Carbohydrate Supply Research Articles

VEGETATIVE AND REPRODUCTIVE DEVELOPMENT OF STRAWBERRY GUAVA IN RELATION TO CARBOHYDRATE STATUS OF THE TREE

Nitrogen triggers production cycle in strawberry guava (Psidium cattleianum), and numbers of shoots and flowers produced seem to depend on carbohydrate availability at the time of nitrogen application. To investigate this relationship, studies were made on the effect of two factors on the vegetative and reproductive characteristics of a triggered production cycle: the leaf-to-fruit ratio at the tree level and the fruit load at the shoot level during the previous production cycle. Leaf-to-fruit ratio was adjusted at 0.8, 2.6 and 13.2 on three trees per treatment. Three modalities of fruit load at the shoot level were considered: no fruit, 1-3 fruit(s) and >3 fruits. Nitrogen was applied about one month after full bloom of the previous cycle. At that time, starch content was determined in the leaves and wood of terminal shoots. After fruit set of the triggered cycle, leaf-to-fruit ratio of each tree was adjusted at 6.0. Numbers of shoots and flowers, and fruit set rate were recorded on the triggered cycle. Harvest data were recorded during both production cycles. Numbers of shoots and flower buds of the triggered cycle were positively correlated with starch content in leaves. However, each factor had a specific effect on vegetative and reproductive development. The number of shoots produced was negatively related to fruit load at the shoot level during the previous cycle. The number of flowers per new shoot was related to the leaf-to-fruit ratio at the tree level during the previous cycle. Any of both factors affected fruit set rate. Carbohydrate availability at the time of nitrogen application had therefore a positive effect on flower induction, and growing fruits seemed to prevent vegetative development. Fruit growth was sensitive to carbohydrate supply. (Resume d'auteur)

Regulation of arbuscular mycorrhization by carbon. The symbiotic interaction cannot be improved by increased carbon availability accomplished by root-specifically enhanced invertase activity.

The mutualistic interaction in arbuscular mycorrhiza (AM) is characterized by an exchange of mineral nutrients and carbon. The major benefit of AM, which is the supply of phosphate to the plant, and the stimulation of mycorrhization by low phosphate fertilization has been well studied. However, less is known about the regulatory function of carbon availability on AM formation. Here the effect of enhanced levels of hexoses in the root, the main form of carbohydrate used by the fungus, on AM formation was analyzed. Modulation of the root carbohydrate status was performed by expressing genes encoding a yeast (Saccharomyces cerevisiae)-derived invertase, which was directed to different subcellular locations. Using tobacco (Nicotiana tabacum) alcc::wINV plants, the yeast invertase was induced in the whole root system or in root parts. Despite increased hexose levels in these roots, we did not detect any effect on the colonization with Glomus intraradices analyzed by assessment of fungal structures and the level of fungus-specific palmitvaccenic acid, indicative for the fungal carbon supply, or the plant phosphate content. Roots of Medicago truncatula, transformed to express genes encoding an apoplast-, cytosol-, or vacuolar-located yeast-derived invertase, had increased hexose-to-sucrose ratios compared to beta-glucuronidase-transformed roots. However, transformations with the invertase genes did not affect mycorrhization. These data suggest the carbohydrate supply in AM cannot be improved by root-specifically increased hexose levels, implying that under normal conditions sufficient carbon is available in mycorrhizal roots. In contrast, tobacco rolC::ppa plants with defective phloem loading and tobacco pyk10::InvInh plants with decreased acid invertase activity in roots exhibited a diminished mycorrhization.

