Alterations in sucrose metabolizing enzyme activities and total phenol content of Curcuma longa L. as affected by different triazole compounds

Changes in the sucrose metabolism of Curcuma longa L. plants were studied under treatment with different triazole compounds viz., triadimefon (TDM) and propiconazole (PCZ). Plants were treated with TDM at 15 mg/L and PCZ at 10 mg/L separately by soil drenching on 80, 110, and 140 days after planting (DAP). The plants were harvested randomly on 90, 120, and 150 DAP to determine the effect of both the triazoles on sucrose metabolizing enzymes and phenol content. The sucrose metabolism was studied by analyzing sucrose metabolizing enzymes like sucrose synthase and sucrose phosphate synthase. All the analyses were assayed in leaves and tubers of both control and treated plants. It was found that both of the triazole compounds had profound effects on these parameters.     

Alterations in sucrose metabolizing enzyme activities and total phenol content of Curcuma Ionga L. as affected by different triazole compounds

Changes in the sucrose metabolism of Cur-cuma longa L. plants were studied under treatment with different triazole compounds viz., triadimefon (TDM) and propiconazole (PCZ). Plants were treated with TDM at 15 mg/L and PCZ at 10 mg/L separately by soil drenching on 80, 110, and 140 days after planting (DAP). The plants were harvested randomly on 90, 120, and 150DAP to determine the effect of both the triazoles on sucrose metabolizing enzymes and phenol content. The sucrose metabolism was studied by analyzing sucrose metaboliz-ing enzymes like sucrose synthase and sucrose phosphate synthase. All the analyses were assayed in leaves and tubers of both control and treated plants. It was found that both of the triazole compounds had profound effects on these parameters.     

Alterations in carbohydrate metabolism and enhancement in tuber production in white yam (<Emphasis Type="Italic">Dioscorea rotundata</Emphasis> Poir.) under triadimefon and hexaconazole applications

The present investigation was carried out with an aim to study the effects of two important fungicides/plant growth regulators, triadimefon (TDM) and hexaconazole (HEX) on white yam (Dioscorea rotundata Poir.). Each plant was treated with 1 l of aqueous solution containing 15 mg l^-1 TDM and 10 mg l⁻¹ HEX by soil drenching on 10, 20 and 30 days after planting (DAP). Starch and sugar contents, and the activities of α, β-amylases, sucrose phosphate synthase (SPS), sucrose synthase (SS) and acid invertase (AI) enzymes were estimated from leaf and tuber samples on 45, 60, 75 and 90 DAP. Results showed that TDM and HEX treatments inhibited the α, β-amylase and increased the fresh and dry weights, starch, sugar and sucrose contents and SPS, SS and AI activities in white yam. The data suggests that, the application of triazole fungicides may be a useful tool to increase the tuber quality as well as quantity in white yam plants, apart from their fungicidal properties.     

Changes in carbohydrate metabolism by triazole growth regulators in cassava (Manihot esculenta Crantz); effects on tuber production and quality

We have evaluated the ability of two triazole growth regulators, viz. triadimefon (TDM) and hexaconazole (HEX), in the enhancement of tuber production and quality in cassava (Manihot esculenta Crantz) through their effects on carbohydrate metabolism. One litre of 20 mg(-1) TDM and 15 mg(-1) HEX solution per plant were used for the treatments and groundwater was given to control plants. Triazole treatments reduced plant height and leaf area, but increased fresh and dry weights. Plants treated with TDM showed an increased net assimilation rate, which is followed by HEX and control plants. Triazole compounds increased the relative growth rate of cassava after 200 DAP, i.e. in the phase of tuber enlargement. Triazole compounds increased the starch and other carbohydrate contents and carbohydrate metabolising enzyme activities. From the results of this study, it can be concluded that these triazoles can significantly enhance the tuber production and quality by affecting the starch metabolism, apart from their fungicidal properties.     

Effect of triadimefon: a triazole fungicide on oxidative stress defense system and eugenol content in <Emphasis Type="Italic">Ocimum tenuiflorum</Emphasis> L.

