Sucrose Translocation Research Articles

Quantifying isotope parameters associated with carbonyl-water oxygen exchange during sucrose translocation in tree phloem.

Stable oxygen isotope ratio of tree-ring α-cellulose (δ18Ocel) yields valuable information on many aspects of tree-climate interactions. However, our current understanding of the mechanistic controls on δ18Ocel is incomplete, with a knowledge gap existent regarding the fractionation effect characterizing carbonyl-water oxygen exchange during sucrose translocation from leaf to phloem. To address this insufficiency, we set up an experimental system integrating a vapor 18O-labeling feature to manipulate leaf-level isotopic signatures in tree saplings enclosed within whole-canopy gas-exchange cuvettes. We applied this experimental system to three different tree species to determine their respective relationships between 18O enrichment of sucrose in leaf lamina (Δ18Ol_suc) and petiole phloem (Δ18Ophl_suc) under environmentally/physiologically stable conditions. Based on the determined Δ18Ophl_suc-Δ18Ol_suc relationships, we estimated that on average, at least 25% of the oxygen atoms in sucrose undergo isotopic exchange with water along the leaf-to-phloem translocation path and that the biochemical fractionation factor accounting for such exchange is c. 34‰, markedly higher than the conventionally assumed value of 27‰. Our study represents a significant step toward quantitative elucidation of the oxygen isotope dynamics during sucrose translocation in trees. This has important implications with respect to improving the δ18Ocel model and its related applications in paleoclimatic and ecophysiological contexts.

Disruptions of sugar utilization and carbohydrate metabolism in rice developing anthers aggravated heat stress-induced pollen abortion

High temperature (HT) stress at reproductive stage is one of most important environment negatively affecting spikelet fertility and rice yield. In this study, the effect of HT exposure on the sugar composition and carbohydrate metabolism in developing anthers and its relation to floret fertility and pollen viability were investigated by different temperature regimes under well-controlled climatic condition. Result showed that HT exposure during microspore development significantly reduced the starch deposition in developing anther and evidently disrupted the spatial distribution of sugar and starch concentrations in different compartments of rice anther, with the higher ratio of sucrose to hexose concentrations in HT-stressed anthers relative to the control ones. Under HT exposure, the amount of starch deposition in the fraction of sporophytic tissues dropped evidently, while the concentrations of sucrose and starch in anther wall tissue enhanced significantly, suggesting that HT exposure impaired the translocation of sucrose from the anther wall tissue to the sporophytic tissues inside rice anther. Furthermore, we presented possible contribution of various genes and key enzymes involving in sugar conversion and carbohydrate metabolism in developing anther to the formation of HT-induced pollen abortion by disrupting the sugar utilization in HT-stressed anther. HT exposure suppressed the activities of cell wall and vacuolar invertase, hexokinase, and ADP-glucose pyrophosphorylase in developing anther, while it was opposite for the effect of HT exposure on sucrose synthase and fructokinase. HT-induced suppression of OsCWIN3 in the anther walls might be strongly responsible for the HT-induced impairments of sugar utilization in HT-stressed anthers.

Garlic Ecotypes Utilise Different Morphological, Physiological and Biochemical Mechanisms to Cope with Drought Stress.