Regulation of Arbuscular Mycorrhization by Carbon. The Symbiotic Interaction Cannot Be Improved by Increased Carbon Availability Accomplished by Root-Specifically Enhanced Invertase Activity

AbstractThe mutualistic interaction in arbuscular mycorrhiza (AM) is characterized by an exchange of mineral nutrients and carbon. The major benefit of AM, which is the supply of phosphate to the plant, and the stimulation of mycorrhization by low phosphate fertilization has been well studied. However, less is known about the regulatory function of carbon availability on AM formation. Here the effect of enhanced levels of hexoses in the root, the main form of carbohydrate used by the fungus, on AM formation was analyzed. Modulation of the root carbohydrate status was performed by expressing genes encoding a yeast (Saccharomyces cerevisiae)-derived invertase, which was directed to different subcellular locations. Using tobacco (Nicotiana tabacum) alc∷cwINV plants, the yeast invertase was induced in the whole root system or in root parts. Despite increased hexose levels in these roots, we did not detect any effect on the colonization with Glomus intraradices analyzed by assessment of fungal structures and the level of fungus-specific palmitvaccenic acid, indicative for the fungal carbon supply, or the plant phosphate content. Roots of Medicago truncatula, transformed to express genes encoding an apoplast-, cytosol-, or vacuolar-located yeast-derived invertase, had increased hexose-to-sucrose ratios compared to β-glucuronidase-transformed roots. However, transformations with the invertase genes did not affect mycorrhization. These data suggest the carbohydrate supply in AM cannot be improved by root-specifically increased hexose levels, implying that under normal conditions sufficient carbon is available in mycorrhizal roots. In contrast, tobacco rolC∷ppa plants with defective phloem loading and tobacco pyk10∷InvInh plants with decreased acid invertase activity in roots exhibited a diminished mycorrhization.

137 ROLE OF GLUCOSE AND FATTY ACID METABOLISM IN PORCINE EARLY EMBRYO DEVELOPMENT

Glucose metabolism plays an important role in the preimplantation development of porcine embryos in vitro. As in mammalian species generally, a proportion of glucose consumed is converted to lactate by aerobic glycolysis generating small amounts of ATP, with the remainder oxidized by the TCA cycle. However, a striking feature of the porcine early embryo is the large amount of lipid present as triglyceride (TG), which represents an alternative energy source. The TG is metabolized via β-oxidation, producing acetyl Co A, which in turn is oxidized by the TCA cycle. This sequence of reactions requires a constant supply of carbohydrate to provide oxaloacetate (OA) to prime the TCA cycle. The provision of OA from pyruvate arising from glycolysis may represent an alternative role for glucose in early pig embryo development. We have therefore sought to determine the importance of interplay between glucose and TG metabolism in porcine embryos in vitro. Porcine embryos were generated in vitro by fertilization of in vitro-matured oocytes collected from abattoir-derived ovaries. Oocytes were matured in defined maturation medium and embryos cultured in NCSU23. Glucose consumption, lactate production, and TG content of single porcine blastocysts cultured throughout development in the presence of methyl palmoxirate (MP), an inhibitor of TG metabolism, were measured as described by Sturmey RG and Leese HJ 2003 (Reprod. 126, 197–204). The capacity of zygotes to form blastocysts when cultured with OA in place of glucose in the presence or absence of MP and the amount of TG in blastocysts grown in either glucose or OA-containing medium were then determined (6 replicates). When TG metabolism was inhibited, porcine blastocysts consumed significantly more glucose (32 � 9 pmol/embryo/h v. 11 � 1 pmol/embryo/h; P < 0.05; n = 34) and produced higher amounts of lactate (35 � 4 pmol/embryo/h v. 10 � 0.8 pmol/embryo/h; P < 0.01; n = 34). Blastocyst rates did not differ significantly between embryos grown in the presence of glucose or OA, and in blastocysts grown in OA-NCSU the TG content was significantly reduced (155 � 8 ng v. 240 � 12 ng; P = 0.015; n = 41). All embryos cultured in OA-containing medium in the presence of MP failed to develop beyond the zygote stage. The data support the notion that porcine embryos can use endogenous TG as a metabolic energy source. When this is prevented by chemical inhibition, the embryo upregulates glycolysis and glucose oxidation as an alternate means of generating ATP. When cultured in medium containing OA, a compound that cannot generate ATP per se, embryo development was similar to controls, again suggesting the ability to use endogenous energy stores, a proposition reinforced by a significant fall in the levels of TG in the presence of OA. However, by inhibiting β-oxidation in the absence of glucose, porcine embryos were unable to develop. The relationship between TG and glucose metabolism by porcine embryos is analogous to the glucose/fatty acid cycle in whole animals where glucose and TG can be used as energy sources, but in a reciprocal manner. The data also demonstrate the plasticity of energy metabolism by porcine early embryos.

