Sucrose Synthase Activity Research Articles

Pretreatment with Trichoderma harzianum alleviates waterlogging-induced growth alterations in tomato seedlings by modulating physiological, biochemical, and molecular mechanisms

We studied the role of Trichoderma harzianum (TH) in improving the physiological, biochemical, hormonal, and molecular parameters of tomato seedlings grown under waterlogging (WL, for 14 and 28 days). Pretreatment with TH significantly improved the growth of tomato by enhancing the chlorophyll synthesis and uptake of essential ions, including nitrogen, phosphorus, and potassium. A reduction in anthocyanin content was also ameliorated significantly by TH pretreatment. TH significantly mitigated the WL-induced decline in height and in fresh and dry biomass accumulation. Accumulation of proline, flavonoids, anthocyanin, sugars, and soluble protein increased with TH pretreatment. At both growth periods (14 and 28 days after treatment [DAT]), the accumulation of secondary metabolites, including total phenols and flavonoids, and the redox components (tocopherols) were increased significantly by TH pretreatment. Increased synthesis of metabolites maintained the antioxidant status of tomato, resulting in amelioration of WL-induced oxidative effects on membranes. WL and TH treatments significantly increased ethylene production and decreased abscisic acid content at both growth periods. The accumulation of reactive oxygen species, like hydrogen peroxide, in TH treated seedlings was correlated with the upregulation of the Fe-SOD gene. WL stress triggered the activity of sucrose synthase (SUS), lactate dehydrogenase (LDH), and pyruvate decarboxylase (PDC), which reached a maximum at 14 DAT, and TH pretreatment resulted in further enhancement above control and WL-stressed levels. Quantitative RT-PCR revealed differential expression of genes, where Fe-SOD and ADH were upregulated due to TH treatment and ARE, ACO, ERF, and aquaporin were downregulated relative to control plants. Pretreatment of tomato seedlings with TH improved tolerance to WL by maintaining the antioxidant status, sugar metabolism, and expression of critical genes. These results suggest that TH pretreatment is an effective way to improve WL tolerance in tomato at vegetative stage.

Effect of biochar on grain yield and leaf photosynthetic physiology of soybean cultivars with different phosphorus efficiencies

This study was conducted with two soybean cultivars, Liaodou 13 (L13, phosphorus (P)-efficient) and Tiefeng 3 (T3, P-inefficient), to investigate the effects of biochar on soybean yield and photosynthetic physiological parameters, at four biochar application rates (0, 1, 5, and 10%, w/w), and two fertilization treatments (0 and 150 kg ha−1). Grain yield, plant biomass, P accumulation, leaf net photosynthetic rate (Pn), chlorophyll index (Chl), nitrogen balance index (NBI), sucrose phosphate synthase (SPS), and sucrose synthase (SS) activities, soluble sugar, sucrose and starch contents, and leaf area duration (LAD) were measured. Biochar had positive effects on Pn, Chl, NBI, SPS, and SS activities, and leaf soluble sugar, sucrose, and starch contents of both genotypes, these effects increased with biochar application rate. L13 benefited more efficiently from biochar than T3 did, as the grain yield of L13 significantly increased by 31.0 and 51.0%, at 5 and 10% biochar, respectively, while that of T3 increased by 40.4 at 10% biochar application rate, as compared with controls. The combined application of biochar and fertilizer boosted the positive effects described, but no difference was found for grain yield in L13 among biochar application rates, while grain yield of T3 continually increased with biochar rate, among which, 1% biochar combined with 150 kg ha−1 fertilizer resulted in T3 yield increment of more than 23%, compared with the application of 150 kg ha−1 fertilizer alone. Altogether, our results indicated that the application of biochar enhanced carbon assimilation in soybean, resulting in increased biomass accumulation and yield. Differences in genotypic responses to biochar highlight the need to consider specific cultivars and biochar rate, when evaluating the potential responses of crops to biochar.

