Changes In Sugar Content Research Articles

Characterizing indirect prey-quality mediated effects of a Bt crop on predatory larvae of the green lacewing, Chrysoperla carnea

There is increasing evidence that insecticidal transgenic crops can indirectly cause detrimental effects on arthropod predators or parasitoids when they prey on or parasitize sublethally affected herbivores. Our studies revealed that Chrysoperla carnea is negatively affected when fed Bt-susceptible but not Cry1Ac-resistant Helicoverpa armigera larvae that had fed Bt-transgenic cotton expressing Cry1Ac. This despite the fact that the predators ingested 3.5 times more Cry1Ac when consuming the resistant caterpillars. In order to detect potential differences in the nutrient composition of prey larvae, we evaluated the glycogen and lipid content plus the sugar and free amino acid content and composition of caterpillars fed non- Bt and Bt cotton. The only change in susceptible H. armigera larvae attributable to Bt cotton feeding were changes in sugar concentration and composition. In case of the Cry1Ac-resistant H. armigera strain, feeding on Bt cotton resulted in a reduced glycogen content in the caterpillars. The predators, however, appeared to compensate for the reduced carbohydrate content of the prey by increasing biomass uptake which caused an excess intake of the other analyzed nutritional compounds. Our study clearly proves that nutritional prey-quality factors other then the Bt protein underlie the observed negative effects when C. carnea larvae are fed with Bt cotton-fed prey. Possible factors were an altered sugar composition or fitness costs associated with the excess intake of other nutrients.

Carbohydrate changes in kiwifruit buds during the onset and release from dormancy

Abstract Carbohydrates were measured in axillary bud meristems from kiwifruit (Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson cultivar Hayward) to determine whether concentrations changed during winter dormancy. Buds were collected from kiwifruit vines growing in four sites, which spanned the climatic range that kiwifruit are grown in New Zealand, and from vines where the time of budbreak had been manipulated using hydrogen cyanamide. During winter, sugars comprised 78% of measured carbohydrates in meristems, with sucrose accounting for more than 86% of sugars detected (up to 200 mg g DW−1). Starch concentrations in bud meristems showed little change during winter. Meristem sucrose and hexose concentrations increased rapidly from autumn until mid-winter, and this was correlated with leaf abscission. Sugar accumulation ceased in mid-winter and concentrations remained stable until spring, suggesting that bud meristem activity was low. Four weeks before visible bud movement, a marked decline in sucrose and increase in hexose concentrations, indicated activity in the meristems had increased prior to budbreak. The patterns of seasonal change and peak sucrose concentrations in meristems were similar at all sites. The only difference was in the timing of events, with changes in meristem sugars occurring earliest in vines growing at the coolest site, coinciding with their earlier cessation of and resumption of vine growth. Advancing budbreak, by applying hydrogen cyanamide to vines in late winter, also advanced changes in sugar concentrations within meristems. This work suggests that the concentration of sucrose in kiwifruit bud meristems has utility as an indicator of whether they are being induced into, maintained or released from winter dormancy.

Sugars and organic acids in Japanese plums (Prunus salicinaLindell) as influenced by maturation, harvest date, storage temperature and period

SummaryThe effects of fruit maturation, harvest date, storage temperature, storage period and shelf life, on the concentrations of individual sugars and organic acids in Japanese plums were investigated. During fruit maturation in ‘Amber Jewel’ plums, sucrose concentration increased significantly from 101 days after full bloom (DAFB) to 1 week after commercial maturity (136 DAFB) with a non‐significant change in the concentration of total organic acids and malic acid, the major organic acid. The changes in concentrations of sugars and organic acids during cold storage of ‘Amber Jewel’ plums harvested on 129 and 136 DAFB appeared to be independent of harvest date. Storage of ‘Amber Jewel’ plums at 5 °C accelerated the loss of sucrose and increased the concentrations of fructose and glucose from the 4th week of storage compared with those stored at 0 °C. ‘Blackamber’ plums did not undergo any significant increase in the total and individual sugars during 5 weeks storage and subsequent shelf‐life of 8 days at 20 °C. Malic acid concentrations declined during storage from 3 weeks onwards with a further substantial loss during ripening at 20 °C. Maturation, harvest date, storage temperature, storage period and shelf‐life affect the concentrations of sugars and organic acids in Japanese plums.

