Sucrose Synthase Activity Research Articles

Genotypic differences in growth behavior and quality parameters of sugarcane (Saccharum officinarum) varieties under moisture stress conditions

A field experiment was conducted at CCS Haryana Agricultural University, Regional Research Station, Karnal to investigate the effect of available soil moisture regimes on productivity potential of sugarcane (Saccharum officinarum L.) varieties during 2014-15 and 2015-16. The experiment consists of three moisture regimes based on available soil moisture (ASM), i.e. irrigation at 50% ASM (control), 40% ASM (mild stress) and 30% ASM (severe stress) in main plots and four commercial sugarcane varieties differing in maturity duration, i.e. CoS 767 (Mid late), CoH 128 (Mid late), CoJ 64 (Early) and Co 0238 (Early) in sub plot was laid out in split-plot design with three replications. Soil moisture treatments were initiated after 45 days of planting (DAP). Higher germination was recorded in CoJ 64 (65.5%) and CoS 767 (58.0%) as compared to Co 0238 (49.0%) and CoH 128 (48.5%) at 45 DAP. At 30% ASM levels, higher reduction in stalk height was recorded in CoH 128 (33.6 and 85.96 cm) and CoJ 64 (36.33 and 83.03cm) as compared to CoS 767 (41.83 and 107.06 cm) and Co 0238 (50.6 and 122.76 cm) in June and July, respectively. Total number of tillers was reduced by 12.99, 14.37 and 14.5% at 40% ASM level and 16.97, 24.29 and 20.04% at 30% ASM level as compared to irrigation at 50% ASM level in the month of May, June and July, respectively. Significantly higher values of brix, pol and CCS (%) were recorded in CoJ 64 and Co 0238 as compared to CoS 767 and CoH 128 at 8th, 10th and 12th month at all levels of ASM. Varieties and ASM levels had no effect on the specific activity of sucrose synthase. Sugar yield significantly reduced by 31.11 per cent at 40% ASM level and 40.57 per cent at 30% ASM level, respectively as compared to 50% ASM level. Co 0238 and CoS 767 showed minimum reduction in yield than CoH 128 and CoJ 64. From the present study it is concluded that Co 0238 and CoS 767 are identified relatively more tolerant at 30% and 40% ASM levels than CoH 128 and CoJ 64.

Carbohydrate Metabolism in the Developing Kernel of Normal, Sweet Corn and Quality Protein Maize

Maize is an important food crop widely used in the milking stage for human consumption. Although some mutants like su1 and sh2 exhibits considerable amount of sweetness during milking stage, but the expression of sugars and the associated enzymes is not well understood in the developing maize kernel. The present study was planned to evaluate the time course expression of sugars (fructose, sucrose, glucose, sorbitol and starch) and enzymes (invertase, sucrose synthase and hexokinase) in the developing kernel of normal, sweet corn and quality protein maize. The results revealed higher concentrations of free sugars in the initial stages of kernel development. Sweet corn possesses significantly higher concentration of sugars and low concentrations of starch as compared to normal and quality protein maize (QPM) genotypes in the milking stage of kernel. The invertase activity was found to be maximum in the initial stages of kernel development and then showed a declining trend. In contrast, the activity of sucrose synthase was found low at 15 DAP but increased at 30 and 45 DAP. The activity of hexokinase was found low at the initial stages which further reduced significantly (47%) with increasing DAP. However, the activity of hexokinase was found lowest in sweet corn at 15 DAP but increased drastically and showed maximum content at 30 and 45 DAP.

Analyses of transgenic fibroblast growth factor 21 mature rice seeds.

Although some studies have been conducted on the effects of foreign protein expression on rice, the results vary with foreign gene types and protein expression. This study reveals the effects of fibroblast growth factor 21 (FGF21) expression on mature rice seeds in various aspects. Results revealed that the grain weight of the transgene rice was lower than that of non-transgenic wild-type. The sucrose content and ADP-glucose pyrophosphorylase (AGPase) activity in transgenic FGF21 rice were higher than that in non-transgenic wild-type rice, while changes in the starch content, starch branching enzyme (SBE), sucrose synthase (SuS), superoxide dismutase (SOD) and peroxidase (POD) activity were lower in transgenic FGF21 rice compared to non-transgenic wild-type. The scanning electron microscope results revealed that mature seeds of the transgenic FGF21 rice contained fewer vascular bundles with irregular arrangement compared to the wild-type. The mature seeds of CK and T1 rice lines were collected for proteome analysis, and 167 differentially expressed proteins (DEPs) were found. In addition, the most enriched pathways in both rice lines were determined to be amino sugar and nucleotide sugar metabolism and starch and sucrose metabolism, etc. This study laid the foundation for revealing the effects of exogenous protein expression on rice bioreactors.

