Sucrose Synthase Activity Research Articles

Effects of Hydrogen-Rich Water on Postharvest Physiology in Scales of Lanzhou Lily during Storage

Hydrogen gas (H2) is considered as a signaling molecule and plays multiple roles in plant growth. However, the effect of H2 on postharvest physiology in lily scales during storage has not been reported. In this study, the regulatory roles of hydrogen-rich water (HRW, a H2 donor, a concentration of 0.45 mM for 100% HRW) in water status, ion balance, and nutrients in Lanzhou lily (Lilium davidii var. unicolor) scales were investigated. The scales were soaked in HRW for 12 d, and sampling was performed every 3 d for a total of 5 times. The results show that HRW (0, 10, 50, and 100%) increased the fresh weight, dry weight, relative water content, and water loss rate in lily scales, with maximum biological response at 50% HRW. Treatment with 50% HRW significantly increased the K+ content and K+/Na+ ratio in lily scales and decreased Na+ content. The Na+ K+-ATPase, and PM H+-ATPase activities were also increased by 50% HRW treatment. Meanwhile, 50% HRW up-regulated the expression of AKT1 and HA3 genes and down-regulated the expression of NHX2 and SOS1 genes. In addition, 50% HRW treatment significantly increased the expression level of PIP1;5, PIP2A, TIP1;3, and TIP2;2 genes. Treatment with 50% HRW significantly increased the content of water-soluble carbohydrate, sucrose, glucose, and fructose in lily scales, and decreased the content of starch. In addition, 50% HRW treatment significantly increased the activity of α-amylase, β-amylase, total amylase, sucrose synthase, and sucrose phosphate synthase. Collectively, H2 might enhance the water retention capacity and nutrient content in lily scales by maintaining ion balance, regulating aquaporin, and increasing sugar-metabolizing enzyme activity, thereby prolonging the storage period of postharvest scales of Lanzhou lily.

RGA1 alleviates low-light-repressed pollen tube elongation by improving the metabolism and allocation of sugars and energy.

Low-light stress compromises photosynthetic and energy efficiency and leads to spikelet sterility; however, the effect of low-light stress on pollen tube elongation in the pistil remains poorly understood. The gene RGA1, which encodes a Gα-subunit of the heterotrimeric G-protein, enhanced low-light tolerance at anthesis by preventing the cessation of pollen tube elongation in the pistil of rice plants. In this process, marked increases in the activities of acid invertase (INV), sucrose synthase (SUS)and mitochondrial respiratory electron transport chain complexes, as well as the relative expression levels of SUTs (sucrose transporter), SWEETs (sugars will eventually be exported transporters), SUSs, INVs, CINs (cell-wall INV 1), SnRK1A (sucrose-nonfermenting 1-related kinase 1)and SnRK1B, were observed in OE-1 plants. Accordingly, notable increases in contents of ATP and ATPase were presented in OE-1 plants under low-light conditions, while they were decreased in d1 plants. Importantly, INV and ATPase activators (sucrose and Na2 SO3 , respectively) increased spikelet fertility by improving the energy status in the pistil under low-light conditions, and the ATPase inhibitor Na2 VO4 induced spikelet sterility and decreased ATPase activity. These results suggest that RGA1 could alleviate the low-light stress-induced impairment of pollen tube elongation to increase spikelet fertility by promoting sucrose unloading in the pistil and improving the metabolism and allocation of energy.

Comparative phosphoproteomic analysis reveals that phosphorylation of sucrose synthase GhSUS2 by Ca2+-dependent protein kinases GhCPK84/93 affects cotton fiber development.

Cotton fiber elongation is a critical growth phase that affects final fiber length. Morphological analysis indicated an asynchronous fiber elongation pattern between two cotton varieties, J7-1 and J14-1. Through phosphoproteomic analysis, a total of 89 differentially-phosphorylated proteins (DPPs) were identified in elongating fibers between J7-1 and J14-1. Gene ontology (GO) analysis showed that these DPPs were mainly enriched in sucrose synthase activity, transferase activity, and UDP-glycosyltransferase activity. In J14-1, the phosphorylation level of GhSUS2, a key sucrose synthase in the sucrose metabolism pathway, was significantly higher than that in J7-1. We further revealed that GhSUS2 positively regulates fiber elongation, and GhSUS2-silenced transgenic cotton displayed the phenotype of 'short fibers' compared with the controls. During fiber development, the residue Ser11 in the GhSUS2 protein is phosphorylated by the Ca2+-dependent protein kinases GhCPK84 and GhCPK93. Phosphorylated GhSUS2 is localized in the cytoplasm, whereas unphosphorylated GhSUS2 is localized in the plasma membrane. Moreover, abscisic acid (ABA) could promote the transcription and translation of GhCPK84 and GhCPK93, thereby enhancing the phosphorylation of GhSUS2 to impede fiber elongation. Thus, our data demonstrates that GhSUS2 plays a positive role in fiber development, but its phosphorylation by GhCPK84 and GhCPK93 hinders fiber elongation of cotton.

