The roles of pH and [Ca<SUP>2+</SUP>] were investigated in relation to the maintenance and regulation of polarity in tip-growing <I>cells of Dryopteris affinis </I>protonemata. Intracellular [ion] was analysed by confocal microscopy of ion-sensitive dyes and ratio imaging. Initially, physiological and cytological aspects of tip growth in apical chlorocytes and rhizoid cells were examined. Findings are discussed in relation to the suitability of protonemata for the study of tip growth and with respect to other commonly studied cell types exhibiting polarised growth. Secondly, the suitability of different methods of introducing ion-sensitive dyes into cells were assessed. Calcium-sensitive dyes failed to load by any method except microinjection, which could not be used routinely because of the poor recovery of cells after injection and rapid vacuolar internalisation of injected dye free-acids. The pH sensitive dyes BCECF and carboxySNARF-1 could both be loaded into cells as their cell permeant AM esters without detrimental effects on cell health. However, sequestration within organelles, particularly the vacuole, proved to be a significant limitation. The problems of dye localisation were compensated for to a certain degree by the use of confocal microscopy and ratiometric analysis. Finally, cytoplasmic pH was examined in growth rhizoids by confocal ratio imaging of AM ester-loaded cSNARF-1. The limits of spatial resolution and precision of pH measurement by this method were estimated at ~ 1μm<SUP>2</SUP> and ~ 0.1 pH unit, respectively (over the pH range 6.9 to 7.3). For rhizoids, average cytoplasmic pH was estimated at 7.1 - 7.3, based on <I>in vitro</I> calibration. No significant cytoplasmic pH gradient (ΔpH of >0.1 unit) was found to be associated with tip growth.

The aim of this project was to investigate the relationship between the metabolism of various secondary metabolites derived from cinnamic acid (phenylpropanoids and related compounds) and the synthesis of capsaicin in fruits and cell cultures of Capsicum frutescens. A variety of compounds derived from cinnamic acid was detected in chilli pepper cultures. However, free phenplics were not detected in callus cultures. Most of the conjugated phenolics were present as O- or ester glycosides. p-Coumaric, ferulic and vanillic acid were detected after release by alkaline, acid or enzymic hydrolysis of water soluble conjugated phenolics. In suspension cultures, several unknown free phenolics were detected in the culture medium. Again as with callus, most phenolics in the cells were present as water soluble conjugates. Over the growth cycle, both callus and suspension cultures accumulated a substantial amount of lignin, but capsaicin was not detected. Apart from capsaicin, a number of water soluble conjugated phenolics were also accumulated in chilli pepper fruits, p- Coumaroyl, caffeoyl and 3,4-dimethyoxycinnamoyl glycosidases (hydroxycinnamoyl glycosides); vanillic acid glycoside; 3- rhamnosyl-quercetin, 7-glycosylluteolin and two unknown flavonoid glycosides were all detected. In addition, several unknown water soluble conjugated phenolics were also present. The proposed free phenolic intermediates in capsaicin biosynthesis were present at vanishingly low levels and only detected after short pulse labelling with [U-14C]-cinnamic acid. The synthesis, accumulation and disappearance of these compounds were studied in relation to the onset of capsaicin synthesis. Before the onset of capsaicin synthesis, the main products of phenyl-propanoid metabolism were the three hydroxycinnamoyl glycosides. During the onset of capsaicin synthesis, fruits were also actively synthesizing lignin and Ce-Ci-phenolic glycosides. There are two major sources of the intermediates for capsaicin, lignin and Ce-Ci phenolic glycosides, 1) the hydroxycinnamoyl glycosides and 2) free phenolics directly synthesized from cinnamic acid. After the onset of capsaicin synthesis, fruits were still actively metabolizing cinnamic acid to produce Ce-Cj phenolic glycosides. Some of these glycosides appeared to be further metabolized during fruit ripening. The metabolism of phenylpropanoids in developing fruits and cell cultures is discussed in relation to the regulation of capsaicin synthesis.

The aim of this study was to identify the cellular and physiological mechanism(s) for the action of the <i>Rht3</i> (dwarfing) allele in near-isogenic lines of wheat (<i>Triticum aestivum</i> L. <i>cv</i> Maris Huntsman). The <i>Rht3</i> allele did not affect the rate of initiation, or total number, of new leaf primordia and therefore stem internodes, formed by the shoot apex. The first observable effect of the <i>Rht3</i> allele was to reduce stem internode lengths, compared to those in the <i>rht3</i> wild-type, beginning <i>ca</i> 15 d after sowing. The second leaf (L2) was chosen as the model system in which to investigate the cellular basis for the effects of the <i>Rht3</i> allele. The <i>Rht3</i> allele did not reduce the maximum relative elemental growth rate (REGR) in L2 grown at 20<SUP>o</SUP>C compared to the <i>rht3</i> wild-type or the distance from the leaf base at which this was achieved. However, distal to the position of maximum REGR within the L2 extension zone the <i>Rht3</i> allele significantly reduced both the REGR and the rate of cell extension compared to the <i>rht3</i> wild-type. At 20<SUP>o</SUP>C, the <i>Rht3</i> allele reduced the length of the L2 extension zone from <i>ca</i> 20 mm to <i>ca</i> 13mm. The <i>Rht3</i> allele reduced both the rate of cell extension and final epidermal cell length, but did not cause any significant reduction in total cell number. In the <i>rht3</i> wild-type the length of the extension zone could be modified by the application of growth regulators, GA<SUB>3</SUB>, 2<i>S</i>, 3<i>S</i> paclobutrazol and/or growth at 10<SUP>o</SUP>C. However, the <i>Rht3</i> mutant allele could be mimicked in the <i>rht3</i> wild-typeby the application of 2<i>S</i>, 3<i>S</i> paclobutrazol and/or growth at 10<SUP>o</SUP>C.

