Sucrose Phosphate Synthase Activity Research Articles

Malate metabolism mediated by the cytoplasmic malate dehydrogenase gene MdcyMDH affects sucrose synthesis in apple fruit.

The types and proportions of soluble sugar and organic acid in fruit significantly affect flavor quality. However, there are few reports on the crosstalk regulation between metabolism of organic acid and sugar in fruit. Here, we found that the overexpression of cytoplasmic malate dehydrogenase genes (MdcyMDHs) not only increased the malate content but also increased the sucrose concentration in transgenic apple calli and mature fruit. Enzyme activity assays indicated that the overexpression of MdcyMDH1 and MdcyMDH5 enhanced sucrose phosphate synthase (SPS) activity in transgenic materials. RNA-seq and expression analysis showed that the expression levels of SPS genes were up-regulated in MdcyMDH1-overexpressed apple fruit and MdcyMDH5-overexpressed apple calli. Further study showed that the inhibition of MdSPSB2 or MdSPSC2 expression in MdcyMDH1 transgenic fruit could reduce or eliminate, respectively, the positive effect of MdcyMDH1 on sucrose accumulation. Moreover, some starch cleavage-related genes (MdBAM6.1/6.2, MdBMY8.1/8.2, MdISA1) and the key gluconeogenesis-related phosphoenolpyruvate carboxykinase MdPEPCK1 gene were significantly up-regulated in the transcriptome differentially expressed genes of mature fruit overexpressing MdcyMDH1. These results indicate that alteration of malate metabolism mediated by MdcyMDH might regulate the expression of MdSPSs and SPS activity via affecting starch metabolism or gluconeogenesis, and thus accelerate sucrose synthesis and accumulation in fruit.

Trehalose maintains the quality of Malus domestica by mediating sucrose and respiratory metabolism

Quality breakdown and decay are the main factors that cause economic losses of fruit and vegetable during storage. Apple fruit (cv. Golden Delicious) were dipped in 1.5 g L−1 trehalose to investigate the changes of quality parameters, activity and gene expression of key enzyme in sucrose and respiratory metabolism. Results showed that trehalose treatment suppressed weight loss and respiratory rate, maintained soluble solid content and flesh firmness in apples. Moreover, trehalose suppressed neutral invertase (NI) and sucrose synthase cleavage (SS-c), cytochrome oxidase (CCO) and succinate dehydrogenase (SDH), glucose phosphate isomerase activities and MdNI, MdSS, MdSDH and MdCCO expressions in apple fruit. Meanwhile, trehalose increased the activities of sucrose phosphate synthase (SPS), sucrose synthase synthesis (SS-s) and glucose 6-phosphate dehydrogenase (G6PDH), and MdSPS, MdG6PDH and MdPFK expressions in apples. These results propose that trehalose treatment maintains storage quality of apples by regulating sucrose and respiratory metabolism during storage.

Effects of Salt-Alkaline Stress on Carbohydrate Metabolism in Rice Seedlings

The aim of this study was to investigate carbohydrate metabolism in rice seedlings subjected to salt-alkaline stress. Two relatively salt-alkaline tolerant (Changbai 9) and sensitive (Jinongda 138) rice cultivars, grown hydroponically, were subjected to salt-alkaline stress via 50 mM of salt-alkaline solution. The carbohydrate content and the activities of metabolism-related enzymes in the leaves and roots were investigated. The results showed that the contents of sucrose, fructose, and glucose in the leaves and roots increased under salt-alkaline stress. Starch content increased in the leaves but decreased in the roots under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, and ADP-glucose pyrophosphorylase increased whereas the activities of neutral invertase and acid invertase decreased in the leaves under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, neutral invertase, and acid invertase increased in the roots under salt-alkaline stress. In conclusion, salt-alkaline stress caused the accumulation of photosynthetic assimilates in the leaves and decreased assimilation export to the roots.

A Vacuolar Invertase CsVI2 Regulates Sucrose Metabolism and Increases Drought Tolerance in Cucumis sativus L.