Effects of dopamine on growth, carbon metabolism, and nitrogen metabolism in cucumber under nitrate stress

Dopamine, which is a catecholamine neurotransmitter, is widely present in plant organs. The accumulation of soil nitrate limits the growth of plants. We investigated the role of dopamine in regulating the growth, carbon metabolism, and nitrogen metabolism in cucumber (Cucumis sativus L. “Jin You No. 1”) under nitrate stress. Under nitrate stress, plants showed significant reductions in growth, chlorophyll concentrations, chlorophyll fluorescence and gas exchange parameters. However, dopamine markedly alleviated such reductions. Excess nitrate led to an increase in sucrose phosphate synthase, acid invertase, and neutral invertase activity, but decreased sucrose synthase activity. Similarly, the expression of the CsSPS4 gene was also up-regulated and the expression of the CsSUS3 gene was down-regulated under nitrate stress. Dopamine significantly increased the activity and gene expression of these enzymes. The CsNRT1.1 gene was up-regulated under nitrate conditions. Dopamine significantly alleviated the accumulation of nitrate nitrogen and ammonium nitrogen under nitrate conditions. Nitrate reductase activity and the expression of the CsNR1 gene were significantly inhibited due to exposure to excess nitrate. We found that glutamine synthetase activity decreased and glutamate dehydrogenase activity increased after nitrate induction, which indicated that ammonium assimilation relied mainly on glutamate dehydrogenase pathway rather than glutamine synthetase/glutamate synthase cycle under nitrate stress. Dopamine significantly enhanced the activity of enzymes and gene expression of nitrogen metabolism. Our results indicated that dopamine plays an important role in mediating plant growth, carbon metabolism, and nitrogen metabolism.

Effect of osmo priming on sucrose metabolism in spring maize, during the period of grain filling, under limited irrigation conditions.

The present study was undertaken to study the effect of osmo priming on sucrose metabolism of spring maize, under limited irrigation conditions. Osmo priming increased the activities of acid invertase, alkaline invertase and sucrose synthase (cleavage) and the contents of reducing sugars and starch in the grains of stressed plants. There was also an increase in sucrose phosphate synthase activity with a parallel increase in sucrose content in leaves of stressed plants in comparison with those of hydro priming treatment. It showed that osmo priming helped in improving sucrose phosphate synthase activity in leaves of plants, leading to higher sucrose content, under stress conditions.

Effects of soil water stress on fruit yield, quality and their relationship with sugar metabolism in ‘Gala’ apple

The aim of this research is to explore apple quality responses to water stress during the fruit growing season in seven-year-old potted ‘Gala’ (Malus domestica Borkh.) trees. Three irrigation levels were applied, including normal irrigation (CK, 70–80%θf), light water stress (LS, 60–70%θf), medium water stress (MS, 50%–60%θf), θf: field capacity. In stage Ⅰ, water stress was applied from stage of young fruit to mature. In stage II, water stress was utilized from stage of fruit expanding to mature. The results showed that MS and LS treatments improve fruit quality by improving the contents of total soluble solid (TSS) and soluble sugar (fructose, glucose and sorbitol) and reducing titratable acidity (TA) levels. But MS and LS treatments applied in stage Ⅰ reduced fruit weight, while LS treatment applied in stage II did not affect fruit weight. Interestingly, the enhancing of activity of Sucrose Synthase (SS) and Acid Invertase (AI) in MS and the increasing of activity of SS in LS promoted the conversion from sucrose to fructose and glucose in stage Ⅰ. In stage II, the enhancing of AI and Sorbitol Oxidase (SOX) in MS and LS promoted the conversion from sucrose to fructose and glucose and the conversion from sorbitol to glucose, respectively. Our observations suggest that different degrees and duration of soil water stress affect different enzymes to promote the increase of fructose and glucose content. In addition, light water control is recommended only during later fruit developmental stages for optimum quality and production.

Modulation of Sucrose and Starch Metabolism by Salicylic Acid Induces Thermotolerance in Spring Maize

Two inbred lines of spring maize (Zea mays L.), CML 32 (stress tolerant) and LM 11 (stress susceptible) were taken to study the effect of salicylic acid (SA) on their carbohydrate status, under heat stress. Heat stress increased the content of total soluble sugars and sucrose in the shoots and residual mass of CML 32 seedlings. On the other hand, the shoots and roots of LM 11 seedlings showed reduced sucrose content. Application of SA increased the contents of total soluble sugars and sucrose in the roots and shoots of both the inbred lines. Heat stress reduced the activities of acid and neutral invertases in the shoots of CML 32 seedings that corresponded with their increased sucrose content. Foliar spray of SA increased acid invertase but decreased neutral invertase activities in shoots of both the inbred lines that might help in maintaining sucrose levels and energy needs for better seedling growth under stress conditions. Heat stress induced CML 32 seedlings to exhibit stress tolerance by increasing amylase activity in their residual masses that led to their reduced starch content. SA application reduced the amylolytic activity of the residual mass of CML 32 seedlings that corresponded with their higher starch content. SA application led to increased sucrose synthase (synthesis) and sucrose phosphate synthase activities in the roots of both the inbred lines and the shoots of CML 32 seedlings. It also decreased sucrose synthase (cleavage) activity in CML 32 roots and LM 11 shoots, under heat stress leading to optimization of their sucrose levels.