A field trial programme was started in 1987 covering the main arable areas of the UK, comparing the Long Ashton (LARS) Crop Equivalent system for determining the need for herbicide in cereals against insurance spraying. In Scotland, 4 trials were established in East and West Lothian with both the LARS system and insurance spraying at full and half the recommended rate of chemical against an untreated control. The trials were to last 4 years with each treatment in the same location throughout the period to allow changes in the weed seed bank to be studied. Cropping years 1988-90 included 4 crops of spring barley, 5 of winter wheat and 3 of winter barley. At all sites there were significant effects of treatments on weed seed numbers in the trial with 3 crops of winter barley at Smiths where <I>Stellaria</I> <I>media</I> seed in the soil increased from 156/m<SUP>2</SUP> of soil in 1988 to 11789/m<SUP>2</SUP> in 1990. There was a large response to herbicide use for all the winter barley crops. but no clear response for spring barley and winter wheat. The half rate and threshold treatments tended to give the best margins for most crops. In some years, weeds were found to have an economic effect on crop harvesting above that predicted by the LARS threshold system. Cost of assessment was thought to be a major drawback of the LARS system and an alternative of reducing herbicide dose to suit field conditions was tested from autumn 1988. This proved successful in finding some of the major factors which affect the optimum dose of herbicide in a given field. Factors included weed species, active ingredient, weed size and weed number.

No description available.

This study was concerned with establishing the changes in pattern of protein synthesis associated with graft formation in Lycopersicon esculentum Mill., using a dual labelling technique. The mechanical strength of the graft was used as a parameter of development. Mechanical strength was found to be related to both cell number and number of tracheary elements for breaking weights up to 130 g after which it was related to tracheary element number alone. The transition between two stages occurred 3-4 days after grafting. The ability of a graft to form in isolation was investigated. It was found that a graft could develop in culture for at least twenty-four hours after excision without significant change in the pattern of development.

While the light regimes of closed forest strands and open pasture have been quantitatively described and modelled, agroforestry involves greater complexity and spatial variability. This research involved intensive measurement of quantum flux density (QFD) above and below re-spaced tree strands of Sitka spruce (<I>Picea sitchensis</I> [Bong.] Carr.) and hybrid larch (<I>Larix x eurolepis</I> Henry) in conjunction with measurement of tree growth. QFD was also measured above and below pasture growing in boxes in imported soil sunk to ground level beneath the trees. The Monteith hypothesis that crop growth in unstressed conditions is linearly related to the amount of QFD intercepted by its canopy was found to hold for above ground growth of trees at agroforestry spacings. The overall dry matter: QFD quotient (<I>e</I>) for <I>Picea sitchensis</I> across the range of tree frequencies was 0.32 g mol<SUP>-1</SUP> which is lower than typical values reported for agricultural crops, young container grown trees of <I>Salix viminalis </I>and <I>Populus trichocarpa</I> and closed-canopy <I>Picea sitchensis</I>, but comparable with previous estimates for a range of mature tree stands. <I>e</I> was unaffected by tree spacing, but was significantly higher for the tall tree stand which had been pruned. The mean annual QFD transmitted to the understorey varied from 39% to 96% of that in the open across the agroforestry treatments. The mean transmittance was similar but spatial variability of QFD was significantly higher in tree stands with crown to ground level when compared with stands having similar crown dimensions but which had been pruned to approximately 1.3 m height. More than 90% of seasonal pasture growth could be explained by a regression of growth on incident QFD.

No description available.

No description available.

The growth of <I>Lolium perenne </I>S23 was studied under different conditions of temperature and shade in laboratory and in garden plots. Data on plant and leaf dry weight were used to establish simple growth models. In the laboratory three light intensities (330, 165 and 85 μmol m<SUP>-2</SUP>s<SUP>-1</SUP>) were combined with temperature regimes of 10/10, 15/10, 15/15, 20/10, 20/15 and 20/20 <SUP>o</SUP>C in a 16h-photoperiod. Harvests were made when each of the first three leaves were fully expanded. In garden plots light quantity, light quality, R:FR ratio, temperature and total rainfall were monitored with seedlings grown in natural light (control), two artificial shade conditions (50 and 25% from total light) or two natural shade conditions effected by use of young poplar trees. Harvests were made at 5 day intervals per experiments conducted in June, July 1992 and August, September and October 1991. As expected significant effects of both light and temperature were found on total plant dry weight and on leaf dry weight. Increasing shade decreased plant weight at the same developmental stage, but tended to increase leaf length. These effects became progressively larger at successive harvests. Light also affected leaf cell number. Variation was largest in leaf three at 20/20 <SUP>0</SUP>C in high light and decreased with shade and temperature. In field experiments the influence of temperature was greater than that of shade on plant and leaf dry weight, leaf length and number of leaves coinciding in the main with laboratory findings. In contrast, cell number was more variable with no clear effect of shade on final cell number per leaf.