Activities Of Sucrose Metabolizing Enzymes Research Articles

Changes in the Differentiation Program of Birch Cambial Derivatives following Trunk Girdling

The mechanisms regulating the tree trunk radial growth can be studied in original experiments. One technique for studying cambium activity (the meristem involved in radial growth) under conditions of an increased photoassimilate level is trunk girdling. We girdled the trunks of 17- to 22-year-old silver birch plants (Betula pendula Roth var. pendula) during the active growth period and collected xylem and phloem samples at two height levels (1 cm and 35 cm) above girdle, 10, 20, and 30 days after girdling. We investigated the changes that occurred at the anatomical level, as well as the activities of sucrose-metabolizing enzymes and antioxidant-system enzymes and the expression of genes that encode proteins involved in sucrose and auxin transport and metabolism. A moderate increase in photoassimilates (35 cm above the girdle) resulted in a change in the ratio of phloem to xylem increments and an increase in the proportion of parenchyma in the conducting tissues. The increase of photoassimilates above the level at which they can be used in the processes of normal tissue growth and development (1 cm above the girdle) led to xylogenesis suppression and the stimulation of phloem formation, a significant increase in the parenchyma proportion in the conducting tissues, and formation of large sclereid complexes. The differentiation of parenchyma and sclereid cells coincided with biochemical and molecular markers of abnormal conducting tissue formation in Karelian birch, which are also characterized by high proportions of parenchyma and sclereid near the cambium. The results obtained are important in understanding the cambium responses to the photoassimilate distribution changes and estimating tree productivity and survival under changing environmental conditions.

Effect of water and salt synergistic regulation at the different growth stages on quality and sucrose-metabolizing enzyme activities of tomato

The objective of this study was to explore the effects of different degrees of water and salt stress on the quality and sucrose-related metabolic enzymes of tomatoes. The greenhouse pot experiment was used to set three influencing factors, the irrigation water salinity (S), different degrees of water deficit (W) and growth period of water shortage (T), each set to three levels, a total of 21 treatments. The changes of each quality in tomatoes at maturity under different treatments were measured and analyzed. And pay attention to the changes in sucrose content and sucrose metabolism-related enzyme activities in tomato leaves and pulp at 45 and 60 days after flowering. The results showed that the synergistic regulation of water and salt at different growth periods significantly improved the quality of tomatoes, with salt stress having the greatest impact on quality, followed by irrigation and finally by periods of water deficit. Leaf and pulp sucrose metabolizing enzyme activities were related to fruit sugar content and increased with increasing water and salt stress levels. Periods of water deficit had no significant effect on sucrose metabolizing enzyme activity. There was no significant interaction between the three factors. Fruit quality was significantly improved under this new irrigation pattern. The best fruit quality was achieved with the S2W3T3 treatment. The results of the study provided a scientific and reliable theoretical basis for improving the quality of local tomatoes and developing suitable irrigation patterns.

Soil Available Phosphorus Deficiency Reduces Boll Biomass and Lint Yield by Affecting Sucrose Metabolism in Cotton-Boll Subtending Leaves

Soil available phosphorus (AP) deficiency and shortage of phosphate rocks limit cotton production in China. Therefore, pool-culture experiments were conducted in 2019 and 2020 using two cotton cultivars (CCRI-79, low-P tolerant; SCRC-28, low-P sensitive) under three soil AP levels (P0: 3 ± 0.5, P1: 6 ± 0.5, and P2 (control): 15 ± 0.5 mg kg−1) to ascertain the effect of soil AP on boll biomass and lint yield. P0 and P1 decreased the P concentration and net photosynthetic rate (Pn) of subtending leaves, thus, reducing boll biomass and lint yield. Additionally, soil AP deficiency decreased boll wall:boll, lint:boll, and lint:seed, and increased seed:boll ratio. Upper fruiting branch positions (FB9–12) had higher lint:seed ratio and proportion of the total lint yield under low soil AP. Moreover, soil AP deficiency also reduced the sucrose transformation rate (Tr) and activities of sucrose-metabolizing enzymes, such as ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), sucrose phosphate synthase (SPS), and sucrose synthase (SuSy), while increased carbohydrate levels (soluble sugar, sucrose, and starch) and the activity of cytosolic fructose-1,6-bisphosphatase (cy-FBPase) in the subtending leaves. The sucrose and starch contents, cy-FBPase, and SPS activities of SCRC-28 were more sensitive to low soil AP than CCRI-79. Higher Tr and activities of initial Rubisco and SuSy in the subtending leaves improved boll biomass and lint yield.