Influence of potassium on mineral content, yield and quality attributes of dragon fruit (Selenicereus monacanthus) in acidic soil of Eastern tropical region of India

Production of quality fruits has always been the priority for ensuring better nutrition and market value. Considering the role of potassium in fruit quality improvement a study was carried out in dragon fruit under open field condition during 2020 and 2021 in the eastern tropical climatic condition of India. The treatments comprised viz., K-absentia as control (T1), K 50 g hill−1 year−1 (T2), K 100 g hill−1 year−1 (T3), K 200 g hill−1 year−1 (T4), K 300 g hill−1 year−1 (T5), K 400 g hill−1 year−1 (T6) and K 500 g hill−1 year−1 (T7). Application of K @300 g hill−1 year−1 exhibited the maximal acquisition of minerals such as N, P, K, Mg, Fe, Mn, Zn, Cu in shoot and fruit pulp of dragon fruit. However, calcium did not exhibit a discernible trend. However, excessive dose of K (500 g hill−1year−1) resulted in declination in mineral acquisition. K 300 g hill−1 year−1 (T5) also demonstrated enhanced absolute fruit growth rate, maximal yield, marketable yield, fruit weight, color attributes, bio-chemical attributes such as TSS, carbohydrate, reducing sugar (∼20%), protein, citric acid, ascorbic acid content (∼2 times). Additionally, the same treatment also manifested an enhancement in biochemical attributes such as betacyanin (∼2.2 times), total phenol (∼55%), total flavonoid (∼2.7 times), α-amylase and sucrose synthase activities, and antioxidative property (FRAP activity). Principal component analysis (PCA) illustrated the maximal proximity of most of the variables (quality attributes and mineral nutrient contents) with T5 (K 300 g hill−1 year−1), exemplifying it as the best representative of all the studied variables.

Application of Exogenous Melatonin Improves Tomato Fruit Quality by Promoting the Accumulation of Primary and Secondary Metabolites.

Melatonin plays key roles in improving fruit quality and yield by regulating various aspects of plant growth. However, the effects of how melatonin regulates primary and secondary metabolites during fruit growth and development are poorly understood. In this study, the surfaces of tomato fruit were sprayed with different concentrations of melatonin (0, 50, and 100 µmol·L-1) on the 20th day after anthesis; we used high-performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS) to determine the changes in primary and secondary metabolite contents during fruit development and measured the activity of sucrose metabolizing enzymes during fruit development. Our results showed that 100 µmol·L-1 melatonin significantly promoted the accumulation of soluble sugar in tomato fruit by increasing the activities of sucrose synthase (SS), sucrose phosphate synthase (SPS), and acid convertase (AI). The application of 100 µmol·L-1 melatonin also increased the contents of ten amino acids in tomato fruit as well as decreased the contents of organic acids. In addition, 100 µmol·L-1 melatonin application also increased the accumulation of some secondary metabolites, such as six phenolic acids, three flavonoids, and volatile substances (including alcohols, aldehydes, and ketones). In conclusion, melatonin application improves the internal nutritional and flavor quality of tomato fruit by regulating the accumulation of primary and secondary metabolites during tomato fruit ripening. In the future, we need to further understand the molecular mechanism of melatonin in tomato fruit to lay a solid foundation for quality improvement breeding.

Magnesium alleviates aluminum-induced growth inhibition by enhancing antioxidant enzyme activity and carbon–nitrogen metabolism in apple seedlings

Previous studies have determined that magnesium (Mg) in appropriate concentrations prevents plants from suffering from abiotic stress. To better understand the mechanism of Mg alleviation of aluminum (Al) stress in apple, we investigated the effect of Mg on plant growth, photosynthetic fluorescence, antioxidant system, and carbon (C) and nitrogen (N) metabolism of apple seedlings under Al toxicity (1.5 mmol/L) via a hydroponic experiment. Al stress induced the production of reactive oxygen in the leaves and roots and reduced the total dry weight (DW) by 52.37 % after 20 days of treatment relative to plants grown without Al, due to hindered photosynthesis and alterations in C and N metabolism. By contrast, total DW decreased by only 11.07 % in the Mg-treated plants under Al stress. Supplementation with 3.0 mmol/L Mg in the Al treatment decreased Al accumulation in the apple plants and reduced Al-induced oxidative damage by enhancing the activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) and reducing the production of H2O2 and malondialdehyde (MDA). Under Al stress, the Mg-treated plants showed a 46.17 % higher photosynthetic rate than the non-treated plants. Supplementation with Mg significantly increased the sucrose content by increasing sucrose synthase (SS) and sucrose-phosphate synthase (SPS) activities. Moreover, Mg facilitated the transport of 13C-carbohydrates from the leaves to roots. Regarding N metabolism, the nitrate reductase (NR), glutamine synthase (GS), and glutamate synthase (GOGAT) activities in the roots and leaves of the Mg-treated plants were significantly higher than those of the non-treated plants under Al stress. Compared with the non-treated plants under Al stress, the Mg-treated plants exhibited a significantly high level of NO3- and soluble protein content in the leaves, roots, and stems, but a low level of free amino acids. Furthermore, Mg significantly improved nitrogen accumulation and enhanced the transport of 15N from the roots to leaves. Overall, our results revealed that Mg alleviates Al-induced growth inhibition by enhancing antioxidant capacity and C-N metabolism in apple seedlings.