Vacuolar invertase (VI) can irreversibly degrade sucrose into glucose and fructose and involve in plants abiotic-stress-tolerance. Cucumber (Cucumis sativus L.) is susceptible to drought stress, especially during the seedling stage. To date, the involvement of VI in drought tolerance in cucumber seedlings is in urgent need of exploration. In the present study, a cucumber vacuolar invertase gene, CsVI2, was isolated and functionally characterized. The results showed that (1) CsVI2 showed vacuolar invertase activity both in vivo and in vitro; (2) the transcript level of CsVI2, along with VI activity, was significantly induced by drought stress. Moreover, the expression of sucrose synthase 3 (CsSUS3) was increased and that of sucrose phosphate synthase 1 (CsSPS1) was decreased after exposure to drought stress, which was followed by an increase in sucrose synthase activity and a decrease in sucrose phosphate synthase activity; (3) CsVI2-overexpressing transformed cucumber seedlings showed enhanced vacuolar invertase activity and drought tolerance and 4) protein–protein interaction modelling indicated that a cucumber invertase inhibitor, CsINVINH3, can interact with CsVI2. In summary, the results indicate that CsVI2 as an invertase can regulate sucrose metabolism and enhance drought stress in cucumber seedlings.

Genotypic variation in root morphology, cotton subtending leaf physiology and fiber quality against nitrogen

BackgroundNitrogen (N) is important for improving various morphological and physiological processes of cotton but their contribution to fiber quality is still lacking.AimsThe current study aimed to explore the relationship between root morphology, subtending leaf physiology, and fiber quality of contrasting N-efficient cotton genotypes in response to N.MethodsWe analyzed the above parameters of CCRI 69 (N-efficient) and Xinluzao-30 (XLZ-30, N-inefficient) under control (2.5 mmol·L−1) and high N (5 mmol·L−1) conditions.ResultsThe results showed that root morphological traits were increased in CCRI-69 under control conditions than high N. Subtending leaf morphology, chlorophyll and carotenoid contents, free amino acids, and soluble proteins were higher under high N as compared with the control. However, soluble sugars, fructose, sucrose contents, and sucrose phosphate synthase were higher under control conditions than high N across the growth stages. Irrespective of the N conditions, all morphological and physiological traits of cotton subtending leaf were higher in CCRI-69 than XLZ-30. Except for fiber uniformity, fiber quality traits like fiber length, strength, micronaire, and elongation were improved under control conditions than high N. Between the genotypes, CCRI-69 had significantly higher fiber length, strength, micronaire, and elongation as compared with XLZ-30. Strong positive correlations were found between root morphology, soluble sugars, sucrose content, and sucrose phosphate synthase activity with fiber quality traits, respectively.ConclusionsThese findings suggest that CCRI-69 performed better in terms of growth and fiber quality under relatively low N condition, which will help to reduce fertilizer use, the cost of production, and environmental pollution.

The effects of straw-returning and inorganic K fertilizer on the carbon\u2013nitrogen balance and reproductive growth of cotton

