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Data on sugar beet yields from a long-term experiment (1965–1993) at IACR Broom's Barn are used, in conjunction with long-term weather data, to assess the degree to which weather affects yield and how this effect is modified by nutrient availability. Mean temperatures and rainfall during July and August were strongly correlated with sugar beet yields, as well as mean temperature during April and the length of time between sowing and harvest. The data from July and August were entered into a factor analysis to generate two factors describing how hot and dry weather conditions are during July and August. These two factors, as well as April temperature and the length of the growing season, were entered into a multiple regression. The regressions revealed strong effects of the principal axis factors on sugar beet yields across treatments, as well as strong effects of the length of the growing season, but weaker effects of April temperatures. The strength of response to weather was dependent on the nutrient regime, and was, in particular, greater with increased application of nitrogen. There was, however, no effect of nutrient regime on the strength of response of yield to the length of the growing season. These results indicate that weather-induced year-to-year variability in sugar beet yields in unirrigated crops is primarily determined by conditions in July and August as well as the length of time between sowing and harvest, and imply that drought limits yields in well-fertilised crops. The practical implications of these results are that the risk of yield losses due to drought may be minimised by maximising the length of growing season, and that there is the potential for developing simple measures to forecast yields through monitoring of rainfall.

The phytoplankton community, physical variables, and nutrient and chlorophyll a (Chl a) concentrations were monitored during the first two of six open-water seasons of hypolimnetic oxygenation in double-basined Amisk Lake, Alberta. Deep mixing of the water column in the treated basin (Zmax = 34 m) in spring was enhanced by hypolimnetic oxygenation. Oxygenation began in June 1988, when stratification was likely already established, but subsequent year-round treatment favoured an extended spring diatom bloom (Asterionella formosa and Cyclotella spp.), followed by a delay in the development of, and reduction in the severity of, cyanobacterial blooms (Aphanizomenon flos-aquae and Anabaena flos-aquae) in 1989. Historically, mean summer Chl a and total phosphorus (TP) concentrations in the euphotic zone (0-6 m) of the treated basin were 15.9 ± 1.6 and 33.5 ± 1.5 µg ·L-1, respectively, indicating a eutrophic lake. In 1988 and 1989, mean summer Chl a (10.0 ± 0.6 and 8.1 ± 0.7 µg ·L-1, respectively) and TP concentrations (29.0 ± 0.5 and 22.5 ± 0.9 µg ·L-1, respectively) in this stratum were lower than historic values (P < 0.05), indicating that the trophic status of Amisk Lake had shifted towards mesotrophy.

Activin A is a member of the transforming growth factor-beta family of growth factors and a potent regulator of cellular activity. A number of binding proteins for activin A have been identified, including alpha 2-macroglobulin (alpha 2M). Alpha 2M has several conformational states that are known to have different growth factor-binding properties. The effect of alpha 2M conformation on activin A binding has not been characterized. The aims of this study were to determine 1) whether activin A binds preferentially to the native (alpha 2M-N) or "activated" (alpha 2M*) conformation of alpha 2M, 2) the affinity of different alpha 2M conformations for activin A, and 3) the fate of activin A complexed with alpha 2M-N or alpha 2M* in vivo. [125I]Activin A associated with alpha 2M in plasma and follicular fluid and with purified alpha 2Ms. In this qualitative assay, more activin A was associated with alpha 2M* than with alpha 2M-N. The affinity of the activin A-alpha 2M interaction was determined. The Kd values for activin A-alpha 2M* and activin A-alpha 2M-N were 190 +/- 30 and 510 +/- 60 nM, respectively. The plasma clearance profiles and tissue distribution of uncomplexed activin A and purified alpha 2M*-activin A complex were determined. Radiolabeled activin A cleared in a biphasic manner, with rapid clearance over the initial 10 min and substantially slower clearance over the subsequent 20 min. During the slow phase of clearance, activin A formed a complex with circulating alpha 2M-N. In contrast, radiolabeled activin A-alpha 2M* complexes were rapidly cleared from plasma with a half-life of approximately 5 min and were specifically targeted to alpha 2M receptors in vivo. These studies reveal that alpha 2M can maintain activin A in the circulation or rapidly target the hormone for plasma clearance depending on the conformational state of the carrier protein in vivo.