Identification of the most sensitive stage of cotton microspore development to water deficit and analysis of carbohydrate metabolism related to pollen viability

Previous studies have shown that drought occurring at anther development period will have a certain effect on pollen viability, however, it is not clear which developmental stage of cotton microspore is most sensitive to drought and the mechanism of the effect of drought during this period on pollen viability is not explored. To that end, a polyethylene glycol simulated drought experiment (Experiment 1), where drought stress was imposed at different stages of microspore development, was conducted, using cv. Yuzaomian 9110, in order to identify the most sensitive developmental stage to water deficit based on changes in microspore structure and pollen germinability. The results indicated that the microspore mother cell meiosis (MCM) stage was the most sensitive to water deficit. According to that, a second study (Experiment 2) was conducted, using the same cultivar, and the effects of drought stress during MCM-stage on pollen’s carbohydrate and energy metabolism were monitored during and after the stress and their influences on pollen viability were revealed. As per our results, MCM-stage drought down-regulated the sucrose transporter gene GhSUT9 expression which inhibited sucrose import to the anthers; however, increases in sucrose phosphate synthase activity with concurrent decreases in sucrose synthase (SuSy) and invertase (INV) activities resulted in high sucrose content in the water-stressed anthers. In spite of the decreased sucrose decomposition, anther hexose contents were higher in the water-stressed anthers than well-watered anthers, probably due to a decrease in hexose oxidation through the tricarboxylic acid cycle as it was later confirmed by the reduced anther adenosine triphosphate (ATP) content under drought. Contrastingly to sucrose and hexose, anther starch content was greatly reduced by drought, due to decreases in the activities of starch synthesizing enzymes, ADP-glucose pyrophosphorylase (AGPase) and soluble starch synthase (SSSase). After the relief of stress, anther sucrose content decreased to levels lower than well-watered anthers, due to unrecovered GhSUT9 expression and increased alkaline INV activity which enhanced sucrose decomposition. Despite the increased fructose content, glucose content decreased to levels lower than well-watered anthers, without however, resulting in higher energy supply as it was indicated by the lower pollen ATP content after the relief of stress. Anther starch remained lower than well-watered anthers, even after the stress was relieved, as starch biosynthesizing enzymes, AGPase and SSSase, remained suppressed. All these findings suggest that drought stress occurring at the MCM-stage has the most detrimental effect to cotton’s pollen viability due to alterations in carbohydrate metabolism that result in inadequate energy supply.

Co-occurring elevated temperature and drought stresses during cotton fiber thickening stage inhibit fiber biomass accumulation and cellulose synthesis

In order to investigate the effect of simultaneous elevated temperature and drought on Gossypium hirsutum fiber development under the background of global climate change, cotton (cv. Sumian 15 and cv. PHY370WR) plants were grown under ambient temperature (AT) or elevated temperature (ET, 2.5–2.7 °C higher than AT) conditions from 2016 to 2018. Meanwhile, three soil relative water content (SRWC) levels including (75 ± 5) % (optimum soil moisture), (60 ± 5) % (moderate drought) and (45 ± 5) % (severe drought) were established under each temperature condition. Results showed that elevated temperature combined with drought more negatively impacted the theoretical maximum of fiber biomass by further reducing the duration of rapid increase and the average increase rate of fiber biomass than any single stress. Elevated temperature and drought had opposite effects on sucrose synthesis in fibers by differently altering sucrose phosphate synthase (SPS) activity and GhSPS isoforms (GhSPS-1, GhSPS-2, and GhSPS-3) expressions, and the two stresses had an antagonistic effect on SPS activity when they were coupled. However, lower sucrose content was observed under all single and coupled stresses, meaning that less carbon was available for cellulose synthesis. Elevated temperature or drought alone also limited cellulose synthesis by decreasing the activities of sucrose synthase (SuSy), soluble acid invertase (VIN) and alkaline invertase (CIN) involved in sucrose degradation. The decrease of SuSy activity should be the result of down-regulation of GhSuSyA, GhSuSyB and GhSuSyC expressions, and the decrease of VIN activity should be the result of down-regulation of GhInv-1 and GhInv-2 expressions under high temperature or drought alone. The combination of the two stresses had more negatively effects on SuSy activity by further down-regulating the iso-forms GhSuSyA and GhSuSyB expressions, on VIN activity by further decreasing GhInv-1 and GhInv-2 expressions, and on CIN activity than any single stress, which would further inhibit sucrose degradation to form UDPG for cellulose synthesis. Moreover, elevated temperature or drought alone enhanced callose accumulation by highly up-regulating GhCalS-5 expression and down-regulating β-1,3-glucanase expression, and the combined stress further increased the callose accumulation, suggesting that more UDPG from sucrose decomposition was allocated to callose synthesis rather than cellulose synthesis. All these confirmed that elevated temperature combined with drought exhibited synergistic negative effects on cotton fiber biomass accumulation and cellulose synthesis during fiber thickening.