Model-based analysis of sugar accumulation in response to source-sink ratio and water supply in grape (Vitis vinifera) berries.

The dynamics of sugar (hexose) concentration in ripening grape berries (Vitis vinifera L.) were simulated with a refined mechanistic model. Changes in sugar concentration were reproduced by the sum of sugar import (S), sugar metabolism (M) and water budget (W). S and W were derived from model inputs of fresh and dry mass, and M was simulated with a relative metabolism rate describing the depletion of hexose. The relative metabolism rate was associated with the relative growth rate of dry mass with a coefficient (k) that was constant for a given cultivar under various growth conditions (temperature, water supply, and source-sink ratio) but varied with genotype. The k value was ~20% higher for cv. Merlot than for cv. Cabernet Sauvignon, indicating more imported sugars would be depleted by Merlot than Cabernet Sauvignon. The model correctly simulated the negative effect of lowered leaf-to-fruit ratio and the positive effect of water shortage on sugar concentration. Sensitivity analysis revealed that the present model was weakly sensitive to k because of sugar accumulation being predominantly controlled by S, with M relatively small (~20%) with respect to the increment of sugar concentration. Model simulation indicated that the decreasing leaf-to-fruit ratio reduced S more than M and W, causing a net decrease in sugar concentration. In contrast, the water shortage decreased S less than M and W, resulting in a net increase in sugar concentration.

Quantifying the dynamics of sugar concentration in berries of Vitis vinifera cv. Shiraz: a novel approach based on allometric analysis

Concentrations of key compounds (e.g. sugar) in berries are the net result of relative changes in the amount of compound per berry and berry size. The complex nature of concentrations is widely recognised, but the widespread use of chronological scales for comparisons implies that ontogenetic drift or size-dependent effects are often overlooked. This paper presents an allometric analysis of sugar concentration in berries of cv. Shiraz as a way to formally account for ontogenetic drift. Our starting point is the double-sigmoid growth pattern of a grape berry where we distinguish Phase 1, from flowering to veraison; Phase 2, from veraison to peak berry fresh mass, and Phase 3, after peak fresh mass. Phase 3 explicitly accounts for the late season shrinkage typical of Shiraz berries. We advance an allometric model of sugar per berry with berry fresh mass, rather than time, as descriptor. The condition for an increase in sugar concentration in Phase 2 is that the relative rate of sugar accumulation per berry (RSB) exceeds the relative rate of berry net accumulation of fresh mass (RFM). This is equivalent to an allometric coefficient, calculated as the slope of the regression between amount of sugar per berry and berry mass in a log-log scale, being greater than 1. For Phase 3, the condition for increase of sugar concentration is that a large reduction in berry mass offsets any putative change of sugar per berry, yielding an allometric coefficient < 1. Such an allometric model was tested against measured data from sixteen contrasting crops resulting from the combination of eight water regimes and two seasons. Berry mass peaked between 96 and 105 days after anthesis, and these dates were used to separate Phases 2 and 3. In Phase 2, the relative rate of increase in sugar per berry varied from 0.01 to 0.02 d-1 in comparison to the relative rate of increase in berry fresh mass that varied from 0.0038 to 0.0066 d-1. Sugar per berry thus increased 2.4–3.3 times faster than berry mass, with allometric coefficients between 1.98 and 2.91 accounting for 78% of the variation in the relative rate of change of sugar concentration. In Phase 3, the relative rate of change in sugar per berry was not different from zero (P 0.05) in most cases, whereas the rate of change in berry size ranged from –0.0013 to –0.0035 d-1 and was significant (P < 0.05) in 14 out 16 cases. The small changes in sugar per berry and the net loss of berry material yielded allometric coefficients between 0.17 and 1.11, which accounted for 72% of the variation in the relative rate of change in sugar concentration. We conclude that a model, which pivots around peak berry mass, with allometric coefficients above 1 in Phase 2 and below 1 in Phase 3, is suitable to quantitatively account for ontogenetic drift in the dynamics of sugar concentration in berries of Shiraz. This allometric approach demonstrated that sugar per berry during the stage of berry shrinkage is a plastic trait under significant environmental influence. For the same genotype, environmental conditions could determine either, a putative backflow of water accounting for net loss of berry fresh mass (RFM < 0) that could also carry some sugar from berries back to the parent vine (RSB < 0) or a small gain of sugar (RSB 0) closely coupled with a net loss of berry fresh mass (P= 0.003).