Drought negatively affects plants by altering morphological, physiological and metabolic processes and ultimately reducing yields. Garlic (Allium sativum L.), an important member of the Alliaceae family, is also sensitive to drought and maximizing the yield of garlic bulbs is largely dependent on water availability. The objective of this study was to determine the effects of drought stress on morphological and physiological characteristics, as well as on phenolic, sugar, inulin and free amino acid content and antioxidant activity in two Croatian garlic ecotypes, 'Istarski crveni' (IC) and Istarski bijeli (IB). Drought was induced by using polyethylene glycol 8000 (PEG) solution (-0.6 MPa) starting 21 days after clove planting and lasted for 20 days. Drought reduced plant height, number of leaves and plant weight, but increased root length in both ecotypes compared to the control treatment. Among the physiological parameters, significant differences were observed between the two ecotypes studied in the spectral characteristics of the leaves, namely reflection in red, green and blue, VAL, values of the vegetation indices related to the chlorophyll content (CHI, GI), and the anthocyanin content (ARI). Ecotype IC showed higher antioxidant activity in the control treatment due to higher total phenolic content (TPC), but under drought conditions higher DPPH radical scavenging activity was determined in ecotype IB and higher values of FRAP in IC. Sucrose and glucose generally decreased under drought, while inulin increased in IB but decreased in IC. Total free amino acid content increased under drought in both ecotypes. In conclusion, drought tolerance of IB might be associated with increased accumulation of inulin and higher levels of amino acids, especially those shown to contribute to drought resistance. In IC, drought tolerance is associated with an increase in some amino acid compounds and better root growth in depth, probably due to a more efficient translocation of sucrose to the underground part of the plant.

Understanding the Active Mechanisms of Plant (Sesuvium portulacastrum L.) against Heavy Metal Toxicity.

Through metabolic analysis, the present research seeks to reveal the defense mechanisms activated by a heavy metals-resistant plant, Sesuvium portulacastrum L. In this regard, shifting metabolisms in this plant were investigated in different heavy metals-contaminated experimental sites, which were 50, 100, 500, 1000, and 5000 m away from a man-fabricated sewage dumping lake, with a wide range of pollutant concentrations. Heavy metals contaminations in contaminated soil and their impact on mineral composition and microbial population were also investigated. The significant findings to emerge from this research were the modifications of nitrogen and carbon metabolisms in plant tissues to cope with heavy metal toxicity. Increased plant amylase enzymes activity in contaminated soils increased starch degradation to soluble sugars as a mechanism to mitigate stress impact. Furthermore, increased activity of sucrose phosphate synthase in contaminated plants led to more accumulation of sucrose. Moreover, no change in the content of sucrose hydrolyzing enzymes (vacuolar invertase and cytosolic invertase) in the contaminated sites can suggest the translocation of sucrose from shoot to root under stress. Similarly, although this study demonstrated a high level of malate in plants exposed to stress, caution must be applied in suggesting a strong link between organic acids and the activation of defense mechanisms in plants, since other key organic acids were not affected by stress. Therefore, activation of other defense mechanisms, especially antioxidant defense molecules including alpha and beta tocopherols, showed a greater role in protecting plants from heavy metals stress. Moreover, the increment in the content of some amino acids (e.g., glycine, alanine, glutamate, arginine, and ornithine) in plants under metal toxicity can be attributed to a high level of stress tolerance. Moreover, strategies in the excitation of the synthesis of the unsaturated fatty acids (oleic and palmitoleic) were involved in enhancing stress tolerance, which was unexpectedly associated with an increase in the accumulation of palmitic and stearic (saturated fatty acids). Taken together, it can be concluded that these multiple mechanisms were involved in the response to stress which may be cooperative and complementary with each other in inducing resistance to the plants.

Genome-wide analysis and characterization of Dendrocalamus farinosus SUT gene family reveal DfSUT4 involvement in sucrose transportation in plants.

