Higher Sucrose Phosphate Synthase Activity Research Articles

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

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

Effects of Soil Salinity on Sucrose Metabolism in Cotton Leaves.

This study investigated sucrose metabolism of the youngest fully expanded main-stem leaf (MSL) and the subtending leaf of cotton (Gossypium hirsutum L.) boll (LSCB) of salt-tolerant (CCRI-79) and salt-sensitive (Simian 3) cultivars and its relationship to boll weight under low, medium and high soil salinity stress in Dafeng, China, in 2013 and 2014. The results showed that with increased soil salinity, 1) both the chlorophyll content and net photosynthetic rate (Pn) decreased, while the internal CO2 concentration firstly declined, and then increased in the MSL and LSCB; 2) carbohydrate contents in the MSL reduced significantly, while sucrose and starch contents in the LSCB increased, as did the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) in both the MSL and LSCB; 3) but invertase activity in both the MSL and LSCB did not change significantly. Our study also showed that the LSCB was more sensitive to soil salinity than was the MSL. Of the measured physiological indices, higher SPS activity, mainly controlled by sps3, may contribute to adaption of the LSCB to soil salinity stress because SPS is beneficial for efficiently sucrose synthesis, reduction of cellular osmotic potential and combined actions of Pn, and sucrose transformation rate and SPS may contribute to the reduction in boll weight under soil salinity stress.

Sucrose metabolism in the subtending leaf to cotton boll at different fruiting branch nodes and the relationship to boll weight

SUMMARYChanges of sucrose metabolism in the subtending leaf to cotton (Gossypium hirsutum L.) boll at different fruiting branch nodes (FBN) were investigated. Two cotton cultivars, Kemian 1 and Sumian 15, were grown in the field at three planting dates in 2009 and 2011. Cotton planted on different dates but experiencing similar climatic factors flowered on the same date and had similar boll opening dates, but had different FBN. In the present study, boll weight and carbohydrate content were significantly affected by both flowering date (FD) and FBN. However, only cystolic fructose-1,6-bisphosphatase (cy-FBPase) and sucrose-phosphate synthase (SPS) activities of the sucrose-metabolizing enzymes were influenced significantly by FBN, and the influence of FBN was lower with delayed FD. In general, effects of FBN on boll weight and sucrose metabolism in the subtending leaf were higher at the optimal FD (13 August) than those at later FD (9 September 2009 and 2 September 2011), and total fruiting branches were used to characterize cotton physiological age in the current study. Sucrose transport capacity (Tn) and SPS in the subtending leaf had significantly positive correlations with boll weight at 17–24 days post anthesis (DPA), a crucial period when boll weight was significantly affected. In addition, higher SPS activity was favourable for sucrose export and boll weight during boll development.

Deciphering the Role of Sucrose Phosphate Synthase in Root Nodules of Medicago sativa (alfalfa)

Leguminous plants, like alfalfa, can form a symbiotic relationship with a N fixing bacteria that can result in the formation root nodules. They have the ability to sustain the N fixing bacteria by providing optimal conditions for the bacterially encoded enzyme, nitrogenase, to reduce N to ammonia. The ammonia is then assimilated and exported to the rest of the plant. The plant provides the bacteria in the nodules with a source of C and energy in the form of sucrose in exchange for the fixed N. Sucrose Phosphate Synthase (SPS) catalyzes the penultimate step in sucrose biosynthesis and plays a key regulatory role in C partitioning in the pathway. Preliminary work form our lab has shown one isoform to have high SPS activity in the nodules, SPSA. To address the issue of what might be role of SPSA gene product in the nodules, we are using both immunolocalization and site of promoter function to localize the site of expression of SPSA in the nodules in context of N fixation, ammonia assimilation, and C metabolism. We are also using a genetic engineering approach to modulate the expression of SPS genes in a cell specific manner to monitor any changes in the function of the nodules.