Regulation of Maize Kernel Carbohydrate Metabolism by Abscisic Acid Applied at the Grain-Filling Stage at Low Soil Water Potential

A water deficit during the grain-filling stage increases the frequency of yield loss in maize (Zea mays L.). Abscisic acid (ABA) plays a regulatory role in many stages of plant growth; however, its effects on sucrose-metabolizing enzyme activities under stress are poorly understood. The activities of cell-wall-bound acid invertase, vacuolar invertase, cytoplasmic invertase, and sucrose synthase decreased continuously under drought stress, whereas ABA treatment partially restored these activities. In addition, the increase and development of sucrose content under drought stress were related to invertase activity. Up-regulation of the activities and gene expression of cell-wall-bound acid invertase and vacuolar invertase with ABA treatment contributed to the increase in the number of rows and number of grains per row. Furthermore, ABA inhibited the increase in the length of the bald tip. Compared with the control group, water stress significantly reduced the yield index, with the lowest yield index on the 10th day of stress. These results suggest that the increase in ABA-induced sucrose-metabolizing enzyme activity might be an effective mechanism to improve maize drought resistance at the grain-filling stage.

In Silico Analysis of Regulatory cis-Elements in the Promoters of Genes Encoding Apoplastic Invertase and Sucrose Synthase in Silver Birch

This work is a continuation of studies on the role of sucrose in the formation of figured wood of Karelian birch (Betula pendula Roth var. carelica (Merckl. Hamet-Ahti). It was previously established that this type of xylogenesis is accompanied by significant changes in activity of sucrose-metabolizing enzymes, sucrose synthase and invertase, in the birch trunk’s tissues. The results of molecular genetic analysis indicate that the activity of these enzymes is regulated mainly at the level of transcription of the genes encoding them (SUS and CWInv). The genes encoding sucrose synthase and cell-wall invertase in the silver birch genome were identified. In silico analysis of the regulatory cis-elements present in the 2-kb promoter region of these genes revealed a number of motifs involved in the regulation of their expression. The largest (in terms of both the number of individual elements and their occurrence) was the group of elements associated with the influence of abiotic factors, mainly light and drought. A number of tissue-specific motifs, the function of which is associated with gene expression in conducting tissues, were identified. Analysis of hormone-dependent elements showed that the formation of figured wood of Karelian birch, which occurs against the background of high apoplastic invertase activity, is obviously not associated with the activation of CWInv genes by a high level of auxin. In the studied promoter sequences, various elements indicating the direct effect of sugar signaling were found. Two most likely candidates for involvement in the regulation of carbohydrate metabolism in the birch trunk tissues—transcription factors (TF) DOF5.6 (HCA2) and DOF5.8—were identified. The identification and functional characteristics of the DOF family TFs of silver birch are of interest from the point of view of the regulation of alternative scenarios of xylogenesis.

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

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

Characterization of Sugar Contents and Sucrose Metabolizing Enzymes in Developing Leaves of Hevea brasiliensis.

Sucrose-metabolizing enzymes in plant leaves have hitherto been investigated mainly in temperate plants, and rarely conducted in tandem with gene expression and sugar analysis. Here, we investigated the sugar content, gene expression, and the activity of sucrose-metabolizing enzymes in the leaves of Hevea brasiliensis, a tropical tree widely cultivated for natural rubber. Sucrose, fructose and glucose were the major sugars detected in Hevea leaves at four developmental stages (I to IV), with starch and quebrachitol as minor saccharides. Fructose and glucose contents increased until stage III, but decreased strongly at stage IV (mature leaves). On the other hand, sucrose increased continuously throughout leaf development. Activities of all sucrose-cleaving enzymes decreased markedly at maturation, consistent with transcript decline for most of their encoding genes. Activity of sucrose phosphate synthase (SPS) was low in spite of its high transcript levels at maturation. Hence, the high sucrose content in mature leaves was not due to increased sucrose-synthesizing activity, but more to the decline in sucrose cleavage. Gene expression and activities of sucrose-metabolizing enzymes in Hevea leaves showed striking differences compared with other plants. Unlike in most other species where vacuolar invertase predominates in sucrose cleavage in developing leaves, cytoplasmic invertase and sucrose synthase (cleavage direction) also featured prominently in Hevea. Whereas SPS is normally responsible for sucrose synthesis in plant leaves, sucrose synthase (synthesis direction) was comparable or higher than that of SPS in Hevea leaves. Mature Hevea leaves had an unusually high sucrose:starch ratio of about 11, the highest reported to date in plants.