COMPOSITIONAL CHANGES OF STRAWBERRY DUE TO DEHYDRATION, COLD STORAGE AND FREEZING–THAWING PROCESSES

Strawberry is an excellent source of food ingredients, although compositional changes might occur in improperly controlled processing, affecting product quality. In this article, changes in sugar composition (glucose, fructose and sucrose), citric acid, water and total soluble content, as induced by partial dehydration and freezing-thawing processes, were analyzed in strawberries (var. Camarosa). Osmotic dehydration (OD) with 65 °Brix sucrose solution, air drying (AD) at 45C, or combined treatments (OD-AD) were applied to reduce strawberries' water content to 70-85%. Fresh and dehydrated samples were frozen (-40C, 24 h) and stored (-18C, 30 and 180 days). All samples processed by OD and OD-AD showed a significant sugar gain, and depending on the dehydration treatment, total or partial sucrose hydrolysis was observed. Dehydration treatments caused small losses of citric acid. During the freezing-thawing process, drip loss and enzymatic action also cause changes in sugar concentration, especially in OD-treated samples.

Flower Choice and Learning in Foraging Bumblebees: Effects of Variation in Nectar Volume and Concentration

AbstractBees collect food from flowers that differ in morphology, color, and scent. Nectar‐seeking foragers can rapidly associate a flower's cues with its profitability, measured as caloric value or ‘net energy gain,’ and generally develop preferences for more profitable species. If two flower types are equally easy to discover and feed from, differences in profitability will arise from differences in the volume or the sugar concentration of their nectar crops. Although there has been much study of how bees respond to one or the other of these two kinds of nectar variation, few studies have considered both at once. We presented free‐foraging bumblebees with two different types of equally rewarding artificial flowers. After a period of familiarization, we made one type more rewarding than the other by increasing its nectar concentration, volume, or both. Bees responded more rapidly to a change in the reward's sugar concentration than to a change in its volume, even if the profitability differences were approximately equal. Sucrose concentration differences (40% vs. 13%) caused bees to virtually abandon the more dilute flower type, whether both types offered the same volume (2 μl) or the less concentrated reward offered higher volume (7 μl vs. 0.85 μl). When the two types of flower differed only in nectar volume (7 μl vs. 0.85 μl), the less rewarding type continued to receive 22% of the visits. We propose three different hypotheses to explain the stronger response of the bees to changes in sugar concentration: (i) their response threshold to sucrose concentration might change; (ii) less time is needed to assess the concentration of a reward than its volume; and (iii) a smaller sample size may be needed for reliable estimation of profitability when flowers differ in concentration.

Heat sensitivity of photosynthetic electron transport varies during the day due to changes in sugars and osmotic potential

In water-stressed leaves, accumulation of neutral osmotica enhances the heat tolerance of photosynthetic electron transport. There are large diurnal and day-to-day changes in leaf sugar content because of variations in net photosynthetic production, respiration and retranslocation. To test the hypothesis that diurnal and day-to-day variations in leaf sugar content and osmotic potential significantly modify the responses to temperature of photosynthetic electron transport rate, we studied chlorophyll fluorescence rise temperatures (i.e. critical temperatures at break-points in fluorescence versus temperature response curves, corresponding to enhanced damage of PSII centers and detachment of pigment-binding complexes) in the dark at a background of weak far-red light (T(FR)) and under actinic light (T(L)), and responses of foliar photosynthetic electron transport rate to temperature using gas-exchange and chlorophyll fluorescence techniques in the temperate tree Populus tremula L. Sucrose and sorbitol feeding experiments demonstrated strong increases of fluorescence rise temperatures T(FR) and T(L) with decreasing leaf osmotic potential and increasing internal sugar concentration. Similar T(FR) and T(L) changes were observed in response to natural variation in leaf sugar concentration throughout the day. Increases in leaf sugar concentration led to an overall down-regulation of the rate of photosynthetic electron transport (J), but increases in the optimum temperature (Topt) of J. For the entire dataset, Topt varied from 33.8 degrees C to 43 degrees C due to natural variation in sugars and from 33.8 degrees C to 52.6 degrees C in the sugar feeding experiments, underscoring the importance of sugars in modifying the response of J to temperature. However, the correlations between the sugar concentration and fluorescence rise temperature varied between the days. This variation in fluorescence rise temperature was best explained by the average temperature of the preceding 5 or 6 days. In addition, there was a significant year-to-year variation in heat sensitivity of photosynthetic electron transport that was associated with year-to-year differences in endogenous sugar content. Our data demonstrate a diurnal variation in leaf heat tolerance due to changes in sugar concentration, but they also show that this short-term modification in heat tolerance is super-imposed by long-term changes in heat resistance driven by average temperature of preceding days.