Identification of Key Genes during Ethylene-Induced Adventitious Root Development in Cucumber (Cucumis sativus L.).

Ethylene (ETH), as a key plant hormone, plays critical roles in various processes of plant growth and development. ETH has been reported to induce adventitious rooting. Moreover, our previous studies have shown that exogenous ETH may induce plant adventitious root development in cucumber (Cucumis sativus L.). However, the key genes involved in this process are still unclear. To explore the key genes in ETH-induced adventitious root development, we employed a transcriptome technique and revealed 1415 differentially expressed genes (DEGs), with 687 DEGs up-regulated and 728 DEGs down-regulated. Using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, we further identified critical pathways that were involved in ETH-induced adventitious root development, including carbon metabolism (starch and sucrose metabolism, glycolysis/gluconeogenesis, citrate cycle (TCA cycle), oxidative phosphorylation, fatty acid biosynthesis, and fatty acid degradation), secondary metabolism (phenylalanine metabolism and flavonoid biosynthesis) and plant hormone signal transduction. In carbon metabolism, ETH reduced the content of sucrose, glucose, starch, the activity of sucrose synthase (SS), sucrose-phosphate synthase (SPS) and hexokinase (HK), and the expressions of CsHK2, pyruvate kinase2 (CsPK2), and CsCYP86A1, whereas it enhanced the expressions of β-amylase 1 (CsBAM1) and β-amylase 3 (CsBAM3). In secondary metabolism, the transcript levels of phenylalanine ammonia-lyase (CsPAL) and flavonoid 3'-monooxygenase (CsF3'M) were negatively regulated, and that of primary-amine oxidase (CsPAO) was positively regulated by ETH. Additionally, the indole-3-acetic acid (IAA) content and the expressions of auxin and ETH signaling transduction-related genes (auxin transporter-like protein 5 (CsLAX5), CsGH3.17, CsSUAR50, and CsERS) were suppressed, whereas the abscisic acid (ABA) content and the expressions of ABA and BR signaling transduction-related genes (CsPYL1, CsPYL5, CsPYL8, BRI1-associated kinase 1 (CsBAK1), and CsXTH3) were promoted by ETH. Furthermore, the mRNA levels of these genes were confirmed by real-time PCR (RT-qPCR). These results indicate that genes related to carbon metabolism, secondary metabolite biosynthesis, and plant hormone signaling transduction are involved in ETH-induced adventitious root development. This work identified the key pathways and genes in ETH-induced adventitious rooting in cucumber, which may provide new insights into ETH-induced adventitious root development and will be useful for investigating the molecular roles of key genes in this process in further studies.

Metabolomic and transcriptomic analyses reveal that sucrose synthase regulates maize pollen viability under heat and drought stress

Maize pollen is highly sensitive to heat and drought, but few studies have investigated the combined effects of heat and drought on pollen viability. In this study, pollen's structural and physiological characteristics were determined after heat, drought, and combined stressors. Furthermore, integrated metabolomic and transcriptomic analyses of maize pollen were conducted to identify potential mechanisms of stress responses. Tassel growth and spikelet development were considerably suppressed, pollen viability was negatively impacted, and pollen starch granules were depleted during anthesis under stress. The inhibitory effects were more significant due to combined stresses than to heat or drought individually. The metabolic analysis identified 71 important metabolites in the combined stress compared to the other treatments, including sugars and their derivatives related to pollen viability. Transcriptomics also revealed that carbohydrate metabolism was significantly altered under stress. Moreover, a comprehensive metabolome-transcriptome analysis identified a central mechanism in the biosynthesis of UDP-glucose involved in reducing the activity of sucrose synthase SH-1 (shrunken 1) and sus1 (sucrose synthase 1) that suppressed sucrose transfer to UDP-glucose, leading to pollen viability exhaustion under stress. In conclusion, the lower pollen viability after heat and drought stress was associated with poor sucrose synthase activity due to the stress treatments.