Apoplastic Invertase Activity Regulation in the Cambial Zone of Karelian Birch

We found that the regulation of apoplastic invertase (ApInv) activity in the cambial growth period in Karelian birch (Betula pendula var. carelica) is provided by the expression of encoding genes. In Karelian birches with normal wood, the content of CWIN1, CWIN1.1, and CWIN4 gene transcripts in xylem is lower than in birches with patterned wood. The regulation of ApInv activity in common silver birch (B. pendula var. pendula) is mainly provided at the posttranslational level by protein inhibitors (cell-wall inhibitor of β-fructosidase, CIF). In the trunk tissues of common silver birch, the expression level of ApInv encoding genes is similar to that of Karelian birch, but the concentration of CIF gene transcripts is increased; high expression rate of the CIF gene is caused by increased sucrose concentration in the apoplast. High activity rate of ApInv in Karelian birch provides high acceptor capacity of the cambial zone; a large amount of formed hexoses is intensely used for the formation of starch, a reserve metabolite. An increase in the wood pattern intensity correlates with the sucrose metabolization rate in the apoplastic pathway. In the trunks of birches with patterned wood, there are only local changes in the ratio of ApInv and sucrose synthase activity rates (ApInv activity higher) in the cambial growth period.

Down-Regulating Cucumber Sucrose Synthase 4 (CsSUS4) Suppresses the Growth and Development of Flowers and Fruits.

Sucrose synthase (SUS), which catalyzes the reversible conversion of sucrose and uridine diphosphate (UDP) into fructose and UDP-glucose, is a key enzyme in sucrose metabolism in higher plants. In this study, we used reverse genetic approaches and carbohydrate analysis to investigate the role of cucumber sucrose synthase gene 4 (CsSUS4) in the growth and development of sink organs. Transcript analyses showed that CsSUS4 was predominantly expressed in sink organs, particularly in flowers, fruits and roots, and that CsSUS4 protein was localized to companion cells and phloem parenchyma cells. Down-regulation of CsSUS4 expression resulted in a decrease in SUS activity in conjunction with lower hexose, starch and cellulose contents in fruits, and led to an overall reduction in the size and weight of flowers and fruits. Furthermore, CsSUS4 overexpression (OE) lines exhibited increased carbohydrate content, and larger and heavier flowers and fruits. The numbers of multi-petal flowers and multi-carpel fruits were greater in CsSUS4-OE plants compared with wild type and were regulated by MADS-box transcription factor. These results demonstrate that CsSUS4 plays important roles in the growth and development of cucumber flowers and fruits.

Acid pretreatment improves microtuberization of potato plantlets

To efficiently produce potato (Solanum tuberosum L.) microtubers, in vitro plantlets were pretreated with an acid solution before culturing in Murashige and Skoog medium supplemented with 60 g L−1 sucrose. The first tubers were formed at 36 h of acid pretreatment (AT), which was 6.2 d earlier than the untreated control. The maximum number of tubers (3.2), and highest fresh weight per tuber (282.5 mg) were also achieved with the AT. During microtuberization, the leaf dry weight of the control was higher than the AT from 1 to 5 d of culture. However, the dry weight of AT leaves increased rapidly after 5 d of culture and reached the same level as the control. The tuber dry weight in the AT was significantly higher (α = 0.05) than the control during the same culture period. Sucrose and starch content, and the enzyme activity of sucrose synthase (SS), ADP-glucose pyrophosphorylase (AGPase), and soluble starch synthase (SSS) in the AT and control exhibited a similar pattern as culture time progressed. However, levels of these biochemical indexes statistically differed (α = 0.05) between the AT and control. In addition to the sucrose content in AT, the starch content and activities of SS, AGPase, and SSS in the leaves were lower, whereas those in tubers were higher than those in the control. The present study suggests that acid pretreatment can efficiently promote microtuber formation and growth, which can be used for industrial production of potato seeds.