Identification of Factors Linked to Higher Water-Deficit Stress Tolerance in Amaranthus hypochondriacus Compared to Other Grain Amaranths and A. hybridus, Their Shared Ancestor.

Water deficit stress (WDS)-tolerance in grain amaranths (Amaranthus hypochondriacus, A. cruentus and A. caudatus), and A. hybridus, their presumed shared ancestor, was examined. A. hypochondriacus was the most WDS-tolerant species, a trait that correlated with an enhanced osmotic adjustment (OA), a stronger expression of abscisic acid (ABA) marker genes and a more robust sugar starvation response (SSR). Superior OA was supported by higher basal hexose (Hex) levels and high Hex/sucrose (Suc) ratios in A. hypochondriacus roots, which were further increased during WDS. This coincided with increased invertase, amylase and sucrose synthase activities and a strong depletion of the starch reserves in leaves and roots. The OA was complemented by the higher accumulation of proline, raffinose, and other probable raffinose-family oligosaccharides of unknown structure in leaves and/or roots. The latter coincided with a stronger expression of Galactinol synthase 1 and Raffinose synthase in leaves. Increased SnRK1 activity and expression levels of the class II AhTPS9 and AhTPS11 trehalose phosphate synthase genes, recognized as part of the SSR network in Arabidopsis, were induced in roots of stressed A. hypochondriacus. It is concluded that these physiological modifications improved WDS in A. hypochondriacus by raising its water use efficiency.

OsVIN2 encodes a vacuolar acid invertase that affects grain size by altering sugar metabolism in rice.

OsVIN2, a vacuolar invertase, affects grain size and yield by altering sugar composition, transport, and starch accumulation in rice. Grain size, a major determinant of rice yield, is influenced by many developmental and environmental factors. Sugar metabolism plays vital roles in plant development. However, the way in which sugar metabolism affects rice grain size remains largely elusive. In this study, we characterized the small grain-size rice mutant sgs1. Histological analyses showed that reduced spikelet hull and endosperm size results from decreased cell size rather than cell number. Map-based cloning and complementation tests revealed that a DaiZ7 transposon insertion in a vacuolar invertase gene OsVIN2 is responsible for the mutant phenotype. Subcellular distribution and biochemical analysis indicated that OsVIN2 is located in the vacuolar lumen, and that its sucrose hydrolysis activity is maintained under acidic conditions. Furthermore, an altered sugar content with increased sucrose and decreased hexose levels, as well as changes in invertase and sucrose synthase activities, sugar transport gene expression, and starch constitution in sgs1 implies that OsVIN2 affects sucrose metabolism, including sugar composition, transport, and conversion from the source to the sink organs. Collectively, OsVIN2 is involved in sugar metabolism, and thus regulates grain size; our findings provide insights into grain development and also suggest a potential strategy to improve grain quality and yield in rice.

Wheat NILs contrasting in grain size show different expansin expression, carbohydrate and nitrogen metabolism that are correlated with grain yield

Two wheat near-isogenic lines (NILs; -GS (small grain size) and + GS (large grain size)) were obtained by backcrossing. We found that the grain volume and weight of + GS were significantly higher than those of -GS. There was a corresponding increase in grain yield associated with the + GS line. For analysis of causes, we investigated and compared the anatomic and physiological characteristics of two NILs during the grain filling stage. The bigger grain size in + GS likely resulted from the longer endosperm cells, which is related to the higher IAA content and expansin activity accompanied by the up-regulation of some expansin-related genes. For the higher grain weight of + GS, starch accumulation was higher in + GS than in -GS, which was consistent with relatively higher glucose (Glu), fructose (Fru), and sucrose (Suc) contents. Elevated sugar level may be correlated with sucrose synthase (SuSy) activity and up-regulation of GBSS I, SSS III, and SBE I. The amount of soluble protein in + GS grains also exceeded that in -GS grains, possibly because of increased NR, NiR, and GS activities and up-regulation of nitrogen assimilation and nitrate transporter genes in + GS grains. Furthermore, the photosynthetic rate was higher in + GS and -GS at the early filling stage before 21 DAA. The same trends were observed in sugar content (Suc, Fru, and Glu) and SPS activity. However, the increase in the rate of grain length and width in + GS plants at the late filling stage was significantly higher than that at the early filling periods. These suggest that high accumulation of dry matter (such as starch and protein) at early filling stage was the important factor in achieving the final increased size of wheat grains, besides cell expansion.