Sucrose is the main transported form of photosynthetic products. Sucrose transporter (SUT) participates in the translocation of sucrose from source to sink, which is important for the growth and development of plants. Dendrocalamus farinosus is an important economic crop in southwestern China because of its high growth rate, high fiber content, and dual usage for food and timber, but the mechanism of sucrose transportation in D. farinosus is unclear. In this study, a total of 12 SUT transporter genes were determined in D. farinosus by whole-genome identification. DfSUT2, DfSUT7, and DfSUT11 were homologs of rice OsSUT2, while DfSUT4 was a homolog of OsSUT4, and these four DfSUT genes were expressed in the leaf, internode, node, and bamboo shoots of D. farinosus. In addition, DfSUT family genes were involved in photosynthetic product distribution, ABA/MeJA responses, and drought resistance, especially DfSUT4. The function of DfSUT4 was then verified in Nicotiana tabacum. DfSUT4 was localized mainly in the leaf mesophyll and stem phloem of pDfSUT4::GUS transgenic plant. The overexpression of DfSUT4 gene in transgenic plant showed increases of photosynthetic rate, above-ground biomass, thousand grain weight, and cellulose content. Our findings altogether indicate that DfSUT4 can be a candidate gene that can be involved in phloem sucrose transportation from the source leaves to the sink organs, phytohormone responses, abiotic stress, and fiber formation in plants, which is very important in the genetic improvement of D. farinosus and other crops.

AtSWEET11 and AtSWEET12: the twin traders of sucrose.

AtSWEET11 and AtSWEET12 are central players in phloem loading and long-distance sucrose translocation. During drought stress, these transporters enhance sucrose transport from shoot to root, increasing root proliferation. Chen et al. have now unravelled novel aspects of sucrose transport regulation, occurring via AtSWEET11 and AtSWEET12 phosphorylation and oligomerisation.

De novo transcriptome analysis provides insights into formation of in vitro adventitious root from leaf explants of Arnebia euchroma

BackgroundAdventitious root formation is considered a major developmental step during the propagation of difficult to root plants, especially in horticultural crops. Recently, adventitious roots induced through plant tissue culture methods have also been used for production of phytochemicals such as flavonoids, anthocyanins and anthraquinones. It is rather well understood which horticultural species will easily form adventitious roots, but the factors affecting this process at molecular level or regulating the induction process in in vitro conditions are far less known. The present study was conducted to identify transcripts involved in in vitro induction and formation of adventitious roots using Arnebia euchroma leaves at different time points (intact leaf (control), 3 h, 12 h, 24 h, 3 d, 7 d, 10 d and 15 d). A. euchroma is an endangered medicinal Himalayan herb whose root contains red naphthoquinone pigments. These phytoconstituents are widely used as an herbal ingredient in Asian traditional medicine as well as natural colouring agent in food and cosmetics.ResultsA total of 137.93 to 293.76 million raw reads were generated and assembled to 54,587 transcripts with average length of 1512.27 bps and N50 of 2193 bps, respectively. In addition, 50,107 differentially expressed genes were identified and found to be involved in plant hormone signal transduction, cell wall modification and wound induced mitogen activated protein kinase signalling. The data exhibited dominance of auxin responsive (AUXIN RESPONSE FACTOR8, IAA13, GRETCHEN HAGEN3.1) and sucrose translocation (BETA-31 FRUCTOFURANOSIDASE and MONOSACCHARIDE-SENSING protein1) genes during induction phase. In the initiation phase, the expression of LATERAL ORGAN BOUNDARIES DOMAIN16, EXPANSIN-B15, ENDOGLUCANASE25 and LEUCINE-rich repeat EXTENSION-like proteins was increased. During the expression phase, the same transcripts, with exception of LATERAL ORGAN BOUNDARIES DOMAIN16 were identified. Overall, the transcriptomic analysis revealed a similar patterns of genes, however, their expression level varied in subsequent phases of in vitro adventitious root formation in A. euchroma.ConclusionThe results presented here will be helpful in understanding key regulators of in vitro adventitious root development in Arnebia species, which may be deployed in the future for phytochemical production at a commercial scale.

Cultivar-Dependent Responses in Plant Growth, Leaf Physiology, Phosphorus Use Efficiency, and Tuber Quality of Potatoes Under Limited Phosphorus Availability Conditions.