Wounds within the oral mucosa, similarly to fetal wounds, exhibit rapid healing with reduced scarring. We hypothesized that a progenitor population resident within the oral mucosal lamina propria (OMLP) contributes to this preferential healing. Progenitor cells (PC) were reliably isolated from the OMLP by differential adhesion to fibronectin. Isolated colonies originating from a single cell demonstrated a rapid initial phase of proliferation, completing in excess of 50 population doublings (PDs) before entering cellular senescence. These data were supported by the expression of active telomerase within both developing colonies and expanded clones as assessed by immunocytochemistry (ICC) and the quantitative telomeric repeat amplification protocol. FACS analysis confirmed expression of the stem cell markers CD44, CD90, CD105, and CD166, but negative expression of CD34 and CD45 ruling out a hematopoietic or fibrocyte origin for these progenitors. A neural crest origin was confirmed by increased colony-forming efficiency (CFE) in the presence of Jagged 1 and the expression of a number of neural crest markers within the developing colonies by ICC and serially passaged clones by Western blotting. The multipotency of this novel PC population was demonstrated by differentiation of the cells down both mesenchymal (chondrogenic, osteoblastic, and adipogenic) and neuronal (neuron and Schwann-like cells) cell lineages. This article reports for the first time, the isolation and characterization of a novel, clonally derived PC population resident within the OMLP. The attributes of this adult stem cell (ASC) population and its accessibility lends itself to future therapeutic applications.

The identification and characterisation of endothelin in 1988 [1] followed the discovery that an endothelium-derived relaxing factor (EDRF) mediates the vascular relaxation to acetylcholine [2] and the subsequent identification of this factor as nitric oxide [3]. An additional important stimulus to the discovery of endothelin was the recognition that endothelial cells in culture generate and release a polypeptide vasoconstrictor factor into the bathing medium [4–6]. In a tour de force for cardiovascular biology, Yanagisawa, Masaki and colleagues [1] identified and characterised endothelin as a 21 amino acid peptide and the most potent constrictor then known. Subsequent studies have shown that the endothelin isolated from endothelial cells (now known as endothelin-1) is one of a family of 21 amino acid isopeptides (Fig.1), each of which contains two intra-chain disulphide bridges linking paired cysteine amino acid residues and all of which are formed through the same processing pathway (Fig. 2). Their respective precursor peptides share high sequence homology but are encoded by distinct genes [7]. It is also clear [8] that the endothelin isopeptides share remarkable structural similarity to the sarafotoxins, peptides isolated from the venom of the Israeli burrowing asp, Atractaspis engaddensis (Fig. 1). The sarafotoxins and endothelins share receptor binding sites, signalling pathways and pharmacological actions. Indeed, isoforms of sarafotoxin have proved valuable tools for characterising endothelin receptors [9].

We have used Thomas-type recessed-tip pH-sensitive microelectrodes to measure the intracellular pH (pHi) in Xenopus eggs during both fertilization and ionophore activation. The average pHi in unfertilized eggs is 7.33 +/- 0.11 (SD; n = 21) with a resting membrane potential of -10.1 +/- 3.5 (SD; n = 38) mV. Within 2 min after the onset of the fertilization potential, there is a slight, transient pHi decrease of 0.03 +/- (SD, n = 8), followed by a distinct, permanent pHi increase of 0.31 +/- 0.11 (SD; n = 7) beginning approximately 10 min after the start of the fertilization potential and becoming complete approximately 1 h later. The pHi remains near this level of 7.67 +/- 0.13 (SD, n = 10) through at least 10 cleavage cycles, but it is possible to discern pHi oscillations with a mean amplitude of 0.03 +/- 0.02 (SD, n = 38). Eggs perfused for at least 2 h in Na+-free solution with 1 mM amiloride exhibited all of these pHi changes, so these changes do not require extracellular Na+. Similar cytoplasmic alkalinizations that accompany the activation of metabolism and the cell cycle in a wide variety of cell types are discussed.

