Epicormic Bud Development in Quercus robur L. Studies of Endogenous IAA, ABA, IAA Polar Transport and Water Potential in Cambial Tissues10

Seasonal measurements of IAA,³ made using GC-MS, ⁴ indicatedthat in Q. robur the spring initiation of cambial activity andonset of visible bud outgrowth in the canopy is preceded byan increase in cambial region IAA. The effects of notch-girdlescut into the bole indicated that IAA in the cambial region laterwas present in separate physiological pools, with only the polar-transportedfraction affecting epicormic bud outgrowth. The stage in thespring when the epicormic buds grew out coincided with an increaseboth in cambial region IAA and in the capacity of cambial explantsfor IAA polar transport. Thus the stimulus needed by the epicormicbuds to overcome inhibition by polar-transported IAA appearedto be self-generated. The observed effects of exogenous hormoneson epicormic bud outgrowth from stem explants indicated thatthis stimulus might be cytokinin. The seasonal changes detectedin cambial region ABA³ were consistent with a role for stress-inducedABA in the induction of epicormic bud dormancy after canopydevelopment during the summer. No consistent effects of standthinning on cambial region IAA, ABA, water potentials or watercontents were detected, although polar transport of exogenousIAA by cambial region explants removed in the spring was reducedby thinning. Key words: Epicormic buds, cambium, hormones     

Structure and Function of Transfer Cells in the Sporophyte Haustorium of Funaria hygrometrica Hedw: III. TRANSLOCATION OF ASSIMILATE INTO THE ATTACHED SPOROPHYTE AND ALONG THE SETA OF ATTACHED AND EXCISED SPOROPHYTES

Translocation of products of photosynthesis from gametophyteto sporophyte was examined in the moss Funaria hygrometricaHedw., as an adjunct to companion studies on the ultrastructureof the sporophyte haustorium and its capacity for absorptionof sugars in vitro. Labelled products derived from gametophyticphotosynthesis are transported to the sporophyte at an approximatelylinear rate for up to 12 h after a pulse treatment with ¹⁴CO₂.Large sporophytes receive label at a greater rate than smallerones. Transport is inhibited under conditions of water stress,and by lack of light, though darkening the sporophyte alonehas no effect. Movement of label from the haustorium along theseta occurs at a velocity of 1–3 mm h^–1, and issimilar to the onward movement of label derived from [³H]glucosesupplied to the haustorium in vitro.     

An assessment of tributyltin contamination in the North Atlantic using imposex in the dogwhelk Nucella lapillus (L.) as a biological indicator of TBT pollution

Summary

Surveys of imposex in the dogwhelk Nucella lapillus suggest that most parts of the north Atlantic are free of TBT contamination at biologically significant levels. Imposex was absent or poorly developed at the large majority of sites, including coasts adjacent to major shipping lanes passing through Pentland Firth, the Minches and North Channel. There were “hot-spots” of TBT pollution at ports and harbours along the northeast coast of England but, with the exception of the stretch of coast which includes the major ports of Hartlepool and Teesside, impacts were highly localised. The severity of imposex has declined dramatically during the past decade in those areas for which there are comparative data from earlier surveys. This can presumably be attributed to the success of regulations prohibiting the use of TBT-based antifoulants on vessels <25 m in length.     

Ultraviolet reflectance mediates pollinator visitation in Mimulus guttatus

Floral colors are widely believed to be an adaptation to attract pollinators. Recently, our understanding of floral reflectance has broadened to include colors that are beyond the spectrum that human eyes can perceive (such as ultraviolet (UV) reflectance), yet we still know relatively little about which plant species reflect UV light or its effectiveness in attracting pollinators. We investigated the effect of UV reflectance in Mimulus guttatus in a number of different populations in British Columbia, Canada. We found that M. guttatus had distinct regions of the corolla where UV light was reflected and absorbed. When we manipulated the degree of contrast between the reflection and absorption area, we found that pollinator visitation was severely disrupted, in terms of frequency and foraging patterns observed. Despite the bright yellow (bee‐green) coloration and visible nectar guides in M. guttatus, we conclude that UV reflectance is critical in pollinator attraction.     

Ecological,morphological and genetic divergence of sympatric North Atlantic killer whale populations

Ecological divergence has a central role in speciation and is therefore an important source of biodiversity. Studying the micro‐evolutionary processes of ecological diversification at its early stages provides an opportunity for investigating the causative mechanisms and ecological conditions promoting divergence. Here we use morphological traits, nitrogen stable isotope ratios and tooth wear to characterize two disparate types of North Atlantic killer whale. We find a highly specialist type, which reaches up to 8.5 m in length and a generalist type which reaches up to 6.6 m in length. There is a single fixed genetic difference in the mtDNA control region between these types, indicating integrity of groupings and a shallow divergence. Phylogenetic analysis indicates this divergence is independent of similar ecological divergences in the Pacific and Antarctic. Niche‐width in the generalist type is more strongly influenced by between‐individual variation rather than within‐individual variation in the composition of the diet. This first step to divergent specialization on different ecological resources provides a rare example of the ecological conditions at the early stages of adaptive radiation.