The limited availability of phosphorus (P) in soils causes a major constraint in the productivity of potatoes, which requires increased knowledge of plant adaptation responses in this condition. In this study, six potato cultivars, namely, Agria, Lady Claire, Milva, Lilly, Sieglinde, and Verdi, were assessed for their responses on plant growth, leaf physiology, P use efficiency (PUE), and tuber quality with three P levels (Plow, Pmed, and Phigh). The results reveal a significant variation in the cultivars in response to different P availabilities. P-efficient cultivars, Agria, Milva, and Lilly, possessed substantial plant biomass, tuber yield, and high P uptake efficiency (PUpE) under low P supply conditions. The P-inefficient cultivars, Lady Claire, Sieglinde, and Verdi, could not produce tubers under P deprivation conditions, as well as the ability to efficiently uptake P under low-level conditions, but they were efficient in P uptake under high soil P conditions. Improved PUpE is important for plant tolerance with limited P availability, which results in the efficient use of the applied P. At the leaf level, increased accumulations of nitrate, sulfate, sucrose, and proline are necessary for a plant to acclimate to P deficiency-induced stress and to mobilize leaf inorganic phosphate to increase internal PUE and photosynthesis. The reduction in plant biomass and tuber yield under P-deficient conditions could be caused by reduced CO2 assimilation. Furthermore, P deficiency significantly reduced tuber yield, dry matter, and starch concentration in Agria, Milva, and Lilly. However, contents of tuber protein, sugars, and minerals, as well as antioxidant capacity, were enhanced under these conditions in these cultivars. These results highlight the important traits contributing to potato plant tolerance under P-deficient conditions and indicate an opportunity to improve the P efficiency and tuber quality of potatoes under deficient conditions using more efficient cultivars. Future research to evaluate molecular mechanisms related to P and sucrose translocation, and minimize tuber yield reduction under limited P availability conditions is necessary.

Coupling kinetic models and advection–diffusion equations. 1. Framework development and application to sucrose translocation and metabolism in sugarcane

AbstractThe sugarcane stalk, besides being the main structural component of the plant, is also the major storage organ for carbohydrates. Previous studies have modelled the sucrose accumulation pathway in the internodal storage parenchyma of sugarcane using kinetic models cast as systems of ordinary differential equations. To address the shortcomings of these models, which did not include subcellular compartmentation or spatial information, the present study extends the original models within an advection–diffusion–reaction framework, requiring the use of partial differential equations to model sucrose metabolism coupled to phloem translocation. We propose a kinetic model of a coupled reaction network where species can be involved in chemical reactions and/or be transported over long distances in a fluid medium by advection or diffusion. Darcy’s law is used to model fluid flow and allows a simplified, phenomenological approach to be applied to translocation in the phloem. Similarly, generic reversible Hill equations are used to model biochemical reaction rates. Numerical solutions to this formulation are demonstrated with time-course analysis of a simplified model of sucrose accumulation. The model shows sucrose accumulation in the vacuoles of stalk parenchyma cells, and is moreover able to demonstrate the upregulation of photosynthesis in response to a change in sink demand. The model presented is able to capture the spatio-temporal evolution of the system from a set of initial conditions by combining phloem flow, diffusion, transport of metabolites between compartments and biochemical enzyme-catalysed reactions in a rigorous, quantitative framework that can form the basis for future modelling and experimental design.

Overexpression of Sugarcane Sucrose Transporter 1 (SoSUT1) Gene Increases Rice Yield

