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.     

Seed Development in the Recalcitrant Species Quercus robur L: Water Status and Endogenous Abscisic Acid Levels

Water status and endogenous ABA levels were measured duringthe development of the embryonic axis and cotyledons in fruitsof Quercus robur L. As dry matter accumulated in the embryoduring development, both moisture content and osmotic potential(     

The Role of ABA in the Control of Apple Seed Dormancy Re-appraised by Combined Gas Chromatography-Mass Spectrometry

Measured by GC—MS²—SIR³, endogenous ABA⁴ in embryonicaxes of seeds of Malus pumila L. cv. Golden Delicious decreased8-fold and cotyledon ABA by only 60%, during 10–50 d ofstratification at 5 ?C, after ABA leaching during an initial24 h soaking. During stratification, the percentage germinationof embryos transferred to 17?C showed a significant linear dependenceon log_e of ABA levels in the axes at transfer. Between 50 and70 d, ABA levels increased markedly in axes and testa both ofstratified seeds and seeds allowed to re-dry at 17 ?C afterinitial soaking. The ability of fully stratified axes with elevatedendogenous ABA to germinate indicated that stratification haddecreased their ABA sensitivity. Changes in cotyledon ABA couldnot account for the promotory effect of cotyledons on germinationduring the first 30 d of stratification. Loss of testa inhibitionof germination during stratification was not linked with changesin testa ABA. Stratification markedly increased the sequestrationin the axes of exogenous ABA supplied via the cotyledons. Changesboth in axis ABA levels and sensitivity were thus correlatedwith dormancy release, but subject to modifying control by thecotyledons and testa not involving ABA. Rehydration of driedseeds affected axis ABA later during storage via mechanismsunconnected with dormancy. Key words: ABA, seed dormancy, stratification     

The Effects of Mother Plant Nitrogen and Phosphorus Nutrition on Hollow Heart and Bleaching of Pea (Pisum sativum L.) Seed

Pea plants were grown in a greenhouse under different conditionsof nitrogen and phosphorus nutrition. In one experiment thetwo treatments, consisting of 450 mg N, 255 mg P and 450 mgN, 422 mg P per plant, produced seeds with a high incidenceof hollow heart (40·1% and 45·3% respectively).In another experiment high nitrogen nutrition levels (800 and1050 mg N per plant) produced an increase in the number of plantswith bleached seeds. Bleached seeds or ones with hollow heartproduced high soak-water conductivity readings and germinatedpoorly in the field.