Cadmium induced changes in carbohydrate status and enzymes of carbohydrate metabolism, glycolysis and pentose phosphate pathway in pea

With 50 μmol/l CdCl 2, reduction of about 40% in shoot and 70% in root lengths was observed in pea seedlings. The reduction in seedling growth was accompanied by decreased water content of shoots and roots. Increasing trend of sucrose was observed in shoots of cadmium-stressed seedlings. Cotyledons of stressed seedlings had lower α-and β-amylase activities resulting in their higher starch content. Reducing sugar and sucrose contents were not significantly affected in roots of cadmium-stressed seedlings but starch content was low in comparison with normal seedlings which appeared to be due to lesser conversion of sucrose into starch rather than its rapid hydrolysis. In general activities of acid and alkaline invertases were low in stressed seedlings with exception to cotyledons where alkaline invertase was more under stress. Cadmium-stressed seedlings had lower sucrose synthase and sucrose phosphate synthase (SPS) activities in roots and shoots but cotyledons had 10–15% higher SPS activity. Phospho glucoisomerase activity was maximum in cotyledons showing its involvement in conversion of glucose-1-phosphate to glucose-6-phosphate whereas the activity of this enzyme was almost negligible in roots. Exogenous cadmium up regulated the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in cotyledons whereas activities of these enzymes were down regulated by 40–50% in shoots. Higher activities of hexokinase (10–15%) and phospho glucoisomerase in roots and shoots of stressed seedlings indicated that hexoses are preferably channeled towards glycolysis than pentose phosphate pathway under cadmium toxicity.

Role of carbohydrates in flower bud opening in rose (Rosa hybrida L.)

SummaryTo explore the relationship between carbohydrate metabolism and flower bud opening in roses, experiments were conducted betweeen 2003 – 2005 on two cultivars of cut-rose (Rosa hybrida L.), ‘Grandgala’ and ‘First Red’. Flower stems were harvested at different developmental stages. Petals were separated from seven different petal whorls in flowers (outermost-to-innermost) of ‘Grandgala’ and ‘First Red’ at six developmental stages [S1, S2 and S3 represented attached blooms, and S4, S5 and S6 were detached (vase) blooms]. A substantial increase in starch accumulation was observed during the first three stages (S1 – S3) of flower bud development, while a pattern of starch degradation was observed in the later developmental stages. Differential patterns of sugar accumulation were noted in the expanding petals of rose. Levels of non-reducing sugars and sucrose increased gradually with flower bud development up to stage S3 of flower bud opening. In contrast, levels of reducing sugars increased continuously during all six stages of flower bud development. The total sugar content of flower petals followed a similar pattern to that observed for reducing sugars. A close relationship was observed between sucrose accumulation and the activity of sucrose phosphate synthase (SPS). This is the first report of high SPS activity in rose petals, and provides preliminary evidence for differential enzyme activity during flower bud opening. Collectively, these data support the hypothesis that carbohydrates play an important role in flower bud opening in rose.

Developmental regulation of photosynthate distribution in leaves of rice

mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N0.5, N3.0). The relative gene expression patterns were similar in all leaves except for 9th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS Vmax, SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS Vmax was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5th and 7th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9th and flag leaves). PEPC activity and SPS Vmax decreased with declining leaf N content. After using 14CO2 the 14C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more 14C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more 14C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the N- or C-pool, respectively, regardless of the leaf N status.

Changes in Sugar Metabolism Enzyme Activities in Cultivars of Two Pumpkin Species (Cucurbita maxima and C. moschata) during Fruit Development

Sugar accumulation and sugar metabolism enzyme activities were measured in two distinct pumpkin cultivars, 'Miyako' (C. maxima) and 'Hayato' (C. moschata) during fruit development. Sugar accumulation levels in the fruits were different between these cultivars. At the harvesting stage, more glucose and fructose were accumulated in 'Hayato' than in 'Miyako'. Sucrose content was low in young fruit when its catabolic enzyme activities were highest. The accumulation of sucrose with fruit development in both cultivars coincided with increasing sucrose phosphate synthase (SPS) activity and decreasing catabolic enzyme activities. The amount of sucrose content was indistinguishable in both cultivars, whereas, higher SPS activity was observed in 'Hayato', SPS contributes to sucrose accumulation in the late stage of pumpkin fruit development, but the amount of accumulated sucrose could not be explained solely on SPS activity.

