Unsaturated Fatty Acid Synthesis During the Development of Isolated Sunflower (Helianthus annuus L.) Seeds

The effect of temperature on unsaturated fatty acid synthesisin developing sunflower seed embryos (Helianthus annuus L.)has been studied using isolated seeds grown in culture. Variabilitybetween individual embryos in the response to temperature wasalso investigated. Oil and dry matter accumulation in cultured embryos were similarto those of embryos allowed to develop in intact plants, andthe effect of increasing temperature in lowering the amountof linoleic acid in seed oil was reproduced in cultured embryos.The isolated seed culture system, therefore, constitutes a suitablemodel system for studies of oil synthesis in developing sunflowerembryos. The decrease in linoleic acid synthesis in response to highertemperature was detectable after only 18 day-degrees incubation,and the incorporation of labelled substrates suggests that alterationsin the fatty acid composition of seed oil in response to temperatureare produced by an effect on the desaturation of newly synthesizedoleate rather than through turnover of existing lipid. Variation in fatty acid composition between individual embryosgrown at constant temperature was considerable. The detectionof embryos with high linoleic acid levels following growth athigh temperature indicates that potential may exist for theselection of cultivars for temperature-stable fatty acid compositionin sunflower oil. Key words: Fatty acid synthesis, Helianthus annuus, Sunflower seeds     

Influence of temperature and duration of leaf wetness on infection of Acyrthosiphon kondoi with Erynia neoaphidis

Bioassays were carried out to examine the influence of temperature and duration of leaf wetness on the infectivity of an isolate of Erynia neoaphidis for its aphid host Acyrthosiphon kondoi. Preliminary experiments demonstrated that primary spores produced in vitro were as infectious as those formed in vivo. No consistent effect of temperature on infectivity of primary spores could be detected. The time taken to kill an aphid increased as temperature decreased, from 3–5 days at 20 °C to 12–15 days at 8 °C, suggesting a threshold for disease development of 4 °C. Increasing duration of the period of leaf wetness up to 24 h after inoculation increased the final level of infection. At 20 °C, a minimum moisture period of 3 h was required for infection with maximum infection occurring after about 7 h. These times increased slightly at 15 °C but extending to 7 and 16 h respectively at 10 °C. The epizootiological implications of these results are discussed with reference to previously published data on in vivo production of primary spores of E. neoaphidis.     

Boundary Layer Effects in Ion Absorption by Roots and Storage Organs of Plants

In plant nutrition studies with culture solutions it is tacitly assumed that replenishment of ions at the root surface is guaranteed by the turbulence of the stirred solution. That this belief may be erroneous is demonstrated in this study with barley roots and discs of beet roots and potato tubers. At very low concentrations of RbCl (in presence of CaCl₂) the uptake of Rb by roots is strongly controlled by the rate of stirring. The results are interpreted in the light of the Nernst hydrodynamic boundary film which surrounds solids and through which ions must diffuse to reach the root surface. “Film-controlled” and “root-controlled” ion uptake is visualized.     

Weight loss of the female during the first brood as a factor influencing second brood initiation in Great Tits Parus major and Blue Tits P. caeruleus

We tested the hypothesis that the weight lost by female Great and Blue Tits Parus major and P. caeruleus while raising their first brood influences their ability to start a second brood. The evening weight of female parents was recorded when the nestlings were 5 and 13 days old, in different years and habitats. Several predictions were tested: (1) both species lose weight while raising nestlings and Great Tit females which start a second brood lose less weight than females which do not; (2) differences in the average weight lost between years and areas correlate with differences in the proportion of second broods; (3) the relative weight loss in Blue Tits, which only rarely undertake second broods, is higher than in Great Tits in which second broods are more common. Other factors also are related to the probability of undertaking a second brood: more second broods are undertaken by more successful females, adult females and females that lay earlier.
The comparison of Great and Blue Tits suggests that the two species use different reproductive strategies.     

Nesting activity,breeding success and colony size for the Wedge-tailed Shearwater Puffinus pacificus on Heron Island

Abstract The Capricorn Group of islands in Australia's Great Barrier Reef Marine Park sustains one of the world's largest breeding populations of the Wedge-tailed Shearwater Puffinus pacificus. Heron Island, a 13.5 ha coral cay which supports tourist and research station leases as well as a national park, is the third largest nesting island in the group. Sample censuses of breeding burrows were conducted each year between 1985 and 1990 and a further survey was completed in 1993. These returned estimates of between 13 264±1387 and 16 337±1545 active burrows (Y±SE). Burrow densities within each of the habitats monitored showed no significant trends between years, although there were large differences in burrow density between habitats. There were roughly the same number of burrows in the developed (west) and national park (east) halves of the cay. A miniature video camera system (burrowscope), which allowed nesting chambers at the ends of burrows to be inspected, was used in 1989, 1990 and 1993. This demonstrated that around half the burrows were occupied by incubating birds. Variations were found in the distribution of incubating birds between habitats, although this did not remain constant between the years. In the 1993 season, breeding activity was traced from the burrow establishment to fledging stage. Fifty-one per cent of burrows were used for breeding (eggs laid), 77% of eggs hatched and 80% of chicks produced a fledgling. Overall breeding success for the island was estimated at 61%. In 1993 the area designated as Buildings was found to have significantly lower hatching success compared with natural habitats. Most mortality occurred at the egg stage; however, in the Fringe habitat, mortality was highest at the chick stage. Previous surveys have estimated the breeding population from burrow counts. It now appears that only about 30% of such burrows produce fledglings.     

Feeding behaviour and mortality of the slug, Deroceras reticulatum in relation to control with molluscicidal baits containing various combinations of metaldehyde with methiocarb

In terms of control of slug pests, the differing modes of action of the two molluscicides metaldehyde and methiocarb appear to provide some advantages for the former during warm, dry weather and for the latter during cool, wet weather. With a view to exploiting these different modes of action, the feeding behaviour of Deroceras reticulatum (Müller) presented with molluscicidal baits containing various combinations of metaldehyde with methiocarb was investigated. Voluntary feeding trials conducted in the laboratory with both candidate and standard treatments (containing metaldehyde or methiocarb alone) are described. By combining the two active ingredients in certain ratios the total concentration of active ingredients may be reduced without adversely affecting the efficacy of a bait formulation in terms of slug mortality.     

Optimal stomatal conductance in relation to photosynthesis in climatically contrasting Eucalyptus species under drought

Models of stomatal conductance (g_s) are based on coupling between g_s and CO₂ assimilation (A_net), and it is often assumed that the slope of this relationship (‘g₁’) is constant across species. However, if different plant species have adapted to different access costs of water, then there will be differences in g₁ among species. We hypothesized that g₁ should vary among species adapted to different climates, and tested the theory and its linkage to plant hydraulics using four Eucalyptus species from different climatic origins in a common garden. Optimal stomatal theory predicts that species from sub‐humid zones have a lower marginal water cost of C gain, hence lower g₁ than humid‐zone species. In agreement with the theory that g₁ is related to tissue carbon costs for water supply, we found a relationship between wood density and g₁ across Eucalyptus species of contrasting climatic origins. There were significant reductions in the parameter g₁ during drought in humid but not sub‐humid species, with the latter group maintaining g₁ in drought. There are strong differences in stomatal behaviour among related tree species in agreement with optimal stomatal theory, and these differences are consistent with the economics involved in water uptake and transport for carbon gain.