The role of NH+4 toxicity in the decline of the submersed macrophyte Vallisneria natans in lakes of the Yangtze River basin, China

Experimental and field studies were conducted to evaluate the effects of NH4+ enrichment on growth and distribution of the submersed macrophyte, Vallisneria natans L, in lakes of the Yangtze River in China, based on the balance between free amino acids (FAA) and soluble carbohydrates (SC) in the plant tissue. Increase of NH4+ rather than NO3– concentrations in the water column caused FAA accumulation and SC depletion of the plant. The plant showed a unimodal pattern of biomass distribution along both FAA/SC ratios and external NH4+ concentrations, indicating that a moderate NH4-N concentration (<0.3 mg L–1) benefited the plant, whereas the high NH4-N concentration (>0.56 mg L–1) eliminated the plant completely. Therefore, 0.56 mg NH4-N mg L–1 in the water column was taken as the upper limit for V. natans in lakes of the Yangtze River basin. The mesocosm experiment showed that at a high external NH4-N (0.81 mg L–1), V. natans failed to propagate with a loss of half SC content (5 mg g–1 DW) in the rhizomes, indicating that the consumption of carbohydrates for detoxification of excess NH4+ into non-toxic FAA significantly diminished carbohydrate supply to the rhizomes. This might consequently inhibit the vegetative reproduction of the plant, and also might be an important cause for the decline and disappearance of the plant with eutrophication. The present study for the first time reports substantial ecophysiological evidences for NH4+ stress to submersed macrophytes, and indicates that NH4+ toxicity arising from eutrophication probably plays a key role in the deterioration of submersed macrophytes like V. natans.

Handbook of seed science and technology

Handbook of seed science and technology

Impact of Sunflower (Helianthus annuus L.) Extracts Upon Reserve Mobilization and Energy Metabolism in Germinating Mustard (Sinapis alba L.) Seeds

One commonly observed effect of phytotoxic compounds is the inhibition or delay of germination of sensitive seeds. Mustard (Sinapis alba L.) seeds were incubated with aqueous extracts of sunflower (Helianthus annuus L.) leaves. Although sunflower phytotoxins did not influence seed viability, extracts completely inhibited seed germination. Inhibition of germination was associated with alterations in reserve mobilization and generation of energy in the catabolic phase of germination. Degradation of lipids was suppressed by sunflower foliar extracts resulting in insufficient carbohydrate supply. The lack of respiratory substrates and decrease in energy (ATP) generation resulted in suppression of the anabolic phase of seed germination and ultimately growth inhibition.

Source/sink ratio and the relationship between maximum water content, maximum volume, and final dry weight of maize kernels

Final kernel weight (KW) is closely related to maximum kernel volume (KV) and maximum kernel water content (KWC). It is not clear, however, how changes in the reproductive sink capacity, assimilate availability during grain filling and physical restriction to kernel expansion affect the relationship between KW and KWC or between KW and KV. Three experiments were conducted at Balcarce, Argentina and Ames, USA. Defoliation, thinning, plant density, restricted pollination and volume restriction treatments were imposed to manipulate KV, sink and source capacity. KW varied from 111 to 436 mg across all hybrid–treatments combinations and was related to the source/sink ratio during grain filling ( r 2 = 0.85). Treatment variation in KW was related primarily to changes in kernel growth rate, except for the complete defoliated treatment, which also shortened the duration of grain filling. KW was correlated with maximum KWC ( r 2 = 0.77, p < 0.001) and with maximum KV ( r 2 = 0.91, p < 0.001). The developmental patterns for KW, KWC and KV during grain filling were not affected by the source/sink manipulations, except for severe defoliation. In the latter case, maximum KWC was not a good estimate of final KW. KV, however, was sensitive to reductions in carbohydrate supply during grain filling and was closely correlated to KW. Physical restriction to kernel expansion reduced kernel weight 13% relative to its control ( p < 0.01). But restricting kernel expansion did not alter the general relationships between KW and KWC or between KW and KV, because kernel density was not affected.