Exogenous sucrose promotes the growth of apple rootstocks under high nitrate supply by modulating carbon and nitrogen metabolism

Excessive nitrogen (N) supply often leads to an imbalance of carbon (C) and N metabolism and inhibits plant growth. Sucrose, an important source and signaling substance of C in plants, is closely linked to N metabolism. However, it is not clear whether exogenous sucrose can mitigate the inhibitory effect of high N on plant growth by regulating C and N metabolism. In this study, we investigated the effects of exogenous sucrose on the growth, N metabolism, and C assimilation in the apple rootstock M26 seedlings under normal (5 mM NO3－, NN) and high (30 mM NO3－, HN) NO3－ concentrations. Our results showed that high NO3－ supply reduced plant growth, photosynthesis, and chlorophyll fluorescence, but spraying with 1% sucrose (HN + 1% Sucrose) significantly alleviated this inhibition. Application of 1% sucrose increased sucrose and sorbitol contents as well as sucrose-phosphate synthase and sucrose synthase activities in the plants under HN treatment and promoted the distribution of 13C photoassimilation products to the root. In addition, spraying with 1% sucrose alleviated the inhibition of N metabolizing enzyme activities by high NO3－ supply, reduced NO3－ accumulation and N content, increased free amino acid content, and promoted 15N distribution to the aboveground parts. However, spraying with 1% sucrose under the NN treatment negatively affected plant photosynthesis and carbon assimilation. In conclusion, exogenous sucrose increased the C level in plants in the presence of excess N, promoted the balance of C and N metabolism, and alleviated the inhibitory effect of high N on the apple plant growth.

Grain oil quality formation and metabolism-related genes difference expression of Paeonia suffruticosa cv. 'Fengdan' grown at different altitudes.

We measured the morphological index, nutritional composition and the expression analysis of key genes during grain development of Paeonia suffruticosa cv. 'Fengdan' grown at altitudes of 100, 650 and 1010 m in Luo-yang. The aim of this study was to examine differences in grain yield traits and the transformation of soluble sugar, starch, soluble protein and fatty acid contents, as well as the related enzyme activity and differential expression of key genes in oil metabolism. The results showed that grain yield traits increased with altitudes and that the growth period of grain at the higher altitudes was longer than that at low and mid altitudes. The soluble sugar and starch in mature grains increased with altitudes, while soluble protein and crude fat did not change. During grain development, the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) first decreased and then increased, with the lowest occurred at 90 d after flowering. The activities of pyruvate dehydrogenase (PDH), glutamic-pyruvic transaminase (GPT) and glutamic-oxalacetic transaminease (GOT) increased rapidly during 50-90 d after flowering and peaked at 90 d. The relative expression of acetyl-CoA carboxylase (ACCase) and stearoyl-ACP desaturase (SAD) peaked at 50 d after flowering, and ω-6 fatty acid desaturase 2 (FAD2) peaked at 90 d, in oil tree peony grain at different altitudes. There was a negative correlation of soluble sugar and starch with the accumulation of soluble protein and crude fat. SPS activity was positively correlated with the contents of soluble sugar and starch, and negatively correlated with the contents of soluble protein and crude fat during grain development. Activities of GPT and GOT were negatively associated with the content of soluble sugar and the content of starch, and had a highly significant positive correlation with the contents of soluble protein and crude fat. Activity of PDH was positively correlated with the content of soluble proteins and activities of GPT and GOT, and negatively correlated with the contents of soluble sugar and starch. It suggested that nutrient accumulation in the process of grain development of tree peony was transformed from sugar to crude fat and protein, and that metabolic enzymes, such as SPS, PDH, GPT and GOT, played an important role in this process. Palmitate acid, stearic acid and linoleic acid were negatively correlated with the relative increment of α-linolenic acid, indicating that fatty acid desaturation process in the grain development of tree peony was towards the direction of α-linolenic acid synthesis. The relative expression of ACCase, SAD, and FAD2 was positively correlated with the relative increment of α-linolenic acid accumulation, which played an important role in α-linolenic acid synthesis. The oil quality of tree peony grain was relatively stable at different altitudes, but grain production increased with altitude. Planting oil tree peony at mid to high altitudes could be an important strategy for the efficient use of marginal land in Luoyang.

Effects of low temperature on distribution and metabolism enzyme activity of carbon and nitrogen of Medicago ruthenica (L.)