Effects of CEPA and 1-MCP on Flower Bud Differentiation of Apple cv. ‘Nagafu No.2’ Grafted on Different Rootstocks

The apple (Malus domestica Borkh.) has a relatively long sapling stage which prevents fruit breeding. The understanding of the flowering system is important to improve breeding efficiency in apple. In this context, 2-year-old “Fuji” apple cv. “Nagafu No.2” trees were grafted onto dwarf self-rooted rootstock M.26, vigorous rootstock M. sieversii and interstock M.26/M. sieversii, respectively. Trees were sprayed with clean water (as controls), 800 mg·L−1 2-chloroethylphosphonic acid (CEPA), and 2 µL·L−1 1-methylcyclopropene (1-MCP). The results showed that CEPA significantly repressed the vegetative growth attributed to the increase of ABA and ZT synthesis, and the decrease of IAA synthesis in leaves and buds. However, there was no significant difference or significant inverse effect between 1-MCP and control. Furthermore, CEPA promoted flower formation, increased the flowering rate, and advanced the blossom period for 2 days compared with the control, which was accompanied by the accumulation of soluble sugar, glucose, and sucrose; and the increase of α-amylase and sucrose phosphate synthase activities; and the decrease of starch contents and sucrose synthase activities in leaves and buds. However, the blossom period was delayed for 2 days after spraying with 1-MCP. Finally, the expression of TFL1 was significantly repressed, whereas AP1 was significantly promoted in buds from M.26 and M.26/M. sieversii after spraying with CEPA, whereas the effect was not significant from M. sieversii. However, the expression levels of TFL1 and AP1 were not significantly different from the control after the application of 1-MCP. In spite of this, CEPA was more susceptible to easy-flowering M.26, followed by M.26/M. sieversii, and still less susceptible to difficult-flowering rootstock M. sieversii.

Sugar metabolism and accumulation in the fruit of transgenic apple trees with decreased sorbitol synthesis

Both sorbitol and sucrose are synthesized in source leaves and transported to fruit for supporting fruit growth in tree fruit species of the Rosaceae family. In apple (Malus domestica), antisense suppression of aldose-6-phosphate reductase, the key enzyme for sorbitol synthesis, significantly decreased the sorbitol concentration but increased the sucrose concentration in leaves, leading to a lower sorbitol but a higher sucrose supply to fruit in these plants. In response to this altered carbon supply, the transgenic fruit had lower concentration of sorbitol and much higher concentration of glucose but similar levels of fructose, sucrose, and starch throughout fruit development relative to the untransformed control. Activities of sorbitol dehydrogenase, fructokinase, and sucrose phosphate synthase were lower, whereas activities of neutral invertase, sucrose synthase, and hexokinase were higher in the transgenic fruit during fruit development. Transcript levels of MdSOT1, MdSDHs, MdFK2, and MdSPS3/6 were downregulated, whereas transcript levels of MdSUC1/4, MdSUSY1-3, MdNIV1/3, MdHKs, and MdTMT1 were upregulated in the transgenic fruit. These findings suggest that the Sucrose cycle and the sugar transport system are very effective in maintaining the level of fructose and provide insights into the roles of sorbitol and sucrose in regulating sugar metabolism and accumulation in sorbitol-synthesizing species.

Non-Structural Carbohydrate Metabolism, Growth, and Productivity of Maize by Increasing Plant Density

Increasing plant density seems to improve the productivity of maize crops, and the understanding of how the metabolism of non-structural carbohydrates is affected in plants under high crop density is critical. Thus, with the objective of further clarifying this issue, maize plants were subjected to densities from 30,000 to 90,000 plants ha−1, and the plant growth, soluble sugars and starch contents, invertase and sucrose synthase activities, and plant production were evaluated. We found that the stalk is more sensitive to the increasing plant density than leaves and kernels. The dry weight of the stalk and leaves per single plant decreased more drastically from low to intermediate plant densities, while grain production was reduced linearly in all plant density ranges, leading to higher values of harvest index in intermediate plant densities. The sucrose concentration did not change in leaves, stalk, or kernels of plants subjected to increasing plant densities at the R4 stage. Also, the specific activity of soluble invertase, bound invertase, and sucrose synthase did not change in leaf, stalk, or kernels of plants subjected to increased plant density. The productivity was increased with the increase in plant density, using narrow row (0.45 m) spacing.