Seasonal periodicity of physical factors, inorganic nutrients and microalgae in Antarctic fellfields

Over 15 months between January 1990 and March 1991, a range of physical, chemical and biological parameters was monitored regularly in fellfield soils of frost-sorted polygons at four sites on Signy Island (South Orkney Islands, maritime Antarctica). These included inorganic nutrients (orthophosphate, available nitrate and, over a more limited period, ammonia), chlorophyll a (as a proxy measure of microalgal biomass) and a range of potential cryoprotectant compounds. Transects across soil polygons revealed neither intrapolygon gradients in concentrations of inorganic nutrients or chlorophyll a nor significant interpolygon differences, in contrast with previous studies. Nitrate was present in much lower concentrations than phosphate, supporting evidence that it is a limiting nutrient in these fellfield ecosystems. Spring snowmelt, although a potential source of nutrient input, was not associated with increased concentrations of inorganic nutrients in the soil, probably through isolation of the soil from overlaying snow by a surface layer of ice. Soil microalgae at the study sites must survive winter temperatures of at least −9°C, even when protected beneath up to 1 m of snow, and it has been proposed that they accumulate sugars and polyols as cryoprotectants. In support of this, concentrations of erythritol, glycerol, glucose, sucrose and trehalose in the soil (both absolute quantity and after correction for chlorophyll a concentration) increased as winter proceeded, suggesting that changes in sugar concentrations were due to accumulation within individual cells.

Use of an Electric Field to extend the Shelf Life of Apples

An effort was made to assess the effect of electric field treatment on the shelf life of Fuji, Rome Beauty, Golden Delicious and Starking Delicious apple varieties. The direct current electric field was generated by a 50 Hz alternating current supply. Ionisation by negative corona discharge was facilitated using needles as the cathode and an aluminium plate (of diameter 180 mm) as the grounded anode. The electrodes were 8 cm apart. Seven days continuous treatment with the electric field (generated by 10 kV) at 23°C air temperature and 75% relative humidity resulted in suppression of CO 2 evolution in the treated apples compared to control samples. Short treatment periods (1 and 2 h) at 10 and 20 kV reduced respiration in the apples. The total colour difference and soluble sugar concentration changes were lower in treated samples compared to control samples. Mechanical properties evaluated from the stress–strain relationship showed that the treated apple tissues were stiffer than the untreated ones.

Changes in food source profitability affect Nasonov gland exposure in honeybee foragers Apis mellifera L.

When arriving at a known artificial food source, foraging honeybees usually perform circular flights around the feeding place prior to landing. During these flights bees expose their Nasonov gland, an exocrine gland located at the base of the 7th tergum, that releases a complex blend of volatiles. This behavior may continue even after the bee starts food ingestion. The proportion of bees exposing the Nasonov gland and the duration of its exposure before and during feeding for individual bees were quantified. Trained bees collected sugar solution during 12 visits from a feeder located at 160 m from the hive. Five different reward programs were presented: three constant and two variable. The constant programs offered 0.6, 1.2 or 2.4 M sugar for all 12 visits, while the variable programs delivered either 0.6, 1.2, 0.6 M or 0.6, 2.4, 0.6 M, four visits for each molarity. Results showed that sugar concentration changed the thresholds and durations of Nasonov gland exposure. However, this relationship was found only for Nasonov exposure before bees began to feed. During feeding, a protruded Nasonov gland was only observed for bees that had exposed it prior to feeding; suggesting that Nasonov gland exposure before feeding is a releaser of the during-feeding exposure. In variable reward programs, changes in sugar concentration were followed by changes in both thresholds and durations of exposure. However, Nasonov gland exposure during feeding did not appear to decrease based on measurements of the low profitability during the current foraging visit. These results suggest that Nasonov gland exposure is programmed on the basis of reward expectations, with the bees having acquired this information in the previous foraging visits to the food source.