AbstractLow temperature is one of the abiotic factors that limit the biomass of Medicago ruthenica (L.), and carbon and nitrogen have important roles in the plant's growth and development. However, the information on the distribution of carbon and nitrogen under low temperature conditions is limited. In this study, we investigated the influence of carbon and nitrogen distribution on M. ruthenica (L.) Trautv. cv. ‘Zhilixing’ based on 13C and 15N isotope tracers in two temperature‐controlled chambers (4–10°C and 25°C, respectively) for 30 days. Results showed that under low temperature, plant height significantly decreased by 22.74%, whereas the ratio of underground to aboveground biomass considerably increased by 146.31% compared to the control plants at 30 days. Moreover, low temperature stress significantly increased the activities of sucrose synthase and glutamine synthase in leaves, shoots and roots. The total carbon content and the abundance of 15N increased in leaves, shoots and roots under low temperature, with a greater level of increase in shoots than in leaves and roots. The weight of leaves, shoots and roots was correlated with δ15N. Hence, low temperature inhibited growth and promoted the transport of carbon and nitrogen.

Abscisic Acid Induces Adventitious Rooting in Cucumber (Cucumis sativus L.) by Enhancing Sugar Synthesis.

Abscisic acid (ABA) affects many important plant processes, such as seed germination, root elongation and stomatal movement. However, little information is available about the relationship between ABA and sugar synthesis during adventitious root formation. The aim of this study was to evaluate the effect of ABA on adventitious root formation in cucumber and whether the effect of this plant hormone on sugar synthesis could be included as a causative factor for adventitious root development. We determined the contents of glucose, sucrose, starch, total sugar and sugar-related enzymes, including sucrose synthase (SS), sucrose phosphate synthase (SPS), hexokinase (HK) and pyruvate kinase (PK) activities in ABA treatment. We also quantified the relative expression of sucrose or glucose synthesis genes during this process. Increasing ABA concentrations significantly improved adventitious root formation, with the most considerable effect at 0.05 μM. Compared to the control, ABA treatment showed higher glucose, sucrose, starch and total sugar contents. Moreover, ABA treatment increased glucose-6-phosphate (G6P), fructose-6-phosphate (F6P) and glucose-1-phosphate (G1P) contents in cucumber explants during adventitious root development, which was followed by an increase of activities of sucrose-related enzymes SS and SPS, glucose-related enzymes HK and PK. ABA, meanwhile, upregulated the expression levels of sucrose or glucose synthesis-related genes, including CsSuSy1, CsSuSy6, CsHK1 and CsHK3. These results suggest that ABA may promote adventitious root development by increasing the contents of glucose, sucrose, starch, total sugar, G6P, F6P and G1P, the activities of SS, SPS, HK, SPS and the expression levels of CsSuSy1, CsSuSy6, CsHK1 and CsHK3 genes. These findings provide evidence for the physiological role of ABA during adventitious root formation and provide a new understanding of the possible relationship between ABA and sugar synthesis during adventitious rooting in plants.

Relationship between epiphyllous bud of tropical waterlily (Brachyceras)umbilics and carbohydrate meta-bolism in different parts of leaves

To understand the development mechanism of the epiphyllous bud of waterlily, we examined the morphological anatomy of the leaf-navel epiphyllous bud by paraffin section technique at four stages, and compared the differences of carbohydrate metabolism between viviparous and non-viviparous waterlily leaves. Three tropical waterlily cultivars of Brachyceras were used, including two viviparous cultivars Nymphaea 'Margaret Mary', Nymphaea 'Ruby', and a non-viviparous cultivar Nymphaea 'Pink Star'. The results showed that parenchyma cells below the epidermis of leaf-navel divided and grew continuously after the leaf unfolded, forming a closely arranged cell cluster in viviparous waterlily and raised upward to a spherical shape. In contrast, no change was observed in leaf-navel of non-viviparous waterlily with the expansion of leaves. With the development of leaves, the contents of all physiological variables except sucrose and enzyme activities in the leaves of viviparous waterlily showed a first increase and then a decrease, which was significantly higher than those of non-viviparous waterlily. The carbohydrate contents in different parts showed the order of leaf > leaf-navel > petiole (except for starch content, which was highest in the leaf-navel). The activities of sucrose synthase (SS) and acid invertase (AI) were higher than those of sucrose phosphate synthase (SPS) and neutral invertase (NI). The activities of SPS and NI in different tissues of viviparous waterlily were significantly higher than those in non-viviparous one, but SS and AI did not show pronounced cultivar advantage in viviparous cultivars. AI activity varied greatly among cultivars, whereas NI activity varied less and was at a low level in different tissues. The sucrose of Nymphaea 'Ruby' leaves was positively correlated with the SPS and AI, and significantly associated with NI. The accumulation of sucrose content increased the activities of SS and NI of waterlily leaves, which was conducive to promoting the formation of epiphyllous buds.

Seed priming with protein hydrolysate promotes seed germination via reserve mobilization, osmolyte accumulation and antioxidant systems under PEG-induced drought stress.