The effect of triadimefon (TDM) a triazole compound on antioxidant potential and eugenol content was studied in Ocimum tenuiflorum L. The plant was subjected to 15 mg/l TDM by soil-drenching on 50th, 70th and 90th days after planting (DAP). Analyses were carried out on 60th, 80th and 100th DAP. Both enzymatic and non-enzymatic antioxidant potential estimation was carried out. The non-enzymatic antioxidant viz ascorbic acid, α-tocopherol and reduced glutathione were found to increase under triadimefon treatment. The antioxidant enzyme like superoxide dismutase, ascorbate peroxidase and catalase activities showed significant increase in TDM treatment. Triazole-treated plants yielded more eugenol (a major component of Ocimum-essential oil) in comparison to control. The study evidenced that TDM residues could be detected in the upper soil layer only and does not accumulate in the soil. These preliminary results suggest that TDM may be useful to increase the antioxidant content in medicinal plants and also to act as an elicitor to enhance the production of secondary metabolites of medicinal plants.     

Interactive effects of triadimefon and salt stress on antioxidative status and ajmalicine accumulation in Catharanthus roseus

The ability of triadimefon (TDM), a triazole group of fungicide, to ameliorate salinity stress was studied in Catharanthus roseus (L.) G. Don. plants subjected to sodium chloride (NaCl) treatment. NaCl treatment at 80 mM level decreased overall growth of this plant and reduced the chlorophyll contents, protein, antioxidant enzymes such as peroxidase (POX), superoxide dismutase (SOD) and polyphenol oxidase (PPO). The root alkaloid ajmalicine got increased under salt treatment. When these stressed plants were treated with TDM at 15 mg l⁻¹ concentration minimized the inhibitory effects of NaCl stress by increasing the root, shoot growth and leaf area and increased dry weight (DW), chlorophyll, protein contents and the activities of antioxidant enzymes like POX, SOD and PPO, thereby paved the way to overcome the salinity injury. The quantity of ajmalicine was again increased with the TDM treatment when compared to both control and NaCl treated plants. From these results, it is proved that the fungicide TDM have great role in the enhancement of plant antioxidative enzymes and the enhanced scavenging of potentially harmful free radicals, as a mechanism of protecting plants against noxious oxidative stress from the environment and also in the enhancement of active principles.     

Sucrose Metabolism in Netted Muskmelon Fruit during Development

Sugar content and composition are major criteria used in judging the quality of netted muskmelon (Cucumis melo L. var reticulatus) fruit. Sugar composition and four enzymes of sucrose metabolism were determined in `Magnum 45' muskmelon fruit at 10-day intervals beginning 10 days after pollination (DAP) until full-slip (35 DAP). Sugar content increased in both outer (green) mesocarp and inner (orange) mesocarp between 20 and 30 DAP. The major proportion of total increase in sugar was attributed to sucrose accumulation. The large increase in sucrose relative to glucose and fructose was accompanied by a dramatic decrease in acid invertase activity, which was highest in both tissues at 10 and 20 DAP, and increases in sucrose phosphate synthase (SPS) and sucrose synthase activities. The green tissue had a lower proportion of total sugar as sucrose, greater invertase activity, and less SPS activity than the orange tissue. Changes in relative sucrose content were highly correlated with changes in enzyme activity. The results strongly suggest that increases in the proportion of sucrose found in melon fruit were associated with a decline in acid invertase activity and an increase in SPS activity approximately 10 days before full-slip. Therefore, these enzymes apparently play a key role in determining sugar composition and the quality of muskmelon fruit.     

Phosphate Deficiency in Maize : III. Changes in Enzyme Activities during the Course of Phosphate Deprivation

The effects of low concentrations of phosphate (low-P) on soluble protein content, the activities of 12 different enzymes, and the rates of photosynthesis and respiration on the basis of leaf area were investigated in maize (Zea mays L.) leaves 16 to 24 days after planting (DAP). With low-P treatment, a drastic decrease in the rate of photosynthesis to only 6% of the maximum rate in control plants was observed by 24 DAP. Low-P treatment had almost no effect on the rate of respiration until 21 DAP, but then the rate of respiration decreased progressively to about 55% of the maximum rate in control plants. The soluble protein content in low-P plants decreased to 56% of the maximum content in control plants. The changes in the activities of enzymes in low-P plants showed several different patterns. The activities of pyruvate, orthophosphate dikinase, 3-phosphoglycerate kinase, phosphoenolpyruvate carboxylase (PEPC), ribulose 1,5-bisphosphate carboxylase, fructose 1,6-bisphosphate aldolase, catalase, phosphohexose isomerase, chloroplastic fructose 1,6-bisphosphatase, and ADP-glucose-pyrophosphorylase decreased steadily from 85 to 100% of the maximum activity found in 18- to 21-day-old control plants (V_max) to 30 to 70% of V_max. The activity of sucrose phosphate synthase remained virtually constant at approximately 85 to 100% of V_max. The activity of UDP-glucose-pyrophosphorylase remained almost constant up to 21 DAP and then decreased to 80% of V_max by 24 DAP. The activity of cytochrome c oxidase increased slightly up to 21 DAP but then decreased to 50% of V_max by 24 DAP. As indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of soluble proteins, the subunit of PEPC stained less intensely in 24-d-old low-P plants. The possibility is discussed that during low-P treatment there is selective degradation of PEPC without a concomitant degradation of sucrose phosphate synthase, both of which are known to be localized in the cytoplasmic compartment of mesophyll cells.     