Sucrose synthase and sucrose phosphate synthase, but not acid invertase, are regulated by cold acclimation and deacclimation in cabbage seedlings

Summary Cabbage seedlings acquire freezing tolerance during exposure to low temperature (acclimation), however, it is lost by returning the plants to moderate temperature (deacclimation). Soluble sugars, except myo -inositol, accumulated during cold acclimation in the leaves of cabbage seedlings. During deacclimation for 5 days, sucrose, glucose and fructose contents decreased rapidly to the same levels as before cold acclimation. To identify the enzymes responsible for changes in sugar concentrations, we investigated changes in activities of sucrose synthase (E.C. 2.4.1.13), sucrose phosphate synthase (E.C. 2.4.1.14) and acid invertase (E.C. 3.2.1.26) during cold acclimation and deacclimation. Activity of sucrose synthase during cold acclimation increased up to 3 times the activity before cold acclimation, but decreased to the level of activity before cold acclimation during deacclimation. The activity of sucrose phosphate synthase also increased during cold acclimation, but decreased to the level of activity before cold acclimation during deacclimation. However, the activity of acid invertase decreased gradually during cold acclimation and did not increase to the level of activity before cold acclimation during deacclimation. These results suggest that SS and SPS, but not acid invertase, are regulated by cold acclimation and deacclimation and play important roles in sugar accumulation and acquisition of freezing tolerance in the leaves of cabbage seedlings.

Carbon supply for storage-product synthesis in developing seeds of oilseed rape

The aim of this work was to find out how the sugars in the endosperm of oilseed rape contribute to the flux of oil synthesis. While the hexose content of the liquid endosperm decreased during development the sucrose content increased. It is important to understand the relative rates of use of the endosperm sugars for two reasons. Firstly we need to know which sugars are used, and at what stages in development, in order to understand the roles of enzymes involved in their metabolism. Secondly, changes in sugar concentration have been implicated in the regulation of expression of genes determining storage-product synthesis [see Weber, Borisjuk and Wobus (1997) Trends Plant Sci. 2, 169-174, for review]. The rate of consumption of sugar is one factor governing its concentration. We present data showing both the concentration-dependence of conversion of sugar to oil, and the in vivo concentrations of sugars; we relate these data sets to each other and discuss the effects of the intracellular pool of sucrose. Glucose, fructose and sucrose are all substrates for oil synthesis, but the rates of their use (particularly sucrose) are underestimated because of dilution by sucrose from the intracellular pool.

Light regulation of assimilatory sulphate reduction in Arabidopsis thaliana.

Adenosine 5'-phosphosulphate reductase (APR) is considered to be a key enzyme of sulphate assimilation in higher plants. We analysed the diurnal fluctuations of total APR activity and protein accumulation together with the mRNA levels of three APR isoforms of Arabidopsis thaliana. The APR activity reached maximum values 4 h after light onset in both shoots and roots; the minimum activity was detected at the beginning of the night. During prolonged light, the activity remained stable and low in shoots, but followed the normal rhythm in roots. On the other hand, the activity decreased rapidly to undetectable levels within 24 h of prolonged darkness both in shoots and roots. Subsequent re-illumination restored the activity to 50% in shoots and to 20% in roots within 8 h. The mRNA levels of all three APR isoforms showed a diurnal rhythm, with a maximum at 2 h after light onset. The variation of APR2 mRNA was more prominent compared to APR1 and APR3. 35SO42- feeding experiments showed that the incorporation of 35S into reduced sulphur compounds in vivo was significantly higher in light than in the dark. A strong increase of mRNA and protein accumulation as well as enzyme activity during the last 4 h of the dark period was observed, implying that light was not the only factor involved in APR regulation. Indeed, addition of 0.5% sucrose to the nutrient solution after 38 h of darkness led to a sevenfold increase of root APR activity over 6 h. We therefore conclude that changes in sugar concentrations are also involved in APR regulation.