BackgroundMany studies have indicated that straw-returning could meet part or even all of the potassium (K) demand for crop growth in the field, but few have compared the effects of crop straw as K source and inorganic K fertilizer on carbon–nitrogen (C–N) balance of cotton and the reproductive growth. To address this, field experiments were conducted using the cotton cultivar, Siza 3, under there treatments (CK as control group one, no crop straw and inorganic K fertilizer were applied; K150 as control group two, 150 kg·ha−1 of K2O was applied; and W9000, 9 000 kg·ha−1 wheat straw, which could provide K2O about 150 kg·ha−1, was incorporated into soil).ResultsAlthough the final reproductive organ biomass did not differ between W9000 and K150, W9000 had a higher ratio of reproductive organ biomass to total biomass (RRT), suggesting that straw-returning was more conducive to the allocation of biomass to reproductive organs. The theoretical maximum biomass of reproductive organ was higher, but the average and maximum accumulation rates of reproductive organ biomass were 2.8%∼8.3% and 2.5%∼8.2% lower under W9000 than K150. Also, the duration of rapid-accumulation period for reproductive organ biomass (T) was 2.0∼2.8 d longer under W9000 than K150, which was a reason for the higher RRT under W9000. Straw-returning altered the dynamics of leaf K with the growth period, so that W9000 had a more drastic effect on leaf C metabolism than K150. Consequently, lower soluble sugar/free amino acid and C/N ratios were measured under W9000 than K150 at boll-setting (BSS) and boll-opening (BOS) stages. Higher leaf net photosynthetic rate, sucrose phosphate synthase and sucrose synthase activities, and lower acid invertase activity were observed under W9000 than K150 at BSS and BOS and these were more conducive to sucrose accumulation. However, less sucrose was measured under W9000 than K150 at these stages. This should be because straw-returning promoted the assimilate transport capacity when compared with inorganic K fertilizer application, which also explained the higher RRT under W9000 than K150. The lower acid invertase activity under W9000 inhibited the conversion of sucrose to other sugars, hence lower contents of soluble sugar and starch were measured under W9000 than K150.ConclusionUnder low K condition, crop straw as K source can increase the assimilate transport from source to sink, leading to lower C/N ratio in leaf and higher allocation of biomass to reproductive organs than inorganic K fertilizer.

Impact of Exogenous Plant Growth Regulators on Physiological Traits, Tendril and Flowering in Horsegram (Macrotyloma uniflorum Lam) under Kharif Season

Background: Horsegram is an important pulse crop grown as Rabi crop in Tamil Nadu. Kharif sown crop could not flowers may be because of more number of tendrils produced as compare to Rabi sown crop. Hence, an attempt was made to reduce the number of tendrils and induce flowering in horsegram during Kharif season by plant growth regulators. Methods: A field experiment was conducted to study the impact of plant growth regulators viz., salicylic acid (100 ppm), chlormequat chloride (CCC - 250 ppm), mepiquat chloride (250 ppm), tri iodo benzoic acid (TIBA - 200 ppm) and nitrobenzene (0.2%) on physiological traits and tendril growth associated with flowering in horsegram during Kharif. Different treatments were applied through foliar application at 25 Days after sowing. Result: Among the PGRs, foliar application of TIBA registered the lowest number of tendrils (2.3) followed by CCC (3.0) compared to other treatments. Higher root length of 16.8 cm and RWC of 82.3% was found in CCC treatment. CCC also registered the highest photosynthetic rate (27.15 µmol m-2 s-1), transpiration rate (18.06 mmol m-2 s-1) and lowest leaf temperature (26°C) compared to other treatments. The highest soluble protein content of 13.1 mg g-1 was also estimated in CCC treatment followed by mepiquat chloride (12.51 mg g-1). Sucrose phosphate synthase (SPS) activity did not show any significant difference between the treatments. Number of flowers buds formed per plant was zero and hence the flowering did not take place in any treatments. Among the plant growth regulators used, TIBA and CCC registered its positive action on reduced the number of tendrils and leaf temperature, but not enough to induce flowering under Kharif season.

Effects of single and combined exogenous application of abscisic acid and melatonin on cotton carbohydrate metabolism and yield under drought stress