Heat stress during grain filling affects activities of enzymes involved in grain protein and starch synthesis in waxy maize

High temperature (temperature over 35 °C) is an extremely important environmental factor that affects the maize grain quality in Southern China. The effects of heat stress after pollination on grain protein and starch deposition and activities of involved enzymes were studied in a pot trail in 2014 and 2015. Results showed that grain dry weight reductions at maturity were 19.8% and 19.1%, whereas starch contents (mg g−1) were reduced by 3.0% and 3.3%, and starch accumulation (mg grain−1) were reduced 22.2% and 21.8% in 2014 and 2015, respectively. Protein content was decreased by heat stress before 15 DAP and increased thereafter. At maturity, protein contents (mg g−1) were increased by 24.5% and 25.3% in 2014 and 2015, while protein accumulation (mg grain−1) were not affected by heat stress. In response to heat stress, glutamate synthase activity was enhanced by 29.1–82.9% in 2014 and 2.0–141.8% in 2015, whereas glutamine synthetase activity was reduced by 1.9–43.5% in 2014 and 0.1–27.4% in 2015 throughout the grain filling. The activities of sucrose phosphate synthase were decreased by heat stress at 10–25DAP (12.7–32.0%) in 2014 and 15–20 DAP (23.2–27.5%) in 2015, and activities of sucrose synthase were decreased by heat stress at 5–15 DAP (20.0–45.0%) in 2014 and 15 DAP (22.0%) in 2015, repectively. The activities of enyzmes that involved in starch synthessis were all suppressed by heat stress during grain filling, and the reduction of adenosine diphosphate-glucose pyrophosphorylase, soluble starch synthase, and starch branching enzyme were decreased by 21.3–43.1%, 19.1–29.2%, and 7.0–45.6% in 2014 and 1.8–78.5%, 21.4–51.2%, and 11.0–48.0% in 2015, respectively. Conclusively, grain weight and starch deposition were suppressed by heat stress due to the decreased activities of enzymes involved in starch synthesis, and the increased protein content was due to the enhanced activity of glutamate synthase.

Sucrose-Metabolizing Enzyme Activities in Response to Plant Growth Substances in Pigeonpea Genotypes

Pigeonpea (Cajanus cajan) is one of the most important pulse crops. Though the crop accumulates maximum biomass, a proportionally low final yield is obtained due to higher partitioning of dry matter towards vegetative growth and flower and fruit/pod drop. Therefore, there is a need to reduce the plant height and improve the source–sink relationship. In the present study, the effect of foliar spray of growth substances such as mepiquat chloride (200 ml/ac), ethrel (200 ppm) and stance (200 ml/ac) at 60, 60 + 75 and 75 days after sowing (DAS) on physiological parameters as well as on sucrose-cleaving enzymes in two pigeonpea genotypes (PAU 88I and AL 201) was investigated. It was observed that the foliar spray of ethrel @ 200 ppm (60 + 75 DAS) significantly decreased the height of PAU 881 and AL 201 by 16.07% and 15.04%, respectively. Higher activities of sucrose synthase (in leaves and stem) and invertase (in leaves, stem, pod wall and developing seed) were observed with ethrel (60 + 75 DAS) treatment in both genotypes. The foliar sprays of growth substances significantly reduced the plant height and improved the fruiting branches/pods, leading to enhanced yield irrespective of genotype.