Dynamic characteristics of sugar accumulation and related enzyme activities in sweet and non-sweet watermelon fruits

Sugar content largely determines watermelon fruit quality. We compared changes in sugar accumulation and activities of carbohydrate enzymes in the flesh (central portion) and mesocarp of elite sweet watermelon line 97103 (Citrullus lanatus subsp. vulgaris) and exotic non-sweet line PI296341-FR (C. lanatus subsp. lanatus) to elucidate the physiological and biochemical mechanisms of sugar accumulation in watermelon fruit. The major translocated sugars, raffinose and stachyose, were more unloaded into sweet watermelon fruit than non-sweet fruit. During the fruit development, acid α-galactosidase activity was much higher in flesh of 97103 than in mesocarp of 97103, in flesh and mesocarp of PI296341-FR fruit. Insoluble acid invertase activity was higher in 97103 flesh than in 97103 mesocarp, PI296341-FR flesh or mesocarp from 18 days after pollination (DAP) to 34 DAP. Changes in soluble acid invertase activity in 97103 flesh were similar to those in PI296341-FR flesh and mesocarp from 18 DAP to full ripening. Sucrose synthase and sucrose phosphate synthase activities in 97103 flesh were significantly higher than those in 97103 mesocarp and PI296341-FR fruits from 18 to 34 DAP. Only insoluble acid invertase and sucrose phosphate synthase activities were significantly positively correlated with sucrose content in 97103 flesh. Therefore, phloem loading, distribution and metabolism of major translocated sugars, which are controlled by key sugar metabolism enzymes, determine fruit sugar accumulation in sweet and non-sweet watermelon and reflect the distribution diversity of translocated sugars between subspecies.     

Occurrence of sucrose and sucrose metabolizing enzymes in achlorophyllous algae

The presence of sucrose and the enzymes related to sucrose metabolism, i.e. sucrose synthase (SS) (UDP-glucose: D-fructose-2-glucosyl transferase, EC 2.4.1.13), sucrose phosphate synthase (SPS) (UDP-glucose: D-fructose-6-phosphate-2-glucosyl transferase, EC 2.4.1.14) and invertase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26) was demonstrated in Prototheca zopfii, a colorless alga. The levels of enzyme activities were lower than those obtained in Chlorella vulgaris, which is generally considered the photosynthetic counterpart of P. zopfii. Whem enzyme activities were measured in bleached cells of C. vulgaris, the levels were of the same order than those found in P. zopfii. These results would indicate that the sucrose metabolizing enzymes are not related to the algae ability to carry on photosynthesis.     

In vitro grown potato microtubers are a suitable system for the study of primary carbohydrate metabolism

The aim of this work was to determine the suitability of tissue culture microtubers for the study of primary carbohydrate metabolism in potato plants (Solanum tuberosum L. cv. Desirée). We have determined the levels of key enzymes and intermediates in the pathways of sucrose metabolism, starch metabolism and glycolysis in wild type microtubers. Comparison of the metabolite levels in microtubers with a range of published studies on soil-grown developing tubers showed that the two systems were similar both in the absolute levels and in the ratios between metabolites, despite some differences in the maximum catalytic activities of some glycolytic enzymes. We conclude that in vitro grown microtubers are an adequate model system for studying primary carbohydrate metabolism in developing potato tubers.     

Responses of antioxidant potentials in Dioscorea rotundata Poir. following paclobutrazol drenching

The effect of paclobutrazol (PBZ) treatments on the antioxidant metabolism of white yam (Dioscorea rotundata Poir.) was investigated in the present study. PBZ @ 15 mg l(-1) plant(-1) was given to plants by soil drenching, 30, 60, and 90 days after planting (DAP). The non-enzymatic antioxidant contents like ascorbic acid (AA), reduced glutathione (GSH) and alpha-tocopherol (alpha-toc), activities of antioxidant enzymes like superoxide dismutase (SOD), ascorbate peroxidase (APX), polyphenol oxidase (PPO) and catalase (CAT) were extracted and assayed on 100 DAP from leaf, stem and tubers of both control and PBZ treated plants. It was found that PBZ has a profound effect on the antioxidant metabolism and caused an enhancement in both non-enzymatic and enzymatic antioxidant potentials under treatments in white yam. Our results have good significance, as this increase the innate antioxidant potential of this food crop, which is helpful to satisfy the needs of antioxidants in diet and thereby make it an economically important food crop.     