Drought is a major abiotic factor that adversely affects plant growth and crop productivity. Abscisic acid (ABA) and melatonin (MT) are two commonly used hormones, whose exogenous application has been shown to improve crop drought tolerance under water deficiency, when used separately; however, studies on the effects of their combined application on crops are scarce. To amend this, pot studies were conducted to study the effects of exogenous ABA and MT application (single or combined) on cotton leaf photosynthetic carbon metabolism and yield under drought. Results revealed that single ABA or MT application significantly improved plant water status under drought by different pathways, which curtailed drought-induced yield losses. ABA+MT application effects on plant water status were similar to those of MT, however, ABA+MT application had synergistic effects on alleviating drought-induced yield losses. ABA spraying had no effects on the net photosynthetic rate (Pn) of drought-stressed leaves, but MT application improved Pn by increasing stomatal conductance and CO2 fixation, and ABA+MT was more effective than MT in alleviating the Pn. Furthermore, ABA application reduced leaf sucrose synthesis by decreasing sucrose synthase (SuSy) activity, and MT and ABA+MT application also inhibited sucrose synthesis by reducing SuSy and sucrose phosphate synthase activities. Extra ABA down-regulated acid invertase activity to inhibit the hydrolysis of sucrose to hexose, but MT spraying decreased both acid and alkaline invertases activities of drought-stressed leaves, and ABA+MT had similar effects as MT. Although ABA or MT down-regulated GhSWEET5, GhSWEET20 and GhSWEET55 expression, thus repressing sucrose transport to the cell wall, their application up-regulated GhSUT3A/D and GhSUT4 expression in drought-stressed leaves, improving in that way sucrose transport to the sieve-companion cell complex and ultimately benefiting yield formation. Similarly, ABA+MT application had additive effects on GhSUT3A/D and GhSUT4 expression under drought. Consequently, ABA or MT application decreased sucrose content in drought-stressed leaves, while ABA+MT application showed a synergistic effect. Hexose, as the substrate for starch biosynthesis, content decreased in ABA- or MT-treated leaves under drought, however, starch accumulation was not affected by ABA application, and MT spraying increased starch content of drought-stressed leaves, by increasing ADP-glucose pyrophosphorylase activity. Nevertheless, ABA+MT application was more effective in increasing starch synthesis under drought than either single hormone application. In conclusion, the effects of ABA+MT on photosynthetic carbon metabolism of cotton leaves were more similar to those of MT under drought, but there were significant synergistic effects in mitigating the negative effects of drought on Pn, sucrose accumulation, sucrose transport, starch synthesis as well as final yield.

Effect of Exogenous Abscisic Acid on Sugar Metabolism in Tomato Fruits

Aims: This research explored the effect of exogenous abscisic acid (ABA) treatment on sugar metabolism in tomato fruits, and provided theoretical basis for the regulation of ABA on the growth and development of tomato fruits.
 Study Design: The whole tomato plant was treated by spraying with 50 mg·L-1 ABA. Spraying distilled water was as the control.
 Place and Duration of Study: College of Biological Science and Technology, between February 2019 and March 2020.
 Methodology: The contents of soluble sugar in tomato fruits were measured with HPLC (High performance liquid chromatography). The enzyme extraction and activities were followed the biochemical method.
 Results: Exogenous ABA treatment reduced the weight and transverse meridians of the fruit at the ripening stage, but increased the contents of fructose, glucose and sucrose in the fruit. At the same time, it also increased the activities of acid invertase, neutral invertase, and sucrose phosphate synthase at the ripening stage.
 Conclusions: Exogenous ABA treatment was beneficial to the accumulation of sugar in tomato fruit and improved tomato quality. Therefore, it could be applied to tomato production.

Changes in Sugar Accumulation and Related Enzyme Activities of Red Bayberry (Myrica rubra) in Greenhouse Cultivation

The harvest period of bayberry fruit cultivated in the open field is short and often suffers from continuous cloudy and rainy days, leading to a decrease in yield and a decline in fruit quality. However, cultivating bayberries in greenhouses could avoid the harm due to rain, improve fruit quality and prolong the supply period, thus significantly increasing economic returns. Bayberry fruit quality, assessed by single fruit weight, vertical and horizontal diameters, soluble solids content and sugar-acid ratios, was significantly superior in fruit produced under greenhouse conditions than in fruit produced in the open field. Analysis of the soluble sugar components and the related enzyme activities indicated that the sucrose accumulation and metabolism of bayberry fruit were significantly improved by greenhouse cultivation, possibly owing to differences in sucrose-phosphate synthase and acid invertase activities.