SummaryThree experiments (1970–2) on calcareous sandy loan tested all combinations of four plant densities (18500–124000 plants/ha), two amounts of potassium (0, 156 kg/K/ha) and sodium (0, 247 kg/Na/ha) fertilizer and two watering treatments on yield and chemical composition of sugar beet. The main effects of the treatments in all three experiments confirmed that at least 75000 plants/ha were needed for maximum sugar yield, that sodium fertilizer increased sugar yield more than potassium (+0.76 and +0.29 t/ha respectively) and that the crop responded to irrigation in some years (+1.35 t sugar/ha in 1970 and +1.67 t/ha in 1972).Analysis of the growth of the crop showed that increasing the plant density increased leaf growth per unit area from singling onwards and giving irrigation increased it from July; the effects persisted until harvest and were reflected in increased sugar yields. Fertilizer increased leaf growth early in the season but the effect disappeared later, although sugar yield was still increased. Interactions between plant density, fertilizer treatment and irrigation were small every year but there were some consistent effects on sugar yield. The results suggest that in commercial practice the optimum density is 75000 plants/ha; where irrigation is not practised, 247 kg/ha of sodium and 70 kg/ha of potassium fertilizer should be given. Where irrigation is applied, only 247 kg/ha of sodium needs to be given as the extra water increases the uptake of soil potassium.

SUMMARYThe objectives and management policy of an experimental farm for studies on the sugar beet crop are described. Farm yields of sugar beet and cereals are discussed in relation to yields in experiments and on a national scale. Some aspects of experimental accuracy and design are considered.

This study examined the effect of early sowing of sugar beet on plant establishment, bolting and yield and whether or not the standard of establishment and degree of bolting determined the most appropriate harvesting sequence. At Arthur Rickwood Experimental Husbandry Farm four experiments were made between 1974 and 1978 testing four sowing dates of four varieties each harvested on three occasions during the autumn. At Broom's Barn three dates of sowing of two varieties were tested in three experiments between 1976 and 1978. Sowing dates throughout the experiments covered a range from late February to late April. Also, at Broom's Barn in 1977 there were many bolters (plants which have a tall, flower-bearing stem) where the crop was sown on 4 March. The effects of bolter-control treatments, either cutting down the inflorescence or removing the plant, on sugar yield were compared. Sowing before mid-March often resulted in very gappy crops and many bolters; in consequence yields were seriously reduced. Late-March sowings were almost free from plant establishment problems and, where the bolting-resistant variety ‘Nomo’ was used, bolters were few; yields of Nomo were greater than where sown in early April. Progressively more yield was lost by delaying sowing throughout April. Variation in the extent of bolting between sites, seasons and sowing-date treatments was accounted for by variation in the number of cool days (with a maximum temperature of less than 12 °C) after sowing. Yield was lost at a rate of 0·7% for every 1% of bolters over the range 5–40% bolting. During the autumn, crops at Arthur Rickwood which had more than 5% bolters and/or less than 60000 plants/ha gained 0·45 t/ha less sugar than did those with full, bolterfree plant stands. In 1977 many of the early-sown plants bolted; pulling the bolters or cutting the inflorescences improved yield, but not sufficiently to raise yields to the level produced by later-sown, bolter-free crops.