Inhibition of sucrose and galactosyl-sucrose oligosaccharide metabolism in leaves and fruits of melon (Cucumis melo L.) under low light stress

Low light stress is a major limiting factor for melon to reach its full potential of fruit yield and quality in cold season production. This study investigated the effect of low light stress on sucrose synthesis and galactosyl-sucrose oligosaccharide loading in melon leaves, galactosyl-sucrose oligosaccharide unloading, and sugar accumulation in fruits under greenhouse conditions using the low light-tolerant cultivar Yujinxiang and the low light-sensitive cultivar Yuxue. The results showed that in melon leaves, sucrose content and activities of related synthase enzymes decreased significantly under low light stress. The reduction of sucrose content and the activity of sucrose phosphate synthase (SPS) and sucrose synthase in the synthesis direction (SS-s) in Yujinxiang (30.9%, 16.5%, 30.0%, respectively) were significantly less than those in Yuxue (60.6%, 31.6%, 40.5%, respectively). The raffinose and stachyose content as well as the activity of stachyose synthase also significantly decreased after shading. The reduction of stachyose synthase activity in Yujinxiang (23.8%) was significantly less than that in Yuxue (32.4%), indicating that sucrose synthesis and galactosyl-sucrose oligosaccharide loading in melon leaves were inhibited under low light stress and the low light-sensitive cultivar was more greatly influenced. In melon fruits, stachyose content and the activities of acid and alkaline α-galactosidases significantly decreased under low light conditions, but the raffinose content was higher from 10 to 20 days after anthesis, indicating that the imported assimilates reduced, and galactosyl-sucrose oligosaccharide unloading was inhibited after shading. During the earlier stage of fruit development, significant decreases in the activities of acid invertase (AI), neutral invertase (NI), and sucrose synthase in the cleavage direction (SS-c) were observed in the two cultivars after shading, sink strength reduced. In the later stage of fruit development, sucrose accumulation was inhibited by decreasing the activities of SPS and SS-s, but no significant difference was observed between the two cultivars suggesting that the difference of sugar content among the two cultivars might be due to the imported assimilates under low light conditions.

Characterization of Fructan Metabolism During Jerusalem Artichoke (Helianthus tuberosus L.) Germination.

The inulin-type fructans in Jerusalem artichoke (Helianthus tuberosus L.) tubers exhibit different degrees of polymerization and are critical for germination. We aimed to characterize the sugar metabolism dynamics in the tubers without bud eyes or shoots (T) and BE/S of indoor- and field-grown Jerusalem artichokes during germination. Ht1-FEH II and Ht1-FEH III (1-fructan exohydrolases II and III, inulin-degrading enzymes) expression increased 5 days after planting indoors, whereas Ht1-FEH II expression increased 72 days after planting in the field in T and BE/S. Ht1-SST (sucrose:sucrose 1-fructosyl transferase, inulin synthesis initiator), and Ht1-FFT (fructan:fructan 1-fructosyl transferase, inulin elongator) expression generally decreased in indoor-grown T. The enzyme activities of 1-FEH and 1-FFT were unchanged during germination in both indoor- and field-grown T and BE/S, whereas 1-SST activity decreased in indoor-grown T, while 1-FEH and 1-FFT activities increased as a function of germination time in BE/S of both indoor- and field-grown tubers. The total soluble sugar content gradually decreased in T after germination indoors or in the field, while at the end of germination, the sucrose and fructan contents decreased, and fructose content increased in the field. The enzyme activities of soluble vacuolar (VI) or neutral invertase (NI) did not change significantly, except at the late germination stage. Sucrose synthase (SS) and sucrose-phosphate synthase (SPS) activities were not significantly changed in T and BE/S in indoor-grown artichokes, while SS activity gradually increased, and SPS activity gradually decreased in field-grown artichokes, alongside sucrose degradation. Compared to T, BE/S generally had higher enzyme activities of 1-FEH and 1-FFT, promoting inulin hydrolysis. This work shows that the process of tuber germination is similar indoors and in the field, and germination studies can therefore be conducted in either environment.

Deciphering source and sink responses of potato plants (Solanum tuberosum L.) to elevated temperatures.