The growth and development of plants are determined by photosynthesis, which ultimately results in sucrose. Sucrose is synthesized in the source then translocated to all parts of the plant (sink). The translocation process of sucrose from source to sink is controlled by sucrose protein called sucrose transporter. SoSUT1 is a gene that encodes a sucrose transporter 1 (SUT1) protein in sugarcane. Rice transformation with the SoSUT1 causes overexpression SUT, which is expected to increase the translocation of sucrose into the seed of rice plants. This research was conducted by introducing SoSUT1 in rice plants Inpari 14 SS. Transformation using Agrobacterium tumefaciens vector in apical bud explant Indica rice cv. Inpari 14 SS results in 26 events positive rice contains genes SoSUT1. This study aims to elucidate the inheritance of transgene in the next generation and to characterize its effect on the morphology and the yields of a subsequent generation. The study is conducted by planting the seeds of T1 and T2 plants in media containing Hygromycin and using PCR analysis for further analysis. As the results, from 26 events on the T1 plant, only 3 events of T3 plants were confirmed on the T3 plant. The overexpression of the SoSUT1 gene could increase the number of tillers, the number of productive tillers, panicle length, and panicle exit length, also increasing the number of spherical grains, reducing the number of empty grains and increasing the weight of 1000 grains.

The transcription factor gene RDD1 promotes carbon and nitrogen transport and photosynthesis in rice

The current rapid increase in the world population is a global issue necessitating an increase in crop productivity. Fertilizers are necessary for enhancing the growth and productivity of plants, but are potential environmental pollutants when they persist in the soil. The transcription factor–encoding gene RDD1 plays a role in improving the uptake and accumulation of various nutrient ions and increasing grain productivity in rice. This study shows that RDD1 functions to promote photosynthetic activity under ambient and high CO2 conditions as well as the translocation of sucrose and glutamine, which are known as translocating substances for carbon and nitrogen, respectively. Moreover, shoot weight was increased in RDD1-overexpressing plants under high CO2 conditions. Metabolite analysis showed that amino acid levels in source tissues were lower, and carbohydrate levels from glycolysis and the pentose phosphate pathway in sink tissues were higher, in the RDD1-overexpressing plants than in wild-type plants, indicating improved carbon and nitrogen translocation from source tissues in the RDD1-overexpressing plants. These results suggest that it would be possible to utilize the effects of RDD1 on carbon and nitrogen translocation and photosynthesis to sustainably increase crop productivity under elevated atmospheric CO2 conditions.

Sugar Starvation Enhances Leaf Senescence and Genes Involved in Sugar Signaling Pathways Regulate Early Leaf Senescence in Mutant Rice

To clarify the complex regulatory relationship between changes in sugar content and leaf senescence during the grain-filling stage of rice, genotype-dependent differences in sugar content and the temporal transcriptional patterns of genes involved in sugar signaling pathways were determined in mutant rice exhibiting early leaf senescence and its wild type Zhefu 142. The effects of exogenous glucose or sucrose on the senescence of detached leaves under dark conditions were also investigated. Chlorophyll, soluble sugar, sucrose and fructose contents decreased, whereas electrolytic leakage and malondialdehyde levels increased in mutant leaves at the grain-filling stage. These results suggested that sugar starvation is positively correlated with the early leaf senescence of mutant plants. Detached leaf segments incubated in exogenous sugar solutions under dark conditions exhibited delayed senescence. The high expression of Hxk1 in leaves of mutant plants at the initial grain-filling stage suggested that Hxk1 is involved in the hexose-sensing process at the early stage of leaf senescence. The low expression levels of Hxk2 and Frk1 in the senescing leaves of mutant rice during the grain-filling stage are indicative of weakened hexose phosphorylation. In addition, the high expression levels of SuSy1, SuSy2 and SuSy4 in leaves of mutant plants at the initial grain-filling stage are accompanied by the high transcript levels of SUT1, which favor sucrose translocation and remobilization from the early senescing leaves of mutant rice. The relatively reduced transcript levels of chFBP, cyFBP, SPS1, SPS2 and SPS6 indicated that during the grain-filling stage, sucrose biosynthesis is weakened in the senescing leaves of mutant rice.