Selenomethionine regulates the sugar-acid ratio of strawberry fruit by modulating the activities of related enzymes

ABSTRACT To study the effects of exogenous organic selenium on the sugar-acid ratio (SAR) of strawberry (Fragaria x ananassa) fruit, we investigated the effects of different concentrations of selenomethionine (SeMet) on the activities of key enzymes in sugar and organic acid metabolism in fruit during Large fruit period (LP, 20 d after flowering), Colour changed period (CP, 24 d after flowering) and Mature period (MP, 28 d after flowering) of fruit. The results showed that SeMet increased the contents of total sugars (TS), sucrose (Suc), glucose (Glu) and fructose (Fru) by improving the activities of acid invertase (AI), sucrose synthase (SS) and sucrose phosphate synthase (SPS), and reducing hexokinase (HK) activity. Meanwhile, SeMet markedly decreased the contents of total acids (TA), citric acid (CA) and malic acid (MA) by reducing the activities of NAD-malic dehydrogenase (NAD-MDH), NADP-malic enzyme (NADP-ME) and citrate synthase (CS). By this way, SeMet improved the SAR of fruit. Among different concentrations, 60 mg L−1 SeMet was the best concentration in improving the value of SAR in ripe fruit and could be used in the production of ‘Sweet Charlie’ strawberry to improve fruit SAR.

Potassium application alleviates the negative effects of salt stress on cotton (Gossypium hirsutum L.) yield by improving the ionic homeostasis, photosynthetic capacity and carbohydrate metabolism of the leaf subtending the cotton boll

• Potassium (K) application alleviated the salt stress damage and improved cotton yield. • K application in saline alkali soil maintained the ionic homeostasis of LSCB (leaf subtending the cotton boll). • Under salt stress, K application improved LSCB photosynthetic capacity. • Under salt stress, K application enhanced the carbon metabolism of LSCB. Field experiments were conducted in 2017 and 2018, in order to investigate the effects of potassium (K) application on photosynthetic capacity and carbohydrate metabolism of the leaf subtending the cotton boll (LSCB) under salt stress. Three salinity treatments (EC = 1.68∼1.78, 6.21∼6.42 and 10.59∼11.08 dS m −1 ) with three K levels (0, 150, 300 kg K 2 O ha -1 ) applied in each salinity treatment, were imposed on two cotton ( Gossypium hirsutum L.) cultivars differing in salt sensitivity (CCRI-79, salt tolerant and Simian 3, salt sensitive). The results indicated that under salt stress: (1) K application increased LSCB K + /Na + ratio since Na + concentration decreased and K + concentration increased. Cotton boll (capsule wall, seed and lint) biomass, total boll number, boll weight and seed cotton yield were also increased; (2) K application improved net photosynthetic rates ( Pn ) of LSCB by increasing stomatal conductance rates ( Gs ), chlorophyll a and b concentrations and chlorophyll a / b ratio; (3) K application decreased soluble sugar, sucrose and starch concentrations of LSCB through increases in sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) activities and decreases in sucrose acid invertase (SAI) activity. The results of this study indicated that K fertilizer application rates have a regulating effect on LSCB’s photosynthetic properties and carbohydrate metabolism under salt stress, thus providing a theoretical foundation for increasing cotton yield under salt stress.

Effects of combined glycine and urea fertilizer application on the photosynthesis, sucrose metabolism, and fruit development of peach