Water stress effects on photosynthesis in different mulberry cultivars

The effect of water stress on photosynthesis was determined in five mulberry cultivars (Morus alba L. cv. K-2, MR-2, BC2-59, S-13 and TR-10). Drought was imposed by withholding water and the plants were maintained at different water potentials ranging from 0.5 -MPa to 2.0 -MPa. Photosynthetic rates, activities of ribulose-1,5-bisphosphate carboxylase and sucrose phosphate synthase, photosystem II activity and chlorophyll content were used as key parameters to assess photosynthetic performance. There was a marked variation in the photosynthetic rates and ribulose-1,5-bisphosphate carboxylase activity among the five mulberry cultivars subjected to water stress. Photosystem II (PSII) and sucrose phosphate synthase activities were also severely reduced as measured by drought conditions. Of the five mulberry cultivars, S-13 and BC2-59 showed higher photosynthetic rates, ribulose-1,5-bisphosphate carboxylase activity, high sucrose phosphate synthase activity and photochemical efficiency of PSII compared to the other varieties.

Muskmelon Fruit Soluble Acid Invertase and Sucrose Phosphate Synthase Activity and Polypeptide Profiles during Growth and Maturation

Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is the single most important consumer preference attribute. During fruit ripening, sucrose accumulates when soluble acid invertase (AI) activity is less then sucrose phosphate synthase (SPS) activity. To genetically heighten fruit sugar content, knowledge of sugar accumulation during fruit development in conjunction with AI and SPS enzyme activities and their peptide immunodetection profiles, is needed. Two netted muskmelon cultivars, Valley Gold a high sugar accumulator, and North Star a low sugar accumulator, with identical maturity indices were assayed for fruit sugars, AI and SPS activity, and immunodetection of AI and SPS polypeptides 2, 5, 10, 15, 20, 25, 30, 35, or 40 (abscission) days after anthesis (DAA). Both cultivars, grown in the Fall, 1998 and Spring, 1999, showed similar total sugar accumulation profiles. Total sugars increased 1.5 fold, from 2 through 5 DAA, then remained unchanged until 30 DAA. From 30 DAA until abscission, total sugar content increased, with `Valley Gold' accumulating significantly more than `North Star'. During both seasons, sucrose was detected at 2 DAA, which coincided with SPS activity higher than AI activity, at 5 through 25 DAA, no sucrose was detected which coincided with SPS activity less than AI activity. At 30 DAA when SPS activity was greater than AI activity, increased sucrose accumulation occurred. `Valley Gold' at abscission had higher total sugar content and SPS activity, and lower AI activity than `North Star'. `North Star' had AI isoforms at 75, 52, 38, and 25 kDa (ku) that generally decreased with maturation, although the isoform at 52 ku remained detectable up to anthesis (40 DAA). `Valley Gold' had the same four AI isoforms, all decreased with maturation and became undetectable by 20 DAA. Both `Valley Gold' and `North Star' had one SPS band at 58 ku that increased with DAA, and coincided with SPS activity. `Valley Gold' had a more intense SPS polypeptide band at abscission than `North Star'. Thus, netted muskmelon fruit sugar accumulation may be increased, either by genetic manipulation or by selecting for cultivars with a specific number of down-regulated AI isoforms, and higher SPS activity during fruit ripening.

174 Muskmelon Fruit Soluble Acid Invertase and Sucrose Phosphate Synthase Activity and Polypeptide Profiles during Growth and Maturation

Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is the single most important consumer preference attribute. During fruit ripening, sucrose accumulates when soluble acid invertase (AI) activity is less then sucrose phosphate synthase (SPS) activity. To genetically heighten fruit sugar content, knowledge of sugar accumulation during fruit development in conjunction with AI and SPS enzyme activities and their peptide immunodetection profiles is needed. Two netted muskmelon cultivars [`Valley Gold' (VG), a high sugar accumulator, and `North Star' (NS), a low sugar accumulator] with similar maturity indices were assayed for fruit sugars, AI, and SPS activity and immunodetection of AI and SPS polypeptides following 2, 5, 10, 15, 20, 25, 30, 35, and 40 (abscission) days after anthesis (DAA). Both cultivars, grown in spring and fall, showed similar total sugar accumulation profiles. Total sugars increased 1.5 fold, from 2 through 5 DAA and then remained unchanged until 30 DAA. From 30 DAA until abscission, total sugar content increased, with VG accumulating significantly more sugar then NS. In both cultivars, during both seasons, sucrose was detected at 2 DAA, which coincided with higher SPS activity than AI activity. At 5 through 25 DAA, SPS activity was less then AI activity resulting in little or no sucrose detection. It was not until 30 DAA that SPS activity was greater than AI activity resulting in increased sucrose accumulation. VG at abscission had higher total sugar content and SPS activity and lower AI activity than NS. Total polypeptides from both cultivars 2 through 40 DAA, were immunodetected with antibodies: anti-AI and anti-SPS. NS had Al isoforms bands at 75, 52, 38, and 25 kDa that generally decreased wtih DAA. One isoform at 52 kDa remained detectable up to anthesis (40 DAA) VG had the same four Al isoforms, all decreased with DAA and became undetectable by 20 DAA. It is unclear if one or all AI isoforms correspond with detected enzyme activity. VG and NS had one SPS band at 58 kDa that increased with DAA and concomitantly with SPS activity. VG had a more intense SPS polypeptide band at abscission then did NS. Thus, netted muskmelon sugar accumulation may be increased by selecting for cultivars with a specific number of AI isoforms, which are down-regulated, and with high SPS activity during fruit ripening.

Sucrose Metabolism at Three Leaf Development Stages in Bean Plants

Sucrose metabolism was studied at three leaf development stages in two Phaseolus vulgaris L. cultivars, Tacarigua and Montalban. The changes of enzyme activities involved in sucrose metabolism at the leaf development stages were: (1) Sink (9-11 % full leaf expansion, FLE): low total sucrose phosphate synthase (SPS) activity, and higher acid invertase (AI) activity accompanied by low sucrose synthase (SuSy) synthetic and sucrolytic activities. (2) Sink to source transition (40-47 % FLE): increase in total SPS and SuSy activities, decrease in AI activity. (3) Source (96-97 % FLE): high total SPS activity, increased SuSy activities, decreased AI activity. The hexose/sucrose ratio decreased from sink to source leaves in both bean cultivars. The neutral invertase activity was lower than that of AI; it showed an insignificant decrease during the sink-source transition.

Differential expression of three sucrose-phosphate synthase isoforms during sucrose accumulation in citrus fruits ( Citrus unshiu Marc.)

The role of sucrose-phosphate synthase (SPS) in sucrose metabolism during citrus fruit development was investigated through sucrose content and enzyme activity in relation to the transcription of three SPS cDNA isoforms. The profiles of sucrose accumulation in edible tissue (juice sacs and segment epidermis) of satsuma mandarin ( Citrus unshiu Marc.) agreed with those of SPS activity, that is, an increase in sucrose content accompanied high SPS activity. However, sucrose accumulation in edible tissue preceded the increase in SPS activity. The sucrose accumulation and the activity of SPS in peel tissue (albedo and flavedo) were lower than those in edible tissue. The expressions of three SPS genes (previously isolated and designated as CitSPS1, CitSPS2, and CitSPS3) were analyzed during the fruit developmental stage. Transcripts of the CitSPS1 in edible tissue were expressed at all stages analyzed and the transcript level was highest at the mature stage (223 days after flowering (DAF)). No transcripts of the CitSPS2 were found in edible tissue before 187 DAF, but thereafter transcripts were detected and increased until the mature stage. However, transcripts of CitSPS3 were undetected in edible tissue throughout the developmental stage. The expression of CitSPS1 in peel tissue was low in young fruit, then increased notably at 148 DAF, retaining its level until the mature stage. Transcripts of CitSPS2 in peel tissue showed the same pattern as that of edible tissue. The expression of CitSPS3 in peel tissue was detected at 148, 187 and 223 DAF, although its level was weak compared with CitSPS1 and CitSPS2. The activity of SPS in edible tissue paralleled the levels of transcription of CitSPS1 and CitSPS2, suggesting that the expression of these two genes might have an important role in determining the sucrose composition or accumulation in citrus fruit. In peel tissue, the patterns of SPS activity mostly agreed with the transcripts of CitSPS1, CitSPS2 and CitSPS3. These results also indicate that SPS genes are independently regulated, resulting in distinct temporal and spatial expression patterns.