Skeletal muscle fiber type comparison of pyruvate dehydrogenase phosphatase activity and isoform expression in fed and food-deprived rats

Fiber type specificity of pyruvate dehydrogenase (PDH) phosphatase (PDP) was determined in fed (CON) and 48-h food-deprived (FD) rats. PDP activity and isoform protein content were determined in soleus (slow-twitch oxidative), red gastrocnemius (RG; fast-twitch oxidative glycolytic), and white gastrocnemius (WG; fast-twitch glycolytic) muscles. When normalized for mitochondrial volume, there was no difference in PDP activity between muscle types or CON and FD. When expressed per gram wet tissue weight, PDP activity was higher in RG compared with soleus and WG in both CON and FD rats. PDP activities from CON muscles were 1.48 +/- 0.19, 2.68 +/- 0.65, and 1.20 +/- 0.33 nmol x min(-1) x g wet tissue wt(-1) in soleus, RG, and WG, respectively, and decreased in FD muscles (1.22 +/- 0.22, 2.00 +/- 0.57, and 0.84 +/- 0.18 nmol x min(-1) x g wet tissue wt(-1)). This correlated with increased PDP2 protein, however, only in RG, as PDP2 was not detectable in soleus or WG. PDP1 protein was not responsive to food deprivation in all fiber types. In conclusion, PDP activity and protein content were higher in fast-twitch oxidative glycolytic muscles from CON and FD rats, identifying a unique inter- and intramuscular distribution. FD induced a small but significant decrease in PDP activity that was partially due to decreases in PDP2 protein. As a result, coordinate changes to PDP activity opposite to those of the other regulatory enzyme, PDH kinase, during food deprivation would maximize the inactivation of skeletal muscle PDH and enhance carbohydrate conservation during periods of limited carbohydrate supply.

Recent literature on lichens—202

Alstrup, V. & A. Aptroot. 2005. Pyrenocarpous lichens from Tanzania and Kenya. Cryptogamie, Mycologie 26(3): 265– 271. [32 taxa reported, most new country records; 12 taxa new to Africa.] Aptroot, A. & V. Wirth. 2006. A saxicolous Arthothelium from the Namib desert. Lichenologist 38(2): 123–126. [New: Arthothelium desertorum sp. nov. (Namibia) on rocks.] Aragon, G., V. J. Rico & R. Belinchon. 2006. Lichen diversity from Cazorla, Segura and Las Villas Biosphere Reserve (SE Spain). Nova Hedwigia 82(1–2): 31–50. [497 species in 125 genera; new to Spain: Involucropyrenium waltheri, Placynthium asperellum, Stangospora deplanata, Verrucaria cinereoviridescens and V. polysticha; 267 taxa are new to Jaen province.] Arup, U. 2006. A new taxonomy of the Caloplaca citrina group in the Nordic countries, except Iceland. Lichenologist 38(1): 1–20. [Treatment of 5 species in the group with a key, descriptions, distribution maps, and color photographs; supporting data includes analysis of ITS ribosomal DNA; new: Caloplaca arcis (Poelt & Vězda) comb. nov., C. dichroa sp. nov.; other species include C. phlogina, C. citrina and C. flavocitrina (mentioned also from Pennsylvania).] Baloch, E. & M. Grube. 2006. Evolution and phylogenetic relationships within Porinaceae (Ostropomycetidae), focusing on foliicolous species. Mycological Research 110(2): 125–136. [Authors recognize 4 main clades. ‘‘The genus Porina as understood by all recent concepts is paraphyletic, and Trichothelium is nested within the Porina nitidulagroup. Species-specific associations with morphologically different trentepohlioid photobionts mapped on the tree suggest that closely related mycobiont species switch between different types of algae.’’] Barreno, E. & S. Perez-Ortega. 2005. The UNESCO-MAB Reserve of Muniellos (Spain, Asturias), an example of high lichen diversity in Europe and the success of conservations strategies. Flora Mediterranea 15: 453–460. [474 lichens and 28 lichenicolous fungi in the 5542 hectare reserve; no nitrophytic habitats were found in this ancient woodland; rare finds include Epigloea renitens, Gyalideopsis calabrica, Cystobacidium hypogymniicola, Rhizocarpon caesium and Porpidia flavicunda.] Beckett, R. P., N. Mayaba, F. V. Minibayeva & A. Alyabyev. 2005. Hardening by partial dehydration and ABA increase desiccation tolerance in the cyanobacterial lichen Peltigera polydactylon. Annals of Botany 96(1): 109–115. [Test material from KwaZulu-Natal, South Africa. ‘‘Results indicate that the photobiont of P. polydactylon possesses inducible tolerance mechanisms that reduce desiccationinduced damage to carbon fixation, and will therefore improve the supply of carbohydrates to the whole thallus following stress. In this lichen, ABA is involved in signal transduction pathways that increase tolerance of the photobiont.’’] Behera, B. C., N. Verma, A. Sonone & U. Makhija. 2005. Antioxidant and antibacterial activities of lichen Usnea ghattensis in vitro. Biotechnology Letters 27(14): 991–995. [‘‘Hence, U. ghattensis deserves to be explored for its bioactive molecules. There is however, a need to improve the growth rate of the cultured tissue in the laboratory to harvest large quantities of cells and thus metabolites.’’] Bellemere, A. & C. Bellemere. 2005. «Pyrenomycetes sensu lato» elements de bibliographie recente. Annees 2003 et 2004 et complements annees 2001 et 2002. Cryptogamie, Mycologie 26(2): 149–185. [A few lichen/lichenicolous papers included.] Bennett, J. P. 2006. What do we know about Wisconsin lichens? Evansia 23(1): 13–18. [‘‘In conclusion, the lichen picture for Wisconsin is incomplete because collecting has not been performed evenly across the state. We do know, however, * The cumulative database for this series is available in searchable form on the World Wide Web at http://www.toyen.uio.no/ botanisk/bot-mus/lav/sok_rll.htm. I owe special thanks to Bill Buck for providing copies of papers by other authors, which were otherwise unavailable to me, and to the cooperating authors who send reprints or electronic versions of their works to me for inclusion in this series.