The unreasonable use of urea and its low nitrogen use efficiency limit peach fruit yield and quality. In this study, six different fertilization treatments—no nitrogen fertilizer, urea (T1), glycine (T2), glycine:urea (1:1) (T3), glycine:urea (3:7) (T4), and glycine:urea (7:3) (T5)—were used to explore the effects of glycine and urea on the growth, photosynthesis, sucrose metabolism, and fruit development of peach. Peach had a higher utilization rate of glycine compared with urea; combined application of glycine-urea improved the utilization rate of urea compared with T1. T5 significantly increased the biomass of peach. High-dose glycine (T2 and T5) promoted the opening of stomata and the efficiency of photosynthetic electron transfer, which increased the net photosynthetic rate (Pn). In addition, the activity of Rubisco was higher in leaves on wild peach treated with T2 and T5, which increased the fixation of CO2. Under high-dose glycine treatment, the lower cell wall invertase activity in leaves and the higher cell wall invertase activity in fruits promoted the transfer of sucrose from source to sink. In addition, high-dose glycine treatment led to higher sucrose phosphate synthase activity in leaves and fruits, which improved the accumulation of soluble sugar in the fruit. The higher sucrose transport efficiency increased the single fruit weight, soluble solid content and ratio of sugar to acid in peach fruits under high-dose glycine treatment.

CmMYB113 regulates ethylene-dependent sucrose accumulation in postharvest climacteric melon fruit

Sucrose is mainly accumulated in mature oriental melon fruit, and it is generally regulated by ethylene. However, the molecular mechanism of sucrose accumulation induced by ethylene remains largely unknown. Here, high sucrose melon cultivar ‘HS’ and low sucrose melon cultivar ‘LW’ fruit were treated with ethylene and 1-MCP at ethylene release initial stage (27 d after anthesis, DAA), we found that the exogenous ethylene treatment promoted the sucrose accumulation, and enhanced the activity of sucrose phosphate synthase (SPS), as well as the transcript of CmSPS1 in postharvest climacteric melon fruit ‘HS’. However, both treatments had no effect on sucrose accumulation, SPS activity and its transcription in ‘LW’ fruit. In addition, exogenous ethylene increased endogenous ethylene production in ‘HS’ fruit, and had no effect in ‘LW’ fruit, except 5 d after treatment. Also, a strong positive correlation between ethylene and the CmACO1 expression level were observed in ‘HS’. The expression of transcription factor CmMYB113, screened from yeast one hybrid library, was induced by exogenous ethylene treatment in ‘HS’ rather than ‘LW’. Moreover, the yeast one hybrid and GUS activity assays indicated that CmMYB113 could activate the transcription of CmACO1 and CmSPS1 by binding directly to their promoters, respectively. From the findings, it was revealed that the targeted up-regulation of CmACO1 and CmSPS1 by CmMYB113 could be involved in ethylene-dependent sucrose accumulation, which enhanced flavor quality in climacteric melon fruit.

Exogenous methyl jasmonate regulates sucrose metabolism in tomato during postharvest ripening

Sucrose metabolism is a fundamental process during tomato ripening. Studies have shown the role of the phytohormone methyl jasmonate (MeJA) in tomato fruit ripening. However, the role of MeJA in regulating sucrose metabolism in tomato is still unclear. In this study, mature green cherry tomato fruit were infiltrated with MeJA (0.5 mM) or sterile deionized water (control). The changes in color, firmness, and ethylene production in fruit, the contents of sucrose, glucose and fructose, and the enzymatic activities and the expression levels of key genes associated with sucrose metabolism were determined periodically during a storage period of 16 d. MeJA-treated fruit showed a significant acceleration in ripening, with higher a* value and ethylene production and lower firmness. MeJA treatment enhanced sucrose phosphate synthase (SPS) activity, whereas it inhibited acid invertase (AI) and neutral invertase (NI) activities. These changes in enzyme activities together resulted in a significantly higher sucrose content and lower glucose and fructose contents. Furthermore, exogenous MeJA upregulated the gene expression levels of sucrose-phosphate synthase1–4 (SPS1-4) and sucrose-phosphate phosphatase2 (SPP2), which were associated with sucrose biosynthesis, and downregulated those related to sucrose degradation, except for sucrose synthase2 (SUS2) and SUS3. The findings indicated that exogenous MeJA might alter sucrose metabolism during tomato ripening by regulating the enzymatic activities and gene expression levels. This research provides valuable information to elucidate the mechanisms via which MeJA regulates tomato sucrose metabolism.