Chitosan nanofertilizer to foster source activity in maize

We, herein, report the effect of chitosan nanofertilizer comprising of copper (Cu) and salicylic acid (SA) on source activity in maize. Seed treatment and foliar application of chitosan nanofertilizer significantly up-regulated the source activity in developing maize plants. Seed treatment with nanofertilizer induced 1.6 folds higher seedling vigour index, 1.7–3.0 folds higher activities of reserve food mobilizing enzymes in seedlings as compared with control. Foliar application of nanofertilizer (0.01–0.16%) statistically significantly increased the activities of antioxidant enzymes (1.06–1.91 folds), reduced malondialdehyde content and enhanced chlorophyll contents (2 folds) in leaves. Application of nanofertilizer remarkably induced sucrose translocation (2.5–3.5 folds) in internodes which gives subtle clue of higher remobilization of nutrients towards growing cob. The elusive bioactivities of nanofertilizer can be attributed to slow release and synergistic effects of Cu and SA. We claim that chitosan nanofertilizer has immense potential to promote source activity in maize for higher crop yield.

Arabidopsis sucrose synthase localization indicates a primary role in sucrose translocation in phloem.

Sucrose synthase (SuSy) is one of two enzyme families capable of catalyzing the first degradative step in sucrose utilization. Several earlier studies examining SuSy mutants in Arabidopsis failed to identify obvious phenotypic abnormalities compared with wild-type plants in normal growth environments, and as such a functional role for SuSy in the previously proposed cellulose biosynthetic process remains unclear. Our study systematically evaluated the precise subcellular localization of all six isoforms of Arabidopsis SuSy via live-cell imaging. We showed that yellow fluorescent protein (YFP)-labeled SuSy1 and SuSy4 were expressed exclusively in phloem companion cells, and the sus1/sus4 double mutant accumulated sucrose under hypoxic conditions. SuSy5 and SuSy6 were found to be parietally localized in sieve elements and restricted only to the cytoplasm. SuSy2 was present in the endosperm and embryo of developing seeds, and SuSy3 was localized to the embryo and leaf stomata. No single isoform of SuSy was detected in developing xylem tissue of elongating stem, the primary site of cellulose deposition in plants. SuSy1 and SuSy4 were also undetectable in the protoxylem tracheary elements, which were induced by the vascular-related transcription factor VND7 during secondary cell wall formation. These findings implicate SuSy in the biological events related to sucrose translocation in phloem.

Roots of the Resurrection Plant Tripogon loliiformis Survive Desiccation Without the Activation of Autophagy Pathways by Maintaining Energy Reserves.

Being sessile, plants must regulate energy balance, potentially via source-sink relations, to compromise growth with survival in stressful conditions. Crops are sensitive, possibly because they allocate their energy resources toward growth and yield rather than stress tolerance. In contrast, resurrection plants tightly regulate sugar metabolism and use a series of physiological adaptations to suppress cell death in their vegetative tissue to regain full metabolic capacity from a desiccated state within 72 h of watering. Previously, we showed that shoots of the resurrection plant Tripogon loliiformis, initiate autophagy upon dehydration as one strategy to reinstate homeostasis and suppress cell death. Here, we describe the relationship between energy status, sugar metabolism, trehalose-mediated activation of autophagy pathways and investigate whether shoots and roots utilize similar desiccation tolerance strategies. We show that despite containing high levels of trehalose, dehydrated Tripogon roots do not display elevated activation of autophagy pathways. Using targeted and non-targeted metabolomics, transmission electron microscopy (TEM) and transcriptomics we show that T. loliiformis engages a strategy similar to the long-term drought responses of sensitive plants and continues to use the roots as a sink even during sustained stress. Dehydrating T. loliiformis roots contained more sucrose and trehalose-6-phosphate compared to shoots at an equivalent water content. The increased resources in the roots provides sufficient energy to cope with stress and thus autophagy is not required. These results were confirmed by the absence of autophagosomes in roots by TEM. Upregulation of sweet genes in both shoots and roots show transcriptional regulation of sucrose translocation from leaves to roots and within roots during dehydration. Differences in the cell’s metabolic status caused starkly different cell death responses between shoots and roots. These findings show how shoots and roots utilize different stress response strategies and may provide candidate targets that can be used as tools for the improvement of stress tolerance in crops.