Propofol infusion syndrome in anaesthesia and intensive care medicine

Propofol infusion syndrome is a rare but often fatal syndrome, characterized by lactacidosis, lipaemic plasma and cardiac failure, associated with propofol infusion over prolonged periods of time. As propofol is used worldwide, knowledge of propofol infusion syndrome is essential for all anaesthesiologists and intensive care physicians. This review will provide an update on reported cases, and describe recent findings relevant to the pathophysiology and clinical presentation of propofol infusion syndrome. Case reports of propofol infusion syndrome have contributed new pathophysiological evidence. Reported cases of similar syndromes may represent initial propofol infusion syndrome, and may help to identify further risk factors such as low carbohydrate supply and early warning signs such as lactacidosis. Newly identified gene defects mimicking propofol infusion syndrome may elicit the underlying genetic susceptibility. Recommendations for the limitation of propofol use have been devised by various institutions. Propofol infusion syndrome must be kept in mind as a rare but highly lethal complication of propofol use, not necessarily confined to the prolonged use of propofol. Dose limitations must be adhered to, and early warning signs such as lactacidosis should lead to the immediate cessation of propofol infusion.

The paradoxical effects of nutrient ratios and supply rates on an outbreaking insect herbivore, the Australian plague locust

1. The Australian plague locust, Chortoicetes terminifera, develops following rainfall in an environment dominated by two host plants, the annual Dactyloctenium radulans and the perennial Astrebla lappacea. This simple system provides an ideal opportunity to explore the relationship between plant quality, individual herbivore performance and population responses. 2. We compared the two grasses chemically and structurally, and the behavioural, physiological and developmental responses of locust nymphs to these diets. 3. The grasses appeared to be of similar nutritional quality in terms of their chemical composition, although they differed in their physical properties. Early instar nymphs performed equally well on both grasses. However, older nymphs consuming D. radulans developed faster, survived better and attained a higher body weight compared with those consuming A. lappacea. 4. The differences in performance by the older nymphs related to the rate and ratio of supply of carbohydrate and protein from the two grasses, with less carbohydrate being assimilated from A. lappacea than D. radulans per unit of protein assimilated. Experiments showed that these differences arose as a direct result of the physical barrier to nutrient extraction provided by cell walls and indirectly through the amount of water contained within each cell. Paradoxically, nitrogen did not limit performance in the traditional sense through shortage,but rather its relative excess in A. lappacea appeared to impede intake and assimilation of adequate carbohydrate. 5. As a consequence, we predict that the length of time D. radulans remains available following rainfall will influence plaguing dynamics, although not for the reasons previously thought. 6. The results highlight the need to consider nutrient balance and actual rates of supply (rather than simply measuring the chemical composition of the plant) when attempting to understand herbivore nutritional ecology.