Effects of Grafting on Sugar Metabolism of Melon (Cucumis melo L.) Seedling under Copper Stress

The experiment was carried out with pumpkin ‘JingXinZhen NO.3’ as the rootstock, thin-skin melon ‘IVF09’ as the scion, and self-rooted seedling as the control. The effect of grafting on the sugar metabolism of melon seedlings under copper stress was studied. The results showed that under the condition of copper stress, the growth of melon seedlings was inhibited, the sugar content of leaves decreased, and the sucrose content decreased significantly, and the total activity of sugar metabolism related enzymes changed. However, under the same conditions, the biomass of the grafted seedlings is greater than that of the self-rooted seedlings, and the greater the stress concentration, the greater the grafting promoting effect; Glucose and fructose in grafted leaves were significantly higher than those in self-rooted seedlings, raffinose and stachyose were significantly lower than self-rooted seedlings, the highest ratio of glucose to fructose increased by 5.26% and 32%; and the total activity of sucrose synthase (SS) in the leaves of grafted seedlings was lower than that of self-rooted seedlings. The total activity of sucrose phosphate synthase (SPS), neutral invertase (NI) and acid invertase (AI) was greater than that of self-rooted seedlings. The results showed that grafting could change the sugar activity of seedling leaves by changing the total activity of sugar metabolism related enzymes in melon seedling leaves, and then change the sugar metabolism of melon seedlings to reduce the toxicity of copper stress on melon seedlings.

The effects of magnesium deficiency on sugar partitioning do not restrict the root growth in eucalyptus young plants

The symptoms of magnesium (Mg) deficiency have been well documented in crop plants. The relationship between sugar partitioning and Mg deficiency consists an important abiotic stress that may restrict root growth and limit the success of planting in the field. Despite of this, the primary physiological effects of low Mg availability remain largely unknown in eucalyptus. This paper aimed to investigate how the Mg deficiency affects biochemical aspects of sugar partitioning associated to dry matter accumulation in roots of young Eucalyptus urophylla plants. Experimental work was carried out at a greenhouse, arranged by completely randomized design, consisted by split plot 5x4, with five Mg concentrations (0, 25, 50, 75 and 100 % Mg levels of nutrient solution) and four times of evaluations – 15, 30, 50 and 120 days after planting (DAP). Soluble (SS) and reducing (RS) sugar contents, invertase and sucrose synthase activity and shoot and root dry matter weight were measured. Increased sugar concentrations, both SS and RS, were found in leaf tissues from 30 DAP. In root tissues, neither RS nor SS content showed differences between Mg deficiency and control. Significant differences were also not found neither in root dry matter accumulation, nor in shoot/root dry matter ratio. Mg deficiency did not affect sucrose cleaving in roots, which was predominantly catalyzed by acidic invertase, followed by susy and neutral invertase. We concluded that Eucalyptus urophylla is tolerant to Mg deficiency, since the sugar accumulation in leaf tissues is not enough to constrain dry matter accumulation in roots.

Effects of exogenous plant hormones on sugar accumulation and related enzyme activities during the development of longan (Dimocarpus Longan Lour.) fruits

ABSTRACTExogenous hormone treatment is a widely used and effective method to promote fruit ripening. To our knowledge, the effects of exogenous hormones on the sugar accumulation and related enzyme activities during the development of longan fruits have not yet been elucidated. In this study, the contents of sucrose, glucose and fructose, activities and transcriptional levels of sucrose phosphate synthase (SPS), sucrose synthase (SS), acid invertase (AI) and neutral invertase (NI) were detected during fruit development of exogenous hormone-treated and non-treated longan. The results indicated that exogenous hormones (IAA, ABA, GA3) could not alter the sugar contents when fruits were ripe but accelerate the sugar accumulation. IAA and ABA increased the gene transcriptional levels and enzyme activities of SS and SPS, and also showed the tendency of increasing the transcriptional levels and enzyme activity of AI. However, GA3 decreased the gene transcriptional levels of SS and SPS, and increased the gene transcriptional level of AI. Interestingly, GA3 also increased the enzyme activity of SPS which indicated GA3 may regulate the SPS activity at post-translational levels. Our results suggested that IAA, ABA and GA3 may regulate sugar accumulation during fruit development of longan.