Genetic Engineering of the Biosynthesis of Glycine Betaine Modulates Phosphate Homeostasis by Regulating Phosphate Acquisition in Tomato.

Glycine betaine (GB), as a putative compatible substance, protects plants against the damaging effects of abiotic stresses. Phosphorus deficiency is one type of abiotic stress that is detrimental to plant growth. Maintenance of phosphate (Pi) homeostasis is crucial. This study demonstrates GB-regulated phosphate homeostasis in the tomato (Solanum lycopersicum cv. ‘Moneymaker’) transformed with the choline oxidase gene codA from Arthrobacter globiformis. The codA-transgenic lines displayed more resistance to low-phosphate stress. The data revealed that the wild-type plants were stunted and consistently retained less Pi than transgenic lines, especially when grown under low-phosphate conditions. This difference in Pi retention was attributable to the enhanced Pi uptake ability in the transgenic lines. The transgenic plants translocated more Pi into the plant cell due to the enhanced enzymatic activity of plasma membrane H+-ATPase and increased Pi/H+ co-transport, which improved Pi uptake. The differential expression of ‘PHO regulon’ genes further maintained intracellular Pi homeostasis. Furthermore, GB maintained a higher photosynthesis rate, thus increasing the production and translocation of sucrose via phloem loading to enhance plant response to low-phosphate stress. We conclude that GB mediates Pi uptake and translocation by regulating physiological and biochemical processes that promote adaptation to environmental changes in Pi availability. These processes eventually lead to better growth and development of the codA-transgenic lines. This finding will help to further elucidate the signaling mechanism of how GB perceives and transmits low-phosphate signals to alleviate Pi nutritional stress.

Using a Multi-compartmental Metabolic Model to Predict Carbon Allocation in Arabidopsis thaliana.

The molecular mechanism of loading/unloading of sucrose into/from the phloem plays an important role in sucrose translocation among plant tissues. Perturbation of this mechanism results in growth phenotypes of a plant. In order to better understand the coupling of sucrose translocation with metabolic processes a multi-compartmental metabolic network of Arabidopsis thaliana was reconstructed and optimized with respect to biomass growth, both in light and in dark conditions. The model can be used to perform flux balance analysis of metabolic fluxes through the central carbon metabolism and catabolic and anabolic pathways. Balances and turnover of energy (ATP/ADP) and redox metabolites (NAD(P)H/NAD(P)) as well as proton concentrations in different compartments can be estimated. Importantly, the model can be used to quantify the translocation of sucrose from source to sink tissues through phloem in association with an integral balance of protons, which in turn is defined by the operational modes of the energy metabolism (light and dark conditions). This chapter describes how a multi-compartmental model to predict carbon allocation is constructed and used.

Regulation of rice sucrose transporter 4 gene expression in response to insect herbivore chewing

ABSTRACT Sucrose is an important carbon source for plant tissue repairing and also a signal involved in defense responses to against insect herbivores. Allocation of sucrose toward to undamaged tissues is an herbivory tolerance mechanism. Sucrose transporters (SUTs) are key factors to control sucrose flow in plants. In this study, herbivory effects caused by rice leaffolder [Cnaphalocrocis medinalis (Guenée)] on OsSUT4 expressions were investigated in rice plants, and the results showed OsSUT4 expression was significantly upregulated by larvae infestation and mechanical wounding. The wounding-induced OsSUT4 expression was not systemically demonstrated in undamaged leaves. The larval chewing-induced OsSUT4 expression was obviously reduced by blocking jasmonic acid (JA) and abscisic acid (ABA) biosynthesis. In addition to JA and ABA, data showed H2O2 generated in wounded tissues also role a signal in the regulatory pathway of herbivore-induced OsSUT4 expressions. Our finding provide insights for further study in signal network of herbivory-induced sucrose translocation.