Potassium Application Affects Key Enzyme Activities of Sucrose Metabolism during Seed Filling in Vegetable Soybean

Pot experiments were conducted in 2014 and 2015 with two vegetable soybean [Glycine max (L.) Merr.] cultivars (‘Zhongkemaodou 1’ and ‘121’) under normal rates of nitrogen and phosphorus application with three potassium (K) fertilization treatments: no K application (K0), 120 kg K2SO4 ha−1 at seeding (K1), and 120 kg K2SO4 ha−1 at seeding + 1% K2SO4 foliar application at flowering (K2). Potassium application significantly increased seed sucrose concentration, and the highest seed sucrose concentrations were uniformly observed in the treatment of foliar K application after flowering. At 7 wk after flowering, the highest stage of seed sucrose concentration, K1 and K2 treatments increased sucrose concentration by 19.8 to 44% and 29.1 to 86.4% for Zhongkemaodou 1, and 7.2 to 42.1% and 26.2 to 63.8% for 121, respectively. Changes of net activities of sucrose‐metabolizing enzymes in seed paralleled the trend of sucrose accumulation. Potassium application increased the activities of sucrose phosphate synthase and sucrose synthase with increased sucrose synthesis but reduced the activity of sucrose synthase with increased sucrose decomposition. Potassium application also reduced the activities of acid invertase and neutral invertase, especially around seed ripening. Potassium fertilization enhanced seed net activities of key enzymes in sucrose metabolism and subsequently induced the increase in sucrose concentration of vegetable soybean.

Carbohydrate accumulation and sucrose metabolism responses in tomato seedling leaves when subjected to different light qualities

Light qualities are thought to affect many plant physiological processes during growth and development. To investigate how light qualities influence tomato (Solanum lycopersicum) seedlings, the present study evaluated the effects of different light qualities generated by light emitting diodes (LEDs) with the same photosynthetic photon flux density (PPFD), including monochromic light red (657nm, R), blue (457nm, B), purple (417nm, P) or white (W), combination of R and B lights (R:B=1:1, 1R1B and R:B=3:1, 3R1B) on the net photosynthetic rate (Pn), growth rate, carbohydrate content and sucrose-metabolizing enzyme activities. The results showed that relative to W, the seedling plant height and stem diameter were significantly promoted by combination of R and B lights and monochromic R light. However, the level of root growth was lower under R and P light, and the seedling growth and Pn were significantly suppressed under the latter. Additionally, R light significantly increased the contents of fructose and glucose, and combination of R and B lights significantly enhanced total carbohydrate, starch and sucrose accumulation, especially for 3R1B treatment. Activity of sucrose synthase (SS) was promoted under the different treatments and reached its highest value under 3R1B, which appeared to be a major contributor to the significantly higher content of starch under this treatment. Furthermore, R, B and P light reduced activity of sucrose phosphate synthase (SPS). Activities of acid invertase (AI) and neutral invertase (NI) were significantly increased by R light, but were markedly reduced under P. The results presented here indicated that monochromic R and combination lights 3R1B, could regulate the plant morphology and photosynthesis by the effects on the metabolism of carbohydrate into fructose, glucose, sucrose and starch, mainly through the enhanced activities of AI and NI under the former treatment, while SS and SPS in the latter treatment, respectively. They also improved the end-product output in tomato leaves, and may ultimately improve the yield and quality of tomato fruit.