Propiconazole induced toxicological alterations in brain of freshwater fish Channa punctata Bloch

Fungicides are a class of pesticides which are used indiscriminately in large amounts and pose a serious threat to the environment. Propiconazole (PCZ) is a systemic foliar fungicide with a broad range of activity. The potential of this fungicide to induce toxicity has not been fully explored. The present study was designed to investigate the dose dependent neurotoxic effect of propiconazole (PCZ), with Channa punctata Bloch as a model organism. Effect of PCZ on the brain specific enzyme activity such as acetylcholinesterase (AChE), monoamine oxidase (MAO) and Na⁺-K⁺-ATPase was determined in the fish brain tissue exposed to sub-lethal concentrations (0.5 and 5 ppm) for 96 h. Also, levels of oxidative stress reflected by various enzymatic and non-enzymatic antioxidants were measured. Neurotransmitter (epinephrine) level was also assessed. PCZ exposure induced oxidative stress as reflected by the significant increase in fish brain lipid peroxidation and protein carbonyl content with decrease in reduced glutathione levels, as well as the significant inhibition of glutathione dependent metabolizing enzymes and CAT activities. In addition, AChE, MAO and Na⁺-K⁺-ATPase activities were significantly lowered along with reduction in epinephrine levels in PCZ exposed fishes than those of the control in a dose dependent manner. Also, histopathological alterations were observed in fish brain of the treated fishes. The results point towards the potential neurotoxicity in the fish caused by PCZ exposure but the application of these findings will need more detailed study before they can be established as special biomarkers for toxicity monitoring the aquatic environment.     

Leaf Phosphate Status, Photosynthesis, and Carbon Partitioning in Sugar Beet: III. Diurnal Changes in Carbon Partitioning and Carbon Export

The effect of low phosphate supply (low P) was determined on the diurnal changes in the rate of carbon export, and on the contents of starch, sucrose, glucose, and fructose 2,6-bisphosphate (F2,6BP) in leaves. Low-P effects on the activities of a number of enzymes involved in starch and sucrose metabolism were also measured. Sugar beets (Beta vulgaris L. cv. F58-554H1) were cultured hydroponically in growth chambers and the low-P treatment induced nutritionally. Low-P treatment decreased carbon export from the leaf much more than it decreased photosynthesis. At growth chamber photon flux density, low P decreased carbon export by 34% in light; in darkness, export rates fell but more so in the control so that the average rate in darkness was higher in low-P leaves. Low P increased starch, sucrose, and glucose contents per leaf area, and decreased F2, 6BP. The total extractable activities of enzymes involved in starch and sucrose synthesis were increased markedly by low P, e.g. adenosine 5-diphosphoglucose pyrophosphorylase, cytoplasmic fructose-1,6-bisphosphatase, uridine 5-diphosphoglucose pyrophosphorylase, and sucrose-phosphate synthase. The activities of some enzymes involved in starch and sucrose breakdown were also increased by low P. We propose that plants adapt to low-P environments by increasing the total activities of several phosphatases and by increasing the concentrations of phosphate-free carbon compounds at the expense of sugar phosphates, thereby conserving Pi. The partitioning of carbon among the various carbon pools in low-P adapted leaves appears to be determined in part by the relative capacities of the enzymes for starch and sucrose metabolism.     

Regulation of sugar metabolism in rice (Oryza sativa L.) seedlings under arsenate toxicity and its improvement by phosphate

The effect of arsenate with or without phosphate on the growth and sugar metabolism in rice seedlings cv. MTU 1010 was studied. Arsenate was found to be more toxic for root growth than shoot growth and water content of the seedlings gradually decreased with increasing concentrations. Arsenate exposure at 20 μM and 100 μM resulted in an increase in reducing sugar content and decrease in non-reducing sugar content. There was a small increase in starch content, the activity of starch phosphorylase was increased but α-amylase activity was found to be decreased. Arsenate toxicity also affected the activities of different carbohydrate metabolizing enzymes. The activities of sucrose degrading enzymes viz., acid invertase and sucrose synthase were increased whereas, the activity of sucrose synthesizing enzyme, viz. sucrose phosphate synthase declined. The combined application of arsenate with phosphate exhibited significant alterations of all the parameters tested under the purview of arsenate treatment alone which was congenial to better growth and efficient sugar metabolism in rice seedlings. Thus, the use of phosphorus enriched fertilizers may serve to ensure the production of healthy rice plants in arsenic contaminated soils.     