Potato is an important staple food with increasing popularity worldwide. Elevated temperatures significantly impair tuber yield and quality. Breeding heat-tolerant cultivars is therefore an urgent need to ensure sustainable potato production in the future. An integrated approach combining physiology, biochemistry, and molecular biology was undertaken to contribute to a better understanding of heat effects on source- (leaves) and sink-organs (tubers) in a heat-susceptible cultivar. An experimental set-up was designed allowing tissue-specific heat application. Elevated day and night (29°C/27°C) temperatures impaired photosynthesis and assimilate production. Biomass allocation shifted away from tubers towards leaves indicating reduced sink strength of developing tubers. Reduced sink strength of tubers was paralleled by decreased sucrose synthase activity and expression under elevated temperatures. Heat-mediated inhibition of tuber growth coincided with a decreased expression of the phloem-mobile tuberization signal SP6A in leaves. SP6A expression and photosynthesis were also affected, when only the belowground space was heated, and leaves were kept under control conditions. By contrast, the negative effects on tuber metabolism were attenuated, when only the shoot was subjected to elevated temperatures. This, together with transcriptional changes discussed, indicated a bidirectional communication between leaves and tubers to adjust the source capacity and/or sink strength to environmental conditions.

The signal metabolite trehalose-6-phosphate inhibits the sucrolytic activity of sucrose synthase from developing castor beans.

In plants, trehalose 6-phosphate (T6P) is a key signaling metabolite that functions as both a signal and negative feedback regulator of sucrose levels. The mode of action by which T6P senses and regulates sucrose is not fully understood. Here, we demonstrate that the sucrolytic activity of RcSUS1, the dominant sucrose synthase isozyme expressed in developing castor beans, is allosterically inhibited by T6P. The feedback inhibition of SUS by T6P may contribute to the control of sink strength and sucrolytic flux in heterotrophic plant tissues.

Sucrose synthase genes: a way forward for cotton fiber improvement

Cotton is a premium source of natural fiber and is considered “white gold” in the textile industry. Fiber length, strength and fineness are the key considerations for the industry. Longer fibers are machine friendly because they are easily spinnable. Recent advancements in genetic engineering, including the development of DNA markers and quantitative trait loci (QTLs), together with genome sequencing and gene expression profiling, have provided new avenues for improving fiber production and quality. In plants, sucrose synthase (SUS) is the key enzyme that catalyzes the reversible cleavage of sucrose and uridine diphosphate (UDP) into fructose and UDP-glucose. Sucrose is the main mobile sugar in plants moving from source to sink. It regulates resource partitioning between active sinks, especially in cotton embryos and fibers, and therefore is directly involved in determining fiber yield and seed quality. SUS actively takes part in regulating the competition for nutrients among sink tissues through balancing osmotic potentials by providing hexoses and an efficient supply of UDP-glucose the substrate for cellulose synthase. Cotton transformation has been used to improve fiber characteristics by altering cell wall properties through the manipulation of expression of fiber genes. Overexpression of the SUS gene from natural or synthetic origins in cotton can be an excellent way to solve potential problems associated with poor fiber length and other fiber quality traits. Increased SUS activity can result in more hexoses, increasing the osmotic potential and thereby driving the water influx that creates high turgor pressure in fiber cells resulting in enhanced fiber elongation. Moreover, increased SUS gene transcript levels in vegetative tissues of the plant will elevate seedling biomass and seed number. Fiber length and seed number both contribute towards final yield and the SUS genes as key regulators of sink strength in cotton perform this dual function that is directly related to cotton productivity. Hence manipulation of the SUS gene family is considered a promising approach to improve cotton fiber yield and quality. This review focuses on the biochemical and physiological roles of the SUS genes and there value for cotton fiber improvement.

OsHAK1 controls the vegetative growth and panicle fertility of rice by its effect on potassium-mediated sugar metabolism

Plant growth and reproduction are both energy-requiring processes; the necessary energy is supplied by the products of photosynthesis. Both the vegetative growth and reproductive success of rice are compromised by the absence of a functional copy of the gene OsHAK1. Here, a comparison between wild type rice and OsHAK1 knockout mutants not only confirmed the known detrimental effect of the absence of OsHAK1 on root growth, pollen viability and fertility, but also showed that sucrose phosphate synthase activity was lowered, and the sucrose content of the leaves was markedly increased, due to a partial block on the up-loading of sucrose into the phloem. The impaired allocation of sugar to the roots and spikelets caused by the knocking out of OsHAK1 was accompanied by a down-regulation in the leaf sheaths and panicle axes of genes encoding sucrose transporters (SUT genes), which are active in the phloem, as well as in the roots and spikelets of those encoding monosaccharide transporters (MST genes), which transport hexose sugars across the plant plasma membrane. The activity of sucrose synthase, acid invertase and neutral invertase in the roots of mutant plants assayed at the tillering stage, and in their spikelets, assayed during grain-filling, was significantly lower than in the equivalent organs of wild type plants. As a result, the supply of total soluble sugar, glucose and fructose to sink organs was reduced, consistent with the effect of the mutation on root growth and panicle fertility. Compared to wild type plants, the mutants accumulated less potassium (K) throughout the plant. The conclusion was that the failure to fully supply the demand of the mutant’s sink organs for assimilate was responsible for its compromised phenotype, and that the deficiency in K uptake induced by the loss of OsHAK1 functionality was responsible for the disruption of sugar metabolism.

