedaleurone layers, and was further increased by 10^–6 M gibberellicacid (GA₃). Release of total acid phosphatase activity fromhalf-seeds and aleurone layers was markedly enhanced by GA₃.Inhibitor studies with cycloheximide and actinomycin D suggestedthat de novo synthesis of acid phosphatase occurred followingimbibition. Gel nitration, electrophoresis, and [¹⁴C]leucineincorporation studies revealed that a single molecular formof acid phosphatase was present in dry seed, whereas on incubationtwo further forms arose. A proportion of the three molecularforms of the enzyme was synthesized de novo. Gibberellic acidstimulated activation, but not de novo synthesis, of all threemolecular forms of acid phosphatase. Although a small amountof one of the molecular forms was secreted in the absence ofGA₃, the presence of gibberellin greatly increased secretionof the same form of acid phosphatase.     

Convergence and parallelism among cicadas of Argentina and the southwestern United States (Hemiptera: Cicadoidea)

Cicadas of the genera Derotettix in Argentina and Okanagodes in the south-western United States resemble each other in colour, live on salt-tolerant plants ( Atriplex spp. etc.), nearly match the colour of their respective host plants and produce songs above the range of avian hearing. The Argentine cicadas are smaller, but have nearly identical thermal limits for activity measured by the minimum temperature for flight (20–24 °C) and a body temperature at heat torpor (48–49 °C). The species shift activity from basking sites to shade at temperatures above 37 °C, although O .  gracilis rises to a significantly higher temperature (40.7 °C) than its congener (38.2 °C) or Derotettix (37.2 °C). The thermal tolerances are the highest reported for cicada species. A third group using halophytes in Argentina ( Babras sonorivox ) has similar temperature tolerances and is cryptically coloured. The genera are convergent with respect to morphology, coloration, body size, behaviour, habitat choice and host plant selection. The similarities of thermal tolerances and their influence on behaviour can be viewed as parallelism because the underlying mechanisms are the same in all species studied.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 281–288.     

Growth and provisioning strategies of Northern Fulmars Fulmarus glacialis

Growth and foraging strategies in procellariiforms show a great deal of variation, but the fulmarine petrels are notable in that chicks are fed frequently and develop unusually rapidly. This study examined age-related and daily variation in provisioning of the Northern Fulmar Fulmarus glacialis throughout the chick-rearing period at Fair Isle in 1997. In common with many other petrels, meal mass showed an initial rise with age, probably because of a gradual increase in chick gut capacity, but then levelled off. By comparison, feeding frequency showed little age-specific variation until chicks reached the oldest age-class, when the number of meals declined to less than a third of the previous level as chicks underwent mass recession prior to fledging. Compared with the limited day-to-day variation in mean provisioning rates for the whole sample, food delivery to particular chicks was much more variable, suggesting that differences in feeding rates were determined by stochastic factors influencing the feeding success of individual parents. The caloric density of feeds and their size in relation to adult mass were lower in Northern Fulmars than in most other Procellariiformes. This implies that adults are not heavily dependent on stomach oil formation to raise the energy content of the payload, but rely on a high feeding frequency to maintain adequate rates of energy transfer to chicks.     

Breeding frequency in Grey-headed Albatrosses Thalassarche chrysostoma

Although Grey-headed Albatrosses Thalassarche chrysostoma are usually regarded as biennial breeders, taking a year off following a successful breeding attempt, a small proportion of successful birds attempt to breed annually. This proportion was higher at Marion Island (5.4%) than at Bird Island, South Georgia (1.0%), suggesting that conditions are more favourable at Marion Island. This hypothesis is supported by higher average breeding success and shorter lags following both successful and failed breeding attempts at Marion Island. Factors favouring reproduction at Marion Island may include reduced intraspecific competition (given the much smaller breeding population) and/or more predictable food supply (owing to production of meso-scale eddies associated with the Indian Ocean Ridge). Although annual breeding appeared to increase the risk of adult mortality, with several birds that attempted to breed annually found dead the following year, at least some birds greatly enhanced their reproductive output, with one male raising five chicks in five successive years. Contrary to life-history theory, there was no evidence that older birds were more likely to attempt annual breeding because of declining reproductive value.     

AN EXPERIMENT IN RABBIT CONTROL

A successful experiment in rabbit control was carried out over one year on a 300-acre farm in Pembrokeshire. The control measures adopted were trapping, gassing and ferreting, in that order. Information on rabbit density was based primarily on counts of rabbit holes and on the number of animals caught. Observations were made on the breeding state and sex ratio of the population. Successful control was attributed to the persistent application of a variety of methods, and not to any one method in particular. Gassing was equally efficient on high and low rabbit populations; the three methods of application, namely pumping, spooning and a combination of both, were found to be equally effective. Re-infestation occurred, but was checked to some extent by trapping around the boundary.
The breeding season appeared to extend from January to June, inclusive. The sex ratio was biased in favour of females throughout the experiment. An almost even sex ratio was observed in embryos.     

Scaling-up knowledge of growing-season net ecosystem exchange for long-term assessment of North Dakota grasslands under the Conservation Reserve Program

Scaling‐up knowledge of land‐atmosphere net ecosystem exchange (NEE) from a single experimental site to numerous perennial grass fields in the Northern Great Plains (NGP) requires appropriate scaling protocols. We addressed this problem using synoptic data available from the Landsat sensor for 10 growing seasons (April 15 to September 30) over a North Dakota field‐site, where we continuously measured CO₂ exchange using a Bowen Ratio Energy Balance (BREB) system. NEE observed during the growing season at our field‐site from 1997 to 2006 vacillated with drought and deluge, with net carbon (C) losses to the atmosphere in 2006. We used stepwise linear regression with 10 years of Landsat and NEE data to construct and validate a model for estimating grassland growing‐season NEE from field to landscape scales. Eighty‐nine percent of the variability in NEE was explained by year, live biomass, carbon : nitrogen ratio, day of image acquisition, and annual precipitation. We then applied this model on 20 620 ha of North Dakota perennial grass fields enrolled in the Conservation Reserve Program (CRP), including 1272 fields east of the Missouri River and 165 fields west‐river. Growing‐season NEE for individual CRP fields was highly variable from 1997 to 2006, ranging from ?366 to 692 g C m^?2 growing season^?1. Mean annual growing‐season fluxes over 10 years for CRP fields located east‐river and west‐river were 317 g C m^?2 growing season^?1 and 239 g C m^?2 growing season^?1, respectively. Average cumulative growing‐season NEE modeled for fields east‐ and west‐river diverged from one another in 2002–2006, when west‐river fields received < 70% of the long‐term annual average precipitation during these years. Results indicate assessment of conservation practices on grassland CO₂ exchange during the growing season can be remotely estimated at field and landscape scales under variable environmental conditions and should be followed up with similar, spatially explicit investigations of NEE during the dormant season.