Triadimefon Induced C and N Metabolism and Root Ultra-Structural Changes for Drought Stress Protection in Soybean at Flowering Stage

Drought is a major abiotic factor limiting agricultural crop production. The objective of this study was to investigate the effect of triadimefon (TDM) on leaf physiology and growth of soybean in response to drought stress. Soybean variety of Nannong 99-6 (Glycine max var.) was used to study the effects of TDM on carbon–nitrogen metabolism and root structure under drought stress with pot experiment. The results showed that drought stress significantly depressed the growth and yield regardless of spraying TDM. However, drought-stressed plants treated with TDM (D+T) showed much higher biomass and yield than those without TDM (D). Leaves of D+T plants exhibited a higher relative water content and chlorophyll content, but lower relative electric conductivity as compared with those of the D plants. Formation of lots of new roots, and more mitochondria and electron density deposits in the cells of root tips in D+T plants were noticed. Foliar glucose, fructose, and soluble sugar were increased by drought during the drought stress period. TDM decreased glucose and fructose a little during stress and the beginning stage of the recovery period but increased it later in the recovery period. Activities of sucrose synthase (SS EC 2.4.1.13), sucrose-phosphate synthase (SPS EC 2.4.1.13), and glutamine synthetase (GS EC6.3.1) and contents of NO₃-N were increased by TDM. Collectively, the results indicated that TDM could effectively alleviate the adverse effects caused by drought stress, which was partially attributable to modifications in morphology and physiological characteristic.     

Biochemical basis for effects of k-deficiency on assimilate export rate and accumulation of soluble sugars in soybean leaves

The effects of K-deficiency on carbon exchange rates (CER), photosynthate partitioning, export rate, and activities of key enzymes involved in sucrose metabolism were studied in soybean (Glycine max [L.] Merr.) leaves. The different parameters were monitored in mature leaves that had expanded prior to, or during, imposition of a complete K-deficiency (plants received K-free nutrition solution). In general, recently expanded leaves had the highest concentration of K, and imposition of K-stress at any stage of leaf expansion resulted in decreased K concentrations relative to control plants (10 millimolar K). A reduction in CER, relative to control plants, was only observed in leaves that expanded during the K-stress. Stomatal conductance also declined, but this was not the primary cause of the decrease in carbon fixation because internal CO₂ concentration was unaffected by K-stress. Assimilate export rate from K-deficient leaves was reduced but relative export, calculated as a percentage of CER, was similar to control leaves. Over all the data, export rate was correlated positively with both CER and activity of sucrose phosphate synthase in leaf extracts. K-deficient leaves had higher concentrations of sucrose and hexose sugars. Accumulation of hexose sugars was associated with increased activities of acid invertase. Neutral invertase activity was low and unaffected by K-nutrition. It is concluded that decreased rates of assimilate export are associated with decreased activities of sucrose phosphate synthase, a key enzyme involved in sucrose formation, and that accumulation of hexose sugars may occur because of increased hydrolysis of sucrose in K-deficient leaves.     

宁夏枸杞果实糖积累和蔗糖代谢相关酶活性的关系

通过对枸杞果实发育过程中果实生长模式、蔗糖、果糖、葡萄糖和淀粉含量及糖代谢相关酶活性的测定,研究了宁夏枸杞果实生长发育过程中糖的代谢积累与相关酶活性的关系.结果表明:(1)宁夏枸杞果实发育呈双S"曲线,果实主要以积累己糖为主.(2)蔗糖磷酸合成酶(SPS)活性在果实发育初期处于下降的趋势,在花后19d开始上升,果实转色后又逐渐下降;蔗糖合成酶(SS)活性总体表现为SS分解方向的活性大于SS合成方向的活性,说明枸杞果实发育过程中,SS的活性主要以分解方向的为主;酸性转化酶(AI)和中性转化酶(NI)的活性随果实发育呈上升趋势,但在果实成熟后期有所下降,且AI和NI活性高于合成酶类的活性,较高的转化酶类活性促进了果实内部己糖的积累.(3)在枸杞果实生长发育中,葡萄糖和果糖含量与AI和NI均呈极显著正相关,而与其它酶不具有相关性.说明AI和NI在宁夏枸杞果实的糖代谢中起着主要的调控作用.