Influence of selenium on carbohydrate accumulation in developing wheat grains

ABSTRACTThe present investigation reports the effects of different doses of sodium selenate and sodium selenite on its uptake, carbohydrate composition, and sucrose and starch metabolizing enzymes in flag leaf and developing grains of wheat grown under greenhouse conditions. Selenium (Se) concentration increased significantly in leaves and developing grains of Se-treated plants compared to control at different intervals post-anthesis. Total soluble sugars and sucrose concentrations in developing grains increased due to various Se treatments. Different selenite treatments increased sucrose synthase activity from 10 to 20 days post-anthesis and increased starch accumulation compared to control plants. Lower starch accumulation in selenate than control and selenite treatments was observed. The activities of α, β and total amylase, invertase and sucrose synthase increased whereas sucrose phosphate synthase declined. Results indicated that Se accumulation causes disturbances in carbohydrate metabolism that is dependent on Se concentration, form and the development stage of the plant.

Effects of nitrogen forms on carbohydrate metabolism and storage‐root formation of sweet potato

AbstractIn this study, we examined the effects of different forms of nitrogen (N) fertilizer on carbohydrate metabolism and storage root formation in sweet potato [Ipomoea batatas L. (Lam.) cv. Shangshu 19 and cv. Jixu 23] in 2015–2016. Two fertilizer treatments, ammonium nitrogen (AN) and amide nitrogen (XN), were applied at 60 kg ha−1 in a two‐factor split‐plot design. The effects of nitrogen form on the morphology of adventitious roots, carbohydrate metabolism in potential storage roots, and number of storage roots per plant in sweet potato were investigated. The results show that during the early growth phase, the AN treatment significantly increased the number of adventitious roots, root tips, root length density, and fresh weight of roots (in pot trials). This treatment also significantly decreased the sucrose concentration of potential storage roots and increased the activities of cell wall, vacuolar, and cytoplasmic invertases. However, XN‐treated potential storage roots showed a relatively high starch concentration, activities of sucrose synthase and ADP‐glucose pyrophosphorylase, and transcription of sporamin genes. At the canopy closure period, the AN treatment significantly increased the number of storage roots of 0.5–5.0 cm in diameter and decreased the number of those > 5 cm in diameter compared to the control. The XN treatment induced the opposite effects. In the harvesting period, the AN treatment produced the highest storage root yield and number of storage roots per plant. Thus, in field trials the AN treatment induced a greater increase in production by increasing the number of storage roots.

Comparison of sucrose metabolism in wheat seedlings during drought stress and subsequent recovery

Sucrose is a dominant sugar transported to the sink organs of a plant where it is metabolized to other compounds or stored. Here, the importance of sucrose metabolism in a drought-tolerant wheat cultivar was compared to a drought-sensitive one. The 4-d-old Triticum aestivum L. seedlings were exposed to drought induced by water cessation for 7 d and recovery after re-watering for further 7 d. Under control conditions, constitutive expression of genes encoding vacuolar invertase (VI) and sucrose synthase (SuS) and activity of sucrose phosphate synthase (SPS) were significantly higher in the tolerant cultivar than in the sensitive one. Drought promoted the expressions of SPS and VI genes in the tolerant cultivar and increased their activities to 175 and 132 %, respectively, of those under control conditions. The activity of SuS and expression of its gene, however, were identical in both cultivars under drought stress. These changes resulted in more remarkable accumulation of sucrose in tolerant than in sensitive cultivar under water stress.