SummaryFour field experiments (1968–71) investigated the effect of changing the length of the growing period on the nitrogen fertilizer requirement of sugar beet. The crop was sown on three occasions (March–May), harvested on three occasions (September–December) and given four amounts of fertilizer (0–225 kg N/ha). Plant samples were analysed at several stages of growth (1969–71) in an attempt to predict the amount of nitrogen fertilizer needed for maximum sugar yield and also at the end of the season to determine the nitrogen uptake. Increasing the length of the growing period increased sugar yield greatly but the amount of nitrogen fertilizer needed for maximum sugar yield was unchanged. The crop given the largest dressing of nitrogen and with the longest growing period contained most total nitrogen, but in every experiment, giving more than 75 kg N/ha neither increased nor decreased the sugar yield significantly. As a result of the small variations in nitrogen requirement, the plant analyses during the growing season were of little value in predicting the needs of the crop.

SUMMARYA field experiment in each year 1963 to 1967 in Suffolk, England, tested the effect on yield of sugar beet of sowing dates ranging from 13 March to 11 May and harvest dates ranging from 20 September to 8 December. Sowings in March or early April gave similar yields of sugar but with later sowings yield decreased progressively faster. The relationship is represented by the equationy = 106·3 (±2·24) + 0·212 (±0·184)x-0·009 (±0·003)x2,y = yield as percentage of mean (60·1 cwt/acre of sugar), x = number of days after 12 March.Delayed harvest increased sugar yield; the relationship is represented by the equationy = 80·22 (±1·51) + 0·836 (±0·09)z-0·006 (±0·001)z2,z = number of days after 19 September. This represents an increase of 0·247 cwt/acre/day of sugar in October and 0·083 cwt/acre/day in November, equivalent to about 2½ tons/acre of roots in October and 1 ton/acre in November.The effect on sugar yield of different lengths of growing period, which ranged from 138 to 271 days, is represented by the equationy = 38·7 (±26·6) + 1·045 (±0·267)a-0·0017 (±0·0007)a2,a = number of days between sowing and harvest.On average, sowing date had negligible effect on sugar percentage at harvest. In 3 years sugar percentage increased after the first harvest to a maximum and then decreased; in 2 years it decreased with consecutive harvests.

SUMMARYDuring 1973–8 six field experiments examined the effect of 0, 41, 82, 124, 166 and 207 kg N/ha with and without irrigation on the growth, yield and quality of sugar beet. The culture of the crops was planned to produce a large yield in order to determine the optimal nitrogen application for the above-average crops which many growers are now seeking to produce. Ammonium nitrate was used as the nitrogen source, broadcast in one dose before sowing as was recommended practice in the early 1970s. The growth of the crop was monitored from the seedling stage to harvest in December, as was nitrogen uptake by the crop, and water removal from the soil using a neutron probe.In 3 years when the weather was dry after drilling, the fertilizer significantly depressed the number of plants which established but plant weights showed that some nitrogen fertilizer was needed early for rapid seedling growth. Changes in the method of applying fertilizer for sugar beet are therefore suggested and are being tested. Soil analyses in the plough layer during establishment (May–June) indicated an optimum concentration of mineral nitrogen of about 40 mg N/kg soil at this stage.Nitrogen fertilizer was very important for a high yield; throughout the growth of the crop it greatly increased total dry-matter yield and at final harvest this was reflected in sugar yield. Considering the six years together, sugar yield was linearly related to both dry-matter yield and total nitrogen uptake. However, within a year, increasing nitrogen uptake above 200 kg N/ha with nitrogen fertilizer did not increase sugar yield; maximum yields of sugar each year were normally obtained with 125 kg N/ha fertilizer or less, and irrigation had little effect on the optimum amount. Explanations for the lack of responsiveness of sugar beet to greater applications of nitrogen fertilizer are being sought in further more detailed analyses of the crop and its environment.