Function, structure and catalytic mechanism of sucrose phosphate synthase: a review

Sucrose is a natural product occurs widely in nature. In living organisms such as plants, sucrose phosphate synthase (SPS) is the key rate-limiting enzyme for sucrose synthesis. SPS catalyzes the synthesis of sucrose-6-phosphate, which is further hydrolyzed by sucrose phosphatase to form sucrose. Researches on SPS in recent decades have been focused on the determination of enzymatic activity of SPS, the identification of the inhibitors and activators of SPS, the covalent modification of SPS, the carbohydrate distribution in plants regulated by SPS, the mechanism for promoting plant growth by SPS, the sweetness of fruit controlled by SPS, and many others. A systematic review of these aspects as well as the crystal structure and catalytic mechanism of SPS are presented.

The Associated With Carbon Conversion Rate and Source-Sink Enzyme Activity in Tomato Fruit Subjected to Water Stress and Potassium Application.

Carbon metabolism in higher plants is a basic physiological metabolism, and carbon allocation and conversion require the activity of various enzymes in metabolic processes that alter the content and overall composition of sugars in the sink organ. However, it is not known how various enzymes affect carbon metabolism when tomato plants are subjected to water stress or treated with potassium. Although the process of carbon metabolism is very complex, we used the carbon conversion rate to compare and analyze the enzyme activities related to sugar metabolism and find out which carbon conversion rate are the most important. Results showed that water stress and potassium increased carbon import flux in the fruit, which was beneficial to carbon accumulation. Water deficit increased the activity of sucrose synthase (SuSy) and starch phosphorylase (SP) and decreased the activity of sucrose phosphate synthase (SPS) and adenosine diphosphate glucose pyrophosphorylase (AGPase) in the source. Water stress increased the activity of acid invertase (AI), SuSy and SP but decreased the activity of AGPase in the sink. Potassium modified the balance of enzymes active in sugar and starch metabolism by increasing the activity of AI, SuSy, SPS and SP and significantly decreasing the activity of AGPase, resulting in increase of hexose. Canonical correlational analysis revealed that the carbon conversion rate was mainly affected by the relative rate of conversion of sucrose to fructose and glucose [p1(t)] and glucose to starch [p5m(t)]. SuSy and AGPase had the greatest effect on enzyme activity in the fruit; respectively regulated p1(t) and p5m(t).

Effects of Seaweed Extracts on the Growth, Physiological Activity, Cane Yield and Sucrose Content of Sugarcane in China.

Seaweed extracts (SEs) have been widely used as biostimulants in crop management due to their growth-promoting and stress-resistant effects. To date, there are few reports of the effect of SEs on sucrose content and cane yield. Here, we conducted field experiments for three consecutive growth seasons (2017∼2019) in two areas (Suixi and Wengyuan) of China, to investigate the yield and sugar content of sugarcane in response to SE treatment at different growth stages. The results showed that spraying SEs once at seedling (S), early elongation (E), and early mature (M) stages, respectively, once at S and E stages, respectively, or once at the S stage increased the cane yield by 9.23, 9.01, and 3.33%, respectively, implying that SEs application at the early elongation stage played a vital role in promoting sugarcane growth. Photosynthetic parameters and nutrient efficiency analysis showed that spraying SEs at S and E stages enhanced the net photosynthetic rate, transpiration rate, and water use efficiency, and increased N, P, or K utilization efficiency, compared with those of the control. Notably, cane yield increasing rate of SEs in 2017 and 2018 were higher than those in 2019 in Wengyuan but lower than those in 2019 in Suixi. Interestingly, the total rainfall and monthly average rainfall in 2017 and 2018 were lower than those in 2019 in Wengyuan but higher than those in 2019 in Suixi. The results suggested that the yield increasing rate of SEs on sugarcane was better in less rainfall years. The sucrose content of sugarcane showed no difference between spraying SEs at the M stage alone or at the three growth stages but was higher than those of SE treatments at S and/or E stages. Enzyme activity analysis showed that spraying SEs at the M stage increased the activity of sucrose phosphate synthase activity by 9.14% in leaves and 15.16% in stems, and decreased soluble acid invertase activity in stems by 16.52%, which contributed to the sucrose increase of 5.00%. The above results suggested that SEs could increase cane yield and promote sucrose accumulation in sugarcane. The yield increasing effect was more obvious under conditions of drought stress.