Changes in Soluble Sugar Accumulation and Activities of Sucrose-Metabolizing Enzymes during Fruit Ripening of Jackfruit

Jackfruit (Artocarpus heterophyllus Lam.) is an important food crop widely grown in the tropical region. However, little is known about sugar metabolism during fruit ripening of jackfruit. Here we examined sugar profiles (sucrose, glucose and fructose) and corresponding enzyme activities (SPS, E.C.2.4.1.14; SuSy, EC 2.4.1.13; IV, EC 3.2.1.26) of four soft type and four firm type varieties of jackfruit during four stages of fruit ripening. We found that during fruit ripening, there was a rapid increase in contents of total soluble sugar and sucrose, whereas increases in glucose and fructose contents were much slower. Ratios of glucose versus fructose varied among different varieties and ripening stages but within the range of 0.9 to 1.2 in the ripe fruits. Five of these varieties exhibited markedly high levels of SuSy activity for sucrose synthesis at early ripening stage, and then decreased towards fully ripe stage. All soft type varieties exhibited a conspicuous peak of AIV activity and had overall higher AIV activities than NIV during ripening. The changing patterns for other enzymes varied among varieties. Our studies support the notion that sucrose was the major sugar species contributing to the fruit sweetness, followed by fructose and glucose. We also demonstrated that AIV and NIV were probably the primary enzymes responsible for sucrose hydrolysis during ripening, while SPS and SuSy were responsible for sucrose synthesis. We propose that during fruit ripening of jackfruit, glucose is released from starch hydrolysis, followed by sucrose hydrolysis leading to increase in both glucose and fructose contents.

Sucrose-metabolizing enzymes and their genes in the arils of two Dimocarpus longan cultivars

This study aimed to investigate sucrose-metabolizing enzymes and their genes in fruits of two longan (Dimocarpus longan Lour) cultivars Cihezhong (CHZ) and Lidongben (LDB). Content of sucrose, glucose, and fructose were measured by high-performance liquid chromatography. The genes of sucrose-metabolizing enzymes were cloned by combining reverse transcription polymerase chain reaction and rapid amplification of cDNA ends, and enzyme activities were analyzed at various points in the fruiting cycle. The total soluble solid (TSS) content of longan arils rose and was positively correlated with sucrose content during maturation and then declined as the fruit senesced. Cihezhong showed a more rapid decrease in sucrose content than LDB. The activities of both sucrose phosphate synthase (SPS) and sucrose synthase (SS) were lower in CHZ, whereas the activities of soluble acid invertase (SAI) and neutral invertase (NI) were higher. The full-length cDNA of the genes of the sucrose-metabolizing enzymes were cloned successfully. The patterns of changes of sucrose synthase-2 (DlSS-2), sucrose synthase-3 (DlSS-3), and neutral invertase-3 (DlNI-3) gene expressions corresponded to those of SS and NI activities. The rate of sucrose decline in the longan fruits was related to sugar receding, sucrose metabolizing enzyme activities, and corresponding gene expressions.

Excess of exogenous nitrates inhibits formation of abnormal wood in the Karelian birch

The effect of exogenous nitrate on the sucrose-metabolizing enzyme activities—sucrose synthase (SS) and apoplastic invertase (ApInv)—in the xylem and phloem of the silver (Betula pendula Roth var. pendula) and Karelian (B. pendula var. carelica) birches (the latter is well known for its abnormal, patterned wood) has been studied. A stable correlation between the enzyme activities and deviations in the growth and development of stem vascular tissues during cambial growth has been demonstrated. Formation of the birch wood with a common structure is associated with high SS activity. In this case, the reaction yields UDP glucose, which is utilized mainly for synthesis of the cell wall components of vessels and fiber tracheids. As for the Karelian birch, the SS activity in the xylem formation zone is decreased, which complies with a higher sucrose level in the tissue. The excess sucrose is released into the apoplast to be cleaved by ApInv. The resulting hexoses induce storage metabolism, thereby increasing the amount of storage substances and the share of storage parenchyma cells in the xylem. As a result, the Karelian birch wood acquires large inclusions in the parenchyma, which render a characteristic pattern. A change in the ratio of SS to ApInv activities underlies a great variety in the degree of wood patterning observed in Karelian birch trees. In the common silver birch, the nitrate application increases the sucrose utilization via SS pathway, which results in an increase in wood growth. In the Karelian birch xylem, nitrates lead to a decrease in both the SS (a decrease in wood growth) and ApInv (a decrease in the amount of parenchyma, i.e., normalization of the wood structure). The sucrose metabolizing in the xylem decreases on the background of an increase in its utilization in the phloem, where both enzyme activities elevate. It is assumed that the fact that the Karelian birch distribution range is limited by rich soils can be determined by a shift from intensive apoplastic sucrose utilization zone towards the phloem caused by high doses of nitrogen nutrition.

