Analysis of cytosolic isocitrate dehydrogenase and glutathione reductase 1 in photoperiod‐influenced responses to ozone using Arabidopsis knockout mutants

Oxidative stress caused by ozone (O₃) affects plant development, but the roles of specific redox‐homeostatic enzymes in O₃ responses are still unclear. While growth day length may affect oxidative stress outcomes, the potential influence of day length context on equal‐time exposures to O₃ is not known. In Arabidopsis Col‐0, day length affected the outcome of O₃ exposure. In short‐days (SD), few lesions were elicited by treatments that caused extensive lesions in long days (LD). Lesion formation was not associated with significant perturbation of glutathione, ascorbate, NADP(H) or NAD(H). To investigate roles of two genes potentially underpinning this redox stability, O₃ responses of mutants for cytosolic NADP‐isocitrate dehydrogenase (icdh) and glutathione reductase 1 (gr1) were analysed. Loss of ICDH function did not affect O₃‐induced lesions, but slightly increased glutathione oxidation, induction of other cytosolic NADPH‐producing enzymes and pathogenesis‐related gene 1 (PR1). In gr1, O₃‐triggered lesions, salicylic acid accumulation, and induction of PR1 were all decreased relative to Col‐0 despite enhanced accumulation of glutathione. Thus, even at identical irradiance and equal‐time exposures, day length strongly influences phenotypes triggered by oxidants of atmospheric origin, while in addition to its antioxidant function, the GR‐glutathione system seems to play novel signalling roles during O₃ exposure.     

Behavioural strategies of cormorants (Phalacrocoracidae) foraging under challenging light conditions

Diving is indicative of foraging in cormorants (Phalacrocoracidae). We have investigated a range of parameters associated with diving in Great Cormorants Phalacrocorax carbo to provide insight into the bases of cormorant predatory strategies. We hypothesize that if vision is important in cormorant foraging behaviour, and if they are not constrained by the position of their prey in the water column, then diving behaviour will be modulated primarily in response to the diel variation in ambient light levels. Specifically, we propose that cormorants forage at shallower depths when light levels are low, and more deeply when light levels are high. We provide evidence that this is the case. We recorded the occurrence of cormorant diving behaviour using implanted data loggers and recorded ambient light levels and water temperature using leg-mounted loggers in a sample of free-living Great Cormorants in Greenland. Our results show that dives are shallower at the beginning and end of each day when light levels are lower. We suggest that these data support the hypothesis that cormorant foraging is visually-guided even though recent evidence has shown that their underwater visual acuity is poor.     

Ecological and Evolutionary Aspects of Integumentary Respiration: Body Size, Diffusion, and the Invertebrata

SYNOPSIS. Most animal phyla lack specialized respiratory surfacesand all phyla contain groups that, for some part of their lifehistory, depend entirely upon integumental diffusion of respiratorygases. Animals that are diffusion-limited, yet function aerobicallyare generally small with large surface areas and there has beenconvergence for this among all phyla including the coelomateinvertebrates. Acoelomates lack specialized respiratory structuresbut have highly modified integuments, functional specializations,and features ranging from symbioses to air gulping that compensatefor diffusion limitation. The diversity of structures functioningfor integumentary respiration is much greater among invertebratesthan vertebrates. Among the higher invertebrates with respiratorysurfaces, accessory integumentary O₂ uptake is usually 20 to50% of total respiration. The high diffusion constant of O₂in air minimizes boundary effects on gas transfer and permitslarger body size, although this is limited by dry conditions.Terrestrial annelids and flatworms, both confined to moist habitats,are larger than aquatic forms which often have accessory gills.Size differences between terrestrial forms in these two phylareflect the presence of a circulation in the annelids. Ontogenetictransitions from skin breathing to other respiratory structuresoccur among marine invertebrates and vertebrates. Vertebratesapparently exercise greater integratory control over integumentalrespiration through adjustment of ventilation and perfusion;however, it is not known if these processes occur in some invertebrates.     

A preparation of the stick insect Carausius morosus for recording intracellularly from identified neurones during walking

ABSTRACT. Using a preparation of the stick insect it is possible to record activity from the neuropile of the mesotheoracic ganglion during sequences of walking behaviour lasting several minutes. The animal walks on two lightweight wheels, counterbalanced to give an upthrust of 0.4 g against the legs. Each wheel may be rotated independently during turning behaviour. The walking behaviour of the operated preparation is compared with the results obtained for free-walking animals, and intact or partially operated preparations, walking on heavier wheels and mercury. Records from several identified retractor motor neurones show the stability and reproducibility obtainable with this preparation.     

Variation among 41 Genotypes of Tomato (Lycopersicon esculentumMill.) for Crossability toL. peruvianum(L.) Mill.

Even with the aid of tissue culture, crosses betweenLycopersiconesculentum(E) andL. peruvianum(P) typically yield few progeny.To determine whether some E genotypes produce more progeny perfruit that others when crossed with P, 41 E genotypes were crossedwith pollen bulked from five P accessions. This first experiment(expt 1) was replicated over 2 years. In a second experiment(expt 2), differences among three genotypes each of E and P,and among individual plants within E genotypes were investigated.The E genotypes for expt 2 were chosen for relatively high andlow crossability based on results of expt 1. The P genotypesfor expt 2 were from different accessions than those used inexpt 1. For both experiments, the 15 largest ovules from eachripe fruit were cultured aseptically for 1 month. Out of 1228fruit, 753 hybrids were obtained. For expt 1, significant genotypeby year interactions were observed. Within each year, therewere significant differences among E genotypes for crossability.In expt 2, significant effects were found for E genotypes, butnot for interactions between E and P genotypes, P genotypes,nor plants within E genotypes. Moreover, general crossabilityfor E genotypes using bulked pollen (expt 1) was indicativeof general crossability with three P accessions not presentin the bulk (expt 2). Thus, selecting E genotypes of high crossabilityto P is the key to obtaining progeny for gene introgression.Rare production of ExP seed which was large and had brown seedcoats typical of E seed indicated strong selection pressureto maintain separate species, but gene exchange in nature maybe possible albeit at a low rate over long periods of time. Interspecific hybridization; Lycopersicon esculentum; Lycopersicon peruvianum; ovule culture; speciation     

Yearly variation in seasonal patterns of honeyeater abundance,flower density and nectar production in heathland near Sydney

Despite a consistent seasonal pattern of daily production of nectar-energy per unit area with peak production around the end of May, the seasonal pattern of honeyeater abundance is not consistent between years and does not correspond to the pattern of nectar-energy production.