Effects of Lime Sulfur and Fish Oil on Pollen Tube Growth, Leaf Photosynthesis and Fruit Set in Apple

The effect of liquid lime sulfur (LS) and fish oil (FO) application during bloom on leaf photosynthesis (Pn) and pollen tube growth in apple (Malus ×domestica) flowers were investigated in order to determine their mode of action as a bloom thinning agent. LS increased the percentage of flowers with fewer than 10 pollen tubes per flower to more than 64% compared to 5% or less in the control. Pollen tubes were completely absent from 27% to 48% of flowers following LS treatment compared with fewer than 4% of flowers having no pollen tubes on control trees. These data indicate that 30% to 50% of flowers that open on the day of LS application are unlikely to set a fruit due to the complete inhibition of embryo fertilization. Increasing the rate of LS from 0.5% to 4% increased the proportion of flowers with limited pollen tube number in a concentration dependent manner. LS suppressed the rate of light saturated Pn; successive LS sprays during the bloom period had an additive effect on suppression of Pn and fruit set. In one study the reduction in Pn was greatest 12 days after application of LS but Pn recovered by about 19 days after initial treatment. In a second study Pn of primary spur leaves had still not recovered when measured 57 days after the first of three applications. FO had no effect on the number of pollen tubes per flower, but reduced Pn and fruit set by about 10% and 20% respectively. An increase in the proportion of flowers with no pollen tubes, and therefore no embryo development, can account, at least in part, for the thinning response following application of LS to apples during bloom. It is likely that suppression of Pn contributes to the thinning response, although the importance of this mechanism will depend on perturbation of the total carbohydrate supply to developing fruit.

Genotypic Difference in Nitrogen Acquisition Ability in Maize Plants Is Related to the Coordination of Leaf and Root Growth

ABSTRACT The capacity of a plant to take up nitrate is a function of the activity of its nitrate-transporter systems and the size and architecture of its root system. It is unclear which of the two components, root system or nitrate-uptake system, is more important in nitrogen (N) acquisition under nitrogen-sufficiency conditions. Two maize (Zea mays L.) inbred lines (478 and Wu312) grown in nutrient solution in a controlled environment were compared for their N acquisition at 0.1, 0.5, 2.5, 5, and 10 mmol L−1 nitrate supply. Genotype 478 could take up more N than Wu312 at all nitrate concentrations, though the shoot biomass of the two genotypes was similar. Genotype 478 had a larger leaf area and longer root length. The specific N uptake rate of 478 (μmol N g−1 root. d−1) was lower than that of Wu312. In an independent nitrate-depletion experiment, the potential nitrate uptake rate of 478 was also lower than that of Wu312. No genotypic difference was found in photosynthesis rate. It was concluded that the greater N acquisition ability in 478 involves the coordination of leaf and root growth. Vigorous leaf growth caused a large demand for N. This demand was met by the genotype's large root system. Besides providing a strong sink for N uptake, the larger leaf area of 478 might also guarantee the carbohydrate supply necessary for its greater root growth.

Gibberellin-dependent induction of tomato extracellular invertase Lin7 is required for pollen development.