Seed priming with pig blood protein hydrolysate improves tomato seed germination and seedling growth via regulation of reserve mobilization, osmotic adjustment, and antioxidant mechanism under drought conditions. Protein hydrolysates obtained from agro-industrial byproducts are widely recognized because of their positive roles in regulating plant responses to environmental stresses. However, little is known regarding the roles of animal protein hydrolysates in mediating seed drought tolerance and its underlying mechanisms. This study investigated the potential effects of seed priming on tomato seed germination and seedling growth under PEG-induced drought stress using protein hydrolysates derived from pig blood(PP). PP priming effectively alleviated the drought-induced reduction in seed germination traits, resulting in improved tomato seedling growth. PP priming enhanced the gene expressions and activities of amylase and sucrose synthase and soluble sugar, soluble protein, and free amino acid levels, thereby promoting reserve mobilization in seeds. PP priming also reduced osmotic toxicity through increased accumulations of proline, soluble protein, and soluble sugar. Drought stress substantially enhanced reactive oxygen species production and the subsequent increases in malondialdehyde levels and Evans blue solution uptake, which were substantially alleviated after PP priming via the improved activities of enzymatic and non-enzymatic antioxidants. Moreover, the increased DPPH free radical scavenging capacity and ferric reducing antioxidant power indicated that PP-treated tomato seedings had high antioxidant activities under drought stress. Therefore, PP priming is a novel, promising, and practicable method for improving tomato seed germination and seedling growth under drought stress.

Alternating red and blue irradiation affects carbohydrate accumulation and sucrose metabolism in butterhead lettuce

• Different irradiation patterns of red (R) and blue LED light (B) including alternating, concurrent, and monochromatic modes have been conducted on lettuce and compared from the angel of growth, energetic efficiency and sugar metabolism of lettuce. • The alternating R/B modes have been proved to increase the biomass and soluble sugar accumulation in lettuce on the basis of the same daily amount of photons and electric energy consumption as the concurrent RB. • The promotion effects of alternating R/B was relevant to the alternating interval of r and B, and the alternating R/B with appropriate interval could be considered as energy efficient irradiation mode for lettuce in a plant factory with artificial light (PFAL). • The alternating R/B modes have been proved to influence the activities and gene expression of the sucrose-metabolism related enzymes in lettuce, thus affected the carbohydrate accumulation and the development of lettuce. Sucrose metabolism and carbohydrate accumulation were evaluated in butterhead lettuce cultured under alternating red light (R) and blue light (B) irradiance. The R/B treatments were respectively R/B(5 m) (i.e. R 5 min/B 5 min), R/B(10 m), R/B(15 m), R/B(30 m) and R/B(60 m). Meanwhile, concurrent R and B (RB) as well as monochromatic R (R) and monochromatic B (B) were conducted. Compared with concurrent RB, all the alternating R/B treatments increased the fresh weight (FW), dry weight (DW) and the content of pigment and soluble sugar in lettuce on the basis of the same daily photon amount and electric energy consumption. Lettuce exposed to R/B(30 m) required the least number of photons (1.82 μmol) and electricity (1.04 MJ) per gram DW produced among all the treatments, thus R/B(30 m) was the recommended lighting mode in terms of the use efficiency of photons and electricity. Relatively higher soluble sugar content and the total sweetness index (TSI), as well as lower crude fiber content were detected in lettuce subjected to R/B(60 m), which was regarded as optimal irradiation mode in terms of lettuce taste. The content of sucrose, glucose and fructose, and the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) in the synthesis direction, as well as the gene expression level of SPS in lettuce were all enhanced by the alternating irradiation of R/B (15 m), R/B (30 m) and R/B (60 m) in comparison to the concurrent RB treatment. Moreover, higher enzyme activities in the synthetic direction of sucrose were found to be accompanied with higher soluble sugar content in lettuce subjected to R/B (30 m), R/B (60 m) and the solely R, indicating that the enzyme activities in sucrose synthetic direction seemed more related to the soluble sugar accumulation in lettuce. The results also showed that SS in lettuce leaves mainly acted on sucrose decomposition rather than synthesis. The hexose (glucose and fructose) content of lettuce subjected to R/B(60 m) basically kept the highest level among all the treatments through the whole processing period, which might be due to that lettuce exposed to R/B (60 m) owned the highest gene expression level of SS and invertase, as well as the highest enzyme activities of SS (cleavage) and invertase among all the treatments. Solely B inhibited the gene expression of sucrose metabolism-related enzymes in lettuce, and the photon use efficiency to R by lettuce was higher than to B from the angle of biomass and soluble sugar accumulation. A low intensity of B (1/9 of the R level) alternating with R improved the photon and electric use efficiency of lettuce in this study.