δ13C analysis of phloem sap carbon: novel means of evaluating seasonal water stress and interpreting carbon isotope signatures of foliage and trunk wood of Eucalyptus globulus.

A recently described phloem-bleeding technique was used to study seasonal changes in δ13C, sugar levels and the amino acid:sugar balance of phloem translocate of 2- to 3-year old trees of Eucalyptus globulus at a rain-fed site (Eulup) and a waste-effluent-irrigated site (Albany) in south-west Australia. δ13C of phloem sap from the Eulup site fluctuated widely between winter (-27.6‰) and peak summer stress (-20.2‰), compared with a much smaller range of -28.4 to -26.3 at Albany. Seasonal changes in sugar concentrations in sap fluctuated closely with those of phloem δ13C, with highest concentrations and least negative δ13C values at times of greatest soil water deficit. Molar ratios of amino acids to sugars in phloem sap were similar between plantations in winter through to early summer. They then remained high at the nitrogen-rich effluent-treated site, but fell dramatically once soils dried out at Eulup. Mature leaf dry matter sampled at peak yearly stress (early autumn) showed more negative δ13C values than concurrently harvested phloem sap or recently initiated shoot apex dry matter, presumably because the sampled foliage had laid down its structural carbon earlier under relatively unstressed winter/spring conditions. Differences between Albany and Eulup were much greater for δ13C of phloem and new apical dry matter than for dry matter of mature foliage. Comparisons of δ13C signatures of phloem sap carbon with those of dry matter of nascent xylem tissues showed seasonal fluctuations in δ13C of phloem translocate which were mirrored a month or so later by those for xylem carbon. δ13C analyses of trunk growth rings from Eulup and Albany showed well-defined seasonal oscillations over the first 2 or 3 years of growth until irrigation commenced at Albany. Fluctuations in δ13C at the latter site then became noticeably less pronounced than at Eulup. Future use of phloem sap δ13C and solute analyses for studying seasonal water and nutrient status of E. globulus is discussed.

Location of a gene regulating cold-induced carbohydrate production on chromosome 5A of wheat

Major changes in osmotic potential during cold acclimation are due to changes in sugar concentration, and there is a good correlation between sugar content and frost tolerance. The objective of the present study was to localize a gene(s) responsible for carbohydrate accumulation during cold acclimation on chromosome 5A of wheat using recombinant lines developed from the cross between the substitution lines Chinese Spring (Cheyenne 5A) and CS(Triticum spelta 5A). Previously, major genes influencing frost resistance (Fr1) and vernalization requirement (Vrn1) had been localized on the long arm of that chromosome. The T. spelta 5A chromosome carrying the Fr1 (frost-sensitive) allele for frost tolerance and the Vrn1 (spring-habit) allele for vernalization requirement did not have a major effect on the sucrose and fructan contents in the Chinese Spring background. On the other hand, the presence of Cheyenne alleles for vernalization requirement, vrn1, and frost tolerance, fr1, significantly increased sugar concentrations. A recombinant line thought to exhibit recombination between the Vrn1 and Fr1 loci suggested that the gene regulating sucrose accumulation was closely associated with, or else represented a pleiotropic effect of, Vrn1, but was separable from the Fr1 locus.

Effect of Elevated Medium Sucrose Levels on Cold Hardiness of `Festival' Red Raspberry in Vitro

Low tissue-water content and increased osmotic concentration of cell sap are associated with frost resistance. Changes in total osmotic concentration of cell sap are due mainly to changes in concentration of sugars. Generally, sugar content increases with hardening and decreases with dehardening. This study examined the effect of elevated sucrose levels (3% to 15%) in the medium on the cold hardiness of `Festival' red raspberry (Rubus idaeus L.) shoots in vitro. To determine whether expected hardening is caused by elevated sucrose levels or by osmotic stress, different levels of mannitol in the media have been tested. After growing raspberry shoots on media with different levels of sucrose and mannitol for 2 weeks, shoot moisture content (percent) was determined. Cold hardiness of the shoots was determined by using differential thermal analysis or artificially freezing the shoots and assessing the survival by regrowth test and visual rating.