The tomato extracellular invertase family comprises four members with different expression patterns. Among the three invertase isoenzymes expressed in floral tissues, Lin5, Lin6 and Lin7, the expression of Lin7 was previously shown to be restricted to the tapetum and pollen. Histochemical analysis of β-glucuronidase (GUS) reporter activity shows Lin7 expression in pollen and pollen tubes of corresponding transgenic plants. The physiological relevance of the identification of gibberellin-responsive cis-acting elements for induction of the Lin7 promoter is supported by the repression of Lin7 expression in pollen grains by the gibberellin biosynthesis inhibitor paclobutrazol. Functional approaches with transgenic tomato plants establish a link between gibberellin action and invertase function in the tapetum for pollen development: both tissue-specific antisense repression of extracellular Lin7 and ectopic inactivation of the biologically active GAs by expression of a GA2-oxidase under control of the Lin7 promoter result in germination deficient pollen. These complementary findings support the idea that the GA requirement of pollen development, pollen germination and pollen tube growth are linked to energy metabolism via the regulation of an extracellular invertase as a key enzyme for carbohydrate supply via an apoplasmic pathway.

Effects of Light, Temperature, Defoliation, and Fruiting on Carbon Assimilation and Partitioning in Potted Cranberry

Carbohydrate supply has been hypothesized to limit fruit set in cranberry (Vaccinium macrocarpon Ait.), however the limitations to carbon gain throughout the season are currently unknown. These experiments investigated the effects of light, temperature, fruit presence, and defoliation on carbon production and partitioning in potted cranberry. Fruiting and vegetative uprights (short vertical stems which bear fruit biennially) reached similar asymptotes with respect to light response, but fruiting uprights reached saturation at a lower light intensity than vegetative uprights. Runners (diageotropic vegetative stems) had a lower asymptote, higher light compensation point, and greater rate of dark respiration than uprights. Temperature had little effect on net carbon exchange rate of uprights or runners. Before new growth, defoliation did not affect the concentration of total nonstructural carbohydrates in the vegetative uprights, or the partitioning of soluble carbohydrates to starch, even though uprights with lower leaf areas had higher net CO2 assimilation. At fruit set and again at fruit maturity, defoliation reduced total nonstructural carbohydrate concentration, while net CO2 assimilation was not affected. Carbohydrate production and partitioning within an upright was unaffected by the presence of a single fruit throughout the experiment.

Differential Antiatherogenic Effects of PPARα Versus PPARγ Agonists

Research during the past decade about the role of the transcription factors known as peroxisome proliferator-activated receptors (PPARs) subtype alpha (-α), delta/beta (-δ/β), and gamma (-γ) indicates that they are master switches controlling tissue-specific physiological adaptations in the use of fatty acids, glucose, and amino acids during feeding and fasting.1,2 These nuclear receptors modulate in concert the expression of genes associated with specific metabolic pathways together with the signaling of hormones involved in energy homeostasis like insulin, glucagon, growth hormone (GH), and cortisol. In this capacity they seamlessly adjust the reversible transitions from storage to use of fatty acids and triglycerides, of glucose and glycogen, and of the more complex ones of amino acids and proteins. Moreover, enzymes and transporters required for the interpathway conversions of glucose into fatty acids and of some amino acids into glucose also are target genes for PPARs, at least when rodents and humans are maintained on a high carbohydrate supply. Endowed with such central functions it is not surprising that the PPARs have impact on metabolic alterations contributing to insulin resistance and diabetes, as well as on abnormalities of lipid metabolism causing dyslipidemias and atherosclerosis. Therefore is also logical that intense research is dedicated to evaluate how modulation of the PPARs could improve the dyslipidema associated with insulin resistance, insulin resistance itself, diabetes, and atherosclerosis. See page 1897 The PPARα agonists, known generically as fibrates, reduce the risk of cardiovascular events especially in patients with the dyslipidemia of insulin resistance.3 At present, no data are available about the effect on cardiovascular events of the two …

Effect of sucrose on activity of starch synthesis enzymes in rice ears in culture

Grain filling of rice (Oryza sativa L.) is thought to be affected not only by the supply of carbohydrate from source organs, but also by sink activity, including the activities of enzymes related in starch synthesis. To examine the effect of translocated carbohydrate on sink activity, we cultured detached ears (cut 7 days after flowering) in a solution containing sucrose at various concentrations, glutamine and vitamins. Grain weights 16 days after the start of ear culture increased with increasing sucrose concentration up to 50–70 g sucrose l−1, but not above this range, probably because of low water potential. Activities of ADP glucose pyrophosphorylase, soluble starch synthase and sucrose synthase rapidly decreased in grains grown without sucrose, but increased with increasing sucrose concentration up to 50–70 g l−1. Expression of mRNAs for these enzymes and for sucrose transporter was also generally increased by sucrose at 50–70 g l−1. Though there was a good correlation between activity and expression of mRNA for sucrose synthase, the correlation for other enzymes was not very good. Thus, we suggested that the sink activity of grains in rice ears, and therefore the grain filling, was affected by the supply of carbohydrate from source organs, and that it was also owing to factors other than transcriptional regulation.