Effect of chlorocholine chloride sprays on the carbohydrate composition and activities of sucrose metabolising enzymes in potato (Solanum tuberosum L.)

Chlorocholine chloride (CCC) was sprayed on a potato crop 25 days after sowing (DAS) at 5 day intervals for a total of 7 sprays. Activity of sucrose synthase (SS) in the sucrose cleavage direction was many fold higher than that of acid invertase in all the tissues. The activity of alkaline invertase was negligible. A sharp decline in the starch content of stolons of the CCC-sprayed crop was observed between 60 DAS and 70 DAS. This could divert the carbon towards tubers and thus enhancing its availability for starch synthesis. The CCC-treated crop, in general, had higher SS (cleavage) activity in stem, stolons and tubers. A higher sucrose content in the stem of the CCC-treated crop could be due to the high sucrose phosphate synthase (SPS) activity observed in this plant part. In tubers of CCC-treated crops a higher SS (cleavage) activity along with a high sucrose content in tubers during the active tuber filling stage could lead to better availability of UDP-glucose for its conversion to glucose-1-phosphate, which could enter into the amyloplast leading to higher starch content. High SPS activity in tubers of CCC-treated plants ensures that reducing sugars formed are reconverted efficiently to sucrose. The efficiency of developing tubers from CCC-sprayed plants to convert 14C sucrose fed through stolons into starch was about 2.5 times more than in the control.

Effects of light and atmospheric carbon dioxide enrichment on photosynthesis and carbon partitioning in the leaves of tomato (Lycopersicon esculentum L.) plants over-expressing sucrose phosphate synthase

Abstract Photosynthetic carbon assimilation, carbon partitioning and foliar carbon budgets were measured in the leaves of transformed tomato plants expressing a maize sucrose-phosphate synthase (SPS) gene in addition to the native enzyme, and in untransformed controls. The maize SPS gene was expressed under control of either the promoter of the small subunit of ribulose 1,5-bisphosphate carboxylase (rbcS promoter; lines 2, 9 and 18) or the 35S promoter from cauliflower mosaic virus (CaMV promoter; line 13). The rate of sucrose synthesis was increased relative to that of starch and sucrose/starch ratios were higher throughout the photoperiod in the leaves of all plants expressing high SPS activity. The leaf carbon budget over the day/night cycle in air at low irradiance (180μmol photon m−2 s−1) was similar in all plants. Net photosynthesis measured in air and at elevated CO2 (800–1500 μl l−1) on whole plants grown in air at 400μmol m−2 s−1 irradiance was significantly increased in the high SPS expressors compared to the untransformed controls and was highest where SPS activity was greatest. At high CO2 the stimulation of photosynthesis was more pronounced. We conclude that SPS activity is a major point of control of photosynthesis particularly under saturating light and CO2.

Sucrose-phosphate synthase is regulated via metabolites and protein phosphorylation in potato tubers, in a manner analogous to the enzyme in leaves