Drought limits pollen tube growth rate by altering carbohydrate metabolism in cotton (Gossypium hirsutum) pistils

It has been reported that drought stress (DS) reduces cotton yield by negatively affecting reproductive activities. Some studies have investigated the effects of DS on pollen physiology and biochemistry, but studies exploring the impact of drought on pistil biochemistry and its relationship with pollen tube growth rates in vivo are scarce. In order to investigate these objectives, a greenhouse study was conducted with a drought sensitive cotton cultivar, Yuzaomian 9110. Two water treatments were imposed at flowering stage, 1. control, where plants were irrigated with optimum quantity of water and 2. DS treatment, where plants were irrigated with 50% of the optimum quantity of water. Results indicated that stored starch content at the early stage of pollen tube growth (12:00 h) was 31.6% lower in drought-stressed pistils than control pistils, and it was highly correlated with pollen tube growth rate. The decline in starch accumulation of drought-stressed pistils could be attributed to the impeded transport of photosynthetic carbon assimilates. Moreover, decreased ADP-glucose pyrophosphorylase and soluble starch synthase activities also resulted in curtailing starch accumulation in drought-stressed pistils. Furthermore, pistil sucrose concentration was significantly higher in droughted plants relative to control plants at 12:00 and 18:00 h (during the rapid growth period), which was due to lower activities of sucrose synthase and acid invertase, and the down-regulated expressions of sucrose synthase genes, GhSusA, GhSusB and GhSusD, and acid invertase genes, GhINV1 and GhINV2, in drought-stressed pistils, limiting as a result the hydrolysis of sucrose into hexose. Drought-stressed pistils sampled at 18:00 h had lower α-amylase activity compared to control pistils, resulting in decreased starch decomposition, which, in conjunction with the decreased hydrolysis of sucrose, led to lower glucose and fructose contents in drought-stressed pistils at 18:00 h. Finally, lower pyruvate level in drought-stressed pistils could not produce enough acetyl-CoA in the tricarboxylic acid cycle to yield sufficient energy (ATP) for pollen tube growth. We conclude that DS disrupts the carbohydrate balance of pistil, reducing as a consequence carbon and energy supply for pollen tube elongation in the style, which will ultimately result in reproductive failure.

The 14-3-3 protein GF14f negatively affects grain filling of inferior spikelets of rice (Oryza sativa L.).

In rice (Oryza sativa L.), later flowering inferior spikelets (IS), which are located on proximal secondary branches, fill slowly and produce smaller and lighter grains than earlier flowering superior spikelets (SS). Many genes have been reported to be involved in poor grain filling of IS, however the underlying molecular mechanisms remain unclear. The present study determined that GF14f, a member of the 14-3-3 protein family, showed temporal and spatial differences in expression patterns between SS and IS. Using GF14f-RNAi plants, we observed that a reduction in GF14f expression in the endosperm resulted in a significant increase in both grain length and weight, which in turn improved grain yield. Furthermore, pull-down assays indicated that GF14f interacts with enzymes that are involved in sucrose breakdown, starch synthesis, tricarboxylic acid (TCA) cycle and glycolysis. At the same time, an increase in the activity of sucrose synthase (SuSase), adenosine diphosphate-glucose pyrophosphorylase (AGPase), and starch synthase (StSase) was observed in the GF14f-RNAi grains. Comprehensive analysis of the proteome and metabolite profiling revealed that the abundance of proteins related to the TCA cycle, and glycolysis increased in the GF14f-RNAi grains together with several carbohydrate intermediates. These results suggested that GF14f negatively affected grain development and filling, and the observed higher abundance of the GF14f protein in IS compared with SS may be responsible for poor IS grain filling. The study provides insights into the molecular mechanisms underlying poor grain filling of IS and suggests that GF14f could serve as a potential tool for improving rice grain filling.

Effects of Low Temperature at Booting Stage on Sucrose Metabolism and Endogenous Hormone Contents in Winter Wheat Spikelet.