The changes in physical, bio-chemical, physiological characteristics and enzyme activities of mango cv. Jinhwang during fruit growth and development

The changes in the physical, bio-chemical and physiological characteristics, and enzyme activities of sucrose metabolism during growth and development in mango fruit cv. Jinhwang were investigated. Fruit was harvested at five stages i.e., 50, 80, 110 and 140 days after anthesis (DAA). Several changes in the fruits were analyzed. The physical parameters like the fruit weight, width and length increased throughout the growth. In turn, fruit firmness, titratable acidity (TA) and starch accumulation increased during the initial growth stage and later then decreased during maturity. Total soluble solids (TSS) tended to decrease throughout fruit development. Respiration rate and ethylene production were higher at 50 DAA compared to other growth stages. Sucrose accumulation occurred later in the fruit development, however fructose was the dominant of the soluble sugars. Starch accumulation was related to the reduction of sucrose phosphate synthase (SPS), acid invertase (AI) and neutral invertase (NI) activities, whereas sucrose synthase activity was increased. Moreover, the AI and NI are the dominate enzymes that plays a major role in sugar accumulation and quality of mango fruit. Therefore, mango fruit should be harvested after physiological maturity at 110 DAA, when the fruit reach the optimum size, weight and starch content including maximum value of firmness, TSS, fructose content, minimum value of TA, low respiration rate and the lowest of ethylene production.

Sucrose metabolism and physiological changes during mango cv. Irwin growth and development

The changes in the enzyme activities of sucrose metabolism and physiological changes were investigated in mango fruit cv. Irwin at five development stages [50, 70, 90, 110, 130 days after anthesis (DAA)]. Changes in the respiration rate and ethylene production were higher at 50 DAA than other growth stages and the lowest at 90 DAA. Sucrose accumulation was related to the reduction of sucrose phosphate synthase (SPS; EC 2.4.1.14) activity, whereas acid invertase (AI; EC 3.2.1.26), neutral invertase (NI; EC 3.2.1.26) and sucrose synthase (SS; EC 2.4.1.13) activities were decreased. Moreover, the AI activity is the dominant enzyme that plays a major role in sugar accumulation and quality of mango fruit. Therefore, mango fruit cv. Irwin should be harvested after physiological maturity at 110 DAA.

Effect of moderately-high temperature stress on photosynthesis and carbohydrate metabolism in tomato (Lycopersico esculentum L.) leaves

Changes in the production and metabolism of photosynthate in tomato leaves were investigated after plants were treated to moderately high temperature stress for 8 h. Plants grown continuously at 25°C served as the controls. Compared to the controls, photosynthetic activity decreased in plants exposed to 35°C for ≥2 h. The net rate of photosynthetic (Pn) and the limitation of stomatal conductance (Ls) decreased, but stomatal conductance (Gs), intercellular CO2 concentration (Ci) and the rate of transpiration (Tr) increased. These results suggested the decreased in Pn under 35°C stress was caused mainly by non-stomatal restriction. In parallel with the decline in photosynthesis, the activities of sucrose-metabolizing enzymes and the contents of carbohydrate of plants that had been exposed to 35°C also changed. The invertase activities increased first then decreased but the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) increased continuously in stressed plants. The contents of fructose and glucose decreased but sucrose content increased compared with controls. It may result from the effects of 35°C on photosynthesis and sucrose-metabolizing enzymes activities that provoked the changes in carbohydrate contents in tomato leaves. Key words: Photosynthesis, carbohydrate, sucrose-metabolizing enzymes.