Excessive nitrogen in field-grown rice suppresses grain filling of inferior spikelets by reducing the accumulation of cytokinin and auxin

Excessive nitrogen fertilizer is often applied to achieve higher rice yield in many regions of the world. However, the effect of excessive nitrogen on grain filling of inferior spikelets and its underlying mechanisms are still poorly understood. A three-year field experiment was conducted to reveal the mechanisms by which excessive nitrogen application regulated grain filling. We found that excessive application of nitrogen reduced the starch biosynthesis and grain weight of inferior spikelets but not superior spikelets. Plant hormone detection revealed that both cytokinin (CTK) and 3-Indoleacetic acid (IAA) were reduced by excessive nitrogen at the early stage of grain filling in inferior spiekelts. Quantitative real-time PCR results showed that inhibition of biosynthesis genes led to a decrease in IAA content, while elevation of CTK oxidase genes resulted in a lower level of CTK under excessive nitrogen treatment. Application of exogenous IAA or CTK significantly impaired the inhibitory effect of excessive nitrogen on starch accumulation and grain weight of inferior spikelets. Further enzyme assays revealed that excessive nitrogen application significantly suppressed the enzyme activities of sucrose synthase (SuS), adenosine diphosphate glucose pyrophosphorylase (AGP) and starch synthase (StS) in inferior spikelets. Application of exogenous IAA or CTK to the panicle under excessive nitrogen treatment significantly increased the enzyme activities of SuS, AGP and StS. Taken together, our results revealed that excessive nitrogen application in field-grown rice suppressed grain filling of inferior spikelets by reducing the accumulation of cytokinin and auxin. • Grain filling of inferior spikelets was reduced by excessive nitrogen application. • HN application reduced the contents of CTK and auxin in inferior spikelets at 6 DAA. • Exogenous CTK and auxin both increased grain filling under HN conditions. • HN downregulated auxin biosynthesis genes while upregulated CTK catabolism genes. • Activities of key enzymes for starch biosynthesis were regulated by CTK and auxin.

Exogenous Si Mitigates the Effects of Cinnamic-Acid-Induced Stress by Regulating Carbon Metabolism and Photosynthetic Pigments in Cucumber Seedlings

(1) Background: Cinnamic acid (CA) is a harmful substance secreted by the roots of continuous-cropping crops. (2) Methods: This study aimed to investigate how exogenous Si affects chlorophyll content and carbon metabolism in cucumber seedlings under CA-induced stress. (3) Results: The levels of chlorophyll a, chlorophyll b, chlorophyll a+b, and carotenoids were significantly reduced due to CA-induced stress. The addition of exogenous Si significantly alleviated this reduction. Under CA-induced stress, exogenous Si significantly increased the activities of ribulose-1,5-bisphosphate carboxylase, glyceraldehyde-3-phosphate dehydrogenase, fructose-1,6-bisphosphatase, fructose-1,6-bisphosphate aldolase, and transketolase. CA-induced stress significantly increased the fructose, glucose, and sucrose contents and reduced the starch content in the leaves and roots of seedlings. Similarly, the sucrose phosphate synthase, sucrose synthase, acid invertase, and neutral invertase activities were significantly reduced in plants under CA-induced stress. Overall, exogenous Si significantly reduced the soluble sugar content, increased the starch content, and promoted sucrose metabolism-related enzymatic activity in seedlings. (4) Conclusion: Exogenous Si can effectively increase the content of photosynthetic pigments in leaves of seedlings and maintain the balance of osmotic potential in the plant by reducing the accumulation of carbon assimilation products, which ultimately promotes tolerance to CA-induced autotoxicity stress.

Activities of Key Enzymes Involved in Starch Accumulation In Sorghum (Sorghum Bicolor L. Moench) Grains With Different Starch Contents

Starch accumulation and the seven metabolic enzyme activities in sorghum grains with different starch contents were investigated under field conditions in Shenyang Agricultural University. The results indicated that the starch accumulation in Tieza17 (high starch content variety) and Liaoza11 (low starch content variety) grains could be fitted with logistic equation. The activities of sucrose synthase (SS), soluble starch synthase (SSS) and uridine diphosphate glucose pyrophosphorylase (UGPase) in Tieza17 were similar to those in Liaoza11. Adenosine diphosphate glucose pyrophosphorylase (AGPase) and granule-bound starch synthase (GBSS) activities in Tieza17 grains were consistently higher than those in Liaoza11 grains. Starch branching enzyme (SBE) and starch debranching enzyme (DBE) activities increased or decreased significantly between the two varieties at different filling stages. It is suggested that the differences in the activities of AGPase, GBSS, SBE and DBE and their tradeoff played an important role in regulating starch accumulation in sorghum grains. Bangladesh J. Bot. 51(2): 217-222, 2022 (June)