Low spring temperatures often occur during the winter wheat booting stage, when the young ears are very sensitive to cold. In this study, we used two wheat varieties differing in cold sensitivity (sensitive variety Yangmai 18 and tolerant variety Yannong 19) to examine the effect of low temperature on wheat grain number at booting stage. Low temperature stress was simulated in an artificial climate chamber at 4°C for 60 h in 2016 and at 2, 0, or −2°C for 24 h in morphological assays, showing that the development of wheat spikelets was inhibited and floret growth was delayed following low temperature stress. However, an increase in the sucrose content of young panicles was also observed, and the activity of enzymes involved in sucrose metabolism was dynamically altered. Sucrose phosphate synthase activity was enhanced, and sucrose synthase activity significantly increased after treatment at 4 and 2°C, respectively. However, activities of sucrose synthase and invertase decreased with a reduction in temperature. Gene expression assays further revealed downregulation of TaSuS1 expression and upregulation of TaSuS2, while expression of CWINV was inhibited. Moreover, phytohormone content assays showed an increase in the content of abscisic acid in young wheat ears, but a decrease in the content of auxin and gibberellins. The grain number per spike and 1000-grain weight also showed a downward trend following low temperature stress. Overall, these findings suggest that low temperature at booting induces abscisic acid accumulation in winter wheat, altering the activity of the enzymes involved in sucrose metabolism, which leads to an accumulation of sucrose in the young ears, thereby having a negative effect on wheat production.

Genotypic differences in sucrose metabolism with cotton bolls in relation to lint percentage

Lint percentage is an important cotton (Gossipium hirsutum L.) lint yield character which may have a close association with photoassimilates partitioning between fibers and seeds. A three-year field experiment was conducted with an aim to determine whether or not the formation of lint percentage is associated with sucrose metabolism in both of fibers and seeds, and potential contributors to the performance of lint percentage. Two upland cotton (Gossypium hirsutum L.) lines A705 and A201 differing in lint percentage and seed size were employed to examine genotypic difference in within-boll yield components, nonstructural carbohydrate components (hexose, sucrose and starch) and key sucrose metabolism enzymes across 2015–2017. A705 had greater lint mass per boll, lint index, and higher lint percentage and cellulose content in fibers, but smaller boll weight, seed mass per boll, seed index and lower oil content in embryos compared to A201. The result indicated that the fiber sink strength was greater in A705 than in A201, but the reverse was true of the seed sink strength. A705 exhibited consistently higher sucrose concentration and sucrose synthase (Sus) activity in fibers during fiber development relative to A201, while the latter recorded consistently higher sucrose concentration and Sus activity in younger ovules during 5–17 days post anthesis (DPA) and in older embryos and seed coats during 24 DPA to 45 DPA. Higher starch concentration and sucrose phosphate synthase (SPS) activity with seed coats were detected in A705 than in A201, implying sucrose synthesized by SPS in A705 at sink storage stage is preferentially partitioned to starch biosynthesis in seed coats. It is concluded that a higher lint percentage in A705 than in A201 is attributable to a combination of greater fiber sink strength and smaller seed sink strength available in the former relative to the latter. Sucrose and Sus may function as key biomarkers for assessing fiber and ovule sink strengths.

Switch from Apoplasmic to Symplasmic Phloem Unloading during Storage Roots Formation and Bulking of Sweetpotato

To clarify the unloading pathway of assimilates in storage roots of sweetpotato (Ipomoea batatas L.), a combination of methods including electron microscopy, movement of the phloem–mobile symplasmic tracer carboxyfluorescein, and assays of invertase and sucrose synthase activities were explored to investigate this pathway from storage roots formation to harvest. The sieve element–companion cell complex was symplasmically connected to surrounding parenchyma cells by plasmodesmata and isolated before storage root bulking (40–140 d after planting). Numerous plasmodesmata appeared among phloem parenchyma throughout storage root bulking. Images of carboxyfluorescein movement indicated that the dye was restricted to phloem and released into surrounding tissues before and after storage root formation, respectively. Sucrose synthase activity increased continually during storage root bulking, and it was much higher than that of insoluble acid invertase. Although this remained low and changed little, that of soluble acid invertase increased and remained high. The starch content in storage roots increased during bulking, but sucrose content decreased. Thus, the predominant unloading pathway switched from apoplasmic to symplasmic during storage root formation and bulking. This switch resulted in enhanced sink potential of storage roots, evidencing opportune sink–source relationships in sweetpotato.