SUMMARYFive experiments (1965–9) on calcareous sandy loam tested all combinations of four amounts of nitrogen (0–1·8 cwt/acre N) and four plant populations (8000–54 000 plants/ acre) given to sugar beet grown with and without irrigation. On average, nitrogen and plant population influenced yields greatly but irrigation relatively little. In all years between 0·6 and 1·2 cwt/acre N and between 17000 and 32000 plants/acre gave largest sugar yield. Giving more nitrogen or increasing the plant population neither increased nor decreased sugar yield much in any year. Irrigation was beneficial in only two out of five years.Sugar yield was linearly related to root dry-matter yield. Although total dry matter was greatest when the largest plant population was given the largest dressing of nitrogen and irrigation, the proportion of dry matter in the roots was decreased by all three factors.

SUMMARYFive experiments (1967–9) on soils formed from calcareous drift examined the effects of soil compaction on seedling emergence and yield of sugar beet, also the interaction between compaction and response to nitrogen fertilizer (N) and phosphate fertilizer (P2O5). Some seedbeds were compacted in winter, others in spring and others prepared with the minimum of compaction; each was tested with 0·6, 1·2 and 1·8 cwt/acre N plus 0·8 cwt/acre additional P2O5. All plots were given a basal dressing of 0–8 cwt/acre P2O6and enough of other major nutrients.Compaction decreased seedling populations in four experiments but increased it in one year, when the weather was dry while the seeds were germinating. However, in every experiment compaction significantly decreased yield of roots and sugar. It also interacted with the fertilizer treatments, significantly on average, increasing nitrogen requirement and decreasing phosphate requirement. On average, 0·6 cwt/acre N and 1·6 cwt/acre P2O5gave the greatest yield without compaction and 1·2 cwt/acre N and 0·8 cwt/acre P2O6with compaction.

SUMMARYFour field experiments in 1972–6 investigated the effect of undersowing trefoil or ryegrass in barley, and of fodder radish sown after barley, on yield and nitrogen requirement of following sugar beet. Autumn applications of isobutylidene diurea or glycoluril (slow-release nitrogen fertilizers) were also included for comparison with green manures. The plots were split in the following spring and dressings of 0, 50, 100 and 150 kg N/ha as ‘Nitro-Chalk’ tested on the sugar-beet crop.The undersown green manure crops slightly decreased the yield of barley but, at the time of ploughing, returned up to 3·7 t dry matter/ha and 50 kg N/ha. In the absence of spring-applied nitrogen fertilizer for the sugar beet, green manures increased root and sugar yield, but when more than 50 kg N/ha was applied for the sugar beet they had no effect on yield. Autumn applications of nitrogen fertilizers such as isobutylidene diurea decreased the requirement for nitrogen in spring, but yields were no greater than from spring-applied nitrogen alone. Top and subsoils sampled in late winter and early summer from plots where green manures had been grown showed no detectable increase in soil organic carbon or total nitrogen, but soil mineral-nitrogen concentrations were increased slightly by green manures as was the potentially available mineralnitrogen released in an incubation test. It is concluded that, on loamy soils, green manures decrease the nitrogen requirement of sugar beet but give no benefits in yield which cannot be obtained from nitrogen fertilizer in spring before sowing the crop. assistance and Miss G. Smith for statistical analyses.

The effect of subsoiling an old arable clay-loam soil at Broom's Barn Experimental Station, Suffolk, was tested with a sequence of wheat, barley and sugar-beet crops, a lucerne ley and a sugar-beet test crop in the fourth year.Subsoiling increased the yield of each crop each year, averages over 3 years were: wheat, 0·6 cwt/acre of grain; barley 0·4 cwt/acre; lucerne 0·6 cwt/acre of dry matter. Average increases of sugar beet over 4 years were 0·7 tons/acre of roots or 2·1 cwt/acre of sugar; the increase was greatest (2·9 cwt/acre of sugar) in the first year.

SUMMARY Twisting of roots of sugar beet has been associated with the application to the soil of certain herbicides. Severe twisting resulted in root constrictions which in some respects resembled ‘strangles’. Symptoms were most severe when the herbicide was intimately mixed with the soil either after or immediately before sowing.