EFFECT OF SALT (NaCl) ON PHOTOSYNTHESIS AND CARBOHYDRATES IN LEAVES OF TWO RAGI (ELEUSINE CORACANA (L.) GAERTN) VARIETIES

Salinity is one of the most widespread environmental threats to global crop production, especially in arid and semi-arid regions. Photosynthesis and carbohydrates were determined in two ragi (Eleusine coracana (L.) Gaertn) varieties (CO13 and PAIYUR-1), subjected to salt stress of different concentrations (0, 40, 80 and 120mM). Salinity was given as a basal dose and sampling was done in leaves on 30th Days. After Treatment (DAT). There was a marked variation in the photosynthetic rates and ribulose-1, 5-bisphosphate carboxylase activity between the two ragi varieties subjected to salt stress. Photosystem II (PSII) and sucrose phosphate synthase activities were also significantly reduced as measured by salt stressed conditions. The quantity of glucose and sucrose decreased with increasing salt stress while starch showed a reverse trend under salt-stressed conditions. The results revealed that CO-13 exhibits higher photosynthetic rates and activities of ribulose-1,5-bisphosphate carboxylase, sucrose phosphate synthase with photochemical efficiency of PSII compared to PAIYUR-1

Comparative transcriptome analysis reveals key genes potentially related to organic acid and sugar accumulation in loquat.

Organic acids and sugars are the primary components that determine the quality and flavor of loquat fruits. In the present study, major organic acids, sugar content, enzyme activities, and the expression of related genes were analyzed during fruit development in two loquat cultivars, 'JieFangZhong' (JFZ) and 'BaiLi' (BL). Our results showed that the sugar content increased during fruit development in the two cultivars; however, the organic acid content dramatically decreased in the later stages of fruit development. The differences in organic acid and sugar content between the two cultivars primarily occured in the late stage of fruit development and the related enzymes showed dynamic changes in activies during development. Phosphoenolpyruvate carboxylase (PEPC) and mNAD malic dehydrogenase (mNAD-MDH) showed higher activities in JFZ at 95 days after flowering (DAF) than in BL. However, NADP-dependent malic enzyme (NADP-ME) activity was the lowest at 95 DAF in both JFZ and BL with BL showing higher activity compared with JFZ. At 125 DAF, the activity of fructokinase (FRK) was significantly higher in JFZ than in BL. The activity of sucrose synthase (SUSY) in the sucrose cleavage direction (SS-C) was low at early stages of fruit development and increased at 125 DAF. SS-C activity was higher in JFZ than in BL. vAI and sucrose phosphate synthase (SPS) activities were similar in the two both cultivars and increased with fruit development. RNA-sequencing was performed to determine the candidate genes for organic acid and sugar metabolism. Our results showed that the differentially expressed genes (DEGs) with the greated fold changes in the later stages of fruit development between the two cultivars were phosphoenolpyruvate carboxylase 2 (PEPC2), mNAD-malate dehydrogenase (mNAD-MDH), cytosolic NADP-ME (cyNADP-ME2), aluminum-activated malate transporter (ALMT9), subunit A of vacuolar H+-ATPase (VHA-A), vacuolar H+-PPase (VHP1), NAD-sorbitol dehydrogenase (NAD-SDH), fructokinase (FK), sucrose synthase in sucrose cleavage (SS-C), sucrose-phosphate synthase 1 (SPS1), neutral invertase (NI), and vacuolar acid invertase (vAI). The expression of 12 key DEGs was validated by quantitative reverese transcription PCR (RT-qPCR). Our findings will help understand the molecular mechanism of organic acid and sugar formation in loquat, which will aid in breeding high-quality loquat cultivars.