Activities of sucrose-metabolizing enzymes in grains of two wheat (Triticum aestivum L.) cultivars subjected to water stress during grain filling

Developmental changes in the starch and soluble sugars content of grains and the activities of sucrose metabolism enzymes in drought-tolerant (Triticum aestivum L. cv. Zagros) and drought-sensitive with high yielding potential under favorable conditions (cv. Marvdasht) wheat genotypes were investigated under controlled water deficit during grain filling. The two cultivars were grown in pots under well-watered (WW) and water-stressed (WS) starting from anthesis until maturity. Water stress caused a marked reduction in glucose, fructose and sucrose content of grains of sensitive cultivar. These changes were paralleled by sharp decline in the activities of cell wall invertase and soluble invertase in the grains of sensitive cultivar. Whereas in tolerant cultivar as the surge in invertase activity faded; in grains it was replaced by a substantial increase in sucrose synthase activity as seed development proceeds. Notwithstanding the increase in sucrose synthase activity in grains of sensitive cultivar; however, this little raise could not be sufficient to compensate for decreased levels of invertases and might restrict transport efficiency of storage material, and together with insufficient photosynthate may be the main reasons for dramatical reduction in the number of kernel and subsequent grain yield under WS treatment in Marvdasht. Key words: Invertase activity, sucrose metabolism, sucrose synthase, water stress, wheat (Triticum aestivum L.).

Tomato Key Sucrose Metabolizing Enzyme Activities and Gene Expression Under NaCl and PEG Iso-Osmotic Stresses

Changes in sucrose metabolism in response to salt (NaCl) and water (polyethylene glycol, PEG6000) iso-osmotic stresses were measured in tomato cultivar Liaoyuan Duoli ( Solanum lycopersicum L.) and the objective was to provide a new evidence for the relationship between salt and osmotic stresses. The carbohydrate contents, as well as sucrose metabolizing enzymes activities and transcript levels were determined. The results indicated that soluble sugar and hexoses accumulated to higher levels and the contents of sucrose and starch were lower in mature fruit under the two stress treatments. Salt and water stresses can enhance the invertase and sucrose synthase activities of tomato fruit in a long period of time (45-60 days after anthesis), and elevate the expression of soluble acid invertase mRNA. It showed that two different stresses could also regulate the soluble acid invertase activity by controlling its gene expression. The activity of sucrose synthase was linked to the changes in soluble sugar levels but not with transcript levels. The effects of salt and water stress treatments on sucrose phosphate synthase activities were weak.

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.

Physiological studies and sucrose metabolism during root development in three sugar beet cultivars

Physiological studies and the functions of different enzymes involved in sucrose metabolism during sugar beet root development have not been properly understood. An experiment was conducted to evaluate the physiological parameters and sucrose metabolism in three different varieties of sugar beet. Statistical analysis of the data revealed that, number of beet roots, beet yield and total sugars in beet juice were significantly higher in HI-0064 as compared to Posada and Dorotea. Significant differences in enzyme activities of sucrose metabolism were documented at 3 and 6 months of crop growth. There was not much difference in juice quality among these varieties. From these results HI-0064 was found to be a promising genotype among the three cultivars.

Osmotic stress-induced changes of sucrose metabolism in cultured sweet potato cells.

The intra- and extracellular sugar contents, the activities of sucrose-metabolizing enzymes, and the metabolism of [U-(14)C] glucose in a pulse-chase experiment were compared between the normal and osmotically stressed (by 0.6 M sorbitol) sweet potato (Ipomoea batatas) suspension cells. The stress enhanced the levels of sucrose and sucrose phosphate synthase (SPS) activity. Northern blot analysis also showed that prolonged osmotic stress enhanced the SPS gene expression at the transcriptional level. Stressed cells also had higher activities of sucrose cleaving enzymes, such as alkaline invertase and sucrose synthase. The (14)C-sucrose isolated from normal and stressed cells had (14)C-fructose and (14)C-glucose ratios of 0.68 and 1, respectively. These data suggest the continual cycling of degradation and synthesis of sucrose in both types of cells. Among the enzymes used in constructing such futile cycling, besides invertase and SPS, sucrose synthase (SS) should be involved in normal cells, but not in stressed ones. It is apparent that the osmotic stress caused a significant change in the pattern of sucrose metabolism.