Sucrose metabolism in cotton subtending leaves influenced by potassium-to-nitrogen ratios

Nutrient management is important for enhancing crop productivity economically, as well as for environmental protection. The present study explored the best relative ratio of potassium (K) to nitrogen (N) under a new short-season, high-density planting model, based on the sucrose metabolism in the subtending leaves of cotton in relation to yield. A 2-year (2016–2017) field experiment was conducted in a randomized complete block design along with four replicates. The treatments were three K relative ratios to N [K08 {K (K2O): N = 0.8:1 (168:210 kg ha−1)}, K10 {K (K2O): N = 1:1 (210:210 kg ha−1)}, and K12 {K (K2O): N = 1.2:1 (252:210 kg ha−1)}]. The plot size was 36.48 m2 comprised of four rows. Plants were sown on raised beds. Row spacing was managed to 0.76 m with a plant-to-plant distance of 0.14 m to maintain a planting density of 9 plants m−2. The results indicated that increased K application ratios substantially favored sucrose metabolism in the subtending leaves to attain higher cotton yields. K10 and K12 upregulated the photosynthetic rate (Pn) of subtending leaves by 17–32% and 33–59%, sucrose phosphate synthase activities by 4–17% and 14–28%, and sucrose synthase activities by 12–25% and 21–36%, respectively. Glucose-6-phosphate dehydrogenase and soluble acid invertase activities were significantly downregulated. K10 improved seed and lint yield by 10–24% with no differences between K10 and K12, suggesting K10 (K2O: N; 1:1) to be the best ratio for cost-effective cotton production under the new planting model in the Yangtze River Valley, China.

CRISPR/Cas9 mutations in the rice Waxy/GBSSI gene induce allele-specific and zygosity-dependent feedback effects on endosperm starch biosynthesis.

Induced mutations in the waxy locus in rice endosperm did not abolish GBSS activity completely. Compensatory mechanisms in endosperm and leaves caused a major reprogramming of the starch biosynthetic machinery. The mutation of genes in the starch biosynthesis pathway has a profound effect on starch quality and quantity and is an important target for plant breeders. Mutations in endosperm starch biosynthetic genes may impact starch metabolism in vegetative tissues such as leaves in unexpected ways due to the complex feedback mechanisms regulating the pathway. Surprisingly this aspect of global starch metabolism has received little attention. We used CRISPR/Cas9 to introduce mutations affecting the Waxy (Wx) locus encoding granule-bound starch synthase I (GBSSI) in rice endosperm. Our specific objective was to develop a mechanistic understanding of how the endogenous starch biosynthetic machinery might be affected at the transcriptional level following the targeted knock out of GBSSI in the endosperm. We found that the mutations reduced but did not abolish GBSS activity in seeds due to partial compensation caused by the upregulation of GBSSII. The GBSS activity in the mutants was 61-71% of wild-type levels, similarly to two irradiation mutants, but the amylose content declined to 8-12% in heterozygous seeds and to as low as 5% in homozygous seeds, accompanied by abnormal cellular organization in the aleurone layer and amorphous starch grain structures. Expression of many other starch biosynthetic genes was modulated in seeds and leaves. This modulation of gene expression resulted in changes in AGPase and sucrose synthase activity that explained the corresponding levels of starch and soluble sugars.

Effects of methyl jasmonate on growth, antioxidants, and carbon and nitrogen metabolism of Glycyrrhiza uralensis under salt stress

We investigated the effects of 0.025 or 0.05 mM methyl jasmonate (MeJA) on the growth characteristics, antioxidant enzyme activities, non-enzymatic antioxidant content, and carbon and nitrogen metabolizing enzyme activities in Glycyrrhiza uralensis exposed to 100 mM NaCl. Results showed that salt stress decreased the stem length and lateral root number and the treatment with 0.025 or 0.05 mM MeJA increased the root length of salt-stressed G. uralensis seedlings but decreased root diameter, stem length, and stem diameter. MeJA application modulated oxidative stress in salt-stressed G. uralensis seedlings. It decreased the catalase activity but enhanced peroxidase activity and ascorbate content. However, treatment with 0.05 mM MeJA significantly increased the malondialdehyde content of salt-stressed seedlings. Salt stress inhibited carbon and nitrogen metabolism. The application of MeJA enhanced the activities of sucrose synthase, and sucrose phosphate synthase, and nitrate reductase in salt-stressed seedlings.