How does Dryobalanops aromatica supply carbohydrate resources for reproduction in a masting year?

The effect on reproduction of the dynamics of resource allocation was studied in an emergent and masting tree species, Dryobalanops aromatica (Dipterocarpaceae), in a lowland dipterocarp forest in Sarawak, Malaysia. Girdling of the reproductive shoots (5 mm diameter) caused an increase in abortion during the flowering period, but did not affect the fruit set at the middle or final stages of seed maturation. In contrast, 50% defoliation significantly affected fruit setting, but had little effect on flowering. The total leaf area of reproductive shoots was significantly correlated with final fruit set and total fruit mass. Control of the carbohydrate supply to reproductive shoots by girdling and defoliation made no difference to fruit size, but the fruit number was highly sensitive to carbohydrate availability. Total non-structural carbohydrate (TNC) decreased during the flowering period mainly in the branch (P<0.05), but fluctuated little in any organs during fruit maturation. Leaf nitrogen and photosynthetic capacity of the reproductive shoots were not significant variables for reproduction. Our results suggest that D. aromatica uses current photosynthates in the leaves of reproductive shoots as a carbon source during fruit development, but requires stored assimilates in the branch for flowering. However, since TNC was still present in all organs even after flowering, our study also suggests that storage of carbohydrate resources might not be the decisive factor in the occurrence or frequency of flowering in this species.

Grain yield and kernel weight of two maize genotypes differing in nitrogen use efficiency at various levels of nitrogen and carbohydrate availability during flowering and grain filling

Grain yield per plant (GYP) and mean kernel weight (KW) of maize (Zea mays L.) are sensitive to changes in the environment during the lag phase of kernel growth (the time after pollination in which the potential kernel size is determined), and during the phase of linear kernel growth. The aim of this study was to assess genotypic differences in the response to environmental stresses associated with N and/or carbohydrate shortage at different phases during plant development. The rate and timing of N and carbohydrate supply were modified by application of fertilizer, shading, and varying the plant density at sowing, at silking or at 14 d after silking. The effects of these treatments on the photosynthetic capacity, grain yield and mean kernel weight were investigated in two hybrids differing in N use efficiency. The total above-ground biomass and grain yield per plant of the efficient hybrid responded little to altered environmental conditions such as suboptimal N supply, enhanced inter-plant competition, and shading for 14 d during flowering, when compared to the less efficient genotype. We conclude that grain yields in the efficient genotype are less sensitive not only to N stress, but also to carbohydrate shortage before grain filling. Shading of N deficient plants from 14 d after silking to maturity did not significantly reduce grain yield in the non-efficient genotype, indicating complete sink limitation of grain yield during grain filling. In the efficient genotype, in contrast, grain yield of N-deficient plants was significantly reduced by shading during grain filling. The rate of photosynthesis declined with decreasing foliar N content. No genotypic differences in photosynthesis were observed at high or low foliar N contents. However, at high plant density and low N supply, the leaf chlorophyll content after flowering in the efficient genotype was higher than that in the non-efficient genotype. Obviously, the higher source capacity of the efficient genotype was not due to higher photosynthetic N use efficiency but due to maintenance of high chlorophyll contents under stressful conditions. In the efficient genotype, the harvest index was not significantly affected by N fertilization, plant density, or shading before the grain filling period. In contrast, in the non-efficient genotype the harvest index was diminished by N deficiency and shading during flowering. We conclude that the high yielding ability of the efficient genotype under stressful conditions was associated with formation of a high sink capacity of the grains under conditions of low carbohydrate and N availability during flowering and with maintenance of high source strength during grain filling under conditions of high plant density and low N availability.