(i) Sucrose-phosphate synthase (SPS) was purified 40-fold from stored potato (Solanum tuberosum L.) tubers to a final specific activity of 33–70 nkat·(mg protein)−1 via batch elution from diethylaminoethyl (DEAE)-sephacel, polyethylene glycol (PEG) precipitation and Mono Q anion-exchange chromatography. (ii) Immunoblotting revealed a major and a minor band with molecular weights of 124.8 kDa and 133.5 kDa, respectively. Both bands were also present in extracts prepared in boiling SDS to exclude proteolysis. No smaller polypeptides were seen, except when the preparations were incubated before application on a polyacrylamide gel. (iii) The enzyme preparation was activated by glucose-6-phosphate and inhibited by inorganic phosphate. Both effectors had a large effect on the K m (fructose-6-phosphate) and the K m (uridine-5-diphosphoglucose) with phosphate acting antagonistically to glucose-6-phosphate. (iv) Preincubation of potato slices with low concentrations of okadaic acid or microcystin resulted in a three- to fourfold decrease in the activity of SPS when the tissue was subsequently extracted and assayed. The decrease was especially marked when the assay contained low concentrations of substrates and glucose-6-phosphate, and inorganic phosphate was included. Preincubation with mannose or in high osmoticum resulted in an increase of SPS activity. (v) Analogous changes were observed in germinating Ricinus communis L. seedlings. After preincubation of the cotyledons in glucose, high SPS activity could be measured, whereas okadaic acid, omission of glucose, or addition of phosphate or sucrose led to a large decrease of SPS activity in the “selective” assay. (vi) It is argued that SPS from non-photosynthetic tissues is regulated by metabolites and by protein phosphorylation in an analogous manner to the leaf enzyme.

Heat Tolerance and Assimilate Transport in Different Potato Genotypes

Six potato genotypes with different degrees of heat tolerance were grown in pots at 38/25 'b0C maximum/minimum temperature at 14 h daylength under natural light glasshouse conditions. Prior to sampling, the plants were given a 14 h dark period. Photosynthesis was measured at 28 'b0C and at a saturating light intensity of more than 1200 μEm-2 s-1. During the optimum photosynthetic period (09.00–12.30 h), the leaves of heat-tolerant potato genotypes (DTO-28, Norchip, and Desiree) had 4–5 times more soluble sugars (mainly sucrose) and higher sucrose-phosphate synthase activity than the leaves of the heat-susceptible genotypes (Kufri Jyoti, Kufri Chandramukhi, and Kufri Muthu). However, starch accumulation in leaves of susceptible genotypes was about twice that in tolerant genotypes. All susceptible genotypes showed a low rate of assimilate transport from leaves and a higher shoot/root ratio which indicated that the shoot remained the predominant sink for photosynthate. Activities of amylase and invertase in leaves were also higher in susceptible genotypes. It is suggested that the poor yield of heat-susceptible genotypes at high temperature and long day conditions is related to insufficient availability of the transportable sugar, sucrose.

Activities of Enzymes Involved in Sucrose and Starch Metabolism in Riella helicophylla (Bory et Mont.) Mont. during Differentiation

Summary The aim of this investigation was to show the changes in activities of enzymes involved in sucrose and starch metabolism in the model plant, Riella helicophylla, during cell differentiation. The activities of sucrose phosphate synthase, sucrose synthase, UDPGlc-pyrophosphorylase, ADPGlc-pyrophosphorylase, phosphorylase and maltase were determined in partially purified extracts from tissue zones in different stages of differentiation. UDPGlc-pyrophosphorylase had the highest activity per cell and per mg protein in the zone of expanding cells, where UDPGlc is required as a precursor for cell wall synthesis. Very high UDPGlc-pyrophosphorylase activity was also measured in the zone of mature cells and in the axis. In the zone of mature cells the main portion of UDPGlc presumably flows into the sucrose synthesis pathway, because the sucrose phosphate synthase activity was much higher here than in the other zones. High sucrose phosphate synthase activity combined with high sucrose content in the zone of mature cells leads to the assumption of an export function of the mature cells. In the axis, sucrose synthase, phosphorylase and invertase showed the highest activity per mg protein. Possibly in the axis, sucrose is degraded by sucrose synthase and invertase in favour of a starch synthesis via phosphorylase, as well as ADPGlc-pyrophosphorylase, because large amounts of starch are accumulated in the cells of the axis. In the meristem sucrose is mainly degraded by invertase, the activities of sucrose phosphate synthase, ADPGlc-pyrophosphorylase and maltase were lower than in the zone of mature cells. In the zone of mature cells starch is degraded mainly via the hydrolytic pathway, as is concluded from the high maltase activity, is synthesised via the ADPGlc-pyrophosphorylase reaction.