Expression analysis of genes associated with sucrose accumulation and its effect on source-sink relationship in high sucrose accumulating early maturing sugarcane variety.

Sucrose synthesis/accumulation in sugarcane depends on the source-sink communication wherein source responds to sink demand for photoassimilate supply. Sucrose in stalk (sink) acts as signal, and sends feedback to restrain further synthesis of sucrose by regulating photosynthetic efficiency of leaves (source). Hence sucrose synthesis/accumulation is controlled by many genes and regulatory sequences including 3 invertases (SAI, CWI, NI), sucrose synthase (SuSy) and sucrose phosphate synthase (SPS). SPS and invertase play key role in enhancing sink strength which ultimately promotes greater sucrose accumulation in the sink tissues. In present study, a significant positive correlation was found between sucrose% of source and sink tissues which was greater in the top (R 2 = 0.679) than middle (R 2 = 0.580) and bottom (R 2 = 0.518) internodes, depicting that sucrose accumulation in the stalk bears a direct relation with sucrose translocation efficiency from source. Results indicated an increased sucrose% with maturity, while reducing sugar content decreased with crop growth. qRT-PCR results exhibited an elevated expression of invertase in immature sink tissues depicting increased sink requirement, which declined with maturity. Similarly, increased PEP carboxylase gene expression as observed supported the fact that higher sink demand results in enhanced photosynthetic rate and thus influences the source activity. SPS was found active at initial stage of cane development indicating its role in sucrose synthesis. Thus by studying expression patterns of the different genes both, in source and sink tissues, a better understanding of the sucrose accumulation pathway in sugarcane is possible, which in turn can help in elucidating ways to enhance sucrose concentration in sink.

Effects of planting dates and shading on carbohydrate content, yield, and fiber quality in cotton with respect to fruiting positions

Two cotton (Gossypium hirsutum L.) cultivars, Kemian 1 (cool temperature-tolerant) and Sumian 15 (cool temperature-sensitive) were used to study the effects of cool temperature on carbohydrates, yield, and fiber quality in cotton bolls located at different fruiting positions (FP). Cool temperatures were created using late planting and low light. The experiment was conducted in 2010 and 2011 using two planting dates (OPD, the optimized planting date, 25 April; LPD, the late planting date, 10 June) and two shading levels of crop relative light rate (CRLR, 100 and 60%). Compared with fruiting position 1 (FP1), cotton yield and yield components (fiber quality, leaf sucrose and starch content, and fiber cellulose) were all decreased on FP3 under all treatments. Compared with OPD-CRLR 100%, other treatments (OPD-CRLR 60%, LPD-CRLR 100%, and LPD-CRLR 60%) had significantly decreased lint yield at both FPs of both cultivars, but especially at FP3 and in Sumian 15; this decrease was mainly caused by a large decline in boll number. All fiber quality indices decreased under late planting and shading except fiber length at FP1 with OPD-CRLR 60%, and a greater reduction was observed at FP3 and in Sumian 15. Sucrose content of the subtending leaf and fiber increased under LPD compared to OPD, whereas it decreased under CRLR 60% compared to CRLR 100%, which led to decreased fiber cellulose content. Therefore, shading primarily decreased the “source” sucrose content in the subtending leaf whereas late planting diminished translocation of sucrose towards cotton fiber. Notably, as planting date was delayed and light was decreased, more carbohydrates were distributed to leaf and bolls at FP1 than those at FP3, resulting in higher yield and better fiber quality at FP1, and a higher proportion of bolls and carbohydrates allocated at FP3 of Kemian 1 compared to that of Sumian 15. In conclusion, cotton yield and fiber quality were reduced less at FP1 compared to those at FP3 under low temperature and low light conditions. Thus, reduced cotton yield and fiber quality loss can be minimized by selecting low temperature tolerant cultivars under both low temperature and light conditions.