Effects of SO2 on the concentrations of carbohydrates and secondary compounds in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings

summaryScots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings of open‐pollinated progenies and clonal cuttings were exposed to various concentrations of SO2 (50–155 nl l−1) in several growth chamber experiments. No visible foliar injury was observed in any SO2 exposure. The total sulphur concentrations of the exposed needles were significantly greater than in the control needles. Exposure to SO2 (100 and 155 nl l−1) reduced concentrations of glucose and fructose and increased concentrations of sucrose in pine needles. By contrast, one spruce clone had more glucose and fructose and less sucrose in needles exposed to SO2 (100 nl l−1), but in other spruces of clonal or open‐pollinated progenies no changes in sugar concentrations were detected in different SO2 exposures (50–155 nl l−1). Exposure to SO2 had no effects on concentrations of individual or total monoterpenes in pine or spruce needles. Concentration of total resin acids was significantly smaller in needles exposed to the greatest concentration of SO2 (155 nl l−1), but no changes were detected in other exposures (50–150 nl l−1) in either tree species. Concentrations of minor individual resin acids, palustric and neoabietic acids, were also affected by SO2 in needles of pine (155 nl l−1 SO2) and clonal spruces (100 nl l−1 SO2). Exposure to SO2 did not affect foliar concentration of total phenolics in pine and spruce seedlings. In exposure to 0, 50, 100 and 150 nl l−1 SO2, total phenolic concentration of spruce roots was increased linearly with elevated SO2 exposure level. By contrast one spruce clone had decreased concentrations of phenolics in roots after exposure to 155 nl l−1 SO2. The present results suggest that in conifers the response of carbohydrate and secondary metabolism to SO2 varies with the origin of tested seedlings and the SO2 concentration. Therefore, generalizations about the SO2 effects on suitability of food quality for folivorous herbivores are difficult to draw, except that a better supply of sulphur will be available from SO2 exposed seedlings.

Interactive effects of elevated CO(2) and mineral nutrition on growth and CO(2) exchange of sweet chestnut seedlings (Castanea sativa).

The effects of elevated atmospheric CO(2) (700 micro mol mol(-1)) and fertilization were investigated on 2-year-old sweet chestnut (Castanea sativa Mill.) seedlings grown outdoors in pots in constantly ventilated open-sided chambers. Plants were divided into four groups: fertilized controls (+F/-CO(2)), unfertilized controls (-F/-CO(2)), fertilized + CO(2)-treated plants (+F/+CO(2)) and unfertilized + CO(2)-treated plants (-F/+CO(2)). Dry matter accumulation and allocation were measured after one growing season and CO(2) exchange of whole shoots was measured throughout the growing season. Shoot growth and total leaf area of unfertilized plants were not affected by elevated CO(2), whereas both parameters were enhanced by elevated CO(2) in fertilized plants. Elevated CO(2) increased total biomass by about 20% in both fertilized and unfertilized plants; however, biomass partitioning differed. In unfertilized plants, elevated CO(2) caused an increase in root growth, whereas in fertilized plants, it stimulated aboveground growth. At the whole-shoot and leaf levels, photosynthetic activity of both fertilized and unfertilized plants increased in response to elevated CO(2), but the seasonal pattern of this enhancement varied with nutrient treatment. In unfertilized plants, a downward acclimation of photosynthesis was observed early in the season (June), and was related to reductions in nitrogen and chlorophyll content and to starch accumulation. The decrease in the slope of the A/C(i) curve suggested a decrease in Rubisco activity. In both fertilized and unfertilized plants, shoot respiration decreased during the night in response to elevated CO(2) until mid-July. The decrease was not related to changes in sugar concentration.

Non‐Invasive Determination of Freezing Effects in Blueberry Fruit Tissue by Magnetic Resonance Imaging

ABSTRACTWater and sugar distribution in a single blueberry were mapped both before and after freeze/thaw using magnetic resonance imaging. Images were obtained using a slice selective spin echo pulse sequence which included a T1 inversion recovery time period, allowing selection of either the water signal or the sugar signal. Freeze/thaw results in the rupture of water retaining membranes within discrete locations of the fruit tissue. This causes a change in the ratio of motion modified water (i.e., hydrogen bonded or chemically exchanged) to unmodified (i.e. mobile and not chemically exchanged) in those regions, as well as a concomitant change in sugar concentration, due to diffusion to other tissues.